Field reports Biyagama water treatment plant

1. 1. Route of the Field Visit.
Figure 1.1 – Route of the field visit.

2. 2. Introduction.

3. 3. Water Purification.
Figure 3.1 – Process of water purification
Water is a basic necessity for all life forms to survive. Water is a precious commodity and is
also scarce one. It is a valuable commodity, which requires careful management of the
water resources and water treatment processes. The water treatment processes should
also suit the raw water quality. With increasing pollution of the waterways and water
catchment areas the widely used coagulation, flocculation and sand filtration technology
may no longer work effectively. As such in time to come the use of advanced water
treatment technology such as membranes may have to be used to remove the natural
organic matters in the water. With these membrane technology even seawater could be
recovered for drinking and potable use.

4. 4. Biyagama Water Treatment Plant.
4.1. Description.
Figure 4.1 – An aerial view of the Water Treatment Plant
Biyagama water treatment plant is a ISO certified water treatment plant for
processing and supplying of drinking water. It is constructed sccording to the
concept of Mahinda Chinthana vision for future to provide safe drinking water
for all. The project was funded by the government of Denmark and The
government of Sri Lanka. National Water Supply and Drainage Board is governing
the treatment plant.
4.2. Project Data.
o Production : 180,000
o Population Coverage : 1,000,000
o Water supply areas : Biyagama Divisional Secretariat
Kelaniya Divisional Secretariat
Mahara Divisional Secretariat
Wattala Divisional Secretariat
Ja-Ela Divisional Secretariat
Dompe Divisional Secretariat
o Salinity Barrier stage 1 : To prevent the raw water from salinity
instrusion.
o Project Cost : Rs. 10,150 million.
o Funded By : Government of Denmark and
Government of Sri Lanka
o Controlling : National Water Supply and Drainage
Board

5. 4.3. Plant Description.
Intake Structure (Stage 1 & 2) 2
Raw Water Regulation tank 1
Mixing Chamber 1
Flocculator / Clarifier 6
Filter 8
Clear Water / Contact Tank 1
4.4. Plant Details.
4.4.1. Raw Water Intake Plant.
Extract raw water from Kelani river.
Removing course and fine (up to 5mm) particles contains in raw water via coarse
and fine screens.
Pumping raw water to mixing chamber at treatment plant.
4.4.2. Mixing Chamber
Figure 4.4.2.1 – Mixing Chamber
Receiving of raw water from the intake plant.
Chemicals are added to start the coagulation.
Pre Chlorine is added at upstr eam via submerged distributor .
Pre lime is added at 1st
compartment using top lime distributor for support the
coagulation by pH correction.
Alum is added at2nd compartment using top alum distributor for coagulation.

6. 4.4.3. Flocculators Tank & Lamella Clarifiers.
The purpose of this process is to remove 80% - 85% of suspended solids
contains in the raw water.
Flocculation Tanks
 Double stage Flocculation.
 2 flocculators in each stage.
 Flocculation retention time : 27 minutes
 Flocculator type : propeller type
 Driver : 1st
& 2nd
stage flocculator with variable speed drive.
Lamella Clarifiers
Sludge settled from clarification process is collected to the hoppers.
Dislodging is achieved hydraulically by pipes installed at the sludge hoppers
Each clarifier tank is having its own impendent sludge draw off control system.
Dislodging is automatic by actuated valves opened on time.
4.4.4. Sand Filters
Figure 4.4.4.1 – Sand Filters
The purpose of sand filters are to remove the fine particle in settled water which cannot be
removed at the clarifier.
8nos. of double – bed rapid gravity sand filter.
Constant flow, constant head type.
False bottom under drain system

7. Filteration rate
All in servise : 8.3 /
One out of service : 9.5 /
Filter media : Sand & Gravel
Sand effective size : 0.9 - 1.0 mm
Uniform coefficient of sand : 1.7
Gravel effective size : 4.0 – 8.0 mm
Deptha of sand layer : 900 mm
Depth of gravel layer : 100 mm
 Filter Oparation.
Designed filter run time : 48 Hours
Control of filter operation : 3 modes
Automatic : Filter backwashing is performed automatically.
Semi Auto : Filter backwashing is manually initiated. However, the backwash
sequence is automatic.
Manual : Filter backwashing is performed by manual. Opening and closing
of valves / penstocks via the filter console.
 Filter Backwashing
Filter backwashing is initiated due to achieving of 48 hrs operation or choke, whichever
comes first
Only one filter can be backwashed at a time.
Backwashing steps;
Lower the water level up to weir level.
Air source only (3 minutes)
Combined wash (5 minutes)
Rising & surface sweeping (5minutes)

8. 4.4.5. Contact / Clear water tanks
Contact tank
The purpose of contact tank is to enhance the disinfection process.
One RC baffled contact tank with 2 compartments.
The post chlorine is dosed at contact tank inlet.
Post lime saturator installed on top of the contact tank, saturated lime is
dosed at outlet weir for pH adjustment.
Clear Water Tank
The purpose of clear water tank is to store the treated water.
One clear water tank with 2 compartments.
Total capacity of the tank 7000
4.4.6. Treated Water Pumps
Pump set Flow & Head Operation
2 set wash water pump (2 duties/ 1 standby) 262 @ 12m Fixed speed
4 set Church Hill pump (3duties/ 1standby) 702 @ 72.95m Fixed speed
2 set Ambatale pump (1 duty/ 1 standby) 5.261 @ 8.74m Fixed speed
4.4.7. Chemical Plant
The purpose of chemical plant is to prepare and dose the chemicals.
All chemical (Alum, Lime & Polymer) except chlorine are supplied in bags.
Chemical bags are handled by semi electric stacker.
Chlorine delivered in drums and handled by an over head crane.
4.4.8. Sludge Treatment Plant
The purpose of sludge treatment plant is to receive the residues of water treatment, recower
the settled water and remove the sludge in solid form.
2 nos. of wash water recovery tanks
1 nos. of sludge balancing tank
1 nos. of sludge thickener tank
1 nos. of thickener sludge tank

9. 5. References.
 Biyagama Water treatment plant leaflet.
 National Water Supply and Drainage Board website.
www.waterboard.lk
 Penang Skills Development Centre web site.
www.psdc.org