Spatial and temporal variations of monitoring performance parameters in horizontal-flow anaerobic immobilized sludge (HAIS) reactor treating synthetic substrate

This paper reports on experiments with a lab-scale horizontal-flow anaerobic immobilized sludge (HAIS) reactor treating synthetic substrate aiming to observe temporal and spatial variations of its monitoring performance parameters. The bench-scale HAIS reactor was filled with polyurethane foam matrices containing immobilized anaerobic sludge taken from an upflow anaerobic sludge blanket (UASB) reactor treating diluted piggery wastewater. A synthetic substrate composed of glucose as the main carbon source (chemical oxygen demand - SOD of 2090 mg l(-1)) was used for feeding the HAIS reactor in two experiments with bed porosities (epsilon) of 0.4 and 0.24 and at hydraulic detention times (HDT) of 8.0 and 4.8 h, respectively. The temperature was maintained at 30 degrees C, and COD, volatile fatty acids (VFA), total alkalinity (TA) and pH were monitored in the effluent stream (length to diameter ratio - L/D of 20) and intermediate ports along the reactor's length (L/D of 4, 8, 12 and 16). CH4 concentration in the gas was determined daily for evaluating the start-up period duration. The short start-up period duration (6 days) in both the experiments confirmed that a HAIS reactor can provide favorable environmental conditions for rapid biomass acclimatization, growth and retention. COD removal efficiencies of 98% were attained in the first experiment (epsilon of 0.4) and the effluent VFA concentration was lowered to 15 mg l(-1). At the L/D ratio of 4 in the first sampling port, corresponding to a HDT of 1.6 h, the COD removal efficiency achieved 72%. In the second experiment (epsilon of 0.24), the maximum COD removal efficiency was 80% and the effluent VFA leveled 350 mg l(-1). Channeling due to the low bed porosity was found to be the main factor responsible for the poor performance of the reactor operating at epsilon of 0.24. (C) 1997 Elsevier Science Ltd.