Selective production of volatile fatty acids at different pH in an anaerobic membrane bioreactor

Abstract

This study investigated the production of major volatile fatty acid (VFA) components in an anaerobic membrane bioreactor (AnMBR) to treat low-strength synthetic wastewater. No selective inhibition was applied for methane production and solvent-extraction method was used for VFA extraction. The results showed acetic and propionic acid were the predominant VFA components at pH 7.0 and 6.0 with concentrations of 1.444 ± 0.051 and 0.516 ± 0.032 mili-mol/l respectively. At pH 12.0 isobutyric acid was the major VFA component with a highest concentration of 0.712 ± 0.008 mili-mol/l. The highest VFA yield was 48.74 ± 1.5 mg VFA/ 100 mg CODfeed at pH 7.0. At different pH, AnMBR performance was evaluated in terms of COD, nutrient removal and membrane fouling rate. It was observed that the membrane fouled at a faster rate in both acidic and alkaline pH conditions, the slowest rate in membrane fouling was observed at pH 7.0.

Energy production in anaerobic membrane bioreactors: Opportunities and challenges

“…Research studies have shown that between pH 5.0 and 6.0, the highest overall VFA concentration is observed regardless of the type of which inoculum was used while producing VFA from food waste [64]. However, Khan et al (2019) reported that the highest VFA yield from low-strength synthetic wastewater recorded 48.74 ± 1.5 mg VFA/ 100 mg CODfeed at pH 7.0, whereas Jie et al…”

“…The fouling layer can eventually retain VFA inside the anaerobic bioreactor, and make the separation and purification processes even more challenging [38,39]. On this issue, Khan et al (2019) carried out an experiment to produce VFA from low strength synthetic wastewater using a single stage AnMBR [3]. There results showed the highest VFA yield of 48.20 ± 1.21% (mg VFA/mg CODfeed) at HRT lasting 8 hrs.…”

“…In fact, a major problem in the AnMBR is the accumulation of VFAs inside the reactor. The accumulation triggers a sharp pH drop, and this disrupts the stability of AnMBR operations [3,61].…”

“…(2014) documented at pH 10.0 the accumulation of VFA reached the maximum limit during anaerobic digestion of excess sludge (ES) [61,65]. As different types of microbial species are present in different inoculums, their optimum growth rates vary at different pH levels.…”

“…A general decrease in HRT of an anaerobic process results in increased VFA production [66]. Khan et al (2019) demonstrated that for an AnMBR treating low-strength synthetic wastewater, 8 hrs of HRT provide the highest VFA production rate and yield [3].…”