The Comparison of Two Water Treatment Plants operating with different processes in Kandy City, Sri Lanka

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1 Technical Report Journal of Ecotechnology Research, 18[1], 1-6 (2016) 2016 International Association of Ecotechnology Research The Comparison of Two Water Treatment Plants operating with different processes in Kandy City, Sri Lanka TOMONORI Kawakami *, AYURI Motoyama**, YUKA Serikawa*, A.A.G.D. Amarasooriya*, and S.K. Weragoda*** *Department of Environmental Engineering, Toyama Prefectural University, 5180 Kurokawa, Imizu-city, Toyama Japan ** Graduate School of Gifu University, 1-1 Yanagido, Gifu-City, , Japan ***National Water Supply and Drainage Board, Kandy 20000, Sri Lanka (Received October 12th, 2015, Accepted November 14th, 2015) Two water treatment plants located in Kandy district, Sri Lanka, which are operating with two different processes, conventional water treatment and Pulsator water treatment followed by rapid sand filtration, were compared from the perspectives of ease and cost of operation. Pulsator technology has an advantage in its compactness, as it incorporates coagulation, flocculation, and clarification in a single unit, while the electricity consumption for the production of a unit of water was 30% higher than for the conventional process. The Pulsator water treatment process was considered to be best suited for populated areas with high land values. Key Words: Pulsator, Conventional, Ease and cost, Sri Lanka 1. Introduction In Kandy District of Sri Lanka s Central Province, there are two water treatment plants, the Greater Kandy water treatment plant (GK-WTP) and the Kandy South water treatment plant (KS-WTP), that have adopted different treatment processes to supply pipe-borne water to residents. The GK-WTP was constructed in 2007 and is currently in phase-three construction to maximize its capacity. It has adopted a conventional water treatment system followed by a rapid sand filtration process 1) based on Japanese technologies. The KS-WTP was constructed in 2010 and adopted a Pulsator water treatment technology 2) developed by a Danish company (MT Hojgaard Co., Ltd.). Since both plants treat water from the Mahaweli River, the raw water quality is regarded as being the same. In addition, the quality of the treated water is the same in that both plants are operated by a single organization, the National Water Supply and Drainage Board (NWSD&B) of Sri Lanka, and are required to meet the same standard for drinking water in Sri Lanka (SLS 614, ) ). It is worthwhile to compare the performance of the two different processes to identify which treatment is the most suitable. Therefore, the two treatment processes were compared from the perspectives of their ease and cost of operation. 2. Site description Both the GK-WTP and the KS-WTP use raw water from Mahaweli River to treat and supply to the residents of Kandy City. The locations of the treatment plants are indicated in Fig. 1. The KS-WTP is located upstream of the GK-WTP on the Mahaweli River. The average raw water quality variation in the Mahaweli River is shown in Table Process description 3.1 The GK-WTP The GK-WTP distributes its water to a population of 413,000 with 58,600 water connections. The current plant capacity is 72,000 ton/day, which was reached by completing phase-two construction in early With growth of the population in the Kandy City area, the capacity will be expanded to 108,000 ton/day after completion of phase three. Total construction will be finished in kawakami@pu-toyama.ac.jp - 1 -

2 TOMONORI Kawakami et al The Comparison of Two Water Treatment Plants operating with different processes in Kandy City, Sri Lanka Fig. 1 Map showing the locations of the two water treatment plants in Kandy City, Sri Lanka. Both are located beside the Mahaweli River. Month Table 1 Average raw water quality variation in River Mahaweli in year 2013 Color (Hazen) Turbidity (NTU) ph EC (ms/m) Alkalinity (meq/l) Hardness (mgcaco 3 /L) January February March April May June July August September October November December Average

