RESPONSES OF AN ANAEROBIC FIXED-FILM REACTOR TO HYDRAULIC SHOCK LOADINGS

The responses of an anaerobic fixed-film reactor (AFFR) to hydraulic s hock loadings were studied. The AFFR was started up with a synthetic w astewater of 3000 mg COD/l at 5.00 d hydraulic retention time (HRT), a chieving 98.1% COD removal efficiency. When stable operation was attai ned, the HRT was sporadically adjusted to 2.50, 1.25, 1.00 and 0.50 d to simulate two, four, five and 10 times hydraulic shock loadings, res pectively, while the COD loading was maintained constant. Under two, f our and jive times hydraulic shock loadings, the COD removal efficienc y was temporarily reduced to between 84.4 and 88.3%, and the pH of the treated effluent and the biogas production were also affected. The AF FR could recover from the temporary inhibition due to these shock load ings and resumed normal operation within eight days. On the other hand , under 10 times hydraulic shock loading, the treatment performance de teriorated drastically. Volatile fatty acids (VFAs) accumulated in the AFFR liquor resulting in reactor souring and failure. When the HRT wa s returned to 5.00 d, the biofilter could be recovered within a few da ys. The ability of the AFFR to recover from critical hydraulic shock l oadings and system failure was attributed to the immobilized-biofilm d esign, which enabled the temporarily inhibited biofilms to be retained in the AFFR and regain activity when favourable conditions were resto red. (C) 1997 Elsevier Science Ltd.