Changes in selected dioxin-like PCB concentration and toxicity in anaerobically stabilized sewage sludge

The process of methane digestion was conducted in two parallel cultures with different sewage sludge. The digestion was conducted three times: the thermophilic one (37 degrees C) for 14 d, the mesophilic one at temperature of 36 degrees C for 15 d and the mesophilic one for 14 d, with a preceding five-d thermophilic hydrolysis. The content of three most detrimental dl-PCB with codes: 77 (3,3',4,4'-tetrachlorobiphenyl), 126 (3,3',4,4',5-pentachlorobiphenyl), and 169 (3,3',4,4',5,5'-hexachlorobiphenyl). Changes in toxicity, caused by the presence of coplanar polychlorinated biphenyls (PCB) in sewage sludge, during digestion were evaluated by means of TEQPCB equivalent. Research results showed that conducted anaerobic stabilization processes of sewage sludge proceeded correctly. It was demonstrated that methane digestion process contributes to some decrease in PCB concentration and in toxicity due to the presence of coplanar PCB in sewage sludge. Intensification of mesophilic digestion by means of thermophilic hydrolysis contributed to some decrease in dl-PCB concentration and toxicity equivalent. The highest reduction in sludge toxicity was obtained during thermophilic digestion. After the process, reduction in WHO98-TEQ(PCB) equivalent value in sewage sludge by 98% on average was demonstrated.