Team 2: Agua Para Vivir. [Water For Life] Calvin College, Grand Rapids, MI. Project Proposal and Feasibility Study

Transcription

1 Team 2: Agua Para Vivir [Water For Life] Calvin College, Grand Rapids, MI Project Proposal and Feasibility Study 15 December 2009

2 <Table of Contents TABLE OF CONTENTS Table of Contents... 1 Table of Figures... 4 Table of Tables... 5 Section 1 : Executive Summary... 6 Section 2 : Introduction Cultural Background Project Background Team Background... 8 Section 3 : Project Objectives Water Distribution Network Filtration Disinfection Sanitation Irrigation Run-off/Erosion Control Section 4 : Method of Approach Christian Perspective Cultural Sensitivity

3 <Table of Contents 4.3 Appropriate Technologies Section 5 : Design Alternatives Water Sources and Systems Rainwater Collection Springs Rivers/Streams Ground Wells Existing System Disinfection Ozonation Ultraviolet Irradiation High ph Treatment Chlorination Filtration Slow Sand Filtration (Biological Filters) Rapid Sand Filtration Upflow-Downflow Filtration Irrigation Sanitation Run-off/Erosion Control

4 <Table of Contents Section 6 : Feasibility & Decision Matrix of Design Feasibility Decision Matrix Section 7 : Preliminary Design Section 8 : Cost Analysis Project Budget Senior Design Budget Section 9 : Project Schedule Gantt Chart Section 10 : Implementation Fundraising Construction Section 11 : Conclusion References Acknowledgements Appendix A Target for chemicals in drinking water Appendix B Target values for microorganisms in drinking water Appendix C Gantt chart for fall semester

5 Table of Figures TABLE OF FIGURES Figure 1 - Team Picture... 9 Figure 2 - Rain gutters Figure 3 - Spring Capturing device Figure 4 - Capturing device Figure 5 - River Weir Figure 6 - Main Stream in Chuchiverachi Figure 7 - Spring North of Dorm Figure 8 - Holding/Break Pressure Tank Figure 9 - Pipe line flow rate Figure 10 - Charged Core and Cylindrical Shell Figure 11 - UV Irradiation, Submersed Lamps Figure 12 - Equilibrium of HOCl and OCl - in Solution Figure 13 - Concentration versus Contact Time for 99% Kill of E. coli virus Figure 14 - Disinfection by Chloramines or Free Chlorine with Varying Dosage Figure 15 - Gravity Filter Figure 16 - Slow Sand Filter Scheme Figure 17 - Rapid Sand Filtration Scheme Figure 18 - Teepee Underdrain System Figure 19 - Upflow-Downflow Filtration Scheme

6 Table of Tables Figure 20 - Single Pit Sealed Latrine Figure 21 - Water Source and Treatment Process Tree Figure 22 - Construction Cost for Slow Sand Filtration Table of Tables Table 1 - Decision Matrix Table 2 - Travel Cost Estimates

7 Executive Summary Section 1 : EXECUTIVE SUMMARY The primary goal of the project is to provide safe drinking water to school children in the village of Cuchiverachi, located in the rural mountains of northern Mexico. Secondary goals include expanding the water system to the entire village and improving sanitation. Other components being investigated include irrigation and erosion control. Currently, the water being used by the school children and villagers is coming from springs. The springs have inconsistent flow rates and are often tainted. The hospital in a nearby town has reported many cases of chronic diarrhea and other water borne illnesses believed to have come from the drinking water. In some severe cases the illnesses have resulted in death. Several alternatives have been considered to provide safe drinking water in this village. While a preliminary design has not been concluded, several of the alternatives have been determined to be inappropriate. The remaining alternatives include supplying the water from ground wells, springs, and rain catchments. Slow sand filtration has been selected for particulate removal. Disinfection alternatives are granular calcium hypochlorite, sodium hypochlorite, and chlorine gas. Section 2 : INTRODUCTION 2.1 Cultural Background Along the deepest canyon in North America, deeper than the Grand Canyon, lies Mexico s Copper Canyon. It is the familiar homeland of the Tarahumara, an ancient indigenous people of northern Mexico. They call themselves Raramuri, meaning runners on foot in their native language. They are renowned for their long-distance running ability. 1 In the 1600 s, the Spaniards arrived in search of gold and silver, as well as to bring Christianity by the Jesuit missionaries to the Tarahumara. The Jesuit era lasted until 1767 when the Tarahumara were expelled from Mexico by Spain. The Tarahumara were pushed westward into less desirable 1 Gorney, Cynthia. "The Tarahumara of Mexico evaded Spanish conquerors in the sixteenth century. but can they survive the onslaught of modernity? A people a part." National Geographic Nov (2008):

8 Introduction mountain lands out of the main lands of the state of Chihuahua and were mostly left alone by the government. Contact was minimized. "Three things in particular are significant about the Tarahumara," says William L. Merrill, a curator of anthropology at the Smithsonian Institution's National Museum of Natural History and a leading authority on the people who inhabit the Copper Canyon region. "They remain among the most traditional of all native peoples in North America. They have maintained a distinctive identity despite nearly 400 years of Spanish and Mexican pressures to assimilate. And, with perhaps as many as 70,000 members, they are also one of the largest Indian societies in all of North America." The Tarahumara have remained isolated from much of society and have developed unique survival strategies to live in the mountainous lands. Their diet is largely vegetarian with maize (corn) accounting for 75% of their diet. In the 18 th century the Spanish introduced them to goats, fish, sheep and beef; however, the Tarahumara seldom milk their cows and goats and only rarely slaughter theses animals for food. Rather, they use the animals manure to fertilize small fields as the soil is poor for growing corn. 2 The Tarahumara are internationally known for their running abilities and endurance. Many foot trails line the canyons where they run long distances, sometimes nonstop for hours, to get from place to place. In his research, Merrill observed a tradition of competing in marathon races. In a race he watched, women wearing sweaters, skirts and tire-sole sandals ran a course longer than an Olympic marathon and a half, up and down alternately rocky and marshy, jumping streams, crawling through fences, all the while flinging cloth hoops ahead of them. Later, two teams of men and boys lined up on the same course and ran twice as long as the women. He estimated each finisher would have run 80 miles. 3 2 Roberts, David. "In the land of the long-distance runners; Mexico's Copper Canyon is home to great athletes, the Tarahumara." Smithsonian May (1998): Roberts, David. "In the land of the long-distance runners; Mexico's Copper Canyon is home to great athletes, the Tarahumara." Smithsonian May (1998): 42. 7

9 Introduction 2.2 Project Background In the spring of 2009, the team was connected with the medical missions organization, Agua Para Suchil, and learned of a Tarahumara community that was experiencing many cases of illness. Agua Para Suchil had been working with this community for about five years and has collaborated with a local hospital (in Guachochi) to treat medical needs. Agua Para Suchil constructed a new dorm building for distant school children who stay in the village during the week. Many of the illnesses the Tarahumara face, such as chronic diarrhea, are a result of tainted drinking water. To address this health concern, Agua Para Suchil contacted Calvin College to generate interest among engineering students to help develop a water system to provide safe drinking water to the community. One of the team members was able to visit the site over the summer and obtain some preliminary data about the land and the water sources available. The scope of this project has been expanded to address aspects of water supply and quality, sanitation improvements, and erosion control. 2.3 Team Background Team 2, Agua Para Vivir, is comprised of four senior engineering students at Calvin College in Grand Rapids, MI. The four members of Agua Para Vivir are earning a Bachelor of Science in Engineering with civil and environmental concentrations. The team came together as a result of a common desire to design a project that would make a positive impact in people s lives. Being culturally sensitive and using appropriate technologies were design norms that were at the forefront of the teams design considerations. Shown below in Figure 1 is a photo of the team. The team members (from left to right in the photo) are Drew Johnson, David Nyenhuis, Jason Van Kampen, Hendrik Vanderloo. 8

10 Project Objectives Drew Johnson David Nyenhuis Jason Van Kampen Hendrik Vanderloo Figure 1 - Team Picture Section 3 : PRO OJECT OBJECTIVES 3.1 Water Distribution Network The objective of the water distribution network is to deliver clean potable drinking water to the dorm that is located in the center of the village. The ultimate goal of this project is to supply enough water to the dorm so the school children have water for drinking, and sanitary purposes. The washing facilities are to include showers, toilets and sinks for both boys and girls. The designed system should be easy to use, simple to construct, made of local material, and have a low level of maintenance. The second objective for the water distribution network is to provide clean potable drinking water to the houses that are scattered throughout the valley. 9

