EFFECT OF LOW-TEMPERATURES ON THE PERFORMANCE OF AN ANAEROBIC BAFFLEDREACTOR (ABR)

The effect of a decrease in operating temperature on the performance o f two 10 dm(3) anaerobic baffled reactors (ABR) was examined in terms of steady state chemical oxygen demand (COD) removal efficiency. To mi nimise variations, and have a totally biodegradable feed, a synthetic carbohydrate (sucrose)protein (meat extract) substrate was used. The r eactors were operated at 20 h hydraulic retention time (HRT), 4 g dm(- 3) COD, and 35 degrees C as a base-line condition, Because of their di fferent histories, the reactors responded differently to a decrease in operating temperature to 25 degrees C. Reactor 1 remained stable at 9 7% COD removal, whereas Reactor 2 decreased to 93% removal, but rose t o 97% after adding an effluent recycle of 0.25. At 15 degrees C, the e fficiency of Reactor 1 dropped to 75%, while the removal of Reactor 2 declined to 83%, and no improvement in efficiency occurred with an eff luent recycle at 0.25. At 25 degrees C, the decreased rare of cataboli sm of the slow-growing syntrophs and methanogens resulted in a shift o f the volatile fatty acids (VFA) peak to the second compartment. Howev er, the biomass present in the reactor prevented VFAs breaking through in the effluent, Nevertheless, at 15 degrees C VFAs were present in t he effluent, perhaps due to the lower rates of metabolism and an incre ase in the K-s for VFAs. Finally, at 15 degrees C part of the increase in the effluent COD was due to the enhanced production of soluble mic robial products (SMP), or a decrease in their metabolism, with these c ompounds constituting some 10% of the inlet COD.