SOUTH EAST KELOWNA IRRIGATION DISTRICT WATER QUALITY IMPROVEMENT STUDY

Transcription

1 SOUTH EAST KELOWNA IRRIGATION DISTRICT WATER QUALITY IMPROVEMENT STUDY Updated May 2006

2 SOUTH EAST KELOWNA IRRIGATION DISTRICT WATER QUALITY IMPROVEMENT STUDY UPDATED MAY Prepared by: Mould Engineering Glenmore Road Kelowna BC V1V 1Y5 Ph: Fax:

3 SOUTH EAST KELOWNA IRRIGATION DISTRICT WATER QUALITY IMPROVEMENT STUDY TABLE OF CONTENTS INTRODUCTION 2. NTRODUCTION BACKGROUND OBJECTIVES EXISTING WATER QUALITY 3. UALITY HYDRAULIC CREEK INTAKE WATER QUALITY FIELD ROAD RESERVOIR WATER QUALITY BENCH SCALE TESTING 4. ESTING COAGULATION AND FLOCCULATION CLARIFICATION FILTRATION WATER TREATMENT WASTE ALTERNATIVE WATER TREATMENT OPTIONS DISINFECTION BY-PRODUCT CONTROL 5. ONTROL BENCH SCALE RESULTS HEALTH RISKS OF CHLORINATION BY-PRODUCTS THM REMOVAL AND CONTROL WATER TREATMENT OPTIONS 6. PTIONS CLARIFICATION OPTIONS WATER TREATMENT AT HYDRAULIC CREEK INTAKE WATER TREATMENT AT FIELD ROAD RESERVOIR RURAL DOMESTIC WATER TREATMENT DURING IRRIGATION SEASON GROUNDWATER SUPPLY MILLER ROAD RESERVOIR 8. UPPLY ESERVOIR DISCUSSION OF WATER QUALITY IMPROVEMENT OPTIONS 9. PTIONS SEPARATE DISTRIBUTION SYSTEM & FULL TREATMENT TREATMENT FACILITY AT HYDRAULIC CREEK INTAKE TREATMENT FACILITY AT FIELD ROAD RESERVOIR GROUNDWATER CONCLUSIONS AND SUMMARY UMMARY

4 FIGURES Page: 1. South East Kelowna Irrigation District Key Map...(opposite) 1 2. Specified Service Area...(following) 4 3. Hydraulic Creek Intake flow, colour, and turbidity...(opposite) 7 4. Field Road Reservoir flow, colour, and turbidity...(opposite) 9 5. Bench Scale Plant Schematic (sedimentation and dissolved air flotation)...(opposite) Bench Scale Plant Schematic (direct filtration and membrane filtration)...(opposite) Sedimenation Results...(opposite) SEKID DAF Results...(opposite) Mould DAF Results 4 USgpm...(opposite) Mould DAF Results 7 USgpm...(opposite) Possible Dissolved Air Flotation Treatment Plant Site Plan...(opposite) Possible Conventional Sedimentation Treatment Plant Site Plan...(opposite) East Kelowna Road Wells to Supply Specified Service Area... (opposite) Groundwater levels in SEKID and Rutland Observation Wells... (opposite) Miller Road Reservoir Service Area... (opposite) 44 TABLES 1. Hydraulic Creek Water Quality 2002/ Field Road Reservoir Water Quality 2002/ Bench Scale Unit Operation Summary Average Water Quality Observed During Bench Scale Project Trihalomethane Formation Comparison Water Treatment Plant Cost Estimates Hydraulic Creek Intake Water Treatment Facility Options Field Road Water Treatment Facility Options Water Quality Comparison of East Kelowna Road Wells and Hydraulic Creek Supply Groundwater Supply Options Separate Distribution System & Full Treatment Treatment Facility at Hydraulic Creek Estimated Cost Treatment Facility at Field Road Reservoir Estimated Cost Groundwater Estimated Cost...49 ANNEXES 1. Cost Estimates 2. Lab Analysis Results 3. Summary of Guidelines for Canadian Drinking Water Quality

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6 SOUTH EAST KELOWNA IRRIGATION DISTRICT WATER QUALITY IMPROVEMENT STUDY INTRODUCTION During the spring and summer of 2003 a bench scale water treatment project, initiated by South East Kelowna Irrigation District, was conducted to test the feasibility of removing colour and turbidity from Hydraulic Creek water. This report outlines the results of the bench scale project and details options to provide domestic consumers with water that meets the Guidelines for Canadian Drinking Water Quality (GCDWQ). This report has been updated from the draft prepared in November Currently, water sources for the District include Hydraulic Creek, O Reilly Road well, and East Kelowna Road Wells 1 and 2. While the groundwater from all three well sources meets the GCDWQ, they are only capable of servicing a small portion of the District. Hydraulic Creek, the main source of water for the District, is prone to high colour and turbidity with the worst water quality occurring during spring freshet. Current treatment of the Hydraulic Creek source, consisting of screening and chlorinating, does not provide water that meets the GCDWQ. Although colour is considered an aesthetic problem, turbidity is considered both an aesthetic and health concern. A high level of turbidity can interfere with the effectiveness of chlorine disinfection against pathogens such as Giardia lamblia, the protozoan responsible for beaver fever. The District s water is considered safe for consumption by Interior Health and there have never been any known outbreaks. It is noted, however, that Interior Health has introduced a new program for the spring of 2006 notifying the public of a health concern, and boil water advisories when turbidity levels in the water increase. Mould Engineering 1