11 Project Objectives 3.2 Filtration The purpose of filtration is to make the water safe to drink by removing particulates. The filtration system removes most of the larger particles, such as bacteria, protozoa, and small amounts of sediment. The designed filtration system should be reliable, easy to use, simple to construct and inexpensive. 3.3 Disinfection The disinfection process is designed to remove the smallest contaminates, such as viruses. The water standards which are to be met are those established by the World Health Organization. The disinfection process should be safe, reliable, easy to use and inexpensive. 3.4 Sanitation Most people in the community do not dispose of their human waste properly. Most locals go into the woods on the mountain side and defecate on the ground. Defecation on the ground contaminates runoff and can lead to tainted water sources. The goal is to educate the community to effectively dispose of their waste, using pit toilets, and to inform the community about the adverse affects of poor hygiene and sanitation. 3.5 Irrigation There are a small number of fruit trees that are located near the dorm. The team would like to supply water to provide a small amount of irrigation for these trees and nearby community crops. 3.6 Run-off/Erosion Control Uphill from the dorm there is an area of the hillside that has undergone severe erosion. The erosion is extensive enough to be visible from satellite images. Erosion can strip land of nutrient rich top soil leaving the land unusable. Erosion can also adversely affect stream water. Sediment from run-off can deposit on stream beds which change the flow patterns of the streams. The 10

12 Method of Approach erosion control system that is put in place will need to prevent any further hillside erosion and prevent sedimentation in the streams. Section 4 : METHOD OF APPROACH 4.1 Christian Perspective The Tarahumara have a unique culture and lifestyle, seemingly untouched by modern civilization. The goal of the project is to reduce illness within the community of Cuchiverachi. The team views the project as an attempt to improve their quality of life. Since the term quality of life can often be misinterpreted and ill-defined, the team extensively discussed and debated what quality of life really means. Does a more modernized life style mean an improved quality of life? Does having more material things produce an improved quality of life? What about increasing longevity? In the gospels, Jesus is frequently noted as having compassion for the sick, poor and hungry. The team feels that the project is an opportunity to show compassion on a community who suffers illness and hardship because it lacks simple elements that many people take for granted: clean drinking water and sanitation. The teams hope is that the project will decrease the severity of illnesses such as chronic diarrhea along with decreasing the number of cases. The team understands that providing clean drinking water could have substantial effects on the Tarahumara community. For example, decreased mortality rates could lead to an increase in population, which could put strain the current food system. With all the above taken into consideration, the team believes that providing the Tarahumara with clean drinking water and improved sanitation is something that Jesus would smile upon. Cultural sensitivity and appropriate technologies are important components. However, the team is not only taking these components into consideration, but is also designing the project around them. The team believes that God has called them to the project to improve the community of Cuchiverachi s quality of life through blessing them with an essential element: Water For Life (Agua Para Vivir). 11

13 Method of Approach 4.2 Cultural Sensitivity In visiting the community this January, the team would like to meet with community leaders to get a clear scope of the community s needs, desires and expectations for the project. The team wants to be careful not to cause conflicts among community members due to unequal access to water. The team will be deliberate in who and where water is supply to and for what purpose the water will be used for. 4.3 Appropriate Technologies Many alternatives could effectively solve this water distribution problem. However, there is a need to understand what a realistic alternative design is and what an unrealistic alternative design is. If an infeasible project is designed, one that works based on the books but cannot be implemented in the real world, much time would have been lost. The energy situation in Cuchiverachi needs to be realistically evaluated. There are a few houses with solar panels, which is a non-reliable source of electricity provided by the Mexican government. In general though, there is no means of obtaining a consistent power supply. Lack of a power supply limits designs which require large amounts of energy, like pumps, lights, and automated control systems. A generator could possibly be imported and used as a power supply, but a noisy generator could be a disruption to the unique culture. Operation of the implemented project will be done by the villagers. Therefore, highly skilled technologies are less favorable. In lesser developed countries, it is often assumed that unskilled labor is cheap and complex equipment is expensive. The village is located several hours from the nearest municipality, and transportation to the village is difficult. Simplicity in operation and maintenance, as well as initial construction costs, is desirable. If chemicals, specialized equipment, or the need for outside skilled workers can be limited transportation costs would be greatly reduced. Having a quality of water that the people in the United States enjoy may be a costly luxury that would drive the project cost too high. This project will aim at fulfilling World Health Organization standards for drinking water, which can be seen in appendix A and appendix B 12

14 Section 5 : DESIGN ALTERNATIVES 5.1 Water Sources and Systems There are four water sources in the village of Cuchiverachi in which drinking water could be obtained from. The four water sources are, rain, springs, river/streams, and ground water. All four of these sources have been successfully used in many third world countries for drinking water. While all these sources have the potential to supply drinking water to the Tarahamara people each source has benefits and drawbacks Rainwater Collection A. Roof Catchments The most widespread way in which rain water is collected is through a roof catchment system. A roof catchment system is made up of four main parts: a roof, a gutter system, a screen or filter, and a holding tank. The technology notes from WaterAid suggested several important design features to ensure both efficient and safe collection of rain water. The roof which is to catch the water is best made of either roofing tiles or steel panels. Whiles roofs which are made out of organic materials do work it becomes very difficult to clean and as a result the rain water often becomes tainted from impurities which grow on the roof. The gutter system which is attached to the bottom edge of the roof collects and transports all the rain which falls on the roof to a holding tank. The gutter itself can be made in many different ways. A simply gutter may be made by cutting a large 3-4 plastic pipe in half or by bending a thin long strip of galvanized steel into a V-shape Figure Aid, Water. Technology Notes

15 Figure 2 - Rain gutters 5 The holding tank, which is best located directly along the outside wall of the building, stores the water so that the villagers will have water between rain storms. The holding tank size depends on three factors, the roofs area, rainfall depth, and rain fall frequency. The tank should be sized such that the volume of water it no bigger than the average total depth of rainfall during the rainy season multiplied by the area of the roof minus the daily consumption of the villagers for the entire rainy season. A screen or filter, which is placed between the gutters and holding tank, is needed to prevent solids from entering the water storage tank. The technology notes created by WaterAid also suggest that the down-pipe should be made to swivel so that the collection of the first run-off can be run to water, thus preventing accumulated bird droppings, leaves, twigs and other vegetable matter as well as dust and debris from entering the storage tank. 6 Rain catchment systems are capable of providing clean water, especially in rural areas where there is little to no pollutants in the air from car exhaust and factories. Another benefit of the rain catchment is its low maintenance costs. The only maintenance needed is cleaning the roof, gutters, and screen or filter of debris. However rain catchment systems are ineffective if there is little rain for most of the year and a secondary water system would be needed to supply water during the dry months. 5 Op. cit, Water Aid, Op. cit, Water Aid, 31 14

16 B. Ground surface catchments/rock catchments Rain collection is not limited to a building roof catchment device. The technology notes produced by WaterAid also explain another option for capturing rain water. If there are large out crops of rock nearby the water which runs off these rocks can be collected. If the rain water is to be used as drinking water, there are several protective measures which must be taken. First, all of the vegetation and soil must be removed from the rock surface. A fence should then be built around the slab of rock to prevent children and animals from climbing on and contaminating the rock surface. It is also important that a diversion ditch be dug just above the rock slab to prevent ground runoff above the rock slab from running onto the rock as surface runoff from soil often becomes contaminated. A gutter system is installed at the bottom of the rock slab which leads to a storage tank. 7 The biggest issue with the rock catchment collection system is that large rock slabs often do not exist near the village. If a large rock slab is not available a second option is possible. Large sheets of metal are put above a large area of ground and the rain which falls on the metal sheets is then collected. However a sheet metal rain collection system is more expensive than both the roof collection system and rock collection system as the roofs often already exist and the rock slab does not cost anything. The benefit of using a these two systems is that both the rock and the large sheets of metal have relatively low maintenance costs as the main maintenance requires a simple cleaning of the surface Springs Water which becomes trapped under an impervious layer of rock and soil becomes pressurized. Most springs occurs when pressurized water flows to the ground surface through a crack or hole in an impervious layer of rock. The water that reaches the surface has very few contaminants as the soil which the water has passed through has acted as a filter. Such springs are most often found in hill sides surrounding a valley. There are four main components to a spring fed water system. These four components are: a protected catchment, a network of gravity fed water lines, a storage/break pressure tank, and a tap stand. 7 Op. cit, Water Aid, 33 15

17 A. Protected spring catchment. The purpose of a protected spring catchment is to capture the water from the spring as well as to protect the water from contamination. There are several ways in which to capture water from a spring each method varies depending on the landscape surrounding the spring. One method requires the eye of the spring to be dug out and filled in with sand, and small rocks. A concrete or stone based box would be built directly in front of the spring to contain the water coming from the spring. The back wall of the box would either have a drain tile pipe connected to it or would be built of permeable material to allow the water to flow into the box. On the front wall of the box a gravity fed pipeline would allow the water to flow to the village. The technology notes written by Water Aid has several different concepts. Figure 3 shows a concept similar to the one described above. As seen in the drawing the design also suggests that a diversion ditch eight meters above the spring be dug to redirect any ground run off away from the spring to prevent contamination. 8 Figure 3 - Spring Capturing device 9 8 Op. cit, Water Aid, 30 9 Op. cit, Water Aid, 30 16

