Influence of micro-aeration in the production of volatile fatty acids (VFA) from wastewaters with high salinity

Abstract

Waste management and valorization are seen as pivotal drivers for adopting a circular economy. The production of volatile fatty acids (VFA) through anaerobic digestion (AD) fits perfectly into these emerging social and industrial dynamics, being the VFA considered valuable products, namely in chemical industries. Therefore, this work focuses on VFA production through AD, using wastes and wastewaters, with high salinity content (20 g/L) in continuous bioreactors. The effect of micro-aeration during acidogenesis of high-salinity wastes/wastewaters was accessed for more than 500 days, divided in 5 main periods, by analysing different physicochemical parameters like oxidationreduction potential (ORP), salinity, pH, COD, and VFA profile. Sludge properties were also analysed through quantitative image analysis (QIA) and integrating Principal Component Analysis (PCA). The results demonstrate that the high salinity does not appear as a limiting factor, with soluble COD (30 g/L) being constant through operation time in both reactors, as well as VFA/sCOD ratio (60 % 80 %). Due to micro-aeration, differences between anoxic (R1) and microaerophilic (R2) reactors were observed, with the second one presenting lower value of ORP in some periods during the assay. This indicates the presence of aerobic or facultative microorganisms, which have consumed oxygen. Also, higher concentrations of hexanoate in the microaerophilic reactor (R2) were obtained in those periods. The application of QIA combined with PCA has revealed that micro-aeration significantly impacts the morphology and size of aggregates.