Effect of low pH start-up on continuous mixed-culture lactic acid fermentation of dairy effluent

Abstract

Mixed-culture fermentation that does not require an energy-intensive sterilization process is a viable approach for the economically feasible production of lactic acid (LA) due to the potential use of organic waste as feedstock. This study investigated mixed-culture LA fermentation of whey, a high-strength organic wastewater, in continuous mode. Variations in the hydraulic retention time (HRT) from 120 to 8 h under different pH regimes in two thermophilic reactors (55 °C) were compared for their fermentation performance. One reactor was maintained at a low pH (pH 3.0) during operation at HRTs of 120 to 24 h and then adjusted to pH 5.5 in the later phases of fermentation at HRTs of 24 to 8 h (R1), while the second reactor was maintained at pH 5.5 throughout the experiment (R2). Although the LA production in R1 was negligible at low pH, it increased dramatically after the pH was raised to 5.5 and exceeded that in R2 when stabilized at HRTs of 8 and 12 h. The maximum yield (0.62 g LA/g substrate fed as the chemical oxygen demand (COD) equivalent), the production rate (11.5 g/L day), and the selectivity (95 %) of LA were all determined at a 12-h HRT in R1. Additionally, molecular and statistical analyses revealed that changes in the HRT and the pH significantly affected the bacterial community structure and thus the fermentation characteristics of the experimental reactors. Bacillus coagulans was likely the predominant LA producer in both reactors. The overall results suggest that low pH start-up has a positive effect on yield and selectivity in mixed-culture LA fermentation.

Repeated-Batch Fermentation of Cheese Whey for Semi-Continuous Lactic Acid Production Using Mixed Cultures at Uncontrolled pH

“…As to the effect of the HRT variation, it could be observed that the adoption of lower values did not strongly affect the lactic acid concentration. As reported in a previous study [38], when low HRTs were adopted (12 h and 8 h), it was possible to reach a high extracted lactic acid mass in the presence of low lactic acid concentrations. HRT variations affected both the yield and the lactic acid productivity.…”

“…Different studies demonstrate that the optimum pH value for lactic acid production is between 5.5 and 5.9 [13,39,40]. The adoption of lower values led to low lactic acid concentrations (below 5 g/L) [14,31,38]. In contrast, the results achieved in this study showed that it was possible to produce a high lactic acid amount (20.1 g/L) at low pH, under the adopted uncontrolled pH conditions.…”

“…The maximum concentration of about 15 g/L was reached, which was again lower than the maximum concentration achieved in the present study. Regarding the lactic acid yields (Y and Y MAX in Table 3), expressed as grams of produced lactic acid (in terms of COD) per gram of fed COD to the reactors, the higher Y MAX value was reached by Choi et al, 2016 [38] using CW and performing the fermentation at a fixed pH of 5.5. When the same reactor was operated at pH 3, the average yields were below the value of 0.1.…”

“…Moreover, they are able to grow at extremely low pH [14,37]. In previous studies, acidic pre-treatments on fermentation inoculum were adopted to favor lactic acid bacteria growth and proliferation [14,38]. This procedure limited the production of undesirable compounds in the fermentation broth, increasing the purity of the produced lactic acid.…”

Co-culture of Bacillus coagulans and Candida utilis efficiently treats Lactobacillus fermentation wastewater

“…As a typical bacterial probiotic strain, Bacillus coagulans can produce lactic acid and has an ability in the sporulation to overcome harsh stresses, which can inhibit the growth of intestinal pathogens and regulate the animal intestinal micro-ecological balance (Riazi et al 2009, 2012), and promote animal digestion, and improve animal immunity (Grata and Nabrdalk 2012; Kodali and Sen 2008). Choi et al (2016) reported that the mixed-culture is a viable approach for the economically feasible production of lactic acid due to the potential use of organic waste for B. coagulans as feedstock.…”