18 A simpler design of catchment also involves digging the eye of the spring out. A pipe is placed in the eye and is covered with stones. A wall is then built to prevent the rocks and sand from being washed away (Figure 4). Figure 4 - Capturing device 10 There are several steps involved in protecting a spring. This first is to build the box or wall. This prevents standing water open to the environment which can become contaminated. Secondly the surrounding area should be fenced off to prevent children and animals from contaminating the site. Thirdly as described above by Water Aid, a diversion channel should be built above the spring to prevent runoff water from entering the spring. 11 Finally if a box is to be built then the box needs to have an access door or removable lid so that the box can be cleaned out regularly. B. Gravity fed lines The gravity fed lines are best made of plastic material which can withstand being buried and laid out above ground on rocks. As well as being buried or laid out on rocks the pipe must also be able to handle various temperatures, both freezing and hot summer days with direct sunlight. The material must also be easy to repair if it breaks or springs a leak. The size(diameter) of the pipe will be based off of the desired flow rate and the head losses through the system. 10 Op. cit, Water Aid, Op. cit, Water Aid, 30 17

19 C. Storage /break pressure tank Depending on the elevation difference and flow rates which are being supplied by the gravity pipe line, a storage/break pressure tank will most likely be needed. The storage tank s size depends on the flow rate of the spring and the desired flow rate of the village. A storage tank allows for a greater water consumption for a village. Higher flow rates are possible because during high water demand water will come from the spring as well as empty out of the tank. During the night and when water is not being used the spring will refill the tank. The storage tank also acts as a break pressure tank. A break pressure tank reduces the pressure of the water coming out of the tap by reestablishing the hydraulic grade line. The pressure at the tap directly correlates to the elevation of the water in the storage tank and not by the elevation of the spring in the hillside. The storage/break pressure tank can be constructed out of a large variety of materials or one can be purchased. While purchasing a tank requires very little assembly time a purchased tank often costs more than building one from local materials such as stone and wood. Like the catchment the storage tank also needs a removable lid or hatch so that the tank can be cleaned out regularly. D. Tap stand The most common way for water from the spring to be accessible to the people is through a common tap stand location. The tap stand should have a shut off valve so that no water is wasted during the day when it is not being used. The location of the tap stand should be such that it is central so that villagers have to walk the least amount. While the tap stand is the most common practice, if the homes have plumbing the water line can be directly connected to the plumbing. There are some restrictions to a spring capture and distribution system. The spring must be a year round spring that does not dry up during the dry season. The spring must be located at an elevation above the village for the gravity supply line to work. If the spring is located at a lower elevation a pump and generator will be needed which increases both the cost and maintenance of the system. While the spring distribution system has a high start up cost the maintenance cost 18

20 is relatively low in comparison to other alternatives and the quality of the water is often good enough that little to no filtration and disinfection is needed Rivers/Streams There are several ways in which water can be collected from a river or stream. The first method is through damming the river or stream by building a weir. This creates a large pool of water to build up behind the weir. If the dam is located at an elevation higher than that of the village it may be possible to insert a gravity fed line into the weir which will allow water to flow to the village see Figure 5. If the villagers are at a higher elevation than the weir a generator and motorized pumps will be needed to lift the water to the village. A pumping system would most likely require a storage tank to be built as well. A storage tank would limit the number of times the pump would be turned on and off during the day. The water tank would be situated at a higher elevation so that water could flow to where it was needed through a network of pipes. An extensive filtration and disinfection would be required as river water often is highly contaminated. Figure 5 - River Weir 12 A second option for safely collecting the stream water is to design personal filtration and disinfection systems. The personal filtration and disinfections systems would allow the villagers 12 Op. cit, Water Aid, 37 19

21 can collect water from the stream and pour it through their own filter to purify the water. A personal filtration system would limit the high maintenance costs associated with running a pump and generator as well as the costs for constructing the dam Ground Wells Also commonly used as a drinking water source is ground water. There are two main types of ground water wells, hand dug and bored wells. Hand dug wells require a lot of local labor and the only machinery needed is a pump to drain water as the well is being dug. According to the Technology notes from Water Aid a hand dug well can take anywhere from a couple of days to a couple of weeks to complete. Hand dug wells can be as deep as 30 meters and are normally around 1.5 meters wide. One way of constructing a hand dug well is by placing a concrete ring on the ground. The interior of the ring is dug out as well us directly underneath the bottom edge of the ring. The ring lowers and acts as the supporting outside wall. More rings are added as the bottom rings continues to move downwards. Other ways require temporary wall supports which are later removed and replaced with brick or stone. Once the well is completed a motorized pump or a bucket and rope can be used to bring the water to the surface. 13 A second type of well is a drilled well. There are many different ways to drill a well all have different advantages and disadvantages depending on the soil and ground conditions. Drilled wells require less local labor and some machinery is needed to pump water. Most drill apparatuses use a long rod which is repeatedly pushed into the ground. The rod is hollow and water flows through the rod so that any soil that has been loosened by the rod is brought to the surface by the water. Once the hole has been completed a 2-4 pipe is inserted in the hole and a pump is added. The pump can be either a hand pump or motorized pump. The total project time can range from 1 day up to 1 week Existing System Currently in Cuchiverachi drinking water is obtained through two methods. The first method is from a stream which runs through the valley see Figure 6. Villagers use buckets to collect the water and bring it to their homes. 13 Op. cit, Water Aid, Op. cit, Water Aid,

22 Figure 6 - Main Stream in Chuchiverachi The second source of drinking water is from springs in the hillside. Currently there are several pipelines which run from several different springs in the hills. One of the pipe lines is connected to a spring about 1 mile north of the newly built dorm. While the current spring has a capturing device, the capturing device appears to have been bypassed see Figure 7. Figure 7 - Spring North of Dorm 21

23 The pipe line also has what appears to be a storage/break pressure tank on the hillside just north of the dorm see Figure 8. From what we could tell from the trip it appears that the pipe line supplies water to one home as well as water to the dorm and school. This pipe line has an exterior diameter of 1.2 inches, and the measured flow rate is just under 2 liters/min (Figure 9). A second pipe line is located at the south end of the valley. The pipe line supplies one home with water. There was not enough time to trace the pipeline back to its source, but the source of water is most likely a spring. The pipe diameter and flow rate are unknown at this time. There are a couple of other pipe lines at various locations in the valley but the location, size and flow rates of these pipes lines have yet to be confirm. Figure 8 - Holding/Break Pressure Tank 22

24 Figure 9 - Pipe line flow rate 5.2 Disinfection Depending on source water quality, disinfection may be a necessary alternative to achieving WHO drinking water standards. Disinfection occurs when microorganisms are inactivated by eliminating their ability to reproduce genetic material. In general, disinfection is more effective against smaller organisms (e.g. viruses) than larger organisms (e.g. protozoa). Residual disinfection, a common element of the disinfection process, ensures the inability of microbial life to recover after inactivation Ozonation Ozone disinfection has been in practice since the 19 th century. The first application of ozone as a disinfectant was in 1893 in Oudshoon, Netherlands. Today, ozonation is a widely used disinfection alternative in Europe, and there are several plants in Canada and the United States. 15 Ozonation has also been used for pool treatment since the mid 20 th century. Ozone is a more common practice in wastewater disinfection than it is in drinking water disinfection. 15 Reynolds, Tom D; Richards, Paul A. Unit Operations and Processes in Environmental Engineering. 2 nd Ed. Boston, Ma: (PWS Publishing Company, 1996):

25 Ozone (O 3 ) is commonly produced in the lower half of the stratosphere; the formation of ozone can be seen in Equation 1 and Equation 2. O 2 + (UV energy) O + O Equation 1 O + O 2 O 3 Equation 2 Harvesting ozone from the atmosphere is not feasible; therefore ozone must be produced by artificial means. Ozone production occurs by passing oxygen gas or air through oppositely charged materials. Materials can often be two oppositely charged plates or it can be a cylindrical core and an outer cylindrical shell, as seen in Figure 10. Figure 10 - Charged Core and Cylindrical Shell 16 High voltage plates essentially replace the UV energy component of Equation 1 with electrical energy. The air is then refrigerated to below the dew point and passed through desiccants. Refrigeration and dessicants are used to help remove humidity, which lowers maintenance costs, increases the lifetime of the units, and increases the efficiency of producing ozone. In comparison to hypochlorous acid, ozone is a more powerful disinfectant. Ozone s powerful disinfectant properties are attributed to the fact that it is a strong oxidant. In water, ozone produces hydrogen peroxy (HO 2 ) and hydroxyl (OH) as free radicals; these free radicals have a 16Nu Energy Horizons. 24

26 high capacity to oxidize bacteria, protozoa, viruses, helminthes and fungi. Microorganisms are believed to be incapacitated by: destruction of the cell wall, reaction with radical by-products or damage to the nucleic acids. 17 Destruction of microorganisms often requires a contact time up to 20 minutes. Ozone decomposes quickly because of its relatively short half-life (often o C); therefore, it must be produced on-site. A short half-life also implies ozone is a poor residual disinfectant, which requires the additional use of chlorine as a residual. Generally speaking, ozonation has a high installation, operation, and maintenance cost; and requires specialized equipment and training. For lesser developed countries, it is recommended that ozone as a disinfectant should not be used, because of its: complexity, high cost, high degree of training required, and the need to import equipment and spare parts Ultraviolet Irradiation Ultraviolet (UV) irradiation has been used as a disinfectant for both drinking water and wastewater; however, it is more effective in the disinfection of wastewater. UV irradiation has been used as a disinfectant for years and is still a current practice, the first application of which dates back to 1916 in the United States. UV irradiation works by exposing microorganisms to UV rays via a mercury arc lamp. Mercury arc lamps produce electromagnetic energy which damages an organism s DNA and RNA, effectively disabling the organism s means of reproduction on a cellular level. 19 These lamps can either be submersed in the water supply by encasing them in a quartz tube, as seen in Figure 11, 17 United States Environmental Protection Agency. Wastewater Technology Factsheet Ozone Disinfection. Office of Water, Washington DC. EPA 832-F , September 1999: Schulz, Christopher R; Okun, Daniel. Surface Water Treatment for Communities in Developing Countries. Washington D.C: (John Wiley & Sons, Inc, 1984): United States Environmental Protection Agency. Wastewater Technology Factsheet Ultraviolet Disinfection. Office of Water, Washington DC. EPA 832-F , September 1999:

