Physicochemical treatment of office and public buildings greywater.

The current study analyses the performance of deep sand filtration of greywater from an office building and the performance of a combined physicochemical process comprising of coagulation, sedimentation and filtration. Raw greywater quality exhibited very high variability with average turbidity of 35 NTU, and TSS, COD(t), and BOD of 45, 240, 75 mg/l respectively. The stand-alone filter removed 50 and 70% of the turbidity and TSS, but failed to remove COD and BOD. Quality of the produced effluent was too low to allow any reuse. Clogging rate of the filter was high and under hydraulic loading of 3-4 m(3)/(m(2) h) the filtration cycle had to be terminated after 5-8 h. Clogging occurred mainly on the upper layer, indicating the dominance of "cake" filtration mechanism. Addition of coagulation and sedimentation prior to sedimentation dramatically improved effluent quality, reaching overall removal efficiencies of 92, 94, 65 and 57% of turbidity, TSS COD(t) and BOD respectively. The filtration cycle could be prolonged to 20 h. The effluent produced was of much better quality, yet, it has to be further treated (either biological treatment or membrane filtration). Most of the removal occurred in the coagulation-sedimentation step, while the filter acted as a polishing unit.