Treatment of tomato processing wastewater by an upflow anaerobic sludge blanket–anoxic–aerobic system

Abstract The main objective of this study is to assess the achievability of stringent discharge criteria i.e. BOD 5 4 -N  5 of 1750–7950 mg/L, TKN of 48–340 mg/L and NH 4 -N of 21–235 mg/L. Two treatment systems, a UASB–aerobic system and a UASB–anoxic–aerobic system were tested. Furthermore due to alkalinity deficiency, in the raw wastewater, the study explored varying UASB effluent recirculation flowrates to the UASB influent to reduce additional alkalinity requirements. The UASB–anoxic–aerobic system was effective in treating tomato canning wastewater at an overall HRT of 1.75 days while achieving 98.5% BOD 5 , 95.6% COD, 84% TSS and 99.5% NH 4 -N removal producing effluent BOD 5 , COD, TSS, NH 4 -N, TKN, NO 2 -N, NO 3 -N and PO 4 -P of 10, 70, 15, 0.5, 3, 0, 60 and 4 mg/L, respectively. The biogas yield was 0.43 m 3 /kg COD removed.