27 Figure 11 - UV Irradiation, Submersed Lamps 20 or they can be an overhead bulb; however, it has been observed that submersed lamps are more effective. 21 A drawback to submerged lamps is the buildup of slime on the quartz covering, requiring cleaning every two to three weeks. The dosage of UV in a system can be described using Equation 3; where I is the average intensity in mw/cm 2, and t is time. D = I x t Equation 3 The removal of organisms is dependent on the UV intensity, the contact time, the reactor configuration and the water or wastewater characteristics. UV disinfection can be greatly hindered with increases in humic materials, ph (precipitates on quartz tube) or TSS. As a disinfectant, UV irradiation is effective at pathogen inactivation. It does not create disinfection by-products. Also, UV irradiation removes safety hazards associated with toxic chemicals and corrosive materials. Compared to ozonation, UV disinfection is less complex and 20 Halma PR Services Op. cit., Reynolds/Richards,

28 cheaper. However, it does require a continuous power supply. Also, UV disinfection does not have residual disinfecting abilities, thus chlorine must be added as a secondary disinfectant for drinking water. Since UV irradiation requires the additional use of chlorine, this alternative seems unnecessary for drinking water disinfection High ph Treatment High ph treatment has historically been applied to treat outhouses, dead animals and battlefield corpses. Treatment was accomplished with the application of calcium hydroxide (Ca(OH) 2 ), otherwise known as lime. In the treatment of water, high ph has been used since the early 20 th century. 23 High ph treatment as a water disinfectant is accomplished by adding lime until a ph greater than 11 is reached, often times the ph will range from 11.1 to Contact time generally ranges from 30 minutes to 90 minutes. As the ph of water increases, the removal of pathogens increases. This disinfection process is more effective against gram-negative bacteria and viruses than gram-positive bacteria and their spores. 24 If ph levels are high enough, the addition of lime can be very effective for destroying microorganisms and viruses. However, after the water is neutralized the supply is still in need of a residual. Therefore, chlorine is required as a secondary disinfectant if high ph treatment is applied. High ph disinfection is a more feasible alternative for wastewater treatment Chlorination The most common form of disinfection is through the use of chlorine. When added to water, chlorine acts as a strong oxidant. The enzymes of microbial cells are oxidized when chlorine is introduced, destroying the microbe s ability to continue metabolic processes. Chlorination is highly effective at low chlorine dosages, a proven technology, generally the lowest cost alternative, and forms a strong residual. Disinfection by chlorine can be applied in a variety of forms: chlorine gas, chlorine dioxide, chloramination, sodium hypochlorite, and granular calcium hypochlorites. 22 Op. cit., Reynolds/Richards, Op. cit., Reynolds/Richards, Grabow, W. O. K; Middendorff, Irmela G; Basson Nerine C. Role of Lime Treatment in the Removal of Bacteria, Enteric Virsues, and Coliphages in a Wastewater Reclamation Plant. American Society of Microbiology: Applied and Environmental Microbiology, April 1978, p

29 E. Chlorine Gas Chlorine gas (Cl 2 ) is a very common disinfection alternative. The gas is often stored and shipped in a liquefied state in steel containers. From the storage containers the gas can be dissolved in a chlorinator, from there it can be directly added to the water system before it reaches the chlorine contact tank. Chlorine reacts with water as shown in Equation 4. Cl 2 + H 2 O HOCl + HCl Equation 4 The hypochlorous acid (HOCl) that is produced in Equation 4 will then dissociates to a hypochlorite ion, which can be seen in Equation 5. HOCl H + + OCl - Equation 5 Equilibrium of hypochlorous acid and the hypochlorite ion are dependent on the ph of the solution, (Figure 12). Figure 12 - Equilibrium of HOCl and OCl - in Solution Feng, Yangang; Smith, Daniel W; Bolton, James R. Photolysis of Aqueous Free Chlorine Species (HOCl and OCl - ) with 254 nm Ultraviolet Light. J Environmental Engineering Science, Volume 6: NRC Canada,

30 At lower ph values, hypochlorous acid dominates the disinfection process; while at higher ph values the hypochlorite ion dominates. Hypochlorous acid requires less contact time for the same kill percent that the hypochlorite ion does, as seen in Figure 13. Figure 13 - Concentration versus Contact Time for 99% Kill of E. coli virus 26 Disinfection by chlorine gas is effective on a broad spectrum of microorganisms; however, it can be less effective against protozoa. Though chlorination by chlorine gas is an effective disinfection alternative, several health risks are associated with this treatment process. First off, chlorine is toxic in its gaseous form. It is a yellowish-green gas, which can cause immediate inflammation of the upper and lower respiratory tract. In World War I chlorine gas was even used as a chemical weapon. Therefore, precautionary efforts to ensure safe transportation, storage and handling of chlorine gas are essential. Chlorine gas storage containers are even becoming more of a liability in the United States, as they may be used as potential terrorist targets. However, a terrorist attack on the small town of Cuchiverachi, Mexico seems highly unlikely. Secondly, there are potential health-related risks due to disinfection by products (DBPs). These by products are produced when dissolved chlorine reacts with either bromine or other organic or inorganic matter. Common DBPs associated with chlorine gas disinfection are trihalomethanes (THMs) and haloacetic acids (HAA5). The group of trihalomethanes includes bromoform, chloroform, bromodichloromethane, and dibromochloromethane. The group of haloacetic acids includes dibromoacetic acid, monobromoacetic acid, trichloroacetic acid, dichloroacetic acid, and 26 Lackey, Laura W; Mines, Richard O. Introduction to Environmental Engineering. Upper Saddle River, New Jersey: (Pearson Education, Inc., 2010):

31 monochloroacetic acid. Regulation of DBPs produced by disinfection is importantbecause they may be harmful to human health. However, disinfection of microbiological organisms should never be compromised for the sake of DBPs. The WHO recommends limiting DBPs as much as is practicable. 27 F. Sodium Hypochlorite The use of sodium hypochlorite (NaOCl) as a disinfectant is another viable and proven technology, effectively working over a broad spectrum of pathogenic organisms. In the late 18 th century, Claude Berthollet first discovered how to create hypochlorite. Other applications include bleaching for laundry, basic household cleaning, and in dentistry to kill pathogens. Dissociation of sodium hypochlorite in water is shown in Equation 6. NaOCl (+ H 2 O) Na + + OCl - Equation 6 Once the sodium hypochlorite dissociates in water, the hypochlorite ion will go into equilibrium with hypochlorous acid, similar to the ph dependent equilibrium in Equation 5. Unlike chlorine gas disinfection, sodium hypochlorite is a liquid at room temperature. Industrial strength sodium hypochlorite ranges from 10-15% concentration; as compared to 5% in common household bleach. Because sodium hypochlorite is a liquid, it is safer in regards to storage and handling than gaseous chlorine. Unfortunately, sodium hypochlorite is unstable which causes it to have a shorter shelf life. Shortened shelf life is more applicable as temperatures increase, as well as if it is exposed to sunlight or other forms of UV radiation. Sodium hypochlorite is also less complex than chlorine gas in regards to transportation, storage, and handling. Because sodium hypochlorite is already in a liquid state, it can easily be fed from a holding tank directly into the main treatment stream without first running through a chlorinator. Disinfection by sodium hypochlorite requires the use of a chlorine contact tank. Generally speaking, in comparison to disinfection by chlorine gas, disinfection by sodium hypochlorite is 27 World Health Organization. Guidelines for Drinking-water Quality. First Addendum to the 3 rd Edition, Volume 1, 2006:

