In this study, the effect of various factors such as C:N ratio, carbon source, percentage P content in the sludge influencing the simultaneous denitrification and enhanced biological phosphorus removal was investigated in batch tests on bean and tomato waste sludge from an upflow anaerobic sludge blanket reactor-anoxic/aerobic system and municipal sludge from a circulating fluidized bed bioreactor. A correlation between the change in redox potential and rate of P release was developed. Interestingly, maximum P release was observed at positive redox potential in some of the batch tests. Simultaneous denitrification and P release under anoxic conditions was observed during all the batch tests. Sludge acclimatization improved the efficiency of the sludge and proved independency of maximum specific denitrification rate and P content of sludges. The contribution of denitrifying PAOs to anoxic P uptake was determined through the denitrification control test at an initial level of PO 4 -P of 100-120 mg dm −3 .

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An upflow anaerobic sludge blanket (UASB)-anoxicaerobic system was used for treatment of tomato and bean processing wastewater. At various hydraulic retention times, ranging from 0.7 to 5 days, excellent removal of chemical oxygen demand (COD), biochemical oxygen demand (BOD), total suspended solids (TSS), ammonia-nitrogen (NH 4 -N), and total Kjeldahl nitrogen was achieved with final effluent BOD/TSS/NH 4 -N concentrations of less than 15/15/1 mg/L. Biogas yield in the UASB reactor varied from 0.33 to 0.44 m 3 /kgCOD removed . The kinetics of anaerobic treatment were investigated. The yield coefficient was 0.03 gVSS/gCOD; maximum specific growth rate was 0.24 day 21 ; Monod half velocity constant was 135 mgCOD/L; and specific substrate utilization rate was 3.25 gCOD/gVSS Á d. Nitrification and denitrification kinetics were studied in batch experiments, and the rates were comparable with those in the continuous flow system. Water Environ. Res., 78, 974 (2006).

An upflow anaerobic sludge blanket (UASB)-anoxic-oxic system was used to achieve biochemical oxygen demand, NH 4 and total suspended solids (TSS) criteria of 15, 1 and 15 mg dm −3 at 1.17 days of system hydraulic retention time during treatment of tomato-processing waste. The incorporation of an anoxic tank was found to affect the improvement in sludge-settling characteristics, as reflected by about 25-33% reduction in the sludge volume index, along with final effluent TSS and soluble biochemical oxygen demand concentrations of 13 and 9 mg dm −3 , respectively, which met the discharge criteria. Despite incomplete denitrification, sludge settleability was very good (sludge volume index <60 cm 3 g −1 ) owing to reduction in volatile suspended solids/TSS ratio from 0.75 to 0.6 as a result of higher alkalinity in the UASB effluent. Also in this study, phosphorus release was observed in the anoxic tank, predominantly due to abundance of acetic acid in the UASB effluent. A phosphate release of 5.4 mg P dm −3 was observed in the anoxic tank with subsequent P uptake in the following aerobic stage.

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