THE EFFECT OF SHOCK LOADS ON THE PERFORMANCE OF AN ANAEROBIC BAFFLED REACTOR (ABR) .2. STEP AND TRANSIENT HYDRAULIC SHOCKS AT CONSTANT FEEDSTRENGTH

Two Anaerobic Baffled Reactors (ABR) were used to examine the effect o f transient and step hydraulic shock loads on reactor performance in t erms of chemical oxygen demand (COD) removal and microbial responses t o hydraulic shocks in each compartment. The reactors were operated at 20-h hydraulic retention time (HRT), 4 g/litre COD and 35 degrees C as a base-line condition. Hydraulic shocks with an HRT of 1 h (an increa se of 20 times in the influent flowrate), 10 h and 5 h were applied to the reactors for 3 h, 2 weeks and 3.5 weeks, respectively, and a vari ety of key intermediates monitored over time in each compartment. The baseline conditions (4.8 kg-COD/m(3) d) resulted in 98% COD removal; h owever, when the HRT decreased to 10 h (9.6 kg-COD/m(3) d) removal dro pped to 90%, and at 5-h HRT (19.2 kg-COD/m(3) d) removal was only 52%. It was found that the ABR was very stable to large transient shocks, and while biomass loss was substantial, it recovered back to its basli ne performance;only 9 h after the shock ceased. Tracer studies found t hat the total dead space in the reactor at 24 g-VS/litre and 20-h HRT was about 18% by volume; however, when the HRT was reduced to 10 and 5 h, this increased to 39%. Comparison of this data with previous resul ts for varying feed concentration and recycle ratio in the ABR reveale d that removal efficiency could be tentatively explained in terms of H RT; organic loading rate; the concentration/activity and kinetics of t he biomass: the dead space in the reactor; the severity and type of ch annelling in each compartment; the substrate concentration in each com partment driving mass transfer into the flocs; and floc size. Hence, i t seems that this type of reactor configuration has potential in treat ing industrial wastes that vary in both flow and concentration, and st ill enable high removal rates to be achieved. (C) 1997 Elsevier Scienc e Ltd.