Bio-digesters in Devikulam

Transcription

1 The University of Western Australia Bio-digesters in Devikulam Engineers Without Borders (EWB) Challenge Written by: Zacchary Hoskins, Tom Copley, Jack Williams, Anthony Rettura, Luke Bock and Tessa McGrath Tutorial 16: Team B May 31, 2011

2 Executive Summary The aim of this project is to improve some aspect of the waste management or sanitation in Devikulam (a rural village in southern India). To this effect we started off with four different design concepts, each focussing on slightly different areas of waste management (hard waste, organic waste or sanitation) and each of these were useful in very ways. As we could not directly compare the use of these concepts we came up with five design requirements to compare them and decide which to develop further. These design requirements were cultural acceptability, cost, how easy the design is to assemble, sustainability and environmental impact. From these design requirements we concluded that the anaerobic bio-digester was the most suitable of our concepts to pursue. Simply put an anaerobic bio-digester is a large chamber that you put organic waste in and let it sit there, in the absence of oxygen, to decompose. This would be useful in Devikulam because it removes their organic waste, which is generally just thrown out and produces useful by-products in the form of a nutrient rich fertiliser and biogas (primarily methane). Our bio-digester is built using polyethylene sheeting to form the chamber, PVC pipe for the input and output, a gas tap to remove the gas and old inner tubing from bike tyres for sealing around the PVC and polyethylene sheeting. In implementing this design in Devikulam we would need to bring many of the materials in from outside the village and assemble them in the village itself. Another important part of the implementation process would be an education program to explain the how to use the biodigesters and what benefits they will have for the community. To do this effectively we intend to ask the volunteers from Pitchandikulam Forest to assist us as they are already set up in the area and have knowledge of local culture and custom. Another advantage if they assist us is that they already have a connection with the community and as such people will be more inclined to listen to what they have to say. This would mean that our education program and the implementation itself would have a greater chance of success. Assuming implementation went smoothly the positive impacts of this bio-digester for Devikulam would include decreased pathogen levels in the ground water and a reduction in methane being released into the atmosphere from decomposing waste. As well as this the community would be provided with a good fertiliser to use or sell and flammable gas, which can be used for cooking or heating. However, there is a drawback with this design as it may constitute a safety risk. It is potentially hazardous because their will be a pressure build up in the chamber as the gas is produced and also the gas is flammable and will be used to create an open flame. To accommodate for this steps will need to be taken to minimise the likelihood of something going wrong. The final advantage of the anaerobic bio-digester is that it is a simple and effective proven technology that can be adapted to suit the scale and context required for implementation in Devikulam. 2

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4 Team Reflection Our group, consisting of Zacc, Anthony, Tom, Luke, Tessa and Jack, have worked together for the past 13 weeks to complete the aim of our project. This aim was to find a solution to waste management in the poverty stricken Indian Village of Devikulam. Together all members of the group have contributed and worked in a professional manner. The factors that made our team bond well together, revolved around our communication, dedication and assistance to one another. The communication between every member in the group was a major factor that helped our team to bond as well as complete the project. Before starting work on our project, each member of the group exchanged addresses and mobile phone numbers. Whenever one member of the group could not attend a time dedicated to working on our project, they always contacted someone else in the group to let them know of the absence. This occurred several times during team meetings. Even though the group member was not present, the others made the absent member aware of what they had missed and what they had to work on for the week. Another way, in which the team communicated well with each other, was when we had discussions. Each member of the group was allowed to voice their opinion and whenever decisions were made everyone had to agree with it in order for it to pass. Each member of the group was willing to do the work set for them through the week and have it completed by the time it was due. This assisted in our team bonding, as we trusted other members in the group to have tasks completed by the deadline. Our group also set the work to members according to their strengths and weaknesses. This was shown for example in our final report. Zacc had the most knowledge on our final chosen concept of the bio-digester. Therefore the team all agreed that he was going to write up the design section of the final report. This reflected our team working well together as we were able to recognise each other s strengths and weaknesses and also trust that others would contribute to the final report. Another factor that helped our group work well together was our willingness to help other members in the group when they encountered problems. This was even shown in units outside of GENG1003. Since we are all doing first year engineering, each member of the group had similar first semester units. Whenever the group had a team meeting we often discussed and helped each other with these other units as well. Overall the group worked extremely well together. We showed that we were capable of completing the project at hand as well as bonding together as a team. This allowed our progress throughout the 13 weeks to be a comfortable and effective process. 4

5 Table of Contents 1 Introduction Current Technologies Incineration Landfills Design Requirements Acceptability Cost Ease of Build Sustainability Environmental Impact Design Concepts Bio-digester Compost Toilet Soakwell Filtration System Design Selection Design Description Summary Problems Description Construction Maintenance Prototype Testing Costs

6 6 Implementation Impacts of Design Social Environmental Economic Risk assessment Conclusion Recommendations References