3 Journal of Ecotechnology Research, 18[1] (2016) Fig. 2 Process flow diagram of the GK-WTP Fig. 2 shows a process flow diagram of the GK-WTP, which is composed of (1) the distribution chamber, (2) the coagulation and flocculation basin, (3) the sedimentation basin, (4) sand filters, and (5) the clear water tank. Fig. 2 shows a process flow diagram of the GK-WTP, which is composed of (1) the distribution chamber, (2) the coagulation and flocculation basin, (3) the sedimentation basin, (4) sand filters, and (5) the clear water tank. The detailed process is as follows: (1) The distribution chamber Raw water from the Mahaweli River is pumped to the distribution chamber. The distribution chamber acts as a rapid mixer for the ph adjustment. Lime (Ca(OH) 2 (aq)) and free chlorine are added as necessary. Poly Aluminum Chloride (PAC) is added as a coagulant at the chemical mixing point, located at the outlet of the distribution chamber. (2) The coagulation and flocculation basin Chemically mixed water from the distribution chamber is transferred to the flocculation basin by gravity. Baffle walls in the basin increase the contact time by increasing the length of the flow path to enhance coagulation and flocculation for larger flocs. (3) The sedimentation basin In the sedimentation basin, most of the flocs are sedimented. Sedimented sludge is removed regularly by scrapers and transferred to a lagoon for dehydration. The settled water that contains unsedimented flocs flows into the sand filters through small holes at the top of the basin. (4) Sand filters Settled water from the sedimentation basin is filtrated through the sand filters to remove unsedimented flocs. Lime is added to increase the ph value after filtration. (5) The clear water tank After disinfection with chlorine, the treated water is sent to the clear water tank. 3.2 The KS-WTP The KS-WTP feeds 6,300 water connections and serves 344,000 people. Plant capacity is 35,000 ton/day. Its purification system is composed of (1) the aerator, (2) the pulsator, (3) rapid sand filter, (4) a clear water tank, as shown in Fig. 3. The detailed process is as follows (1) The aerator Raw water from the Mahaweli River arrives first at the aerator. The following four effects are expected during aeration: 1. Increased dissolved oxygen to oxidation of Fe 2+ and Mn Removal of anaerobic/ bad odor gasses, such as CH4, H 2 S, and NH 3 3. Adjustment of ph by adding lime, if necessary 4. Destruction of anaerobic bacteria by increasing dissolved oxygen. (2) Pulsator The original Pulsator Clarifier 4) was developed in the early 1950s to combine the flocculation and clarification processes. The Pulsator Clarifier consists of five main components (Fig. 4): 1. Raw water inlet and reagent inlet 2. Vacuum chamber 3. Raw water perforated distribution pipes 4. Stilling plates 5. Sludge concentrators. Before water enters the Pulsator Clarifier, a coagulant is added to the raw water at the regent inlet in the Pulsator s raw water inlet pipe. The coagulated water is transferred to the vacuum chamber. In the vacuum chamber, the water level rises to a predetermined level by vacuum pressure created by a vacuum fan. When the water reaches the predetermined level, the automatic vacuum breaker - 3 -

4 TOMONORI Kawakami et al The Comparison of Two Water Treatment Plants operating with different processes in Kandy City, Sri Lanka Fig. 3 Process flow diagram of the KS-WTP valve opens to release the vacuum and create a surge of water into the perforated distribution pipes on the bottom. Gently stirring turbulence caused by the pulse enhances coagulation as the water is distributed through the stilling plates. The flocs accumulated on the stilling plates as a sludge blanket overflow to the sludge concentrators from which the concentrated sludge is drawn off periodically. The clarified water is collected from the top part of the clarifier. After the water level in the vacuum chamber reaches its lowest, the automatic vacuum breaker closes, and the vacuum is established in the vacuum chamber again to repeat the cycle of (3) Rapid sand filter and (4) Clear water tank. The clarified water is filtered by rapid sand filters and stored in the clear water tank for distribution. 4. Comparison of the two water treatment processes 4.1 Advantages and disadvantages Table 2 summarizes the advantages and disadvantages of the water treatment processes adopted by the GK-WTP and the KS-WTP, based on interviews with the operators. The Pulsator process has an advantage with the size of the plant, since it incorporates coagulation/flocculation and clarification in a single unit; however, it has a disadvantage in its sensitivity to raw water quality, especially against turbidity shock loads. The pulse operation would make it difficult to maintain the sludge blanket at a proper level, which is the key to the process. Therefore, highly skilled labor is necessary. Fig. 4 Schematic flow diagram of Pulsator Clarifier at the KS-WTP In the figure, and the dashed line show the desired level of the sludge blanket

