Acknowledgement

I am immensely grateful to Almighty God for helping me completing my industrial project. Also grateful to honorable teachers & Industries we've visited. In this project , we've learnt about the manufacturing process of the industries , also learnt about what type of raw materials & machineries they use. I've tried to present all the processes about CWASA that i've learnt in this project .

I acquired a lot of knowledge & experience by visiting CWASA.

Reference of resources : As the mojor things didn't change about the CWASA, and our seniors visited the industry & had reported directly to the department, but  didn't published anywhere. So major information have been taken from previous reports. 

 Background

WASA, Chittagong a semi-government organisation named Chittagong Water Supply and Sewerage Authority was established on 16 October 1963 (EP Ordinance No XIX, 1963) under the Ministry of Local Government, Rural Development and Cooperatives. This organisation was created home specific consideration of construction, improvement, expansion, operation and maintenance of necessary infrastructure for domestic, industrial and commercial purpose; construction, operation and maintenance of sewerage system and drainage facilities to discharge rain, flood and surface water and solid waste management dividing the port city's Public Heath Engineering Department. [ reference: banglapedia ]

Major Components

1.   Intake and raw water pumping station.

2.   Desilting basins.

3.   Rapid mixers.

4.   Clarifiers.

5.   Filters.

6.   Clear well and high lift pump station.

7.   Chemical facilities.

8.   Sludge and back wash facilities.

9.   Power supply and stand-by generator.

10.  Laboratory.

11.  Plan monitoring system.

Intake And Raw Water Pumping Station 

Ø 20 MGD with necessary provision and space for expansion up to 40 MGD.

Ø Intake and raw water pumping station constructed for 40 MGD capacity to meet future requirement.

Ø Since construction of Intake structure on the river bank is difficult and expensive2 Nos. duty and 3 Nos. Stand by raw water pumps on capacity 11 MGD and 132/160 KW each.

Desilting Basins 

Ø  Turbidity level varies from 20 NTU to 800 NTU.

Ø  Provision for tow Desilting basins has been made.

Ø  During monsoon river water first brought to the desilting basins. Turbidity reduced by the settlement of mud sludge etc.

Ø  In the winter, water directly passes to the rapid mix. Chamber through a by-pass system.

Rapid Mixture 

1. Water from desilting basins/raw water pump station comes in the Rapid mix chamber.

2. Alum and lime is mixed with water.

3. Alum and lime are injected at the rapid mix chamber from the Chemical building.

Two rapid mixture of 7.5hp each with detention time 10 second/chamber.

Clarifiers 

1. 24 Nos. hopper bottomed up-flow type clarifiers.

2. Water from rapid mix chamber come to the bottom of clarifier through 12” dia ductile iron pipe from incoming channel.

3. Velocity of incoming water is reduced considerably when it comes to the top of the clarifier.

4. Almost all the settle able materials settle down in the clarifiers and clean water are collected to the filters.

Minimum flow velocity of 8.9 ft/hr with detention time 1.2hrs and over flow rate 1333 gpd/sft. 

Filters

1. 8 Nos. cells down flow conventional type rapid gravity filters.

2. Water from clarifiers comes to the filter and passes through sand and gravel media.

3. All suspended materials and most of the bacteria are entrapped in filter media and clean water is collected in the contact chamber for disinfections.

4. After the disinfection collected in the clear well.

5. Each filter has an area of 480 sft.

6. Filter media is sand mono sized 0.85-1.0 mm and 4” depth.

7. The average loading 3.8 gpm/sft & back wash rate 20 gpm/sft.

8. Provision is kept for regular cleaning of filter media by back wash system.

9. Water from clear water channel of filter passes in a reverse direction from the bottom of filter, cleaning the accumulated film of deposits.

To ensure top of the media adequately cleaned, an auxiliary fixed nozzle surface wash is provided.

Clear Well & High Lift Pump Station 

1. Treated water from the filters is received in a 2.5 MG reservoir after disinfections in the chlorine contact chamber.

2. Treated and disinfected water is pumped to the city by 4 Nos. duty& 1 no. stand-by high lift pumps of capacity   3475 gpm and 320 KW each.

3. Chlorine contact time in the contact chamber is 30 minute at 20 mgd.

Chemical Facilities  

1. Alum & lime are added to the water for aiding the flock formation & pH adjustment.

2. Provision is made to add alum to the water at the raw water venturi meter vault to aid in the settling of suspended solids in the desilting basin during high turbidity.

3. Chlorine also injected to the water at rapid mixture and at contact chamber of clear well for preventing any growth of algae & disinfections purpose.

4. Necessary storage, mixing & dosing of chlorine, alum and lime are done by pumps centrally from the chemical building.

5. Re-circulation pumps of capacity 167 gpm re-circulate the alum solution within the alum tank to promote the dissolution of lump alum to keep the alum solution mixed.

6. Hydrated lime is mixed by turbine impeller type mixture to make suspension of lime slurry.

Sludge & Backwash Facilities

1. Sludge that are collected at the bottom of clarifiers & desilting basins and back wash water from filters are collected to sludge tank.

2. From where it is pumped out to the river Halda at a safe distance.

There are 4 pumps (with one standby) of each 2245 gpm at 13 ft and 30 hp capacities 

Power Supply & Generator  

1. High lift pumps are operated at 3.3 KV.

2. Two 33 KV Feeder line from PDB directly from Madunaghat Grid Substation and Mohara   Substation.

3. One stand-by diesel generator of 2000 KVA/1600KW installed for use during any power failure.

Laboratory 

1. The objective of the Mohara WTP are not only to provide water safe for human consumption & appealing to consumers. But to bring the treated water quality within the limits of the maximum allowable standards set by the World Health Organization (WHO).

2. To this end laboratory in the plant is equipped with various sophisticated instruments for regular testing of turbidity, pH, residual chlorine, alkalinity, hardness, TDS etc.

Depending on raw water quality the quantity of chemicals such as alum, lime and chlorine are also determined through various tests. 

Plant Monitoring System 

1. This plant fully controlled by Distributed Control System (DCS) including PLC and SCADA system.

2. Monitoring PC and Server installed in the Central Control Room (CCR) of main administrative building.

3. PC monitor contains total plant overview, graphic display, plant alarm, and status indicators of treatment plant process. 

Plant intercoms paging systems for easy communication of the operation staffs within the plant installed.