7 Table of Figures Figure 4.1: Large Farm Bio-digester Figure 4.2: Anaerobic Digestion Process Figure 4.3: Blue barrel composting toilet Figure 4.4: Toilets That Make Compost Figure 4.5: Concrete Soakwell Figure 4.6: Polypropylene Versitank Figure 4.7: Polypropylene Soakwell Figure 5.1: Small Farm bio-digester Figure 5.2: Biogas as produced by bio-digesters in Costa Rica Figure 5.3: Bio-digester Trench Figure 5.4: Our First Prototype Figure 5.5: Gas Tap Design Figure 5.6: Gas Tap design

8 1 Introduction Devikulam is a small rural village located near Pitchandikulam Forest in southern India. India is a country that possesses a high economic growth but still struggles with large-scale poverty, especially in rural areas. Devikulam is one such area with surveys showing that the average income per household varies from about $200-$900 AUD (Engineers Without Borders, 2011). The village itself is made up of approximately 90 families with household sizes ranging from 2-11 people with the majority containing 4-7 people. Most of the community have lived in the area their whole life, with the dominant religion being Hinduism (Engineers Without Borders, 2011). The main industry in the village is agriculture and many people in the village own their own land, which they use to grow crops such as sugar cane and rice. Those who don t own their own farms are mostly daily wagers, landless labourers or self employed householders. One of the major issues facing Devikulam at the moment is their waste and sanitation. The village currently has no form of waste disposal or waste management with the closest waste management site being in the village of Kadapakkam, located ~22km away from Devikulam (Engineers Without Borders, 2011). In the past campaigns have been used to help clean up the village, however no long term solution has been put in place. Due to this lack in waste management much of the waste is simply dumped behind peoples houses meaning that garbage often scatters across the landscape and during the monsoon season the garbage gets mixed up with what will become their drinking water. This causes another major effect in that it increases the amount of bacteria present and so increases the likelihood of getting a bacterial disease like Bacterial Diarrhea (Lenntech, 2009). The issue of waste management is a very broad problem that spans across the globe, but even in just the one village there are different sections to the problem. As a starting point we divided the problem into three sections, hard waste, organic waste, human waste and sanitation. Originally our research was focussed on the area of hard waste but as we continued we delved more into ways to manage organic waste and remove the excess water. 8

9 2 Current Technologies 2.1 Incineration An effective current technology that deals with hard waste is incineration. Simply put incineration is a process that involves the burning of waste materials. It involves the method of combustion also known as thermal treatment. By being burnt, the waste is turned into ash, flue gas and heat. Contemporary incinerators are also built to utilise the by-product from the heat to generate electricity, converting waste into energy. It can be used for waste materials of any size ranging from small, to large scale. There are many benefits that the method of incineration offers over other types of waste treatment technologies. However there are also some negative effects. Some of the pros and cons of using the method of incineration are listed as follows: Pros Cons Reduced volume of solid waste Less need for landfills Water pollution is lowered Energy can be generated and used for example power to run electricity Burnt waste volume is reduced by 90% High costs to run Dioxins are produced which pollute the atmosphere Not environmentally accepted due to pollutant it emits Toxic ash is produced Incinerators emit varying levels of certain heavy metals like manganese which are toxic Note. Data from Pros and Cons of Burning Solid Waste, Chen C. So although incineration can be an effective method for waste management it also can be a hazardous process both for the people involved and the environment. 2.2 Landfills Landfills are open pits built on the principle of eliminating solid waste or garbage while being both environmentally and socially accepted. The basic structure of a landfill is as a deep depression in the ground. The solid wastes are placed into the pit where it is properly managed, with the gas and contaminated liquid produced from the garbage breakdown in the landfill having systems to collect and dispose of them. Landfills need to be carefully located, 9

10 managed and operated in an environmentally friendly manner. This helps to minimise wastes such as the disposal of household, organic, commercial as well as some industrial wastes. Once the landfill is built the first step in the process is for the waste to be transported by truck to the location. The waste is then placed into the pit where heavy machinery is used to reduce its volume by compaction. Finally a layer of soil is placed over the waste to prevent odours from spreading and the wind from blowing litter around. This process is a daily cycle for the lifespan of the landfill. Pros Methane gas can be captured from the waste and used to make energy Stores wastes that are disposed Eliminated harmful agents that can cause illness Can hold large amounts of waste Cons Litter can be produced by garbage being blown by the wind if the fill is not covered properly with soil thus creating more rubbish The odour of the wastes can attract pests and animals Contaminated liquid from the garbage can pollute groundwater if not managed properly Takes a lot of time as well as money to build a landfill Note. Data from Landfills: Pros and Cons, Writer09 Landfills can contain hazardous wastes which if not treated properly can be harmful to communities 10

