Nov 27, 2011

Pagla Sewage Treatment Plant in Dhaka

In Dhaka city, the sewage system was first established in 1923. During the period 1923 to 1947 Dhaka was very small district town. The sewerage master plan was formulated in 1950's to cope with the population growth in Dhaka City. Dhaka WASA was established in 1963 as implementing agency for water supply and sewage disposal. Then Dhaka WASA has started implementing for water supply and sewage disposal. Then Dhaka WASA has started extension of its sewerage network day by day and established a lagoon which consists of three stabilization ponds for treatment of sewage of Dhaka city at Pagla in 1977. During 1989 to 1992 the present Pagla Sewage Treatment Plant (PSTP) achieved present status by the technical and financial support of Japanese Government and Government of Bangladesh. 
Pagla Lagoon
The expanded and rehabilitated Pagla Sewage Treatment Plant has been put into operation in march 1992. The designed treatment capacity of the Pagla Sewage Treatment plant is 120000 M3/day. The existing sewerage system covers more than one third of Dhaka city area. 

Outline of Pagla Sewage Treatment Plant 
Location : Pagla, Dhaka city, Dhaka. 
Site Area : 95.5 hectare. 

Treatment Method 
Sewage Treatment : Primary Sedimentation Tank + Facultative Lagoon. 
Sludge Treatment : Sludge Lagoon (Digestion and Drying) 
Design Capacity : 120,000 m3/day. 
Disposed To : Buriganga River. 

Operational System 
Operational  System

Intake Pipe : The intake pipe is an old brick arch construction with diameters of 54 inch. 

Inlet Chamber : Sewage from Dhaka City goes to the inlet chamber. To eliminate coarse particles (plastic, Polythene etc) from the sewage water. 

Lift Pump Station : There are three Sewage pumps in the lift pump station to lift the sewage up to the grit chamber. One pump is provided as standby. These are all screw pumps. 

Grit Chamber and Fine Screen : After the lift pumps, fine grit is removed by two parallel screens. The screens are cleaned manually. 

Sedimentation Tank
Primary Sedimentation Tanks : There are four Primary Sedimentation tanks, The diameter of the each tank is 33m and depth is 3m. Sludge sediments on the bottom of the tanks and is discharged by the sludge pump and sent to the sludge lagoons. 

Measuring & Distribution Chamber : Primary treated waste water goes to the facultative lagoons though this chamber by gravitational flow. 60% of the water goes to the lagoons 'A' And rest 40% goes to the lagoon 'B‘. 

Facultative Lagoon : Water from the primary sedimentation tanks flows into the facultative lagoon by gravitational flow. In the lagoon wastewater is decomposed through natural re-aeration and the photosynthesis reaction of algae. The standard retention time of the wastewater in the facultative lagoons is 7 days. 

Disinfections facility : To kill pathogenic organisms, the water leaving from Lagoons is disinfected by liquid chlorine. 

Outfall Pump Station : In the dry season, water from the lagoons flows to the Buriganga river by gravity, while in the rainy season the discharged pump is used due to the rise of water level of the river. 

Distribution Chamber : Distribution chamber receives the sewage water from the grit chamber through gravitational flow and distribute to the four primary sedimentation tanks. The diameter of the chamber is 9.5 m and the depth of the chamber is 7m. 

Sludge Pump station : There are 5 sludge pumps & two scum return pumps in this station. Sedimented sludge on the bottom place of the tank is discharged to the sludge lagoon by these pumps. 

Sludge lagoon : Sludge from the primary sedimen-tation tank is treated through a digestion process in sludge lagoons and is dried in the sun. The lagoons are then cleaned manually and the sludge is carried away for disposal.