Use of response surface analysis in selective bioconversion of starch wastewater to acetic acid using a mixed culture of anaerobes

Starch-processing wastewater was treated to maximize acetic acid production using a mixed culture of acidogenic anaerobes, which were identified as Acetobacterium woodi, Centipede periodontii, Desulfobulbus elongatus, Lactobacillus rhamnosus, Lactobacillus casei, and Lactococcus plantarum. The maximum production of acetic acid associated with simultaneous changes in hydraulic retention time (HRT), pH, and temperature was investigated. The conversion efficiency of organics in the wastewater to acetic, propionic, and butyric acids ranged from 71.1 to 98.3%. The concentrations of estimated total organic carbons (TOCs) due to the formation of acetic acid ranged from 268 to 672 mg/l, which accounted for 29.7 and 72.2% of influent TOC concentration, respectively. Using a response surface methodology (RSM) with an orthogonal cube design, the maximum production of acetic acid was 1681±49 mg/l at 0.56 day HRT, pH 5.9 and 36.1 °C, which was 75.2% conversion efficiency. Systematic model-building along with statistical analysis using a RSM, could play an important roles in elucidating basic mechanisms in complex situations and thus providing better process control in maximizing acetic acid production with respect to the effects of HRT, pH, and temperature.