Characterization of and Bioproduction of Short-Chain Organic Acids From Mixed Dairy-Processingwastewater

Mixed wastewater from the cheese-processing industry was characterized and biologically treated to produceshort-chain organic acids (i.e., acetic, propionic, butyric, and valeric acids) in laboratory-scale continuously stirred tankreactors. 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 inoculumsystem, an anaerobic continuously stirred tank reactor (CSTR) with 1.5 L working volume, was used to minimize theexperimental 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 35C at 0.5 days hydraulic retention time (HRT). Two identical 2.8 L anaerobicCSTRs equipped with temperature and pH controllers were separately used to evaluate system performance. Severaldifferent HRTs (0.6 days, washout points) were randomly tried and the organics in the wastewater were converted to thesefour organic acids at up to 62.4% at pH 7.01, 36.2C, and 0.45 days HRT.