11 3 Design Requirements The design option we chose needs to be as useful as possible for the village but must also be realistically achievable. Designs that are high-cost, require specific expertise to implement or have to be replaced frequently are of no use no matter how effective they may be in solving the problem. To reflect this we have decided on five design requirements to assist us in selecting which of our design concepts we will use. They are: 3.1 Acceptability Our design concepts are not designed for us but for the people of Devikulam so we need to consider their lifestyle and most importantly their culture before we consider implementing anything. This is an extremely important consideration and is not so much something that can be compared between concepts, but it is something that is essential to the process. If any of our research leads us to believe that our idea will conflict with the culture then that design will be unsuitable to develop. 3.2 Cost The average family in Devikulam has an annual income of between thousand Rupees ($200 $900 AUD) (Engineers Without Borders, 2011) and we expect funding for this project to be limited so it is necessary to keep our design cost as low as possible. As such we will need to be careful to keep the cost of our design as low as possible. 3.3 Ease of Build To keep the project feasible and the cost low the project cannot realistically require any specific skilled labour to build. So our design must one be such that any person given the instructions and materials would be capable of putting it together. To compare the ease of building our concepts we must consider the basic steps involved and figure out whether any specialist training or tools are required and also to put some consideration into how long they will take to build. 3.4 Sustainability This project is a long-term project so our design needs to be cheap and simple to maintain as well as having a relatively long working lifespan. To measure the sustainability of our concepts we can firstly consider the lifespan of each of the components in our designs and how cheap or easy they will be to replace. 11

12 3.5 Environmental Impact This project involves not only helping the Devikulam community but also helping the environment so we need to consider whether our concepts will have a negative impact on the environment. To begin with all we will do to consider this is to observe the process and materials of the concept and to think through whether they are harmful to the surrounding environment. 12

13 4 Design Concepts 4.1 Bio-digester Bio-digesters are devices used to dispose of organic waste and produce useful products. The three essential advantages of the device are: Reduces disease spreading bacteria, Produces a nutrient rich fertilizer and Produces biogas Figure 4.1: Large Farm Bio-digester (British Biogen, 2005) These devices are currently being implemented globally within developing countries (Appropriate Infrastructure Development Group, n.d.). The bio-digesters provide a cost effective fuel source and prevent pollution of the environment caused by untreated and harmful waste products (Appropriate Infrastructure Development Group, n.d.) Rather than using chemicals such as propane, biogas is a sustainable replacement for the community when it comes to domestic energy needs. For those who purchase their fuel, a biodigester can save a large amount of money every year. This would be highly regarded in a village like Devikulam where the residents are not wealthy and in many cases suffer from poverty. It some cases this can also reduce the workload of people who collect their own wood for fires. This is also an advantage environmentally as it can prevent deforestation in areas where firewood is seen as an essential. The biogas produced by these bio-digesters has a composition of methane (CH %), carbon dioxide (CO %), hydrogen (H 2 1%), nitrogen (N 2 0.5%) and very small quantities (about 0.1%) of carbon monoxide (CO), oxygen (O 2 ) and hydrogen sulphide (H 2 S) (Appropriate Infrastructure Development Group, n.d.). This biogas is trapped as it is produced, making easy access to cooking fuel or (given the right devices) electricity. By preventing this gas escaping into the atmosphere it is also helps reduce emissions that contribute to atmospheric pollution. 13

14 4.1.1 Aerobic Bio-digestion Aerobic bio-digestion (or treatment) is a biological process, of which the key idea is to use oxygen produced by microorganisms to assist in the degradation of organic wastes. The main advantageous outcomes of this system are the reduced odour when properly loaded and maintained, provision of a quality effluent, it allows treatment of waste at a high-rate and eliminates many pathogens in organic and agricultural wastes (Zhu, J., n.d.). However, the system also has drawbacks, as it requires a constant source of energy to adequately maintain the aerobic conditions; this would be impractical in a village such as Devikulam, where the average household is not financially equipped to maintain these conditions. To compensate for this, it would be possible to reduce the energy input and maintenance but this would yield a pungent odour and take much longer to gain the same results. Also, the aerobic system requires potentially dry environments, and during the monsoon season these conditions would be hard to maintain Anaerobic Bio-digestion Rather than relying on mechanical or chemical means to induce this process, anaerobic biodigestion utilizes a complex range of bio-chemical reactions to breakdown organic waste in the absence of oxygen (primarily through a variety of naturally occurring bacteria) (British Biogen, 2005). Normally this process occurs in large sceptic tanks or digestion chambers. One important consideration for the anaerobic digester is the temperature. The bio-digester prefers warmer temperatures (ideally between C) as this increases the speed of hydrolysis and hence breakdown of organic waste (Appropriate Infrastructure Development Group, n.d.). As the average temperature in the area of Devikulam is approximately 35 C (Engineers Without Borders, 2011), it is in an ideal area for bio-digester implementation. Figure 4.2: Anaerobic Digestion Process (British Biogen, 2005) 14

