Potential assessment and kinetic modeling of carboxylic acids production using dairy wastewater as substrate

Carboxylic acids (CA) are high added-value compounds that can be produced via anaerobic fermentation by using agroindustrial residues as substrates. However, different compounds in wastewater impose uncontrolled metabolic pathways, in which the acidogenic fermentation kinetics need to be elucidated. This work aimed to assess the potential production of CA from dairy wastewater (DW) and to perform the kinetic modeling of the process. The experiments were conducted in quadruplicate batch reactors (250 mL of working volume) with inoculum from a brewery UASB at 0.61 +/- 0.04 gCOD gVSS(-1). To inhibit methanogenesis, 0.05 % (v/v) chloroform was added to the reactors. The tests showed that DW is a readily fermentable substrate to acidogenic microorganisms because it presents high rates of short-chain CA formation in the first two days of the experiment. The low concentrations of medium-chain CA found indicate that fats and proteins did not function as the main carbon source for DW fermentation. The yield obtained was 0.66 mgCA mgCOD(A)(-1), which corresponds to 0.83 mgCOD(CA) mgCOD(A)(-1). Kinetic modeling studies have shown that mathematical models that can describe an exponential phase, such as First-order and Fitzhugh models, are suitable for simulating the production of carboxylic acids. Finally, DW seems to be a promising substrate to be investigated in the carboxylic platform.