Effect of initial pH and substrate concentration on the lactic acid production from cassava wastewater fermentation by an enriched culture of acidogenic microorganisms

Abstract

Recently, cassava processing wastewater has been considered an alternative substrate for lactic acid production due to its appreciable carbohydrate levels. The authors carried out different batch reactor trials aiming to favor the production of lactic acid through the fermentation of non‐sterilized cassava wastewater by an enriched culture of acidogenic microorganisms. To this end, the impact of different initial pHs (4.5, 5.0, 5.7, 6.5, and 7.0) and different initial substrate concentrations (10, 15.8, 30, 44.2, and 50 g/L) in terms of glucose on lactic acid production yield (Y) was evaluated by applying the design of experiment (DoE) known as central composite rotatable design (CCRD). The highest rate of lactic acid production (40 g/L) occurred with an initial pH of 6.5 and an initial substrate concentration of 50 g/L. The maximum yield was higher in trials T1, T2, T4, T5, and T8, reaching values of 0.80, 0.62, 0.60, 0.96, and 0.70 g/g, respectively. The maximum lactic acid productivity (P), of 0.60 and 0.73 g L−1 hr−1, was observed in trials T5 and T8, respectively. The enriched culture of acidogenic microorganisms was shown to favor the production of lactic acid, since the production of other acids, such as acetic and propionic acid, did not exceed 3.5 and 4.5 g/L, respectively. © 2020 Water Environment Federation Practitioner points Cassava wastewater presented potential to lactic acid production. The CCRD showed that highest lactic acid concentrations (40 g/L). The adoption of cassava wastewater or manipueira as a substrate resulted in important information on the tendency to obtain value‐added products such as lactic acid.

Volatile Fatty Acids Production by Acidogenic Fermentation of Wastewater: A Bibliometric Analysis

“…In recent years, there has been increasing research interest in the recovery of VFA from solid waste [37] and wastewater [38,39]. Research has aimed to evaluate and optimize operational parameters such as pH, temperature, organic loading rate, substrate concentration, hydraulic retention time and inoculum [7,38,40,41], through laboratory-scale experiments in continuous [38,42] and batch [43] reactors. VFA production presents additional challenges because the products are soluble and there is no automatic phase separation [44].…”

“…In addition, the aim of the studies must be taken into account because, while a significant number of works are oriented towards identifying the pH necessary to optimize the total production of carboxylic acids, others seek the optimization of a specific acid. Da Silva et al [42] used wastewater from cassava processing to optimize lactic acid production, while the work of Dareioti et al [68], despite having evaluated VFA production, took optimize hydrogen production as its main objective.…”

“…However, some studies that did not assess the impact of HRT reported the fermentation time in which the maximum concentration of organic acids was observed. Da Silva et al [42] aimed to evaluate the effect of initial pH on the lactic acid production from cassava processing wastewater in 48 h experiments. The authors indicated a rapid decrease in pH to 4.5 within 6 h after starting fermentation, but after 24 h pH remained stable between 4.0 and 4.5 until the end of the process.…”

“…Dinopoulou et al [27] conducted experiments with influent COD concentrations of 3.15 and 12 g/L and similar HRT and showed that the degree of acidification achieved during the first series (3.15 g/L) was significantly higher than that obtained during the second (12 g/L), evidencing a negative effect at higher initial substrate concentrations. Da Silva et al [42] evaluated the effect of initial pH and five glucose concentrations (10, 15.8, 30, 44.2 and 50 g/L) on lactic acid production from cassava processing wastewater. In the experiments with higher initial glucose concentrations, the authors observed a stabilization of fermentation 24 h after the start of the process.…”

Compositional variability as a major hindering factor in continuous biohydrogen production from cassava starch wastewater: Possible solutions for complex substrates

“…38 In limiting conditions, such as the carbohydrate shortage, strong selection pressures favor the appearance of a dominant population (HPB) and reduce the possibilities of colonization by undesired populations (non-hydrogen producing), which can compromise the performance and stability of the process. 25 CSW is considered a potential substrate for lactic acid production through anaerobic processes due to its high organic content, 59 suggesting that the conversion of the carbohydrates to lactic acid is a factual approach to be explored in the hydrogen evolution from cassava processing residues.…”