7 Introduction As the number of domestic connections within the District grows, so does the level of concern over water quality and the number of complaints from residents. Likewise, water quality has been receiving increased attention at Provincial and Federal levels of government as a result of waterborne disease outbreaks. Locally, the City of Kelowna, Black Mountain Irrigation District, and the City of Penticton have experienced outbreaks. Nationally, outbreaks have been highly publicized in Walkerton, Ontario and North Battleford, Saskatchewan. In 2003, Interior Health began requesting the preparation of long term plans for source, treatment, and distribution system improvements as a condition of the District s operating permit. This study of water quality improvement options is a first step. It is expected that input and recommendations from District trustees, staff, domestic users, and public health officials will be considered prior to selecting a treatment option. Once a final option is chosen, a long term plan will be prepared outlining the option, service area, project phasing and timing, operating parameters, capital and operating costs as well as funding source. This water quality plan will complement the 10-year 2006 Capital Works Program which outlines the water availability and capital charge rates required to fund improvements to supply growth within the District through to BACKGROUND South East Kelowna Irrigation District (SEKID) is the second largest irrigation district in British Columbia. The District is located on Kelowna s east bench and is bordered on the north and east by Mission Creek. This historical irrigation water purveyor currently services a total of 2349 ha, (5803 ac), of agricultural land and 1973 domestic connections. The major residential developments of O Reilly Road and Gallagher s Canyon / McCulloch Road areas represent approximately 70 % of total domestic connections with the balance being dispersed throughout the agricultural area. South East Kelowna Irrigation District is illustrated in the key map, Figure 1. Mould Engineering 2

8 Introduction Previous investigations into water treatment options for SEKID have suggested possible water quality solutions. Proposed solutions have included a dual distribution system to distribute treated drinking water to domestic connections throughout the District. However, due to the geographical spread of the District, with an approximate total pipe length of 90 km, 34 pressure reducing stations, and an average agricultural lot size of 6 ha (15 ac), a dual distribution system would be cost prohibitive. Dayton & Knight Ltd support this conclusion in their report of May 1994 that estimated the cost of such a system at $ 23 million. One significant complication facing water treatment options is the magnitude of demand fluctuations throughout the year due to irrigation. For example, flows during winter months are as low as 30 litres per second (lps) (500 USgpm), while summer maximum daily demands can reach about 1770 lps (28,000 USgpm); this represents a variation in flow of over 5000 %. Dayton & Knight Ltd estimated in their 1994 report that treating all water entering the distribution system from Hydraulic Creek intake would cost approximately $ 45 million. For the past several years, residential growth has been concentrated in the Gallaghers Canyon development and the adjacent McCulloch Road corridor to the west. Presently, the area encompasses approximately 1200 (60%)of the District s 1973 domestic connections. This area precedes the agriculture area on the mainline. Prior to some recent distribution system upgrades, chlorine contact time during summer flows was insufficient to ensure effective Giardia inactivation to this domestic area. In 1999, a 2.5 million-litre reservoir and re-chlorination station was constructed at the south end of Field Road. Water is diverted from the mainline to this facility is at the head of the distribution system that supplies the Gallaghers Canyon area which provides increased chlorine contact time as well as fire flow storage. Mould Engineering 3

9 Introduction During selection of the Field Road Reservoir Site, the potential for a future water treatment plant was recognized, and additional land was rezoned for this purpose. A treatment plant at this location has the potential to supply improved drinking water to approximately 60% of the existing domestic users. The possible Specified Service Area, which could be supplied from Field Road Reservoir throughout the year, is illustrated in Figure 2 and encompasses the McCulloch Road corridor from the Gallaghers Canyon area west to June Springs Road. Potential also exists to supply treated water from this location to the majority of the District during the winter season. The City of Kelowna Official Community Plan estimates that 704 residential units will be developed in SEKID over a period of 20 years with the majority within the McCulloch Road corridor. Thus, the proportion of domestic connections within the Specified Service Area is anticipated to increase with future growth OBJECTIVES This report aims to evaluate a number of water treatment options to provide drinking water that meets the Guidelines for Canadian Drinking Water Quality. Due to the extreme costs of treating the entire flow, the objective is to improve quantities sufficient to supply domestic customers within the Specified Service Area. Options to distribute this water during off peak periods to the balance of the District will be investigated as well as options to meet the ultimate goal of supplying all domestic users with improved water quality. Jar tests initiated and completed by Mould Engineering in the spring of 2002 indicated that it was possible to remove colour and turbidity from Hydraulic Creek water. Thus, the primary objective in operating the bench scale water treatment plant was a proof of concept at the bench scale. This provided the opportunity to examine finished water quality that can be achieved through the processes modeled. It should be noted, however, that flows through the bench scale plant were small and the data obtained is not Mould Engineering 4

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11 Introduction intended for the purpose of scaling up to design a full size plant. All trials involved coagulation and varying lengths of flocculation times. Four types of clarification were tested: 1. Sedimentation, & Filtration 2. Dissolved Air Flotation (DAF), & Filtration 3. Direct Filtration 4. Membrane Filtration A secondary aim of colour and turbidity removal is the reduction of chlorination byproducts such as trihalomethanes and/or their precursors. These by-products are formed by reactions between precursors such as organic matter and chlorine added to disinfect water. Bench scale plant testing is an integral part of developing a water quality improvement strategy. The information gained is important to determine capital and operating costs, in addition to providing data to assist in determining the optimal water treatment process with regards to water quality. Mould Engineering 5

