FLOW AND LOAD EQUALIZATION USING PRIMARY CLARIFIERS IN A BNR PLANT

A full-scale 18 month study at Pihlajaniemi treatment plant in Savonlinna Finland (PE 30 000) investigated the feasibility of using the primary clarifiers for flow and load equalization as well as for volatile fatty acid (VFA) production. The objective was to improve the process performance of the biological nutrient removal (BNR) process and find better use for the old primary clarifiers.Equalization in this study decreased flow rate variations by 38% on an average. During the best months the flow to the biological process was practically constant. Hydrolysis was successful. The VFA concentration increased by 50%. The simultaneous removal of raw sludge did not cause any problems. The use of primary clarifiers for equalization and fermentation influenced the biological process in three ways: It improved the hydraulic control of the process, it equalized the load and conditions in the process and it increased the amount of readily usable organic matter. The transformation of old primary clarifiers for multipurpose primary tanks proved to be economically and technically feasible solution for responding to the requirements of BNR process.