Effect of DAF configuration on the removal of phosphorus and organic matter by a pilot plant treating combined sewer overflows

Pollutant removal by dissolved air flotation (DAF) at combined sewer overflows (CSOs) was analyzed with operating parameters such as recycling ratio and CODcr concentration. The nozzle of the CO-Current DAF system is normally operated co-currently with the flocculated water. In this study, the Counter-Current DAF system was used to remove organic matter concentration and total phosphorus to prevent water pollution of river when CSOs occurred. Counter-Current flow with ejection of saturated water was studied, because the acceleration of the flow increased collisions of microbubbles with floc. The experiments showed higher removal efficiency of DAF with Counter-Current flow compared with other configurations. In addition, the direction of the DAF nozzle and variation of angle of the contact zone were studied in detail for better operation. Efficiencies were analyzed for T-P, CODcr, and turbidity. The optimized conditions for DAF were a flow rate of 4.3 L/min with the Counter-Current nozzle setting. The optimum angle of contact zone was 60° rather than 45°. The removal of T-P, CODcr, and turbidity at optimum conditions were shown as 82.5%, 72.9%, and 91.2%, respectively. In particular, phosphorous removal was enhanced by using the Counter-Current nozzle and by the angle of the contact zone. The removal of CODcr, turbidity, T-P and SS for pilot plant showed as 75%, 82%, 80% and 92% respectively at 25 m/h of the hydraulic loading. The recycle ratio was 25%, which is considered to be an effective technique for treating CSOs.