Can salt-tolerant sludge mitigate the salt inhibition to acidogenic fermentation of food waste? Insight into volatile fatty acid production microbial community

For treatment of saline wastewater, the feasible approach to mitigate the salt inhibition is using the acclimated salt-tolerant sludge. The aim of this work was to verify if the use of the acclimated sludge (AS) also could alleviate salinity stress on acidogenic fermentation of food waste (FW) under saline environment. The responses of volatile fatty acid (VFA) production and the microbial community to salt stress were investigated. Results showed that VFA production was reduced by high salinity (30 g/L and 70 g/L NaCl) compared with the control (0 g/L NaCl), especially for groups inoculated with the AS, whereas inoculating with the non-acclimated sludge (non-AS) caused less reduction. The impact of salinity was seen on VFA production with accumulation of more propionic acid and acetic acid along with traces of butyric acid. Significant shift on microbial community composition occurred upon biomass exposure to salt. The microbial communities of the non-AS and AS groups at the same NaCl concentrations converged over time. The non-AS groups contained a more proportion of the phyla Bacteroidetes, Atribacteria and Chloroflexi at high salt levels. These findings demonstrate that the non-AS was more conducive to VFA production due to the presence of higher proportions of hydrolytic and fermenting bacteria.Statement of NoveltyAlthough anaerobic digestion (AD) would be the most cost‐effective and sustainable technology, the salinity is considered to be inhibitory to anaerobic biological treatment processes. The recent applications of salt‐tolerant cultures for the treatment of saline wastewaters suggest that biological treatment is promising. Previous studies also reported that acidogenic fermentation as the first step of AD process is inhibited under saline conditions. However, no study to date has focused on acidogenic fermentation for volatile fatty acid production from food waste using salt-tolerant sludge. Therefore, there is a need for improved understanding of high salt stress to resource recovery from organic wastes. This understanding can help in the design of an operating strategy to alleviate the inhibition of waste treatment by salinity.