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.

How does the polyhexamethylene guanidine interact with waste activated sludge and affect the metabolic functions in anaerobic fermentation for volatile fatty acids production.

Antibacterial agents are frequently used to ensure public hygiene. Most of the massively consumed chemicals are discarded and accumulated in waste activated sludge (WAS), which might influence the subsequent anaerobic fermentation process for WAS treatment. This study mainly investigated the impacts of polyhexamethylene guanidine (PHMG, considered as a safe and efficient broad-spectrum antibacterial agent) on the volatile fatty acids (VFAs) production derived from WAS anaerobic fermentation and disclosed the key mechanisms. Results demonstrated that low level of PHMG evidently increased the VFAs accumulation as well as the acetic acid proportion, while the excessive dose posed evident negative effects. Further analysis found that appropriate PHMG synchronously stimulated the solubilization/hydrolysis and acidification processes but inhibited methanogenesis. Mechanistic exploration revealed that PHMG firstly absorbed on WAS due to electric attraction but then interacted with WAS to promote extracellular polymeric substance (EPS) disintegration and organics release (especially proteinaceous matter). Moreover, PHMG affected the microbial community structure and metabolic functions. The low level of PHMG evidently enriched functional VFAs producers (i.e., Desulfobulbus, Macellibacteroides and Sporanaerobacter) and upregulated the critical genes expression responsible for substrates metabolism (particularly the proteins) and VFAs biosynthesis (i.e., aldehyde dehydrogenase (NAD+) (K00128) and molybdopterin oxidoreductase (K00184)). This study provides an in-depth understanding of emerging pollutant impacts on WAS fermentation and provides insightful guidance on WAS disposal.

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.

Distribution patterns of functional microbial community in anaerobic digesters under different operational circumstances: A review.

Anaerobic digestion (AD) processes are promising to effectively recover resources from organic wastes or wastewater. As a microbial-driven process, the functional anaerobic species played critical roles in AD. However, the lack of effective understanding of the correlations of varying microbial communities with different operational factors hinders the microbial regulation to improve the AD performance. In this paper, the main anaerobic functional microorganisms involved in different stages of AD processes were first demonstrated. Then, the response of anaerobic microbial community to different operating parameters, exogenous interfering substances and digestion substrates, as well as the digestion efficiency, were discussed. Finally, the research gaps and future directions on the understanding of functional microorganisms in AD were proposed. This review provides insightful knowledge of distribution patterns of functional microbial community in anaerobic digesters, and gives critical guidance to regulate and enrich specific functional microorganisms to accumulate certain AD products.

Insights into the accelerated venlafaxine degradation by cysteine-assisted Fe2+/persulfate: Key influencing factors, mechanisms and transformation pathways with DFT study.

The effective removal of refractory antidepressant in wastewater is challenging. In this study, a novel strategy of cysteine-assisted Fe2+/persulfate system (Fe2+/Cys/PS) was applied for the venlafaxine (Ven, as a typical antidepressant) degradation. The obtained results revealed that the Ven removal was evidently accelerated and enhanced in Fe2+/Cys/PS process, and achieved complete degradation in 5 min with optimal dosage. Further analysis indicated that the Ven degradation efficiency was associated with the chemical concentrations (i.e. Fe2+, Cys and PS) and operational conditions (i.e. pH and temperature). Moreover, the reactions were not impacted by the co-occurring organic matters (i.e. fulvic acid) and inorganic ions (i.e. Cl-) potentially existing in real wastewater matrices. Mechanistic explorations demonstrated that the presence of Cys promoted the Fe3+/Fe2+ redox cycle, and thus enhanced the reactive oxygen species yields (ROS). The OH was considered as the primary ROS in Fe2+/Cys/PS process for Ven degradation via the radical scavenger verification. Also, the main intermediates of Ven degradation were identified, and the possible transformation pathway was proposed, in which the hydroxylation attacked by the OH was the main reaction. Moreover, the active reaction sites in Ven were calculated with the density function theory (DFT), which was consistent with the observed metabolic routes.