Effect of process configuration and substrate complexity on the performance of anaerobic processes

The roles of substrate complexity (molecular size of the substrate) and pro cess configuration in anaerobic wastewater treatment were investigated to d etermine optimal methanogenic technology parameters. Five substrates (gluco se, propionate, butyrate, ethanol, and lactate) plus a mixed waste (60% car bohydrate, 34% protein, and 6% lipids) were studied under five reactor conf igurations: batch-fed single-stage continuous stirred tank reactor (CSTR), continuously fed single-stage CSTR, two-phase CSTR, two-stage CSTR, and sin gle-stage upflow anaerobic sludge blanket (UASB). The substrate feed concen tration was 20,000 mg/L as COD. The solids retention time (SRT) and hydraul ic retention lime (HRT) in the CSTR reactors were 20 d, while HRT in the UA SB was 2d. All reactors were operated for at least 60 d (equal to 3SRT). Substrate complexity was observed to be less significant under two-phase, t wo-stage and UASB reactor configurations. Two-phase CSTR, two-stage CSTR, a nd single-stage UASB configurations yielded the lowest effluent chemical ox ygen demands (130-550, 60-700, and 50-250 mg/L, respectively). The highest effluent chemical oxygen demands were detected when feeding glucose, propio nate, and lactate to continuously fed single-stage CSTRs (10, 400, 9900, an d 4700 mg/L GOD, respectively) and to batch-fed single-stage CSTRs (11, 200 , 2500, and 2700 mg/L GOD, respectively). Ironically, the one stage CSTR mo st commonly utilized in the field - was the worst possible reactor configur ation. (C) 2001 Elsevier Science Ltd. All rights reserved.