12 Existing Water Quality EXISTING WATER QUALITY Hydraulic Creek, the principal water source, supplies over 99 % of the District s annual demand. As mentioned, the water is screened and chlorinated; the resulting water quality does not meet aesthetic objectives of the Guidelines for Canadian Drinking Water Quality. Since 1994, only two boil water advisories have been issued for the District, one of which was the result of chlorine cylinders being removed from the intake site for safety reasons during the 2003 Okanagan Mountain Park fire. The small area of the District s watershed that was damaged by fire will have a minor impact on water quality, as will the low levels of McCulloch Reservoir at the head of Hydraulic Creek. In 1998, concern over water quality led a number of residents in the O Reilly Road area to press for a groundwater supply in place of the current surface water source. As a result of a vote to increase their water rates, the O Reilly Road area of 172 domestic connections is now supplied with groundwater. The other two wells on East Kelowna Road are able to supply domestic connections in the lower KLO benches, the northern most area of the District, during low demand periods of the year. All three wells in the District draw from the Rutland Aquifer and reliably produce good water quality. In O Reilly Road well for example, colour is undetectable, turbidity averages approximately 0.2 NTU, and iron content is between 0.01 and 0.03 mg/l. The hardness of the District s groundwater is higher than that of Hydraulic Creek water averaging approximately 200 mg/l. However, hardness is not a concern with regard to public health. With the use of hard water, consumers may notice a lowered capacity to produce a rich lather with soap. There is currently no treatment of well water supplied to the system as it meets GCDWQ for all parameters. More details regarding groundwater within the District and the potential to increase the groundwater service area are discussed in Section 6. Mould Engineering 6

13 120 Figure 3: Hydraulic Creek Intake Flow, colour, and turbidity 3 year averages Flow rate (MLD), Colour (TCU) Turbidity (NTU) 20 AO 1 15 TCU 2 0 MAC 2 1 NTU Dec Feb Apr May Jul Sep Oct Dec Month 0 Notes: Data shown is an average of 2000, 2001, and 2002 data. Flow data and raw turbidity data is based on a single value per day recorded by operators in daily log. Colour data based on monthly true colour readings of raw creek water. 1 AO = aesthetic objective, 2 MAC = maximum acceptable concentration Flow rate (lps) Colour (TCU) 15 TCU Turbidity (NTU) 1 NTU

14 Existing Water Quality HYDRAULIC CREEK INTAKE WATER QUALITY The water quality of Hydraulic Creek at South East Kelowna Irrigation District s intake varies seasonally with colour and turbidity, peaking during the spring freshet. The colour is due to both iron and organic acids from decaying vegetation as water runs through the forest floor into McCulloch Reservoir. Raw colour and turbidity levels at the Hydraulic Creek intake exceed GCDWQ levels throughout the year. Figure 3 illustrates colour, turbidity, and flow trends recorded at the Hydraulic Creek intake. Colour and turbidity are lowest during the winter months when there is the least amount of water moving over land into the creek. As spring runoff begins, colour and turbidity increase from February through April. Once the spring freshet has passed, colour and turbidity gradually decline. Turbidity rises again in midsummer as a result of increased flows being released from McCulloch Reservoir to meet peak irrigation demand; these high flows carry more silt down the creek bed to the intake pond. A summary of 2002 and 2003 water quality is provided in Table 1 on the following page. Mould Engineering 7

15 Existing Water Quality Table 1 Hydraulic Creek Raw Water Quality 2002/03 Apparent True Colour Colour Iron Turbidity Temp ph TOC DOC PtCo T.C.U. mg/l NTU C mg/l mg/l Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Min Mean Max GCDWQ* = 15 = 0.3 = * Data in this row represents current Guidelines for Canadian Drinking Water Quality. Colour, iron, turbidity, temperature, and ph Guidelines are listed as aesthetic objectives. Mould Engineering 8

16 35 Figure 4: Field Road Reservoir Flow, colour, and turbidity 2 year averages Flow rate (lps) and Colour (TCU) AO 1 15TCU Turbidity (NTU) 5 MAC 2 1NTU 1 0 Dec Feb Apr May Jul Sep Oct Dec Month 0 operators in log. Turbidity and colour are based on monthly readings. 1 AO = aesthetic objective, 2 MAC = maximum acceptable concentration Flow (lps) Colour (TCU) 15 TCU Turbidity (NTU) 1 NTU

17 Existing Water Quality FIELD ROAD RESERVOIR WATER QUALITY Water entering the reservoir at Field Road from the mainline has been chlorinated at the intake with a residence time relative to demand rates. Table 2 contains a summary of 2002/03 water quality data for water leaving the Field Road reservoir. Figure 4 illustrates the variations in flow, colour and turbidity recorded at Field Road Reservoir. Water quality trends illustrated in Figure 4 follow a very similar pattern to those shown in Figure 3 for the Hydraulic Creek intake with some exceptions. Colour, having been oxidized by chlorine disinfection at the intake Field Road Reservoir, falls below the GCDWQ aesthetic objective of 15 TCU through fall and winter while turbidity remains above the maximum acceptable concentration of 1 NTU throughout the year. After the initial turbidity peak from spring freshet has passed, turbidity leaving Field Road Reservoir declines as fine particles settle out in the distribution system and reservoir. Turbidity rises again when demand picks up in the warmer months. During peak summer demand, turbidity patterns closely match those of the intake. Mould Engineering 9