15 Pros Energy is produced which is renewable and cleansed Deforestation is lowered due to less firewood being used as instead biogas is used to run fire Money is saved in a poverty struck area Fuel is easily accessed due to the biogas created Greenhouse gas emissions are decreased. Biogas when combusted creates a reduced amount of greenhouse gases Cons Time consuming process for example food scraps need to be cut into smaller pieces The bio-digester effluent needs to be removed from the tank daily In colder weather/climate functioning decreases unless heat from an external source is applied (not ideal for colder areas) Requires daily work to keep the anaerobic digestion process going continually Creates much less energy to such fuels as propane and natural gas Water on the surface, ground water and other used resources have less contaminants Pathogens as well as odours in the air are reduced. Bio-digested sewage has over 90% less bacterial levels Organic fertilizers are created by waste that can be converted A wide variety of organic wastes can be used by the bio-digester for example wastewater and food scraps Require little maintenance due to high reliability Reduces odour s produced by wastes Note. Data from Fact Sheet Anaerobic Digestion, Residua In the chamber of a bio-digester a conversion takes place, as the organic waste decomposes it becomes a nutrient rich fertiliser which can then be removed from the chamber and used to assist in the growth of crops or other plant life. When the organic waste is broken down a variety of gases are released with a large percentage being methane, an environmentally hazardous greenhouse gas that degrades the ozone layer. This is not a problem however as the bio-digesters can collect this biogas and it becomes an asset instead of a problem. Once collected the biogas can be used for heating, cooking or even as a means of generating electricity. Currently bio-digesters are being used in developing countries around the world. Bio-digesters provide a cheap cost effective source of fuel, prevent pollution of the environment and reduce the spread of diseases caused by the untreated waste. 15

16 4.2 Compost Toilet Toilet Systems One of our initial ideas for a design area to undertake was the problem Devikulam have with sanitation. And the major issue here was that open defecation is commonly practiced and socially accepted amongst the village. This has the potential to cause and spread disease, especially in the monsoon season when this waste is mixed with floodwaters and flows down the streets as sewerage. Our proposal to solve this problem was to design a waterless toilet, which is low in cost and easy to build with the materials available in the village. Along with introducing toilets to the village we would also implement an education program, the aim of which would be to explain the advantages of implementing such a system and to work towards making using them socially acceptable Compost Toilet A compost toilet or dry toilet is a toilet that requires no water but still operates hygienically and effectively. The dry waste collected from use could then be used to fertilise crops in Devikulam or be sold to other villages for a small profit for use on their crops. The design and build process for one of these toilets is quite simple meaning it could easily be built using the tools, skills and knowledge found in the village. Also the cost of building such a toilet is minimal compared to what is to be gained by the use of it. Figure 4.3: Blue barrel composting toilet (EcoFilms Australia n.d.) The design that would work best for implementation in Devikulam would have a wooden platform containing the seat and a 44-gallon drum below catching the waste. The wooden platform would be built off the ground to reduce the risk of contaminating floodwater during 16

17 the monsoon season. The materials needed to build this platform are readily available in the village (bamboo) and the skills required are basic carpentry, which many villagers would possess. The 44-gallon drum below the platform collecting the waste could be acquired from local businesses or businesses in a nearby city which would normally put them to waste by disposing of them directly to landfill. For smaller households such a large drum may not be required so the design allows for the use of smaller containers. After research into implementing this design it came to our attention through the EWB website that it would be against local beliefs and values to use human waste as fertiliser. So the fertiliser collected could not be used to benefit the village. As such this design is unsuitable and we moved on to consider the next design option where the waste would not be collected but just buried Compost Pit A compost pit is basically the same as a compost or dry toilet but instead of the waste being collected in a drum there is a hole in the ground were the waste accumulates over time. Once the hole is full it is then covered over and the toilet is moved to a new location were another hole is dug underneath it. The main problem with this design is the possibility of these holes turning into sewerage pits during the heavy rainfall of the monsoon season. This could be problem could be minimised by making sure the pits are dug on high ground, reducing the amount of flow into the hole. The pit design eliminates the problem of human waste being used as fertiliser. The design and build process for the compost pit is essentially the same as for the compost toilet and is therefore relatively straightforward. Figure 4.4: Toilets That Make Compost (Morgan, P. 2007) The major design difference between the compost pit and compost toilet is that the toilet frame needs to be portable so it can be moved around to different locations. This means that the frame needs to be built on top of the ground and fastened down at each location. This would require a slightly different design to the compost toilet but nothing too complicated that would require specialised skills. As with the compost toilet all of the materials that are required are readily available in the village. 17

