Characterization of and bioproduction of short-chain organic acids from mixed dairy-processing wastewater

Abstract

Mixed wastewater from the cheese-processing industry was characterized and biologically treated to produce short-chain organic acids (i.e., acetic, propionic, butyric, and valeric acids) in laboratory-scale continuously stirred tank reactors. A total of 97.7% of total chemical oxygen demand (TCOD) in this wastewater was due to the presence of lactose, lactate, protein, and fat, which respectively composed 66.6%, 10.6%, 17.2%, and 3.3% of the TCOD. A constant inoculum system, an anaerobic continuously stirred tank reactor (CSTR) with 1.5 L working volume, was used to minimize the experimental error due to the use of inconsistent inoculum. The inoculum system was operated with dilute mixed waste, 5000 mg soluble COD/L at pH 6.5 and 35 degrees C at 0.5 days hydraulic retention time (HRT). Two identical 2.8 L anaerobic CSTRs equipped with temperature and pH controllers wc?re separately used to evaluate system performance. Several different HRTs (0.6 days, washout points) were randomly tried and the organics in the wastewater were converted to these four organic acids at up to 62.4% at pH 7.01, 36.2 degrees C, and 0.45 days HRT.