18 Existing Water Quality Table 2 Field Road Reservoir Water Quality 2002/03 Apparent True Colour Colour Iron Turbidity Temp ph PtCo T.C.U. mg/l NTU C Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Min Mean Max GCDWQ* = 15 = 0.3 = * Data in this row represents current Guidelines for Canadian Drinking Water Quality. Colour, iron, turbidity, temperature, and ph Guidelines are listed as aesthetic objectives. Mould Engineering 10

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20 Bench Scale Testing BENCH SCALE TESTING Bench scale testing involves the construction of small water treatment plant components to provide data where no previous water treatment data exists. The purpose of this testing is to determine the feasibility of treatment prior to pilot water treatment plant design. Bench scale testing for this study involved four treatment configurations: sedimentation, dissolved air floatation, direct filtration, and membrane filtration. Figures 5 shows schematics of sedimentation and dissolved air flotation (DAF) treatment trains. Schematics of direct filtration and membrane filtration are shown in Figure 6. In the spring of 2003, bench scale water treatment plant units were assembled at the sodium hypochlorite station at Field Road. Aside from the bench scale units, a partial lab was set up for on-site water quality analysis while other samples were taken to a professional laboratory. Okanagan University College loaned one dual media filter, one membrane filter unit, a chemical-dosing pump, and various lab equipment for use during bench scale testing. Mould Engineering also contributed various items including a jar tester and large DAF unit. Spring trials began the first week of May, in time to catch the cold waters of the latter end of freshet, and ran until the first week of June. Summer trials ran August 19 through 28 with the exception of fire evacuation days. The majority of trials were run on pre-chlorinated water as it entered the reservoir while some trials were run on water collected at the intake and brought by tanker truck to the Field Road site. Pre-chlorinating the water reduces the colour significantly and oxidizes species such as iron and manganese making them easier to remove. However, chlorinating the water prior to treatment also reduces ph and alkalinity (resistance to ph change with the addition of acid). This may be of concern as the alkalinity of water is further reduced with the addition of chemicals during treatment. Water with a low alkalinity and low ph can cause corrosion problems within the Mould Engineering 11

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22 Bench Scale Testing distribution system; thus, alkalinity and/or ph adjustment prior to distribution will almost certainly be necessary. Pre-chlorinating the water also causes the formation of disinfection by-products (DBPs) such as trihalomethanes (THMs). These are formed when chlorine reacts with precursor material such as small, humus substance. Bench scale findings and analysis with regard to DBPs are discussed in detail in Section 4. Table 3 summarizes the unit operations used during bench scale testing. Table 3 Bench Scale Unit Operation Summary Area Volume Flows Overflow Rates Peak % Removal Unit m 2 ft 2 m 3 gal lps gpm m/h gpm/ft 2 Apparent Colour Turbidity Flocculation Tank Sedimentation Basin (after enlarging) DAF unit #1 (SEKID DAF) DAF unit #2 (Mould DAF) OUC filter Mould filter (spring trials) Mould filter (summer trials) % 26 % % 76 % % 75 % %* 95 % %* 95 % %* 95 % Membrane filter %* 97 % * Measurement of low colour values is unrealiable, particularly < 5 TCU. The Hach DR 700 colorimeter often returned negative values, these are considered here as having removed 100 % of measureable colour. Mould Engineering 12

23 Bench Scale Testing Water quality parameters that were frequently observed throughout the project included the following: Temperature Apparent colour (unfiltered) ph Turbidity Other parameters that were monitored less frequently are as follows: Conductivity Chlorine (free and total) Aluminum Hardness Iron Alkalinity True colour (filtered) Both true colour and apparent colour were observed during bench scale testing while the GCDWQ lists a guideline for true colour only of 15 TCU. True colour readings are taken by first filtering the water sample through a fine membrane to remove turbidity. Apparent colour, however, is measured on an unfiltered water sample and thus the colour is due to both true colour and turbidity. Apparent colour better indicates the colour that would be observed by consumers. Table 4 is an overview of the average water quality values observed for some parameters entering and leaving the bench scale plant and lab analysis are included in Annex 2. Table 4 Average Water Quality Observed during Bench Scale Project Average Values GCDWQ Parameter Before After Unit Alkalinity mg/l as CaCO 3 Aluminum mg/l Colour (Apparent) 1 64 note 2 - PtCo Colour (True) 1 28 note 2 15 TCU Iron (total) mg/l Turbidity 3.8 note 2 1 NTU ph ph 1 Colour varied significantly between chlorinated and un-chlorinated water. The above values are for chlorinated water; raw water average values were 51 TCU true colour, and 102 PtCo apparent colour. 2 Colour and turbidity results varied between treatment processes; results are discussed in Sections 3.2 and 3.3. Mould Engineering 13