18 This design proposal is feasible for implementation in Devikulam due to the low cost and ease of manufacture. It would also, with the implementation of an education program, help to solve the problem of open defecation, which is accepted as normal in the village. The only major problem with this design is that similar toilet systems have been implemented in other rural areas in India and have had very limited success of solving problem with most people simply not using the toilet (Wordpress, 2011). 4.3 Soakwell Background Information Devikulam receives a large amount of rainfall in the monsoon season. Flooding occurs and all kinds of wastes and grey water mix into the floodwater. Due to this the village has sanitation issues, which expose them to waterborne diseases. The village does not have the money for a modern drainage system and there is a great deal of space in the village with the bare ground almost everywhere. Rainfall Southern India has an average annual rainfall of approximately 800mm; most of which comes during the monsoon season. Rainfall during monsoon season of three towns near Devikulam Nagpattanam Cuddalor Madras 5.4mm each day 5.8mm each day 5.75mm each day Note. Data from Some Characteristics of the Average Monsoon Rainfall Along the Coasts of India and Burma, Gangopadhyaya, M. Sreenivasan, P.S. & Venkatarman, R What they are Soakwells are a cheap and effective way to drain water into the ground. A drain takes water into the soakwell where it will dissipate into the ground through a hole at the bottom. Putting soakwells in the ground is not very difficult and if enough soakwells were placed around the village they would be able to benefit Devikulam by removing the excess surface water. Materials Dimensions Capacity Cost Pre cast concrete soakwell 700mmx700mm 1078L $70 Plastic with concrete lid 700mmx700mm 1078L $27 18

19 Large scale strutted box soakwell system Note. Data from Bunnings Warehouse per m 3 per 1000L $15-20 DIY soakwells are not very difficult to make and could be made in the village from concrete or bricks, which would be the cheaper option. Extra materials such as large rocks could also be placed around the soakwells to make them more effective. Figure 4.5: Concrete Soakwell (Maddington Landscape and Garden Supplies) Figure 4.6: Polypropylene Versitank (All About Soakwells, 2011) Figure 4.7: Polypropylene Soakwell (Kijiji International, 2011) Possible problems Although soakwells have some useful aspects they also have downsides such as: 19

20 Readymade soakwells are not cheap and may need to be shipped which will be an added cost and while it is possible to build soakwells it may be a struggle to access the necessary materials from near the village. In order to get grey water directly into the soakwell the villager may have to physically carry the water in a bucket to the nearest soakwell drain. It may stop working if the ground becomes completely saturated (which tends to happen in the monsoon season). This could lead to standing water becoming toxic. They are not designed to save water in any way. Due to these problems while soakwells are in principle a sound idea they may not be of much use in the Devikulam context. 4.4 Filtration System Our final design concept for Devikulam was that of a filtration system. This design incorporates a way to collect most of the grey water that is discarded by the villagers and a filter mechanism that would enhance the water to a suitable quality. This water would then be available for villagers to re-use in their homes or possibly for farmers to use on their crops depending on how effective the filter is. The first aspect of the concept allows for the collection of this grey water, created when villagers wash clothes, wash dishes, bathe etc, by installing pipes or drains that run into a main collection tank. Within the tank is a grill with very small gaps (Around 2mm by 2mm gaps.) to stop any large foreign materials from processing any further. After which the proposal was to use a combination of sand, charcoal and gravel for the water to filter through, purifying the water to a more advanced level (Ryan, V. 2009). At this point a purifier is added to kill any hazardous bacteria and remove unwanted pathogens that could constitute a serious health risk to people using this recycled water (Ryan, V. 2009). The final step is for the water to be either collected in a water pump so that villagers may re-use it for their daily duties, or if required made available to farmers as a source of water for their crops in the dry season. Probably the greatest positive to come out of this filtration system would be the prevention of grey water being thrown out to sit and soak into the ground, be washed away by rain or in some cases contaminate the water regularly used by the villagers for drinking. The reduction of this risk makes the drinking water safer to drink and thus would hopefully result in an eventual decrease in sickness and disease in Devikulam. Re-using grey water could also increase the amount of clean drinking water as grey water can be used for washing and bathing, rather than using the drinking water. 20

