Effect of Soluble Organic, Particulate Organic, and Hydraulic Shock Loads on the Performance and Stability of Anaerobic Sequencing Batch Reactors treating Slaughterhouse Wastewater at 20°C

Abstract

Anaerobic sequencing batch reactors (ASBRs) treating slaughterhouse wastewater at 20°C were subjected to soluble organic, particulate organic and hydraulic shock loads, which increased the average regular organic loading rate (OLR) by a factor ranging from 1.5 to 3.6. During the soluble organic shock load, effluent soluble chemical oxygen demand (SCOD) increased from an average of 200 mg/l in control reactors to a maximum of 5626 mg/l in overloaded reactors. Effluent volatile fatty acid (VFA) concentration increased from 58 mg/l in controls to a maximum of 1642 mg/l in overloaded ASBRs, and effluent suspended solids (SS) concentration, from 249 mg/l in controls to a maximum of 10723 mg/l in overloaded reactors. However, effluent SCOD, VFA and SS concentrations were rapidly reduced to pre-shock load levels shortly after regular operating conditions were resumed. The particulate and hydraulic shock loads had small and temporary effects on effluent SCOD and VFA concentrations. However, high SS concentrations, reaching up to 5501 mg/l, were observed in the effluent. Solids loss during effluent discharge did not significantly affect long-term performance of the ASBRs, probably because the sludge bed had high initial volatile SS (VSS) concentration (21.9 ± 3.2 mg/l), and also a fraction of the VSS removed from the reactors during effluent discharge was composed of undegraded colloidal solids from the slaughterhouse wastewater, as opposed to bacterial flocs. Nevertheless, maintaining a high VSS concentration in the sludge bed will probably prevent long-term negative effect of possible biomass loss during sudden shock loads.