24 Bench Scale Testing COAGULATION AND FLOCCULATION Chemical coagulation and flocculation were common features of all treatment options used in this study. These processes are necessary to remove colloidal contaminants from water. Colloidal particles are surrounded by common electrostatic charges making them similar to like poles of a magnet that repel each other. These charges prevent the particles from agglomerating and becoming large enough to precipitate out, thus they are held stable in solution. The purpose of chemical coagulants is to destabilize the charges of colloidal materials in water so particles will form flocs. These flocs can then be removed during a clarification step. Coagulants typically contain salts of aluminum or iron. The positively charged cations of aluminum and iron destabilize negatively charged colloids allowing them to form larger particles. Polymers are often added to enhance the size and strength of floc. ISOPAC2 was selected for use in bench scale testing to treat both raw intake and chlorinated water from the distribution system. This coagulant consists of 30 60% (W/W%) Polyhydroxy Aluminum Chloride with % (W/W%) Poly Quarternary Amine (polymer). However, in a full-scale water treatment plant, coagulant and polymer are typically dosed separately. ISOPAC2 was found to produce a satisfactory floc in prechlorinated water with 35 parts per million (ppm) during spring trials while the average dose was close to 25 ppm throughout summer trials. Dosages as high as 75 to 80 ppm were employed to treat raw water from the intake at Hydraulic Creek during spring trials. In practice, there is a range of dosage that will produce a satisfactory floc. However, it was found during bench scale testing that alkalinity is likely a limiting factor in dosing. For example, it was found in bench scale testing that as the raw water alkalinity drops, the dose of coagulant must be reduced to maintain proper floc development. Due to the low Mould Engineering 14

25 Bench Scale Testing alkalinity that is characteristic of The District s water, adjustment will likely be necessary to optimize coagulation. Caustic soda and/or soda ash are often added prior to distribution to reduce the corrosiveness of finished water by raising the alkalinity and ph, however, this was not involved for the pilot. Water treated with polyaluminum chloride coagulants can carry a residual aluminum concentration. However, with proper treatment, finished water aluminum concentrations can be lower than that of the source water, depending on raw water concentration. Therefore, aluminum concentration in effluent can be considered an indicator of coagulation chemistry and treatment efficiency. Lab analysis of three water samples treated in the bench scale project showed aluminum concentrations of 0.09, 0.11 and 0.08 mg/l indicating good coagulation chemistry (Edzwald, Tobiason, Amato, Maggi, 1999). Dosage rates used for these trials were 80, 45, and 40 ppm respectively. The sample dosed at 80 ppm had been clarified with the sedimentation basin while the other two samples had been clarified by dissolved air flotation. It is likely that treatment in a full sized plant could be optimized to produce water with lower residual aluminum than observed in the bench scale tests. The GCDWQ limit approved in 1998 for aluminum in drinking water is 0.1 mg/l, although BC s Ministry of Water, Land, and Air Protection limits total aluminum in drinking water to 0.2 mg/l. The process of flocculation begins immediately after coagulation chemical is flash mixed with the raw water. Suspended and colloidal solids become destabilized and begin to form tiny flocs. Flocculation continues by gradually slowing down the mixing rate of treated water and the tiny flocs grow into larger flocs. Traditional flocculation time for gravity settling is 20 to 30 min. In bench scale testing, flocculation times were varied from approximately 6 to 26 minutes. Sedimentation trials were run with 23 to 26 min flocculation times, which were sufficient Mould Engineering 15

26 Bench Scale Testing to produce a large floc. Some DAF trial floc times were reduced to just over 6 minutes. These shortened floc times appeared to improve DAF performance compared to longer floc times as smaller floc particles are easier to float out. An added benefit of a short flocculation time is that a smaller structure is required for that purpose CLARIFICATION The flocculation stage is typically followed by a clarification stage to remove flocs; this can be achieved through a variety of processes. During bench scale testing, sedimentation, and dissolved air floatation were used to clarify water. Some treatment trains skip the clarification stage and go directly to a filtration stage; this was modeled at the bench scale as well using direct filtration and membrane filtration and is discussed later in Section 3.3. Other methods of clarification not tested during the bench scale project are discussed in Section 3.5, Alternative Water Treatment Options..1 SEDIMENTATION The most common method of removing solids from water is by gravity settling. Settling of solids is achieved by floc particles having a sufficient density to settle out. Particles with less density have a slower downward velocity and are carried up and over the outlet weir. If coagulation chemistry and flocculation are optimized, and the settling basins are large enough to allow slow velocities, effluent can be expected to have very low turbidity. Initially, the bench scale sedimentation basin was tested at an approximate volume of 1,100 L (300 USgal) giving an approximate detention time of 2.5 hours; however, considerable floc exited over the outlet weir. After being enlarged to approximately 1,440 L (380 USgal), the detention time was approximately hr at lps (2 USgpm). Mould Engineering 16

27 Figure 7: Sedimentation Result Apparent colour and turbidity through sedimentation process average of data gathered May 12, Apparent Colour Turbidity Apparent Colour (PtCo) Turbidity (NTU) AO 1 15TCU MAC 2 1 NTU Pre-chlorinated supply water Flocculation effluent Sedimentation effluent Filter effluent 1 AO = aethetic objective, 2 MAC = maximum acceptable concentration 0