21 This concept unfortunately has major negative points as well. The cost of a system such as this would be fairly high, and therefore finding money to pay for it could be a problem. This especially holds true when considering both the main filtration tank, that would probably have to be located underground and also if it is decided to use the recycled water for agriculture then the method of delivery could be difficult, time consuming and expensive. Another negative of this concept is the sustainability. The filtration system would have to be cleaned fairly regularly to stop the build up of solids in the grill and if this were not done thoroughly, the filtration system would stop working. The other sustainability issue is that the drains may not last to well due to wear and tear from the weather and if the drains were to stop working the system would stop working until they were replaced which could prove to be costly in the long-term. 4.5 Design Selection Each of our design concepts have both good and bad points and to decide which concept to develop we considered how they fitted into the five design requirements that we decided were the most important considerations. Note: The exception to this is that the concepts found to be culturally unacceptable will not be compared in the other sections, as they will no longer be considered for our final design Acceptability During our research we did not come across any evidence to suggest that anything in the biodigesters, soakwells or filtration system would be culturally unacceptable, but in saying this we also acknowledge that the culture in Devikulam is not the same as ours and as such communication with the village is required to get a definite answer as to whether or not the designs would be accepted. Also from our research it quickly became clear that the compost toilet would not be suitable as it involved using human faeces as fertiliser and this is culturally unacceptable (Engineers Without Borders, 2011). The other thing we found during our research was that in the past programs have been implemented by the government to get toilets into rural areas of India but that they had a very limited success rate and many people simply chose not to use the toilets (Wordpress, 2011). So while it may not be culturally unacceptable it also may not be of much use if implemented. 21

22 4.5.2 Cost The most expensive of our designs is the filtration system, as it requires tanks and an extensive drainage system, which would take a large amount of time and money to set up. The next most expensive would be the bio-digester because although each individual unit costs about the same as a ready-made soakwell more bio-digesters would be required to be effective Ease of Build Both the ready-made soakwell and the bio-digester are quick and simple to assemble with no specific building skills necessary but the filtration system and the DIY soakwell are more complicated. Both the filtration system and the DIY soakwell will take quite a long time to make and while the soakwell does not require any specific skills the filtration system would to ensure that all the drainage pipes worked properly, the tanks were properly installed and that the filter was working properly Sustainability Both the bio-digester and the soakwells (both ready-made and DIY) should last for a long time but the filtration system would require more upkeep. The bio-digester is made of durable materials with the least durable being the polyethylene sheeting which is still rated to last ~10 years and if the plastic sheeting does fail then the pipes and gas tap can be re-used. The soakwells also have a long lifespan with no particularly fragile or degrading parts. However, for the filtration the drains may be affected by severe weather and could end up having to be replaced on a regular basis Environmental Impact None of our designs have any serious negative environmental impacts while they are being used but if they stopped being used after a period of time then they may have an impact as so that they are sustainable they are non-degradable Conclusion From this the design that best fits the design requirements is the ready-made soakwells, but as it was fairly close between that and the bio-digester in making our final decision we also considered which design we thought would be the most useful for the community. Firstly the soakwell does not actually assist with any of the problems that lead to the water being contaminated but just removes the water from the surface but the bio-digester helps to remove some of the problem and also returns something to the village. The other consideration was 22

23 that the soakwells may not work if totally saturated which could quite easily happen during the monsoon season and as the monsoon season is when the excess water is a real problem they may end up being of little use so we decided to develop the anaerobic bio-digester as our final design concept. 23

24 5 Design Description 5.1 Summary As indicated in section 4.1 bio-digesters are an appropriate solution to dealing with the organic wastes in the village of Devikulam. Not only are they effective but is also a proven, reliable technology. For the Devikulam context we chose to optimise the process by making an anaerobic bio-digester. This process as detailed above (section 4.1) uses a sequence of complex bio-chemical reactions created by bacteria to break down almost any organic waste (British Biogen, 2005, pg 2-4). These wastes include plant matter, food wastes, agricultural wastes and even faeces if desired. In addition to disposing of these wastes the villagers are able to obtain nutrient rich fertilizers and biogas as useful products of the system. However, in order to make this system usable for our context we needed to scale down the size of the general bio-digester currently implemented on farms around the world. In addition to the scale, to make it viable we had to make it easy to construct with a low build and maintenance cost. The base material of plastic sheeting required some research but in the end we chose a chemical resistant polyethylene sheet (as this will not disintegrate easily over time) to be our digestion chamber. Figure 5.1: Small Farm bio-digester (British Biogen, 2005) As materials and financial costs are somewhat restricted we attempted to use natural materials found in the region of India to replace some of the more modernized components. This digester will in effect act somewhat like the conventional bin for the villagers, making the disposal of organic wastes convenient and rewarding. Given the average temperature of the region, the digester would require little costs to maintain the approximate 30 C that yields the more favourable biomass breakdown. 24