32 more expensive, it is less sophisticated, and it requires more transportation due to a shorter shelf life. G. Granular Calcium Hypochlorite Disinfection by granular calcium hypochlorite (Ca(OCl) 2 ) has very similar chemical properties to that of sodium hypochlorite. Calcium hypochlorite therefore shares the similar household uses of bleaching and disinfecting. However, it is much more stable than sodium hypochlorite and has more available chlorine for disinfection use. It is a proven technology covering a broad spectrum of treatment of pathogenic organisms. Dissociation of granular calcium hypochlorite can be seen in Equation 7. Ca(OCl) 2 (+ H 2 O) Ca OCl - Equation 7 Because calcium hypochlorite is in a solid state, it must be dissolved in water prior to being fed to the main water supply. Handling of granular calcium hypochlorite should not be taken lightly, as it is corrosive to the eyes, skin, digestive and respiratory tracts. In remote areas, where transportation of materials is few and far between, granular calcium hypochlorite offers a non-sophisticated, economical solution to disinfection of drinking water. Granular calcium hypochlorite is economical because of its properties of relatively high stability and greater availability of effective chlorine. 28 H. Chloramination In water, chlorine reacts with ammonia creating chloramines. These chloramines have disinfecting capabilities; the process of disinfecting by chloramines is referred to as chloramination. The reaction of dissolved chlorine gas with dissolved ammonia gas results in the formation of monochloramines, dichloramines, and nitrogen trichlorides. These reactions can be seen in Equation 8, Equation 9, and Equation 10, respectively. 28 Op. cit., Schulz/Okun,

33 NH 3 + HOCl NH 2 Cl + H 2 O Equation 8 Monochloramine NH 2 Cl + 2HOCl NHCl 2 + 2H 2 O Equation 9 Dichloramine NHCl 2 + 3HOCl NCl 3 + 3H 2 O Equation 10 Nitrogen trichloride The formation of various types of chlorines is correlated with the ph of the water. The formation of monochloramines is more abundant at a ph of greater the 6, dichloramines are more abundant at a ph of closer to 5, and nitrogen trichlorides are more abundant at even lower ph levels. 29 The chlorine dosage also directly affects chloramination. At lower chlorine dosages, disinfection is carried out predominantly by chloramination. Whereas at higher chlorine dosages, free chlorine is the major player in disinfection, as can be seen in Figure Op. cit., Reynolds/Richards,

34 Figure 14 - Disinfection by Chloramines or Free Chlorine with Varying Dosage 30 With disinfection by chloramination there are some aesthetic issues with the taste of the drinking water. In comparison with free chlorine disinfection by chlorine gas, chloramination is slightly weaker; however, chloramination is more stable. There are also fewer risks of DBPs with chloramination. 31 Chloramination is also more expensive and more complex than disinfection by chlorine gas. I. Chlorine Dioxide Chlorine dioxide (ClO 2 ) is a highly efficient form of disinfection. The use of chlorine dioxide gas as a disinfectant has been a full scale treatment alternative since the mid 20 th century, where it was originally used to treat taste and odor problems that came about through chlorination of phenolic contaminants. Since then it has been discovered that chlorine dioxide gas can also be used for iron and manganese removal and also as a disinfection alternative by itself. In comparison to chlorine gas, chlorine dioxide gas is a more powerful oxidant capable of higher kill rates at lower contact times. There are several common methods for producing chlorine dioxide gas, as shown by the following equations: NaClO 2 + HCl ClO 2 + NaCl + H + Equation 11 Acid and Sodium Chlorite (Cl 2 + H 2 O HOCl + HCl) HOCl + HCl +2NaClO 2 2ClO 2 + 2NaCl + H 2 O Equation 12 Chlorine Gas and Sodium Chlorite (excess chlorine) 30 Wolfe, R L; Ward, N R; Olson B H. Inorganic Chloramines as Drinking Water Disinfectants: A Review. J. American Water Works Association, 1984: Martin-Doole, Melanie; Collins, Robin M; Pope, Greg P; Speitel Jr., Gerald E. Predicting DXAA Formation During Chloramination. 33

35 2NaClO 2 + NaOCl + 2HCl 2ClO 2 + 3NaCl + H 2 Equation 13 Sodium Hypochlorite and Sodium Chlorite The most common method used in water treatment is the excess chlorine method, which can be seen in Equation 12. Some benefits of chlorine dioxide gas are its strength as a disinfectant, its durability as a residual disinfectant, its non-reactivity with ammonia, its relatively easy ability to be removed by aeration, its ability to help with taste and odor controls, and its reduced risk in DBPs. 32 But there are some drawbacks to disinfection by chlorine dioxide gas: it is more expensive than chlorine gas systems, more complex than chlorine gas systems, and produces the chlorite ion (ClO - 2 ) which may cause damage to the nervous system. 33 Because of the complexity of chlorine dioxide gas in regards to production selection and implementation, it may not be suitable for use in developing countries. 5.3 Filtration The use of sand or gravel media as a filtration method has been historically recorded in ancient Greek and Sanskrit writings dating as far back as 2000 BC. Filtration is the process of removing particles (including pathogenic microorganisms) of a water supply by means of straining, sedimentation, diffusion and advection. These processes are described as follows: Straining Passing the fluid through a media in which the diameter of the particle is too large to pass through. Sedimentation Settling, by means of gravity, of suspended particles onto the filter media. Diffusion Transport mechanism where random motion of a particle from a region of higher concentration to a region of lower concentration: results in particles colliding and sticking (by adsorption) to filter media. 32 Environmental Protection Agency. Chlorine Dioxide. Chapter 4. Environmental Protection Agency Guidance Manual - Alternative Disinfectants and Oxidants: April Op. cit., Reynolds/Richards,

36 Advection Transport mechanism where the inertia of a particle results in particles colliding and sticking (by adsorption) to filter media as the fluid flows changes direction. The filtering of a water supply can be accomplished by two common filter types pressure filters and gravity filters. Pressure filters are commonly used in industrial settings, and are desired because of their compatibility with automated processes. This report, however, will not analyze the use of pressure filters as a filtration alternative. An alternative type of filter is a gravity filter. Gravity filters, as implied by the name, rely upon on moving water through the filter media by stacking water above the media in a water column. An example of a gravity filter is illustrated in Figure 15. Figure 15 - Gravity Filter 34 A water column creates the driving force, based on its height, to overcome pressure losses through the media filter. When the water is forced through the media, the processes of filtration as stated previously effectively remove particles from the water supply. Three common types of gravity filtration are slow sand filtration, rapid gravity filtration, and upflow-downflow filtration Slow Sand Filtration (Biological Filters) The first slow sand filtration application dates back to the early 19 th century. In the year 1804, John Gibbs built a slow sand filter for his private bleachery in Praisley, Scotland. It wasn t applied to a full-scale public operation until 1829 in London, where James Simpson built a slow sand filter 34 Lackeby Water Group. 35

37 for the Chelsea Water Company. At the time the water was being treated for aesthetic reasons, the removal of suspended solids and turbidity. 35 They were unaware of the removal of bacteria as an additional benefit to slow sand filtration. In time, slow sand filters have become increasingly popular because of their great capacity to treat bacterial pathogens. Even today, many cities rely on slow sand filtration as part of their water treatment scheme. Cities using large scale slow sand filtration processes include Amsterdam, London, Paris and many others. Slow sand filtration has several components that work together to filter water. A slow sand filtration scheme is illustrated in Figure 16. Figure 16 - Slow Sand Filter Scheme 36 Starting at the beginning of the process, the water is fed into the filter bed. The bed is open to the atmosphere, often times even outside in the open air. Depending on winter temperatures in the region, the filter bed may be artificially heated or placed in a building or structure. The water column (which the supply is fed into) is known as the supernatant water reservoir. Water often remains here for 3 to 12 hours. This supernatant reservoir s ultimate function is to provide adequate head to force the water through the filter media. The reservoir can also provide additional storage in case of fluctuations in supply or demand. The box containing the reservoir is often concrete, and located partially (if not fully) underground. Ideally, the water level in the supernatant reservoir should be kept constant at approximately meters. 35 Huisman, L. Slow Sand Filtration. Geneva, Switzerland: (World Health Organization, 1974): Op. cit., Huisman,

38 Before the water passes through the filter media, it passes through the schmutzdecke. The schmutzdecke is a thin layer which sits on top of the filter media. Essentially, the schmutzdecke is a layer of biologically active slime resting on sand particles. The bacteria located in this layer feed on organic matter and on bacteria in the water supply, which in turn accounts for a significant portion of the filtration of pathogenic organisms. The slow sand filter is often referred to as a biological filter in reference to the schmutzdecke. After passing through the Schmutzdecke, the water supply then passes through the filter media. The filter media is responsible for the removal of particles. Common materials used in slow sand filters are: silica sand (rounded and angular), Ottawa sand, silica gravel, garnet, crushed anthracite, and plastic. The filter media material used in slow sand filters is generally fine sand. 37 Water can take up to 2 hours to completely pass through the filter media, which ranges in thickness from 0.6 to 1.2 meters. Particles passing through the filter media are filtered through straining, sedimentation, diffusion and advection, as previously discussed. Periodically the top layer of the filter needs to be scraped and disposed of which includes the schmutzdecke plus an additional 1 to 2 inches. Cleaning may not need to be done for several weeks, or possibly even a few months. The scraping of the top layer of the filter can be done manually with shovels, which is a benefit in lesser developed countries. The increase in pressure losses is due to the schmutzdecke growing, which consequently restricts flow. Supernatant water levels will then rise in order to maintain the same outflow, which is undesirable. Beneath the filter media is the supporting gravel and the underdrain. Both the gravel and the underdrain act as a support for the filter media. The underdrain serves the purpose of recapturing the water, which employs variations on perforated piping systems. The perforated pipe allows water to enter the pipe, while at the same time keeps sand and gravel from entering the pipe. The control valve and the outlet weir both provide important functions. The control valve is used to control the velocity of the water coming through the filter. The valve is also used to prevent backfilling when the filter bed is being cleaned. The weir also has multiple functions. First, it controls head in the supernatant water reservoir so the water level does not drop below the 37 Droste, Ronald L. Theory and Practice of Water and Wastewater Treatment. Hoboken, NJ: (John Wiley and Sons, 1997). 37

