Selective control of volatile fatty acids production from food waste by regulating biosystem buffering: A comprehensive study

The biological production of volatile fatty acids (VFA) or short chain carboxylic acids (SCCAs) from biogenic wastes is gaining perceptible interest. The acidogenesis catalyzed by mixed consortia faces the disadvantage of redox imbalance with inconsistent low VFA production, which needs to be addressed. Thus, the present study was performed with the objective of investigating the role of different buffering/neutralizing agents viz. sodium hydroxide (NaOH), sodium carbonate (Na2CO3), calcium carbonate (CaCO3) and calcium hydroxide [Ca(OH)(2)] towards selective production of acetic (H-Ac), butyric (H-Bu) and propionic (H-pr) acid from food waste fermentation. The study was performed in two approaches, where systems were buffered initially (IBS) and regularly in controlled mode (CBS) with the respective studied buffering/neutralizing agent. Higher selective HA. production was observed with Na2CO3 CBS (5.85 +/- 0.29 g VFA/L) followed by NaOH CBS (4.2 +/- 0.12 g VFA/L) while highest H-Bu production (2.62 +/- 0.13 g VFA/L) followed by 1.55 +/- 0.04 g VFA/L was achieved with the CBS and IBS operated with the combination of NaOH + CaCO3 (1:2) respectively. Highest total VFA productivity was achieved with NaOH CBS (11.4 +/- 0.34 g VFA/L) followed by Na2CO3 CBS (10.02 +/- 0.3 g VFA/L) and least with Ca(OH)(2) CBS (4.35 +/- 0.13 g VFA/L). A higher degree of acidification was observed in the NaOH CBS (34.98%) while higher buffering and biohydrogen production (54 +/- 2.6%) was achieved with systems operated with Na2CO3 CBS and IBS respectively. Buffering intensity graphs revealed the role of supplemented and system in situ developed carbonic acid, bicarbonate (pKa 6.35), carbonate (pKa 10.33), ammonium (pKa 9.25) and equilibrium between these buffers towards the selective VFA production in the respective systems. The results illustrated the specific role of buffering/neutralizing agents towards enhanced and selective VFA production.