25 The by products of bio-digesters are very valuable. By collecting the biogas and effluent the villagers can save costs on other fuels in addition to obtaining a high quality fertiliser, which can be either sold or used on crops. Figure 5.2: Biogas as produced by bio-digesters in Costa Rica (Carmona, 2008) 5.2 Problems During our planning and testing we encountered many problems that we had to take into consideration. After time spent planning, we decided the design had to be low cost, sustainable, easy to operate and appropriately sized for each household. With this in mind we addressed each issue first individually and then as a whole. First of all we considered the available materials that are available in India. We chose to go with the standard polyethylene that makes up larger bio-digesters. This is also necessary as polyethylene is chemically resistant, making ideal for containing such organic wastes during the digestion process. For the inlet pipes we suggest PVC piping, due to its hard nature and smooth surface. However, depending on the types of plant life present in the area it may be possible to make inlet pipes and outlet pipes from Bamboo if it is more convenient. Through research we determined that a specific species of bamboo (Dendrocalamus Giganteus), which has a diameter of approx 25-30cm when fully grown (Guadua Bamboo, ) would be suitable. When rifled properly so as to smooth the internal tube, it could very well be used as a substitute to the more expensive piping used in the standard bio-digester. Given its durability and strength, we concluded that this would be a suitable substitute to the general pipes that allow the inlet of waste and outlet of effluent. However, unless the bamboo grows in the local area it would be almost as (if not more) expensive than PVC piping. Smaller and cheaper species of Bamboo may be usable at the expensive of more work required to break down the waste to a much, thinner slurry. For the gas valve we suggested buying a hose tap, and use standard hosing to redirect captured gas to the household for everyday use. After selecting appropriate materials we were faced with a new problem, the plastic itself required sealing. Normally we would suggest heat sealing but such a device may be both hard 25

26 and expensive for the villagers of Devikulam to acquire and use. To make up for this we researched the strength of the standard natural glue. Given the small scale size of the bio- naturally by digester it may be possible to seal the majority of the device with glues obtained tapping trees. From our prototype tests we determined that using glue (from a hot glue gun) that a digestion chamber of ~200x400mm could hold fivelitres of water without splitting. However there were some cases where the container leaked so a great deal of care must be taken when gluing to form an effective seal. From this we deduced that with careful gluing the digestion chamber would be suitably secure to maintain the capacity of the digester. We decided that this was within acceptable limits as the average household is between 4-5 residents (Engineers Without Borders, 2011) meaning that it should suffice for the estimated 20L waste that will be required to input to the system per day. While this is still an option we would suggest that it is not very practical as the gluing would be tricky and time-consuming. One other option that we researched was polyethylene bags. Instead of just getting sheeting certain industries buy bags and this could be a possible substitute for this design because it would not require sealing along the side, only around the inlet and outlet pipes. However due to the time constraints of our testing we were unable to fully research and testt the viability and cost of this option. Another problem we faced was the rolling. The bio-digester is going to be located on solid ground (preferably behind the household) and is susceptible to leaking if the inlet /outlet pipes aren t angled upward. To address this problem we decided that some type of stand would be required to hold the digester (or at least to make it stable). First of all we thought of making a stand out of wood/bamboo. However this would prove to be very costly for the villagers and so instead of elevating the digester above the ground we decided to dig a small trench with angled sides as illustrated below. Figure 5.3: Bio-digester Trench The angled sides allow the inlet and outlet pipes to remain at an angle to prevent leakage of effluent. Also we would suggest placing leaves or hay beneath the digester to provide some additional support. This scenario led to another problem, during the monsoon season the bio- the digester would probably sink into the mud like soil, so as to prevent this we suggested use 26

27 of an additional sheet of polyethylene as a base in the trench and overlay the surrounding ground to shield the soil from the water and prevent the bio-digester from sinking in. Unfortunately this led to another problem, it would cause a lot of water to sink into the biodigesters trench. This problem may not be too severe, as the bio-digester is a water tight and enclosed environment, but a large enough amount of water may alter the temperature of the bio-digester. This would result in a slower digestion rate and a lower biogas yield. Another option could be to place a soakwell under each bio-digester. Unfortunately due to time constraints we were unable to test the viability of these options and this aspect of the design requires further thought and testing to ensure a suitable solution is reached. Capturing and using the biogas also proved to be a problem. Initially we believed that using a hose would be the straightforward and simple method of redirected the gas. We suggest that the hose run s into the household where ideally the natural gas pressure from the digestion chamber can keep the flame going. It may also be possible to make a pressure relief point in the hosing. This would be ideal for when the villagers have no use of the flame. Rather than keeping a dangerous fire burning, they can cap off the hose and the valve would provide a release when gas pressure gets too high. However we were unable to test this theory (see the prototype section) due to lack of materials and time but in our research we found strong evidence that it may be a viable approach. Our last major problem was the collection of the effluent. This is a valuable product of the digestion process. To collect it we think it may be possible to have the angle of the outlet pipe lower than that of the inlet. This would force any overflow out of the outlet pipe. We then thought that we could dig a hole at the end of the digester where any overflow will be collected by a bucket or container beneath it (as illustrated above Figure 5.3). This collection vessel will be attached via string, rope or vines to a rod resting on the top, where the villagers can easily raise it and collect it. We also had to consider that in monsoon season the ground may flood and so the container would need to be suspended and sheltered so as to stop rainwater diluting the fertilizer. This is not a critical issue, as the fertilizer overflowing the bucket will merely fertilize the nearby ground, however they would be unable to benefit from the fertiliser and it would go to waste. 5.3 Description The bio-digester works as described in section 4.1 of the report and is basically a chamber designed to create the ideal environment for a series of complex biological reaction s that cause the breakdown of organic wastes into biogas and a nutrient rich effluent. 27