28 Bench Scale Testing The most common design parameter for settling is overflow rate; this is expressed as units of flow divided by units of area. For example, an overflow rate expressed as m/h is calculated by dividing m 3 /h by m 2. The recommended overflow rate for colour removal is m/h ( USgpm/ft 2 ), and should be lower for colder or highly coloured water (AWWA 1997). Sedimentation overflow rates were varied between m/h (0.18 and 0.26 USgpm/ft 2 ) based on the surface area of the tank. The lowest measured effluent turbidity was just less than 2 NTU with a treatment flow of lps (2 USgpm) pre-chlorinated water, dosing at 70 ppm. The maximum percent reduction of apparent colour from raw water to sedimentation effluent was 76% although the average was much lower due in part to operational instabilities. As can be seen in Figure 7, the flocculated water has increased colour and turbidity; this is due to the flocs that have formed. After sedimentation, the colour and turbidity is only slightly lower than before coagulation. Subsequent filtration then contributes further polishing to bring colour and turbidity below GCDWQ limits. It should be noted here that coagulant dosing during the sedimentation trials was unreliable prior to obtaining a peristaltic pump May 22, and therefore not all water entering the sedimentation basin was properly coagulated and flocculated. It should also be noted that at least some floc was observed falling over the weir throughout these trials even during optimal dosing conditions. This suggests there was excessive loading, inefficient hydraulics (short circuiting), or possibly both; a larger basin would likely be more efficient. The most probable explanation for poor removal rates using sedimentation, however, is two fold. Firstly, the flocs produced from water that is high in organic content and low in turbidity are typically lightweight and difficult to settle. Secondly, sedimentation is difficult to effectively model at the bench scale as suggested by AWWA s Water Treatment Plant Design Mould Engineering 17

29 Figure 8: First DAF Process Results Apparent colour and turbidity through DAF process at 4 USgpm average of samples May 30, Apparent colour Turbidity Apparent Colour (PtCo) Turbidity (NTU) AO 1 15TCU MAC 2 1 NTU Pre-chlorinated supply water Flocculation effluent DAF effluent Filter effluent 1 AO = aethetic objective, 2 MAC = maximum acceptable concentration 0

30 Bench Scale Testing.2 DISSOLVED AIR FLOTATION Dissolved air flotation (DAF) clarification units use dissolved air to float solids out of water instead of gravity settling of floc. This is achieved by recirculating a portion of clarified water through a saturator that adds pressurised air to the water. This air-saturated water is then released at the inlet end of the DAF. When released at the diffuser, the drop in pressure causes the dissolved air to form tiny bubbles that join with floc particles and carry them to the surface. The fine bubbles form a white-water blanket in the top portion of the tank and clarified water is collected from below this air bubble blanket. DAF units have traditionally been designed for loading rates of or 5 10 m/h (2 4 USgpm/ft 2 ), though recent studies indicate that loading rates of up to m/h may be viable depending on source water quality and temperature. Higher overflow rates can be achieved in warmer months, when demand is higher, because the warmer water allows for faster rise rates. A higher overflow rate makes it possible to design a smaller structure. The SEKID DAF unit, used in the spring trials, had an area of 0.08 m 2 (0.9 ft 2 ). The volume was approximately 32 L (8.6 USgal). This DAF unit demonstrated air bubble carry-over at very low loading rates. It was assumed this was largely due to the minimal depth over the effluent pipe that would prevent air bubble penetration. In August the Mould DAF was built with a total depth of over 1.3 m, approximately 1 m deeper than the SEKID DAF. This unit, with a virtually identical surface area, performed much better than the SEKID DAF and demonstrated significantly less air bubble carry-over. However, it should also be considered in comparing the performance of both DAF units that the second DAF was run with much higher water temperature; this alone would have improved performance of the SEKID DAF to some extent. Mould Engineering 18

31 Figure 9: Second DAF Tank Results Apparent colour and turbidity through DAF process at 4 USgpm average of daily samples August 20, Apparent Colour Turbidity Apparent Colour (PtCo) Turbidity (NTU) AO 1 15TCU MAC 2 1 NTU Pre-chlorinated supply water Flocculation effluent DAF effluent Filter effluent 1 AO = aethetic objective, 2 MAC = maximum acceptable concentration 0

32 Bench Scale Testing During spring trials with the SEKID DAF unit, loading rates were varied between 2.7 to 11.7 m/h, ( gpm/ft 2 ), at to 0.27 lps (1 4.3 USgpm) flow. These loading rates gave approximate detention times of 8 to 2 min. The DAF unit removed apparent colour by as much as 78% and turbidity by as much as 76%. These removal rates are based on the difference between water entering the treatment plant and DAF effluent. Much of the turbidity remaining in DAF effluent was due to air bubbles. During spring bench scale testing, it became apparent that the physical separation between the DAF tank surface and the effluent outlet was inadequate. The air bubble blanket was able to reach the bottom of the tank even at the lowest loading rate causing air and turbidity carryover to the filter. During summer trials, with the deeper DAF unit, loading rates varied between 7 17 m/h (3 7 USgpm/ft 2 ). The best percent removal rates for apparent colour and turbidity using this DAF were 95% and 99% respectively based on the difference between water entering the plant and leaving the DAF. Effluent turbidity stabilised between 0.5 and 1.0 NTU during the majority of operation. Small amounts of air bubbles could be seen entering the effluent pipe but performance was excellent overall. As can be seen by comparing Figures 8 and 9, the turbidity carryover in the DAF effluent was significantly less during summer trials with the deeper DAF unit. Many variables affected DAF performance such as air pressure, loading rate, and flocculation time. Air pressure supplied to the saturator affected the size and quantity of air bubbles. During spring trials the pressure difference between compressor running cycles was sufficient to reduce air bubble production before the compressor turned on again. Bubble quantity and size is very important to the clarification process and as a result DAF effluent samples could vary greatly over a small period of time due to fluctuations in saturator pressure. Changes made to Mould Engineering 19

