Effect of an organic shock load on the stability of an anaerobic migrating blanket reactor

The goal of this study was to examine the effect of an organic shock load on the performance and stability of a laboratoryscale anaerobic migrating blanket reactor (AMBR). To accomplish an organic shock load, nonacidified sucrose solution was almost doubled in concentration, while maintaining a constant hydraulic retention time. The volumetric loading rate (VLR) was increased from 27 to 50 9 chemical oxygen demand (COD) L-1 day(-1) for a period of six hydraulic retention times (42 h). This resulted in an increase in the standard methane production rate (liters of methane at standard temperature and pressure per liter reactor volume per day) from 7 to 12 LL-1 day(-1). The pH levels stayed favorable and biomass washout was limited during the shock load due to the damping effects of a compartmentalized configuration. During the shock load, the propionate production in the initial compartments of the AMBR remained at the same level as before the shock load, while the acetate production rose sharply. Because propionate is the most difficult volatile fatty acid to be removed, unstable conditions due to excessive propionate accumulation during the shock load were prevented. Meanwhile, the acetate concentration in the liquid phase and hydrogen content in the headspace of the final compartments remained low, which ensured propionate degradation. Due to these intrinsic characteristics of the AMBR, the soluble COD removal efficiency stayed above 87% under these stressed conditions. Moreover, the performance of the AMBR reached pre-shock-load levels immediately after the VLR was restored to 25 g COD L-1 day(-1).