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 — COD of 2090 mg 1−1) was used for feeding the HAIS reactor in two experiments with bed porosities ( ) 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°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 reactorʹs 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 ( of 0.4) and the effluent VFA concentration was lowered to 15 mg 1−1. 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 ( of 0.24), the maximum COD removal efficiency was 80% and the effluent VFA leveled 350 mg 1−1. Channeling due to the low bed porosity was found to be the main factor responsible for the poor performance of the reactor operating at of 0.24.