REMOVAL OF ORGANIC HALOGENS (AOX) FROM MUNICIPAL WASTE-WATER BY POWDERED ACTIVATED CARBON (PAC) ACTIVATED-SLUDGE (AS) TREATMENT

The effectiveness of different treatments with powdered activated carb ons (PAC) to reduce the AOX-levels in municipal wastewater was investi gated in a bench-scale activated sludge (AS) treatment plant. The PAC was added either directly to the aerated basin (simultaneous PAC-treat ment), or to a partial stream of clarified effluent, which was treated with PAC in an agitated tank and recirculated to the aerated basin (s ubsequent PAC-treatment with recirculation). The standard advanced bio logical treatment reduced the AOX-content by 24%. In the pilot-plant, three types of powdered activated carbons were tested for a simultaneo us treatment. The treatment with 100 mg/l PICA PCO Super produced an a dditional reduction of AOX by 20%, whereas a dosage of 50 mg/l NORIT W -20 showed no enhancement effect, and W-35 led to an additional AOX-re moval of about 9%. Also, an improved removal of DOG, NH4-N and PO4-P w as observed. In all cases, the PAC addition caused a significantly imp roved settling of the AS, reducing the sludge-volume-index, and increa sing the content of volatile solids of the PAC-sludge. In general, no evidence of a synergistic effect of the PAC addition to activated slud ge, nor bioregeneration of the activated carbon, could be observed. Th is suggests, that the observed effects probably are caused only by sim ple adsorption. (C) 1997 IAWQ. Published by Elsevier Science Ltd.