This project involves turnkey construction of a wastewater treatment plant in Calafat, next to the River Danube, Romania.
The Client, Aegek SA, was awarded the contract for both the wastewater treatment plant (Lot 1) and sewerage network (Lot 2) by the Romanian Ministry of European Integration under PHARE 2001 Economic and social cohesion program.
The contract includes a 504 m /h biCOM compact wastewater treatment plant that will serve the entire population (30,000) of Calafat.
The domestic wastewater from the city of Calafat is collected (under the Lot 2 contract) and directed to the wastewater treatment plant which is built in the southwest side of the city.
Industrial wastewater from a local starch factory will also be connected to the inlet chamber of the wastewater treatment plant.
The plant is a compact type treatment plant providing a simple and reliable method of treatment for domestic sewage. The treatment is based on an extended aeration activated sludge process with denitrification to remove nitrogen. Although nitrogen removal is not a requirement for this contract, Biwater's biCOM compact plants are designed and equipped to do so.
Once all the wastewater has been treated it is then discharged by gravity to the Danube.
The quality of the treated effluent complies with the EU Directive 91/271/ EEC and
Romanian wastewater discharge standards, NTPA 001/2002 and NTPA 011/2002 as demonstrated below.
BOD5 25 mg/l
COD 125 mg/l
SS 35 mg/l
The compact plant comprises of four main stages:
- Inlet Works and Raw Sewage Pumping Station
- Preliminary Treatment
- Biological Treatment
- Sludge Treatment
Inlet Works and Raw Sewage Pumping Station
A concrete pump sump is built to the level of the incoming sewer. A fixed bar, manually cleaned coarse screen is installed at the discharge of the incoming sewer. Submersible sewage pumps with a stand-by facility are installed with an automatic level control system. The sewage is lifted to the inlet of an elevated screen channel.
Preliminary Treatment
Preliminary treatment consists of screening and grit removal units. A rotating mechanically cleaned fine screen is installed in a steel fabricated channel. The screenings are collected in a trailer by a belt conveyor.
Circular vortex type grit removal tanks are provided. The tanks are fabricated in stainless steel and equipped with centrally driven turbine mixer units. Settled grit is pumped continuously into a screw type sand separator. The separated grit is periodically discharged into the same trailer while the liquor returns to the raw water pumping station.
Biological Treatment
Biological treatment by extended aeration activated sludge process is carried out in a combined glass fused steel circular tanks. The space between the inner and outer shells is divided into two sections.
The first section is used as the anoxic zone where pre-treated sewage is mixed with returned liquor and is constantly mixed without aeration. Returned nitrate is metabolised by a denitrification process into nitrogen gas so that the required nitrogen content in the final effluent is achieved, however sludge floatation in final settlement tank is avoided.
Denitrified effluent from the anoxic zone passes into the aeration zone where it is subjected to full aeration to provide oxidation of carbonaceous material and nitrogen containing substances. The aerated liquor flows into the central zone, which serves as a settlement tank. It is equipped with a sludge scraper mechanism which directs settled sludge into the central sludge discharge hopper.
Air is supplied by two duty and one stand by blower sets. Blowers are housed in a kiosk with ventilation and sound proofing facilities. Fine bubble membrane diffusers are used to dissolve the oxygen in the liquor efficiently. Automatic airflow control system using dissolved oxygen controllers are provided for economic and efficient operation.
Sludge Treatment
Surplus sludge from biological treatment is collected in a glass fused steel sludge holding tank where it is continuously mixed with a submersible mixer then pumped over a belt type mechanical gravity thickener. Thickened sludge flows by gravity on to a belt press for dewatering with a dosing of flocculants prepared by a package type polyelectrolyte dissolving and dosing unit. Sludge cake from belt press is loaded into a trailer by a belt conveyor and filtrate is drained back into the raw sewage pump sump by gravity.