Thermal and alkaline pre-treatments of inoculum halt methanogenesis and enables cheese whey valorization by batch acidogenic fermentation

Abstract

Carboxylates like volatile fatty acids (VFAs) can be produced by acidogenic fermentation (AF) of dairy wastes like cheese whey, a massive residue produced at 160.67 million m3of which 42% are not valorized and impact the environment. In mixed-culture fermentations, selection pressures are needed to favor AF and halt methanogenesis. Inoculum pre-treatment was studied here as elective pressure for AF demineralized cheese whey in batch processes. Alkaline (NaOH, pH 8.0, 6 h) and thermal (90 °C for 5 min, ice-bath until 23 °C) pre-treatments, were tested together with batch operations run at initial pH 7.0 and 9.0, food-to-microorganism (F/M) ratios of 0.5 to 4.0 g COD g-1VS, and under pressurized and non-pressurized headspace, in experiments duplicated in two institutes. Acetic acid was highly produced (1.36 and 1.40 g CODAcOH L-1) at the expense of methanogenesis by combining a thermal pre-treatment of inoculum with a non-pressurized batch operation started at pH 9.0. Microbial communities comprised of VFAs and alcohol producers, such asClostridium,Fonticella, andIntestinimonas, and fermenters such asLongilineaandLeptolinea. Communities also presented the lipid-accumulating and bulk and foamingCandidatus Microthrixand the metanogenicMethanosaetaregardless of no methane production. An F/M ratio of 0.5 g COD g-1VS led to the best VFA production of 1,769.38 mg L-1. Overall, inoculum thermal pre-treatment, initial pH 9.0, and non-pressurized headspace acted as a selective pressure for halting methanogen and producing VFAs, valorizing cheese whey via batch acidogenic fermentation.

Got Whey? Sustainability Endpoints for the Dairy Industry through Resource Biorecovery

“…Mixotrophic microalgae can display a combination of photolithoautotrophic and/or chemoorganoheterotrophic regimes. Hence, they are able to grow through using both the carbon dioxide produced via photosynthesis and organic carbon sources (e.g., cheese whey, permeate, second cheese whey, and volatile fatty acids resulting from cheese whey acidogenic fermentation) [36,37,181].…”

“…Even though there has been substantial research into utilizing cheese whey in microalgal growth and co-digestion processes (e.g., biomass, biofuel, and value-added product production; CO 2 mitigation; or wastewater treatment), the potential of tailored microalgalbacterial mixed-culture biotechnologies for cheese whey bio-valorization remains relatively unexplored. The challenges associated with integrating mixed cultures include the costs and energy requirement associated with harvesting microalgae biomass, the complex dynamics of micro-ecosystems that can rapidly shift, and the absorption of light across mixed liquors and biofilms beyond the photic zone [36,181,192].…”