No abstract

Four laboratory-scale reactors were used to study the effects of mixing intensity and mixing duration on the anaerobic treatment of potato-processing wastewater at 20 °C. The mixing intensities were set at impeller speeds of 0, 20, 50, and 100 rpm. Two mixing durations were studied: 45 and 15 min/h. It was found that both mixing intensities and mixing durations studied and their joint effect significantly affected the steady-state performance of the anaerobic reactors in treating the potato-processing wastewater with respect to organics and solids removals and methane production. Key words: mixing effects, anaerobic treatment, potato-processing wastewater, organics and solids removal, methane production.

A study investigating the effects of temperature and organic loading on the performance of upflow anaerobic sludge blanket reactors was carried out in the laboratory. Laboratory-scale rcactors of 3.2 L volume were semicontinuously fed a synthetic substrate consisting of beef consommC and macroand micro-nutrient compounds. Temperatures ranged from 10 to 42°C; organic loadings ranged from 2.0 to 30 kg COD/(m3. d). Steady-state process kinetics and efficiencies were evaluated for the various conditions. Based on the assumption that upflow anaerobic sludge blanket reactor kinetics in the temperature range of 10-30°C could be approximated by Monod and modified Arrhenius equation relationships, effluent SCOD concentrations and removals were used to determine the maximum rate of substrate utilization, the half-velocity constant, and the temperature coefficient. A design and operating chart was constructed based on the kinetic coefficients determined from the experimental data.

An anaerobic lagoon–filter system was operated in the laboratory to treat potato-processing waste water at 20 °C and pH 7 under three loading rates varying from 0.149 to 0.719 kg BOD∙m−3 ∙day−1. The overall removals of biochemical oxygen demand (BOD) and suspended solids (SS) were high, in the ranges of 97–98 and 89–97%, respectively. The system was consistently stable in effluent quality despite periods of shock loads and zero input.The optimum loading rates to the lagoon and the filter were 0.3 and 0.4 kg BOD∙m−3∙day−1, respectively. Most of the BOD and SS removals occurred in the bottom portion of the reactors. A base had to be added to the waste water to maintain the pH at 7 for good performance. No lagoon desludging is expected for full-scale operation. Filter clogging is also unlikely under the optimum loading rates.

Laboratory-scale models consisting of a simple upflow anaerobic sludge blanket reactor (UASBR) and an upflow anaerobic filter (UAF) in series were subjected to organic loadings of 0.19 to 0.55 kg COD m -3 d ~ at 20 °C. COD and SS removals were 95 to 98% and 98 to 99%, respectively. Biogas produced by the system amounted to 0.31 to 0.32 m 3 CH 4 kg < COD removed. The UASBR was. more stable than the UAF in performance. No sign of deterioration in final effluent quality was observed during 420 days of operation under low loading.