5 Table 2 Summary of advantages and disadvantages of the two treatment plants GK-WTP KS-WTP Advantages 1. More tolerance to turbidity shock loads 2. Predictable performance under most conditions 3. Easy operation and low maintenance costs 4. Easy adaptation to high-rate settling modules for future expansion 5. Lower electricity cost 1. Incorporates coagulation/flocculation and clarification in one unit 2. Compact and economical design 3. Tolerates limited changes in raw water quality and flow rate 4. Preferable in highly turbid raw water 5. Suitable for populated area with high land values Journal of Ecotechnology Research, 18[1] (2016) Disadvantages 1. Subject to density flow creation in the basin 2. Requires careful design of the inlet and outlet structures 3. Usually requires separate flocculation facilities 4. Not suitable for populated area with high land values due to larger area required 5. Difficult to operate under seasons of high turbidity 1. Very sensitive to turbidity shock loads 2. Sensitive to temperature change 3. Several days are required to build up the necessary sludge blanket 4. Plant operation depends on a single mechanical part 5. Requires greater operational skill 6. Inefficient treatment at a lower treatment capacity due to the delicate operation of maintaining the sludge blanket properly 7. Higher electricity cost 4.2 Production costs The required cost for one month of operation was estimated using the water volume delivered and the unit cost of electricity and chemicals based on data on December 31, For electricity consumption, 1 kwh of electricity was supposed to cost 14 Sri Lankan rupees (Rs), based on data regarding the price of electricity on December 31, For the chemical consumption, 1 kg of Poly Aluminum Chloride (PAC) was supposed to cost Rs. The exchange rate was 1 US $ to Rs Energy consumption At the GK-WTP, the electricity consumption was 16,600 kwh on December 31, When the same amount of electricity was supposed to be used in a month, monthly consumption and cost are calculated to be 16,600 (kwh) 31 (days) = 514,600 (kwh/month) 514,600 (kwh/month) 14 (Rs/kWh) = 7,204,400 (Rs/month). At the KS-WTP, the electricity consumption was 12,000 kwh on December 31, We applied the same calculation as follows: 12,000 (kwh) 31 (days) = 372,000 (kwh/month) 372,000 (kwh/month) 14 (Rs/kWh) = 5,208,000 (Rs/month) PAC consumption At the GK-WTP, the concentration of PAC was 7 mg/l equivalent to 7g/m 3. As the total water production was 40,000m 3 per day, the PAC consumption was estimated to be 7 40,000 = 280,000 (g/day) = 280 (kg/day). When the daily consumption was converted into monthly consumption, 280 (kg/day) 31 (day/month) = 8,680 (kg/month) was obtained as the monthly consumption, which cost 8,680 (kg/month) 67 (Rs/kg) = 581,560 (Rs/month). At KS-WTP, the concentration of PAC was 8 mg/l, equivalent to 8g/m 3. As the total water production was 20,000m 3 per day, the PAC consumption was estimated to be 8 20,000 = 160,000 (g/day) = 160 (kg/day). When the daily consumption was converted into monthly consumption, 160 (kg/day) 31 (day/month) = 4,960 (kg/month) was obtained as the monthly consumption, which cost 4,960 (kg/month) 67 (Rs/kg) = 332,320 (Rs/month). In accordance with the above calculations, the cost estimates are summarized in Table 3. When the costs of electricity and PAC were evaluated, the GK-WTP was 30% less expensive to run than was the KS-WTP. Between the two plants, the cost of PAC did not differ much as compared to the cost of producing a unit of water because the - 5 -

6 TOMONORI Kawakami et al The Comparison of Two Water Treatment Plants operating with different processes in Kandy City, Sri Lanka Table 3 Cost estimates for GK-WTP and KS-WTP GK-WTP KS-WTP Electricity Consumption 7,204,400 5,208,000 Rs/month PAC 581, ,320 Rs/month Total running cost 7,785,960 5,540,320 Rs/month Total Water Production 40,000 20,000 m 3 /day Total Water Production 1,240, ,000 m 3 /month Cost per unit water production Rs/m 3 plants treated raw water with the same quality; however, the cost of electricity was much higher at the KS-WTP than at the GK-WTP, even though the elevation of the plant from the water surface at the GK-WTP is higher than at the KS-WTP. This difference in energy consumption could be attributed to differences in the process, especially in producing a vacuum in the vacuum chamber. 5. Conclusions Two water treatment plants operating in Kandy City, Sri Lanka, were evaluated from the perspectives of ease and cost of operation. The Pulsator technology adopted at the KS-WTP has an advantage in its compactness, since it incorporates coagulation, flocculation, and clarification in a single unit; however, the electricity consumption required to produce a unit of water was 30% higher than that required by the rapid filtration technology adopted at the GK-WTP. The GK-WTP has the advantage of being easier to operate, especially in the event of turbidity shock loads. Acknowledgements We thank National Water Supply and Drainage Board for collection of data at the water treatment plants. References 1) Nicholas, P. and Cheremisinoff, Handbook of Water and Wastewater Treatment Technologies, Elsevier, 8, (2002). 2) Salam, K. Al-Dawery, Raad, M. Hussain and Kadhem, M., Performance of Pulsator Clarifier (Low Turbidity), Iraqi Journal of Chemical and Petroleum Engineering, 8, 1, 9-17(2007). 3) SLS 614:1983, Potable drinking water quality standard, Sri Lankan Standard Institute, (1983). 4) Black and Veatch, Conceptual Design Report Haverstraw Water Supply Project for United Water New York, New York LLP, (2008)