Boosting short-chain fatty acids production from co-fermentation of orange peel waste and waste activated sludge: Critical role of pH on fermentation steps and microbial function traits.

The anaerobic co-fermentation of orange peel waste (OPW) and waste activated sludge (WAS) for useful short-chain fatty acids (SCFAs) generation presents an environmentally friendly and efficient method for their disposal. This study amied to investigate the effects of pH regulation on OPW/WAS co-fermentation, and found that the alkaline pH regulation (pH 9) significantly enhanced the promotion of SCFAs (11843 ± 424 mg COD/L), with a high proportion of acetate (51%). Further analysis revealed that alkaline pH regulation facilitated solubilization, hydrolysis, and acidification while simultaneously inhibiting methanogenesis. Furthermore, the functional anaerobes, as well as the expressions of corresponding gene involved in SCFAs biosynthesis, were generally improved under alkaline pH regulation. Alkaline treatment might played a critical role in alleviating the toxicity of OPW, resulting in improving microbial metabolic activity. This work provided an effective strategy to recover biomass waste as high-value products, and insightful understanding of microbial traits during OPW/WAS co-fermentation.

Upgrading volatile fatty acids production from anaerobic co-fermentation of orange peel waste and sewage sludge: Critical roles of limonene on functional consortia and microbial metabolic traits.

Orange peel waste (OPW) and sewage sludge (SS) valorization for volatile fatty acids (VFAs) production from anaerobic co-fermentation are attractive and feasible. The highest VFAs reached 11996.3 mg COD/L within 10 d at the mass ratio (TS/TS) of 1:1, which was approximately 30-fold of that in sole SS fermentation. The OPW provided plenty of organic substrates and facilitated the fermentation processes by disintegrating SS structure and inhibiting methanogenesis due to the abundant limonene. Also, the OPW feeds reshaped the microbial community and enriched fermentative bacteria, especially those saccharolytic ones (i.e. Prevotella-7). The key genes involved in membrane transport (i.e. ptsG), glycolysis (i.e. pgk), pyruvate metabolism (i.e. ace), and fatty acid biosynthesis (i.e. accA), which are associated with VFAs biosynthesis, were up-regulated in OPW/SS reactors. Overall, it was the increase in bioavailable organic matter and functional microorganisms, and the simultaneous enhancement of metabolic activity that improved the efficient VFAs production.

Waste-to-energy: Cellulase induced waste activated sludge and paper waste co-fermentation for efficient volatile fatty acids production and underlying mechanisms.

This study mainly investigated the feasibility of utilizing cellulase to enhance waste activated sludge (WAS) and paper waste (PW) co-fermentation for the generation of volatile fatty acids (VFAs). The introduction of cellulase effectively enhanced the co-fermentation efficiency, and the maximum VFAs generation reached 3014 mg COD/L with 60 mg cellulase/g TSS while it was 1512 mg COD/L in the control reactor. The presence of cellulase evidently improved the concentration of soluble bioavailable substrates (e.g., carbohydrates and proteins) via inducing the EPS disintegration and PW disruption. More importantly, the functional anaerobes (i.e., Macellibacteroides and Bacteroides) and the microbial activities (i.e., ATP, key acid-forming enzymes, and genetic expressions) that related with the VFAs biosynthesis were enriched and enhanced due to the stimulation of cellulase, contributing to the ultimate VFAs promotion. This study provided a novel strategy to recover valuable products from waste biomass with constructive mechanistic exploration.