39 filter bed. Second, it provides an opportunity for unpleasant gases (odors) to escape to the atmosphere that may have formed in the schmutzdecke. It also allows oxygen to absorb into the water supply. 38 There are several advantages to using slow sand filtration in developing countries: low construction costs, simplicity of design and materials/equipment, unskilled labor for maintenance, imports are negligible, power is not required if gravity head is utilized, can handle variations in water quality and temperature, and it saves water because backwashing is not required Rapid Sand Filtration Rapid sand filtration has been a viable treatment process since the late 19 th century. In 1885 the first rapid sand filtration filter for a municipal supply was built in Somerville, New Jersey. This type of filtration is very common in industrialized countries, even though some countries like England and Switzerland still predominantly use slow sand filtration. Rapid sand filters are more costly to construct, yet because of their complexity and automation they reduce labor costs. They have a stratified coarse media, starting with layers of larger grain sand, or perhaps anthracite, for the top layer. The media progressively decreases in diameter as the water moves through the bed; that is, until it reached the gravel support layer. Rapid sand filtration can filter at higher flow rates than slow sand. However, particulates penetrate deeper into the bed which in turn requires frequent backwashing. Backwashing prevents the development of the schmutzdecke that is present in the filter bed of slow sand filtration. 40 Rapid sand filtration is often preceded by flocculation and sedimentation, in response to high levels of turbidity and color in the water source. If turbidity and color are not an issue, the flocculation and sedimentation process can be reduced in a process known as direct filtration. Direct filtration is a cost saving endeavor because it reduces chemical costs and construction costs. A disadvantage to direct filtration is that it could require up to twice as much washwater 38 Op. cit., Huisman, Op. cit., Schulz/Okun, Op. cit., Schulz/Okun,

40 for backwash than rapid sand filtration does, because impurities are not removed through the sedimentation and flocculation process. 41 There are several ways to categorize rapid filters: by media type, by the system used to control flow rates, by orientation and direction of flow, and by gravity or pressure operation. A rapid sand filter has a slightly different layout than that of a slow sand filter, even though they operate on the same essential principle of sand filtration. An illustration of a rapid gravity filter can be seen in Figure 17. Figure 17 - Rapid Sand Filtration Scheme 42 When designing a rapid gravity filtration system there are several design factors that must be determined: filter media, underdrainage system, backwashing system, auxiliary wash system, and flow-rate controls. 43 Historically, sand has been the preference for filter media because of its abundance and low cost association. Even today sand is the choice filter media in lesser developing regions for that 41 Op. cit., Schulz/Okun, Mountain Empire Community College Op. cit., Schulz/Okun,

41 reason. Other filter materials include anthracite, indigenous coals, crushed coconut shells, pea gravel, berry seeds, pits of stone fruit, boiler clinker, crushed stone, and rice hull ash. It has been learned that sedimentation and flocculation increase the efficiency of rapid sand filters, because they decrease the amount of larger particles that would occupy the upper layer, which previously restricted flow and reduced the flow rate capacity. Besides sedimentation and flocculation, dual and multi-media filter beds have been utilized. Dual and multi-media filter beds use either a combination of different sized media, or a combination of different media types, or both. This allows for deeper penetration of particulates into the bed. In industrialized countries these media alternatives have replaced the use of sand as a solitary filter material. Typical ranges for the depth of the coarse upper layer are 0.40 to 0.75 meters, ranges for the depth of the fine sand layer are 0.15 to 0.30 meters, and an approximation for the depth of the gravel layer is 0.6 meters. 44 Underneath the media filter material lays the filter bottom and underdrain. The underdrain should allow effluent to pass through, it should uniformly distribute the wash water, and it should support the filter media. One common underdrain system is a reinforced concrete slab in a teepee system with glass or plastic orifices, and is illustrated in Figure Op. cit., Schulz/Okun,

42 Figure 18 - Teepee Underdrain System 45 In a teepee system beams are cast in a triangular shape and placed with their bottom edges touching. They are supported by the walls of the filter box. The teepee underdrain system has been successfully implemented in lesser developed regions, like Latin America. 46 A more common underdrain system used in industrialized countries is the perforated pipe lateral system. Perforated pipe lateral systems are comprised of several lateral perforated pipes connected to a central manifold. The laterals should be located so that uniform distribution can occur. The orifice diameters should be set to maintain proper head when backwash occurs. The perforated pipe lateral underdrain system could be a viable option if it were constructed within the country itself. 47 A key component to the design of a rapid filter system is its backwash capabilities. Backwashing of the filter media is used to remove solids trapped from the filtration process. Often backwashing is necessary every 12 to 72 hours. Washwater is collected, usually by means of a trough and/or gullets, and is removed as wastewater. When backwashing, the filter media must be completely fluidized. Fluidization is dependent on the size of the media, the specific gravity of the media, and the water temperature. If too large of a flow is used in backwashing, the supporting gravel may be disturbed and a significant amount of water would be wasted. Timing for backwashes could range from 3 to 15 minutes. Three common methods of backwashing in developing countries are by an elevated water tank, by using water from a high pressure distribution tank, and by using one filter to backwash another (inter filter washing systems). The use of elevated and high pressure tanks requires purchasing a minimum of two pumps. However, using inter filter washing systems may eliminate the need for typical backwashing system equipment (including pumps). 48 Auxiliary scour wash systems are used to aid in the backwashing process. They work by installiong a piping system just above the filter media. When activated, they force a high velocity 45 F.B. Leopold Company Op. cit., Schulz/Okun, Op. cit., Schulz/Okun, Op. cit., Schulz/Okun,

43 jet of either air or water directly into the filter media. As well as assisting in cleaning the filter media, the auxiliary scouring is beneficial in preventing filter cracking and mud buildup. 49 As time passes between backwashes, the head losses will begin to increase. An increase in head loss results in a declining flow rate. If desirable to maintain a constant rate between backwashing, two options can be pursued: allowing the water level in the filter to rise with time, or controlling the flow within the outlet pipe with a valve. On the other hand, sometimes it is more desirable to let the flow rate decrease (declining-rate filtration). The advantage to declining-rate filter systems is that they decrease the chance of particulates breaking through at the end of a run Upflow-Downflow Filtration Another alternative filtration method is upflow-downflow filtration. An illustration of an upflowdownflow filtration scheme can be seen in Figure 19. Figure 19 - Upflow-Downflow Filtration Scheme Op. cit., Schulz/Okun, Op. cit., Schulz/Okun,

44 This system can be beneficial to lesser developed countries because it can handle large variations in water quality, while replacing the common sedimentation and flocculation processes with upflow roughing filters. A reduction in operation, maintenance and construction costs is the result of simplifying to roughing filters. The upflow-downflow filtration system can be delivered as a package system, which is desirable when on-site construction cannot be accomplished. 51 There are basically two sides to an upflow-downflow filter. The first side is commonly known as the contact clarifier. Water is fed from the bottom of the clarifier where alum can be added. The raw water is then forced through the media flowing upwards towards the water level. It first passes through several orifices. In a dual-media filter, the raw water then passes through a layer of gravel followed by a layer of coarse sand with an effective size ranging from 0.7 to 2.0 millimeters. A single media filter could use either coarse sand or gravel, or another type of media; pilot testing should be done to verify the best media for a specific system. The contact clarifier should have backwash capabilities. Once the clarified water reaches the water level, it flows into the second part of the upflow-downflow filter: the rapid sand filter. Rapid sand filters have been described in detail previously in this report. Backwash capabilities and the water level are maintained by control valves and an elevated storage tank, but pumps may be used as well Irrigation Irrigation is a critical component to farming in dry climates where access to water is limited. An irrigation system would also make growing fruit and crops much less labor intensive since water would not have to be carried from the water source to the plants. One of the major crops for the Tarahumaren people is corn. A respectable yield from one acre of corn in the United States requires approximately inches of water during a 100 day growing season. The required amount of water is about 540,000 to 675,000 gallons of water per acre of corn. 53 Weather data from the nearby city of Choix, Mexico, shows that during the wet season about ten inches of the 51 Op. cit., Schulz/Okun, Schulz, Christopher R; Okun, Daniel. Surface Water Treatment for Communities in Developing Countries. Washington D.C: (John Wiley & Sons, Inc, 1984): Extention, Michigan State University. Corn, Water Requirements. March 28, (accessed November 13, 2009). 43

