Chemical precipitation of phosphorus at Brest WWTP, Belarus
Phosphorus removal can be increased with AO (anaerobic-oxic) process and complementary phosphorus removal by chemical precipitation.
The recommended dosing points of precipitation chemical are the receiving chambers of influent wastewater and the distribution chambers were activated sludge coming from the aeration basins is divided to the secondary clarifiers. In addition, the reject waters originating in the dewatering of digested sludge and possible overflows from the digesters should be precipitated before they are directed to the plant in order to maximize the efficiency of chemical use. The dosing should be controlled by continuous measurement of plant inflow and reject inflow.
In the AO process, the beginning of the aeration line is mixed and the rest is aerated. Phosphorus is released from the phosphorus accumulating organism (PAO) cells in the anaerobic zone and taken up in the aerobic zone. In addition, BOD is oxidized in the aerobic zone. Nitrification is suppressed by keeping the sludge retention time short.
Components installed in the solution
The main items of the plan are the following:
- civil works (excavation, concrete walls, dismantling of old walls, PE lining etc.);
- 8 dosing pumps with frequency transformers;
- mixer in the dosing tank;
- bag hopper, screw feeder and lifting crane for granular and powder products;
- piping from pumping room to dosing points, trace heated;
- ventilation and heating as required;
- electrics, instrumentation and automation.
In 2013 an accelerated phosphorus removal was installed at Brest WWTP. First of all, on-line analysis of total phosphorus and phosphate phosphorus were implemented in the pre-clarified and effluent wastewater. In addition, the laboratory of the WWTP were equipped with facilities for analyzing total phosphorus. These include a spectrophotometer, a heating reactor and a first supply of reagents.
The chemical precipitation units financed by the PURE project are dimensioned to treat the estimated phosphorus load of municipal wastewater and digester rejects. The dimensioning chemical consumption in case of Brest was 6.3 m3/d.
The chemical storage and dosing station was implemented in the old, unused preaeration basins. One half of the tank was divided into storage tank (200 m3), dosing tank (100 m3) and pumping room (100 m3). A room for electrical switchboards was constructed on top of the chemical tanks.