ABSTRACT
One of the main disadvantages of anaerobic wastewater treatment at a low pH is the significant operational cost due to the addition of necessary alkali. To reduce alkali supplement and thus the cost, this study proposes a sequential multi-feed [SqMF] mode [distributed feeding] and effluent recycle [ER] mode. Experiments were conducted with a pilot-scale [2.5 m[3]] thermophilic [55°C] multi-staged up-flow anaerobic sludge blanket reactor. Alcohol distillery wastewater [shochu], a major source of industrial wastewater in Japan, was used for the study. The SqMF mode of operation [influent pH: 5.0; organic loading rate: 45 kgCOD/m[3]/day; HRT: 12 hours; influent COD concentration: 20,900 mgCOD/L] successfully reduced the alkali supplement [24% NaOH solution] requirement by 67.2% compared with the single-feed mode. For the ER mode operation [organic loading rate: 35 kgCOD/m[3]/day; HRT: 12 hours; influent COD concentration: 17,400 mgCOD/L], operation was possible without any alkali supplement since the system uses the alkalinity generated during microbial metabolism