45 20 inches of water is achieved from rainfall. 54 The fields in the village are not likely high yield fields like in the US and do not require nearly as much water to have a successful crop. For one acre of corn, the irrigation system would likely have to provide anywhere from 1 inch of water up to 10 inches, or 27,000 gallons to 271,500 gallons. The wide range of water required will be narrowed down to a more exact quantity once the team visits the village and gathers data on the current irrigation techniques that the villagers use and how much water is used to irrigate the corn. The 27,000 gallon to 271,500 gallon range is a much more feasible amount of water for a small gravity fed system to provide over a growing season of approximately 100 days. One of the simplest irrigation techniques is to flood the fields and allow the water to flow over the crops and soak into the ground. The flooding can either be done via pumping water into the field or by using gates to control a water source that is at a higher elevation. The flooding method is not very conservative with water. Around half of the water that is delivered to the field does not make it to the crops because of evaporation and transpiration. A more conservative method of irrigating a field is drip irrigation. With the drip method, water flows through tubes and there can either be smaller tubes coming off the main tube or holes punched in the tube where the water comes out directly at the base of the plant. The drip method can become expensive since there can be many tubes involved in watering a large field. Therefore, the drip method is better suited to small fields where the supply of fresh water is a concern. 55 These are the two best methods of irrigation for areas where machinery and power are not available. 5.5 Sanitation A large health concern in many developing regions is sanitation and wastewater. There can be many adverse health effects if waste is not properly disposed. Adverse health effects can also greatly increase the spread of disease within the village. The easiest way to improve the sanitation of the village is to construct a latrine pit for each family. The minimum requirements 54 Underground, Weather. History for Choix, Mexico. November 11, (accessed November 11, 2009). 55 USGS. Irrigation techniques. May 13, (accessed November 13, 2009). 44

46 for dimensions of a latrine pit, according to Water Aid, are about 1.2 meters wide (circular or square) and about three meters deep. These pits can easily be dug by hand with a few people. Some constraints on these pits are that they must be above the ground water level and away from any wells. If these constraints are not met, the pits will allow contaminates to soak into the soil. The contaminates will then be absorbed into the ground water creating many health problems for people using nearby wells. The pits should have enough volume for the average family, meaning the contents of the pit will always have time to biodegrade into stable and safe byproducts. Therefore, the pit should never need to be emptied. The pits will also need a concrete cover, or well constructed wood cover, to keep the odor under control since there will not likely be a vent pipe in the pits. The cover should have an opening for a lid that can be put in place when the latrine is not being used. If the family desires some privacy when they are using the latrine, a small superstructure can be built out of local material and placed over the latrine. If a pit does manage to get full, it must remain enclosed for a year before it can be cleaned by hand. In the event that the pit must be cleaned before a year there will need to be some sort of pump used because there is a still the danger of the waste containing hazardous byproducts Aid, Water. Technology Notes (accessed November 13, 2009). 45

47 Figure 20 - Single Pit Sealed Latrine The dorm in the village currently has a toilet that is attached to a septic tank. It is not known at this time how reliable the septic system is or how full the tank is. The septic system is only connected to the dorm and likely does not have the capacity to be expanded to collect waste from nearby houses. The septic tank will not likely be able to handle water that comes from the showers that are planned to be installed either. There will have to be some sort of greywater to deal with this water. If the greywater is not overly contaminated it can be used in a drip irrigation system to provide water to crops. The greywater system would consist of piping water from the shower and sink drains to either a holding tank or directly onto the field. If a storage tank is used, it must be ensured that the water is not held in the tank for an extended period of time since the extra storage time will encourage the growth of bacteria. 5.6 Run-off/Erosion Control Soil erosion in can have many undesirable affects in rural undeveloped villages like Cuchiverachi. It can lead to a loss of usable land and can also adversely affect the drinking water by adding 46

48 Feasibility & Decision Matrix of Design sediment to the supply. The sediment can quickly clog the filters that are being used to treat the water ensuring that cleaning will have to be performed more frequently. Erosion and run-off is a larger concern during the wet season when rainfall is more frequent. One of the main causes of erosion in the village and the surrounding areas is most likely overgrazing by livestock. Overgrazing removes vegetation from the area and allows wind and water to have a greater affect on the soil, which therefore speeds up the erosion process. Water erosion is the most severe type of erosion. The only feasible solution for a rural village with an extremely low budget is to reduce the amount of runoff that goes across the soil by placing a drainage ditch in the area to control the flow of water across the land. 57 The drainage ditches must discharge downstream of any water filtration system since the water will be heavily contaminated with sediment. Section 6 : FEASIBILITY & DECISION MATRIX OF DESIGN 6.1 Feasibility There are several different approaches that could be taken to meet each one of the goals of the project. No electricity is available and the nearest fuel station is a three hour drive away, so alternatives requiring the use of fuel, electricity, or a constant supply of materials is not ideal. Some alternatives are more feasible than others, but it is difficult at this point to determine which one is the best as more information is needed about the landscape and water availability. To get the necessary information, the team plans to visit in January (2010). While visiting Cuchiverachi, the team plans to collect data including: the community leaders direct desires and expectations for the project; locations (GPS coordinates), elevations, and reliability (estimate current flow rates and ask locals about dry season flow rates) of all springs with potential for providing water to the dorm; coordinates, number of occupants, and current water sources of each home and building in the community; 57 Park, Dr. Julian, Dr. John Finn, Richard Cooke, and Dr. Clare Lawson. Soil Erosion. July (accessed November 13, 2009). 47

49 Feasibility & Decision Matrix of Design water quality of potential water sources (by using a water testing kit); soil conditions (for potential piping routes and at erosion site); topography around the erosion site; current sanitation practices; and location of potential building materials (rocks, gravel, sand and wood). 6.2 Decision Matrix In determining the feasibility of the various alternatives and components of the water system several design norms were examined: cultural appropriateness, reliability, safety, maintenance, environmental stewardship, capital cost, energy costs, and easy of construction. Each alternative has its advantages and disadvantages and can be seen in Table 1. However, each components feasibility depends largely on the physical properties of the geography, topography, and hydrology of the land. For this reason, the alternatives that are feasible will not be narrowed down until the visit to the village. Table 1 - Decision Matrix 48

50 Feasibility & Decision Matrix of Design Worth (1-5) Rainwater Collection Springs Rivers/ Streams Ground Wells Ozonation Ultraviolet Irradiation High ph Treatment Chlorine Gas Chlorine Dioxide Granular Calcium Hypochlorite Sodium Hypochlorite Chloramination Slow Sand Filtration Rapid Sand Filtration Components Cultural Appropriateness Reliability Saftey Maintenance Environmental Stewardship Capital Cost Energy Costs Ease of Construction Upflow-Downflow Filtration Total The necessity and level of treatment for each water source can be predicted with reasonable accuracy; however, water quality tests will be conducted during the visit to make a more accurate assessment to determine the final design of the system. The typical treatment requirements are visually represented in Figure

51 Preliminary Design Figure 21 - Water Source and Treatment Process Tree After returning from the visit to Cuchiverachi, the team plans to submit a report containing a summary of the trip, the collected data, and conclusions made. It will outline the preliminary design that will be determined based on the data and experiences from the trip Section 7 : PRELIMINARY DESIGN The preliminary design is largely dependent on the source of water. Possible water sources analyzed in the decision matrix are: rain water collection, springs, ground water, and rivers/streams. Currently the team has been unable to gather sufficient data on viable source options. Therefore, the team is planning to visit the site at the end of January. During the visit, different source options will be analyzed for water quality, coordinates and elevation, consistency of supply etc. Once the possible sources have been identified, it will be possible to make a decision. Right now, however, the only design decisions to be made are those concerning alternatives that are inappropriate given the circumstances of the project. In the decision matrix, several sources seemed to be viable options. Rain water collection is an easy way to capture clean water; however, it may need to be supplemented by an additional source in the dry 50

52 Preliminary Design season. Springs are a very clean source of water, but their proximity to the dormitory would require extensive piping and construction. Ground water wells would also be an excellent and reliable source of water. At this time, more research needs to be done on the location of the water table to see if a well would be a viable source option. Water quality is the factor which will determine whether it is necessary to disinfect, filter, or treat the water. Most sources require some sort of disinfection; an exception is a protected spring. As raw water quality decreases, filtration may be required. As the raw water quality decreases further, sedimentation and flocculation may also be necessary. If the raw quality decreases past levels unacceptable to WHO levels, the source will be rejected as a viable water supply. Several disinfection alternatives have been deemed inappropriate for this design project regardless of the source being analyzed: ozonation, ultraviolet radiation, high ph, and chlorine dioxide gas. Ozonation and chlorine dioxide gas systems require on-site production of their respective gases. The production of ozone and chlorine dioxide gas both require highly complex equipment and skilled labor, which are highly unrealistic options in lesser developed countries. Ozonation, ultraviolet radiation and high ph treatment require additional chlorine application for residual effect. Therefore, treatment with these alternatives at a small scale facility is superfluous. The high score from the decision matrix for disinfection was granular calcium hypochlorite, because of its overall simplicity and low cost association. Slow sand filtration was chosen as the best alternative from the decision matrix, because slow sand filtration requires neither skilled labor nor automated machinery. Also, slow sand filtration neither requires pumping nor does it require backwashing. Water is saved by eliminating the backwashing process. The ability to work without pumping is desirable because there is not a readily available power source in Cuchiverachi. The medical missions organization requested the system be designed in stages. Staging would allow the construction and implementation to be done when the money is available. Also, staging will give the community a chance to determine if the results are desirable before pursuing further construction. 51

