Production of volatile fatty acids and alcohols from dairy wastewater under thermophilic conditions

Abstract

The influence of substrate strength on thermophilic anaerobic acidogenesis of a simulated dairy-processing wastewater was investigated. Six series of experimental runs at chemical oxygen demand (COD) of 2, 4, 8, 12, 20, and 30 g/L were conducted at 55 ° C. Carbohydrate was readily degraded in all the runs, while the conversions of protein and lipid decreased when substrate concentration increased. The degree of acidification also decreased when the substrate COD increased, from 61.4% at 2 g-COD/L to 31.3% at 30 g-COD/L. The predominant acidogenic products were acetate, propionate, butyrate, and ethanol, while i-butyrate, i-valerate, valerate, caproate, and methanol were present in the effluents in lesser quantities. Propanol and butanol were found at high substrate concentrations. The metabolic pathways were significantly influenced by the substrate concentration. Only 4.15% to 9.52% of COD in wastewater was converted to hydrogen/methane. The net yield of acidogenic biomass was 0.25g-VSS/g-COD.