33 Figure 10: Second DAF Tank Results Apparent colour and turbidity through DAF process at 7 USgpm average of daily samples August 28, Apparent Colour Turbidity Apparent Colour (PtCo) Turbidity (NTU) AO 1 15TCU MAC 2 1 NTU Raw Hydraulic Creek Water* Flocculation effluent DAF effluent Filter effluent 0 1 AO = aethetic objective, 2 MAC = maximum acceptable concentration

34 Bench Scale Testing the saturator during summer trials stabilised the flow of air-saturated water through the DAF. Surface loading rate, or overflow rate, affected the blanket position within the DAF greatly, particularly with the smaller DAF unit. At lower loading rates, far less floc was forced down to the effluent pipe. Another major factor affecting DAF performance was the size and nature of flocs entering the unit. Large flocs, formed with longer flocculation times, were difficult to float out of the treatment flow whereas small, dense flocs floated best. During the summer trial, un-chlorinated Hydraulic Creek water was run through the plant at 0.44 lps 1 (7 USgpm). This resulted in an approximate floc time of just over 6 min and a DAF overflow rate of 17 m/hr (7 gpm/ft 2 ). This was the highest loading rate attempted using the DAF unit and demonstrated excellent removal of colour and turbidity. As seen in Figure 10, effluent from the DAF meets the aesthetic objective for colour and the maximum acceptable concentration for turbidity prior to filtration FILTRATION Bench scale testing involved the use of both membrane and granular media filters. Various configurations of granular media filters are used in water treatment consisting of layers of, sand, anthracite coal, and sometimes other media such as garnet. 1 Water treated during this trial was from the distribution system as it entered Field Road Reservoir on August 28 th This normally chlorinated water was not chlorinated as a result of the chlorine gas tonners being removed due to the threat from the Okanagan Mountain Park Fire. Mould Engineering 20

35 Bench Scale Testing Two types of high rate filters were used in the bench scale trials. The first was a dual media filter on loan from OUC consisting of gravel, sand and anthracite. Typical loading rates for this type of filter are between 2-6 gpm/ft 2. A second granular media filter used the SEKID filter, and was designed and constructedto be a higher rate filter than the OUC filter with less silica sand and more anthracite than the OUC filter..1 DIRECT FILTRATION Direct filtration removes solids from coagulated and flocculated water without prior settling or flotation. This is considered a potential option in waters that do not exceed 5 NTU turbidity or 40 colour units (Hammer). South East Kelowna Irrigation District s raw water is known to exceed these values during the spring freshet. One day of bench scale testing was dedicated to direct filtration. Pre-chlorinated water was run through the system and dosed at 35 ppm ISOPAC2 which produced fair removal of true colour. The raw water had a turbidity of 5.0 NTU and true colour of 31 TCU (using DR2400). After coagulation and flocculation the true colour was reduced to 10 TCU (using DR2400). The total time the OUC filter was online during this trial was 54 minutes. The Mould filter ran longer at 248 minutes with little change in effluent turbidity. The OUC filter failed to produce an effluent of lower turbidity than 3 NTU, while the lowest turbidity produced by the Mould filter was 1.35 NTU. The Mould filter effluent turbidity ranged from 1.35 NTU to 2.45 NTU while the OUC filter ranged from 3.15 NTU to 4.65 NTU. Better results may have been observed if a constant head within each filter had been maintained manually by restricting the effluent flow. When this trial was conducted, treatment flow was allowed to move through the filter unrestricted. Mould Engineering 21

36 Bench Scale Testing.2 MEMBRANE FILTRATION Experimenting was completed by Okanagan University College during spring bench scale trials using a ZW10 membrane from ZENON Environmental Inc from May 22 to June 6. The performance of the membrane was consistently excellent despite that the membrane had previously been allowed to dry, potentially damaging the membrane. The removal rate of apparent colour using the membrane filter averaged 99.6 % while turbidity removal rates averaged 98 %. Further testing by the membrane manufacturer is required to establish commercial operational parameters..3 OUC DUAL MEDIA FILTER The filter loaned from Okanagan University College consists of 500 mm of small rocks, 400 mm course gravel, 50 mm sand, and 270 mm anthracite coal. The diameter of the filter is 163 mm, making the surface area 0.02 m 2. It is unknown how much loading the media in this filter received prior to using it for these trials. The lowest turbidity produced from this filter was 0.29 NTU during a summer DAF trial. Results for percent removal of turbidity and colour based on flocculation effluent during spring trials can be seen in figure 6. The flow rates run through this filter were lps (1-2.5 USgpm); this is equivalent to an overflow rate of m/h ( gpm/ft 2 ) loading..4 MOULD HIGH RATE FILTER The Mould filter was originally filled with approximately 300 mm small rocks, 200 mm fine sand, and 1000 mm anthracite coal. It was backwashed prior to use and run for a few days before being backwashed again. Immediately the fine sand layer was mostly washed down into the small rock layer so there was very little Mould Engineering 22