53 Cost Analysis Section 8 : COST ANALYSIS 8.1 Project Budget Funding for construction, operation, and maintenance of the design is being covered by Salud Para Suchil and funds raised by the design team. Salud Para Suchil is limited to a yearly budget of approximately $20,000. Therefore, highly efficient and effective construction costs are an essential aspect to the overall design. The overall system is being designed so that the villagers, volunteers from the medical mission, and our design team can complete a large portion of the overall construction. The project budget consists of material, labor, and travel costs. Depending on which alternative is chosen, material costs could include concrete, piping, chemicals, tanks, valves, pumps, filter media, etc.. Material and labor costs vary greatly depending on location, and will be analyzed more in depth on the trip to Cuchiverachi. Costs for filtration and disinfection will vary depending on water quality and volume. Slow sand filtration construction costs can roughly be estimated using Figure 22, which has been developed based on small scale slow sand filtration plants in Washington State. 52

54 Cost Analysis Figure 22 - Construction Cost for Slow Sand Filtration 58 By extrapolating the equation for a system demand of 260 L/day (69 gpd) the construction costs of a slow sand filtration system is approximately $1700. For a design life of 10 years, at 69 gpd, approximately 250,000 gallons of water will be treated. A onepound bag of granular calcium hypochlorite can treat approximately 10,000 gallons of water. For a design life of 10 years, 25 pounds of granular calcium hypochlorite is needed; which costs about $100 in the United States. 59 Again, costs will be analyzed more closely during the visit to determine if materials should be purchased in Mexico or in the United States. 8.2 Senior Design Budget The senior design team has been budgeted $300 from the Calvin College Engineering Program for expenses due to the project. Expenses attributed to the budget will include an altimeter, a Hach water 58 Slow Sand Filtration and Diatomaceous Earth Filtration for Small Water Systems. Washington State Department of Health: Environmental Health Programs Division. Olympia, WA (April, 2003): Environmental Protection Agency. 53

55 Project Schedule testing kit, a physical model of the finalized design, sample piping, and possibly pilot testing. At this time, the entire $300 is projected to be spent on this project. The design team is also planning on sending two members to Cuchiverachi, Mexico at the end of January for six days. Travel costs for the trip are shown in Table 2. Table 2 - Travel Cost Estimates Item Quantity Unit Cost Total Cost Plane Ticket 2 $ 300 $ 600 Travel Expenses 2 $ 425 $ 850 Equipment 1 $ 175 $ 175 Total = $ 1,625 Travel expenses include food, lodging, and ground transportation. Equipment is in reference to testing supplies and other miscellaneous equipment. The total cost for the trip will be approximately $1625 dollars. Plane tickets and travel expenses will be out of pocket expenses of individual team members. Section 9 : PROJECT SCHEDULE 9.1 Gantt Chart The Gantt chart for the fall semester can be seen in Appendix C. The team is currently preparing a Gantt chart for the trip in January to ensure that we make the most of the few days that we will actually be in the village. A Gantt chart is also being made for the spring semester at this time. 54

56 Implementation Section 10 : IMPLEMENTATION 10.1 Fundraising For the project to be successfully implemented some fundraising will be needed. Currently the missions group Agua Para Suchil has a yearly budget of $ The budget includes transportation lodging, food and visas for those who are a part of the missions group as well as food, medical supplies for the Tarahumara people living in the village. We anticipate that there may be less than $5 000 set aside currently for the project. While the team will be designing the solution to be as inexpensive as possible they also want to ensure that quality and reliability will be present in the solution. Currently, the team does not believe that $5 000 will be enough to cover the costs of the implementing the project and so they are anticipating to raise money for the community. The fundraising will not begin until next semester at which point the team will have a better understanding of the final costs of the project. The team is currently in the process of raising funds for their trip at the end of January and is hoping to apply what will be learned from this experience to the fundraising goals Construction At this time the team has no construction plan as the design has yet to be completed. However, the team is praying that the fundraising will be successful so that they will be able to visit the village in June of 2010 to begin construction of the new drinking water system. Section 11 : CONCLUSION Through research, several alternatives were found that would meet the project objectives. Many of the methods found that are being used for capturing and distributing water, filtration and disinfection, sanitation improvements, and erosion control have been successfully implemented in lesser developed areas. More data of the land and water needs to be acquired before determining the best alternatives and the preliminary design. To obtain the data, members of the team are planning to visit the community in January. Based upon the data collected, the team will determine which alternatives for each component will be used for the design. 55

57 References While a preliminary design has not been determined, several of the alternatives have been determined to be inappropriate. The remaining source alternatives include ground wells, springs, and rain catchment. The remaining filtration alternative is slow sand filtration. The remaining disinfection alternatives are granular calcium hypochlorite, sodium hypochlorite, and chlorine gas. REFERENCES Aid, Water. Technology Notes Droste, Ronald L. Theory and Practice of Water and Wastewater Treatment. Hoboken, NJ: (John Wiley and Sons, 1997). Environmental Protection Agency. Chlorine Dioxide. Chapter 4. Environmental Protection Agency Guidance Manual - Alternative Disinfectants and Oxidants: April Environmental Protection Agency. Extention, Michigan State University. Corn, Water Requirements. March 28, (accessed November 13, 2009). F.B. Leopold Company. Feng, Yangang; Smith, Daniel W; Bolton, James R. Photolysis of Aqueous Free Chlorine Species (HOCl and OCl - ) with 254 nm Ultraviolet Light. J Environmental Engineering Science, Volume 6: NRC Canada, Gorney, Cynthia. "The Tarahumara of Mexico evaded Spanish conquerors in the sixteenth century. but can they survive the onslaught of modernity? A people a part." National Geographic Nov (2008). Grabow, W. O. K; Middendorff, Irmela G; Basson Nerine C. Role of Lime Treatment in the Removal of Bacteria, Enteric Virsues, and Coliphages in a Wastewater Reclamation Plant. American Society of Microbiology: Applied and Environmental Microbiology, April

58 References Halma PR Services. Huisman, L. Slow Sand Filtration. Geneva, Switzerland: (World Health Organization, 1974). Lackeby Water Group. Lackey, Laura W; Mines, Richard O. Introduction to Environmental Engineering. Upper Saddle River, New Jersey: (Pearson Education, Inc., 2010). Martin-Doole, Melanie; Collins, Robin M; Pope, Greg P; Speitel Jr., Gerald E. Predicting DXAA Formation During Chloramination. Mountain Empire Community College. Nu Energy Horizons. Park, Dr. Julian, Dr. John Finn, Richard Cooke, and Dr. Clare Lawson. Soil Erosion. July (accessed November 13, 2009). Reynolds, Tom D; Richards, Paul A. Unit Operations and Processes in Environmental Engineering. 2 nd Ed. Boston, Ma: (PWS Publishing Company, 1996). Roberts, David. "In the land of the long-distance runners; Mexico's Copper Canyon is home to great athletes, the Tarahumara." Smithsonian May (1998). Schulz, Christopher R; Okun, Daniel. Surface Water Treatment for Communities in Developing Countries. Washington D.C: (John Wiley & Sons, Inc, 1984). Slow Sand Filtration and Diatomaceous Earth Filtration for Small Water Systems. Washington State Department of Health: Environmental Health Programs Division. Olympia, WA (April, 2003). Underground, Weather. History for Choix, Mexico. November 11, (accessed November 11, 2009). 57

59 Acknowledgements United States Environmental Protection Agency. Wastewater Technology Factsheet Ozone Disinfection. Office of Water, Washington DC. EPA 832-F , September 1999: 1-2. United States Environmental Protection Agency. Wastewater Technology Factsheet Ultraviolet Disinfection. Office of Water, Washington DC. EPA 832-F , September USGS. Irrigation techniques. May 13, (accessed November 13, 2009). Wolfe, R L; Ward, N R; Olson B H. Inorganic Chloramines as Drinking Water Disinfectants: A Review. J. American Water Works Association, World Health Organization. Guidelines for Drinking-water Quality. First Addendum to the 3 rd Edition, Volume 1, ACKNOWLEDGEMENTS Professor Aubrey Sykes, Calvin College Professor David Wunder, Calvin College Dan VanderHeide, Williams and Works Richard Stam and Lorenzo Dominguez, Salud Para Suchil Breese Stam, Grand Rapids Engineering Department Ryan and Shelly Maness, Highways and Hedges Ministries James Kamps, American Association of Independent Architects 58

60 Appendix A Target for chemicals in drinking water APPENDIX A TARGET FOR CHEMICALS IN DRINKING WATER Guidelines for Drinking Water Quality. 3 rd Edition, Volume 1. Geneva, Switzerland: (World Health Organization, 2008): Table A4.3,

61 Appendix A Target for chemicals in drinking water 60

62 Appendix B Target for microorganisms in drinking water APPENDIX B TARGET FOR MICROORGANISMS IN DRINKING WATER Guidelines for Drinking Water Quality. 3 rd Edition, Volume 1. Geneva, Switzerland: (World Health Organization, 2008): Table 7.4,