Lactic Acid Production from Cow Manure: Experimental Process Conditions Analysis

Abstract

The production of cow manure far exceeds the quantity that can be utilized in primary applications such as fertilizer or for the generation of biogas. As a result, alternative value-added applications are being investigated. The purpose of this study is to evaluate the production of lactic acid, using cow manure as the raw material. The methodology involved the implementation of thermochemical pretreatment for the cow manure, followed by simultaneous saccharification and fermentation for lactic acid production. Response surface methodology based on a central composite design was employed to analyze the simultaneous saccharification and fermentation process. The factorial design of the experiments was carried out with three factors, cow manure concentration, temperature, and enzyme concentration, with 80 g·L−1, 50 °C, and 212.5 IU/gCMDry Matter as central point values, respectively. Following the addition of Bacillus coagulans DSM2314 inoculum to enzymatically hydrolyzed cow manure at pH 5.0, after a 24 h period the concentration of lactic acid was recorded at 13.65 g·L−1, with a conversion efficiency of 33.1%. Studies were conducted until 48 h to analyze time impact. Characterization studies for native cow manure and that pretreated using acid reagent were conducted. Sugar content and by-product formation were analyzed, resulting in 23.24 g·L−1 of sugar remaining as the maximum after fermentation, while low values of furfural (1.04 g·L−1), 5-hydroxymethylfurfural (1.35 g·L−1), and acetic acid (1.45 g·L−1) were found. Optimal conditions were calculated at 24 and 48 h with R software, obtaining the lactic acid, with yields of 13.4 g·L−1, 36.28% (for 24 h) and 15.27 g·L−1, 32.76% (for 48 h), respectively. Experimental and statistical studies of enzymatic hydrolysis and fermentation stated that cow manure was a feasible substrate for the production of lactic acid.