37 Bench Scale Testing sand filtration occurring between the anthracite and outlet. Fine sand was also visible in the effluent catch basin indicating that some had washed through the filter outlet. When media was measured on June 9 after completion of the spring trials there was 250 mm of mixed small rocks and sand below 1100 mm anthracite coal. Some sand was visible mixed with the anthracite. The lowest turbidity produced from this filter was 0.2 NTU, while turbidities in the range of NTU were most common while treating water from the Mould DAF unit. Flow rates varied between lps (1-7 USgpm); this is equivalent to an overflow rate between m/h ( USgpm/ft 2 ). Although this filter seemed to maintain good turbidity removal over a longer period of time, the maximum overflow rate applied to it was relatively low. Prior to trials in August, much of the filter media was removed to allow for the addition of course gravel, medium gravel, and to replace the fine silica sand. After refilling the filter, the subsequent media arrangement consisted of approximately 400 mm of mixed gravel with pockets of anthracite where backwash was unevenly distributed. Atop the gravel was 200 mm sand and 700 mm anthracite coal. Results treating effluent from the Mould DAF demonstrated turbidity as low as 0.2 NTU WATER TREATMENT WASTE The sources of waste in the drinking water treatment processes include solids from clarification and filter backwash water. Clarification solids vary with each type of coagulant, dosage, and method of clarification. Mould Engineering 23

38 Bench Scale Testing The filter backwash water generated during bench scale testing was not analysed. However, backwash water contains very low solids concentration and is typically recycled within the treatment train. Further investigation at the pilot plant scale is required to determine the best way to manage this waste flow. The results of lab analysis of solid waste produced during bench scale testing can be seen in Annex 1..1 SEDIMENTATION SOLIDS Lab analysis of two sedimentation sludge samples showed a solids content of 3.6% W / W in the first and 0.4% W / W in the second. As the character of this sludge seemed fairly wet, and also to take a conservative approach, a solids content of 0.4% will be assumed as a maximum solids content. The volume of solids produced during the sedimentation trials after the basin was enlarged was approximately 0.5% of the volume of treated water flow. The actual sludge volume produced from 30,400 L was 150 L. However, due to dosing pump complications, not all of the 30,400 L was properly dosed. At a treatment flow of 145 lps (2,300 USgpm), this would produce approximately 62,600 lpd (16,600 USgpd) of sludge before decanting or thickening. Approximately 100 L of wet sedimentation sludge dried almost entirely in one day once placed into an open pit of dry ground with an area of approximately 1 m 2. Analysis of raw sedimentation sludge by Caro Environmental indicates that the aluminum content was 2,800 to 120,000 mg/kg, ( %) dry weight basis. Mould Engineering 24

39 Bench Scale Testing.2 FLOTATION SOLIDS Solids floated during the DAF trials were typically drier than solids produced by sedimentation. For example, on May 28 a total volume of approximately 4 m 3 was treated and produced about 7 L of sludge before clear subnatant was removed, which reduced to 4 L after subnatant was removed. This places the solids production at 0.2 % of treated flow before dewatering. Floated solids production during the August trials averaged 0.1% V / V of treatment flow. At a flow of 2500 USgpm, this would produce approximately 16 m 3 /day of waste. Floated sludge had an average dry weight solids content of 2.1 %. From a volume of 16 m 3, approximately 190 kg of dry solids would result. Aluminum content was approximately 100,000 mg/kg on dry weight basis. For solids lab analysis results see Annex 1..3 SOLIDS DISPOSAL Solid waste produced from the clarification process using a polyaluminum coagulant would be disposed of in a landfill or by land application. The volume produced will be dependent on the coagulant dosage, treatment flow, and the effectiveness of sludge dewatering. Water treatment solid waste will most likely be accumulated in drying beds for some time before it may be necessary to truck it away to landfill..4 FILTER BACKWASH Filter backwash water contains a small percentage of solids. This flow is collected in a holding basin that acts to balance the recycle flow of backwash water to the headworks of the plant while allowing some solids to settle out. Mould Engineering 25

40 Bench Scale Testing ALTERNATIVE WATER TREATMENT OPTIONS Not all potential water treatment options were modeled during bench scale testing. The following are examples of alternative water treatment options that were not modeled at the bench scale..1 PLATE AND TUBE SETTLERS The most significant design parameter affecting gravity settling is overflow rates. This is defined as the flow rate divided by the area of the settling basin. Plate settlers and tube settlers take advantage of this by increasing the effective settling area within a basin. These types of settling basins employ a layer of tilted tubes or plates submerged below the water surface. These serve to increase the effective area for settling while reducing the effects of density, temperature, and wind currents. This allows for a smaller footprint than a conventional settling basin..2 ACTIFLO ENHANCED SETTLING SYSTEM The Actiflo system uses a polymer-coated microsand added in the flocculation stage to quickly form large, heavy floc particles that are easily settled. Loading rates for this type of system are significantly higher than conventional settling basins allowing for a very small footprint. The microsand added during flocculation, in addition to lamella plate settlers, greatly increases the settling rate of floc. The settled sludge is centrifuged to recover and reuse the majority of microsand while the remaining solids are removed for thickening and subsequent disposal. Actiflow is offered by John Meunier Canada/US Filter. Mould Engineering 26