Abstract

Fermentation of waste activated sludge (WAS) is an alternative approach to reduce solid wastes while providing valuable soluble products, such as volatile fatty acids and alcohols. This study systematically identified optimal fermentation conditions and key microbial populations by conducting two sets of experiments under different combinations of biochemical and physical parameters. Based on fermentation product concentrations, methane production, and solid removal, fermentation performance was enhanced under the combined treatments of inoculum heat shock (>60°C), pH 5, 55°C, and short solid retention time (<10 days). An ecogenomics-based mass balance (EGMB) approach was used to determine the net growth rates of individual microbial populations, and classified them into four microbial groups: known syntrophs, known methanogens, fermenters, and WAS-associated populations. Their growth rates were observed to be affected by the treatment conditions. The growth rates of syntrophs and fermenters, such as Syntrophomonas and Parabacteroides increased with a decrease in SRT. In contrast, treatment conditions, such as inoculum heat shock and high incubation temperature inhibited the growth of WAS-associated populations, such as Terrimonas and Bryobacter. There were also populations insensitive to the treatment conditions, such as those related to Microbacter and Rikenellaceae. Overall, the EGMB approach clearly revealed the ecological roles of important microbial guilds in the WAS fermentation system, and guided the selection of optimal conditions for WAS fermentation in future pilot-scale operation.

Highlights

  • Microorganisms play a variety of roles in the biogeochemical cycles in natural and engineered ecosystems because of the diverse activities they carry out (Madigan et al, 2018)

  • The parameters tested in this study

  • In experiment II that determined the effects of solids retention time (SRT) (2.5–37.5 days), most treatments exhibited the highest volatile fatty acids (VFAs) concentrations at day 18, which decreased toward the end of incubation (Supplementary Figure S2)

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Summary

Introduction

Microorganisms play a variety of roles in the biogeochemical cycles in natural and engineered ecosystems because of the diverse activities they carry out (Madigan et al, 2018). It can be from a cell that is still alive but enters dormancy, which is a non-growing inactive stage (Kamagata, 2015) Another scenario is that the population represented by the DNA can carry out very weak activity while it is in the decaying process. An anaerobic sludge fermenter receives massive influx of microorganisms from distinct biological processes, such as activated sludge While those exogenous aerobic microorganisms can still be detected as part of the fermenter microbial community (Kim et al, 2006; Lee et al, 2011; Chen et al, 2017), some of them are inactive or even dead, which would obscure the identification of the real fermentation contributors. Microbial activities are sensitive to the fluctuation of conditions, which has not been well-characterized

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