Feature

Bracu Ms Biotech Students Visit SWTP

Md. Riajul Hossain

A group of seven students of MS Biotechnology programme, BRAC University visited the Saidabad Water Treatment Plant on 25 July. Five young teachers accompanied the group from BRACU Biotechnology and Microbiology Programme. The group of students and teachers was led by Dr. Mahbub Hossain, Associate Professor, Microbiology programme. The group left BRACU for SWTP, which is located beside Dhalpur city Palli, Saidabad. A warm reception from SWTP officials followed by a PowerPoint presentation about the plant and then the laboratory and field visit made it a complete study trip. At the entrance, Md. Riajul Hossain, Lecturer, Biotechnology signed on behalf of the group to officially start the plant visit. Then they were taken to the conference room where the executive engineer, operation of SWTP, Mostafa Kamal Majumdar showed a PowerPoint presentation about SWTP through which the students and also the teachers came to know about the establishment of the plant, about its operation and the water supply scenario of Dhaka city and future possibilities regarding water supply in this area. After the presentation, there was a short discussion session presided over by Eng. Abul Hasnat. The ground water supply is being consumed at a greater rate than it should be. Moreover, the city is expanding day by day and also the ground water level has already been gone down. Eventually, we are running short of water supply in terms of ground water. The alternative is therefore expected and water treatment opens up the possibility to meet the daily need of water supply of Dhaka city. The Saidabad Water Treatment Plant started its journey on 27 July 2002 and had been operated and maintained by the foreign company for four years. After that local engineers and expertise took over the responsibility of operation and maintenance in 2006 as it saved a lot of money that would go to the foreign company otherwise.

The SWTP collects water for treatment from two rivers, Shitalaxya and Balu. The distance between the plant and the river is about 8 to 9 kilometers. The water supply is abundant and also the water quality remains good in rainy season when even water flows normally into the plant without pumping. But in dry season, the picture is completely opposite as various industrial and domestic effluents come with water to the plant. Because of increasing concentration of waste materials, lots of chemicals are required then to treat the contaminated water. The total water treatment process is divided into seven steps where the very first step is water collection. The water is collected from Shitalaxya and Balu River by Sarulia pump station and through RCC culvert the water comes to the DND canal, which was actually used for irrigation, near the plant where twin culvert has been made to be the final gateway for entry of water into the raw water building of the plant. Five vertical pumps, three of which run at a time while two others remain stand by, do this. After collection of water through culverts the pumping of water into raw water building constitutes the second step. The third step uses the dividing chamber where mixing of chemical starts. Three types of chemicals are used in the total treatment procedure: chlorine gas (95% or above), aluminum sulfate, and lime. Chlorination is done in two stages, pre-chlorination and post-chlorination. From dividing chamber water flow is divided equally into four clarifiers for clarification, which are operated simultaneously and in parallel. Clarification is the fourth step of the treatment process and the clarifiers are called pulsator clarifiers because pulse is generated downward in those clarifiers. The sludge extraction valves extract depending on the sludge volume created by the pulsator clarifiers sludge. The clarified water is separated in this way and goes to clarification bed where 80 to 90 percent of waste has been removed already in the process. Filtration is the fifth step where rapid sand filter is used consisting of sand and gravel placing sand over the gravel layer in twelve separate filters. Here back washing is done through four sub steps: draining, blowing by air, unclogging by air and water and finally rinsing by water. The filtered water then goes to filter bed. The next step is the final water quality adjustment in terms of chlorine and pH of water and storage of this treated water. The last step is the pumping of treated water by treated water pumping station where seven pumps are there five of which are active at a time while others two are kept stand by. The plant does not provide water directly to the consumers. The reason is the high pressure created to supply water through the transmission network needs to be maintained until it reaches the entrance of zonal distribution channel which is about 36 km far away from the plant. Then at the zonal distribution channel, which is 10 in number for Dhaka city, with the help of valves for lowering the water pressure, finally the water goes to the consumers through different zonal distribution channel. The Saidabad Water Treatment Plant at its Phase II project meets only 30 percent of total demand of water supply that is 225 million liters per day. DWASA (Dhaka WASA) is furthermore looking to increase the capacity into 450 million liters per day in the third phase of this project.

After the presentation a short discussion was held at the conference room. In reply to a question of Md. Riajul Hossain about the sludge disposal produced in the plant, Dr. Alamgir said that the sludge is reused in the treatment process and then taken to separate drying beds and then disposed into nearby landfill sites. In reply to a question of Mr. Mahbubul Hasan siddiqee about the assessment of chemicals found in raw water, it was said that they do the test by sending sample to BUET. Ms Zeenat Jahan asked about the contamination in the water and high microbial count in final drinking water sometimes. In reply to her question, it was said that they have nothing to do with the old pipes through which final zonal distribution channels supply the water finally to the consumer. Any sort of leakage may result in contaminated, bad odor containing water to the consumers. However, they said there is a project to be taken to replace the existing old pipes in the distribution channels very soon. Moreover, to meet the increasing water demand, as Dhaka city is expanding and population is increasing, two other water treatment plant is going to be established-one is Meghna Water Treatment Plant near the River Meghna and another one is Mawa Water Treatment Plant near the Padma River- the executive engineer informed the group.

From the conference room, the students along with the faculty members of the group were taken to the laboratory where continuous assessment is done for raw water, clarified water, filtered water and finally for the treated water. The students then went outside for the field visit and observed the entry of water through twin culverts to the raw water building where around 125 m3 of raw water is pumped every minute. Then they saw the chlorination building, alum tanks, lime tanks, dividing chambers, the pulsator clarifiers, filter beds and finally the operation building where pre and post chlorination is maintained and finally treated water from the storage tank is supplied to the transmission network from the treated water pump station. With the brief of total operation of the treatment plant starting from the raw water entry ending with the treated water supply the team ends their visit thanking the engineers and officials of the Plant. Professor Naiyyum Chowdhury, Coordinator, Biotechnology arranged the visit in consultation with his former student Dr. Alamgir, Deputy Chief of Microbiology division, SWTP.