28 To achieve this process the bio-digester should first be initially loaded with animal manure and water to form a base slurry in which bio-digestion will take place. After leaving that for a day or two it should be ready to accept additional organic wastes. When loading the biodigester organic wastes should first be mixed with water and mashed down until it is fairly liquid in appearance. This will speed up the rate of digestion and help prevent any unnecessary blockages in the input pipe. In order for the organic matter to break down it must go undergo certain processes. The first stage of anaerobic digestion is a bio-chemical reaction called hydrolysis, where complex organic molecules are broken down into simple sugars, amino acids, and fatty acids with the addition of hydroxyl groups (Friends of the Earth, 2007). After hydrolysis comes acidogenesis. In this stage molecules are broken down even further to create volatile fatty acids, ammonia, CO 2 and small traces of hydrogen sulphide (H 2 S) (Friends of the Earth, 2007). After that the molecules are absorbed by bacteria to produce more CO 2, hydrogen and acetic acid (Friends of the Earth, 2007). These bacteria are than absorbed by methanogens, which produce the large quantities of methane that make up the majority of the biogas (Friends of the Earth, 2007). While the bio-digester does create a useful biogas, it also produces a quantity of hydrogen sulphide. This gas is produced during the acidogenesis stage of hydrolysis. These H 2 S emissions occur naturally during the breakdown of organic matter and while the bio-digester does not completely neutralize the H 2 S emissions studies have shown that they are well below hazardous levels due to the digesters enclosed chamber (Friends of the Earth, 2007). 5.4 Construction Prototypes We originally built two prototypes, one of which was a miniature scale model using a plastic drink bottle and small PVC pipes. The second model was made using plastic sheeting originally used for green houses. Figure 5.4: Our First Prototype 28

29 The plastic bottle was our first model (this was partly due to the fact that we had been unable to acquire plastic sheeting at this point). We first began by puncturing 2 holes in the bottle, one at the base and one in the centre. We then used a grinder to make the holes larger to the point where our piping would only just fit. After the piping fit in the base snugly we used a hot glue gun to seal the piping in place. We then place a small elbow pipe in the centre of the bottle, and likewise glued it in place (figure 5.4). Our second model was a lot more complicated. Once we had acquired a large sheet of plastic (about 1.2m x 10m) we had to decide on the overall size of our model. We chose to keep it small and cut three 1.2m x 1..8m strips. Not only was this convenient but it also allowed us to alter the design to accommodate any problems we encountered. We began the larger model by gluing the bio-digester along the seam making giving it a cylinder shaped appearance. We then placed our PVC tube inside and rolled the corners up so they tapered toward the pipe. After doing that we wrapped the old inner tubing from a bike tire around the pipe and plastic to form an airtight seal. Before doing the same to the other side of the bio-digester we used a knife to make a very small incision in the top of the digester. We then intended to use force to push a small pipe with an external taper through the digester. We would then make a washer out of the same material as the bike tire and push down so as to make an airtight seal around the pipe. Unfortunately we were unable to test this part of the design due to material constraints. Below is an image of the pipe set-up we intended to use. Figure 5.5: Gas Tap Design 1 Alternatively we could use the glue around the circumference of the tube at the point where it passes through the digester wall. We believe this would remove the need of the nut and we could use merely a wood disk to apply the necessary pressure to keep the digester airtight. In order to do this we would first place a hard surface below the incision in the digester wall. We would apply glue to the inside and outside of the incision and place all the components into 29

30 position. Apply pressure to the disk onto the flange until the glue is dried (e.g. leave a large book on top of it). Figure 5.6: Gas Tap design Devikulam In Devikulam the construction would take on a similar process. As described in the implementation section of the report. We suggest working with the group known as Pitchandikulam forest to help supply the plastic sheeting and other materials to the villagers. Once materials have been transported to the villagers, they will be able to make them on site using the similar techniques we used on our prototype. After learning the necessary skills to build and use the digester (see implementation) we suggest giving the villagers a measuring cup to demonstrate the amount of organic waste that can be successfully loaded into the digester without over loading it. 5.5 Maintenance Maintaining the bio-digester is relatively easy. The digester should regularly be checked for punctures and/or any damage to the bag. Any puncture to the digester can be patched up similar to a bike tire and any leaked effluent will be drastically reduced in pathogen content. If the damage is critical, it will be necessary to replace the digestion chamber completely. In which case it will be quite possible to recycle the other parts (e.g. PVC, hose tap, tire material) and use them on the new chamber. Additionally, it may be necessary to clean out the digester every few years depending on the quantity of indigestible material put into the digester. 30