Biostimulation of sewage sludge solubilization and methanization by hyper-thermophilic pre-hydrolysis stage and the shifts of microbial structure profiles

Unraveling the effects and mechanisms of microplastics on anaerobic fermentation: Exploring microbial communities and metabolic pathways

To investigate the effects of microplastics (MPs) on hydrolysis, acidification and microbial characteristics during waste activated sludge (WAS) anaerobic fermentation process, five different kinds of MPs were added into the WAS fermentation system and results indicated that, compared to the control group, the addition of polyvinyl chloride (PVC)-MPs exhibited the least inhibition on volatile fatty acids (VFAs), reducing them by 13.49 %. Conversely, polyethylene (PE)-MPs resulted in the greatest inhibition, with a reduction of 29.57 %. MPs, while accelerated the dissolution of WAS that evidenced by an increase of lactate dehydrogenase (LDH) release, concurrently inhibited the activities of relevant hydrolytic enzymes (α-Glucosidase, protease). For microbial mechanisms, MPs addition affected the proliferation of key microorganisms (norank_f_Bacteroidetes_vadinHA17, Ottowia, and Propioniclava) and reduced the abundance of genes associated with hydrolysis and acidification (pfkb, gpmI, ilvE, and aces). Additionally, MPs decreased the levels of key hydrolytic and acidogenic enzymes to inhibit hydrolysis and acidification processes. This research provides a basis for understanding and unveils impact mechanisms of the impact of MPs on sludge anaerobic fermentation.

Sewage sludge management and enhanced energy recovery using anaerobic digestion: an insight

Sewage sludge (SS) is a potential source of bioenergy, yet its management is a global concern. Anaerobic digestion (AD) is applied to effectively valorize SS by reclaiming energy in the form of methane. However, the complex floc structure of SS hinders hydrolysis during AD process, thus resulting in lower process efficiency. To overcome the rate-limiting hydrolysis, various pre-treatment methods have been developed to enhance AD efficiency. This review aims to provide insights into recent advancements in pre-treatment technologies, including mechanical, chemical, thermal, and biological methods. Each technology was critically evaluated and compared, and its relative worth was summarized based on full-scale applicability, along with economic benefits, AD performance improvements, and impact on digested sludge. The paper illuminates the readers about existing research gaps, and the future research needed for successful implementation of these approaches at full scale.

Sewage sludge pretreatment: current status and future prospects

Sewage sludge is regarded by wastewater treatment plants as problematic, from a financial and managerial point of view. Thus, a variety of disposal routes are used, but the most popular is methane fermentation. The proportion of macromolecular compounds in sewage sludges varies, and substrates treated in methane fermentation provide different amounts of biogas with various quality and quantity. Depending on the equipment and financial capabilities for methane fermentation, different methods of sewage sludge pretreatment are available. This review presents the challenges associated with the recalcitrant structure of sewage sludge and the presence of process inhibitors. We also examined the diverse methods of sewage sludge pretreatment that increase methane yield. Moreover, in the field of biological sewage sludge treatment, three future study propositions are proposed: improved pretreatment of sewage sludge using biological methods, assess the changes in microbial consortia caused with pretreatment methods, and verification of microbial impact on biomass degradation.

Zinc pyrithione induced volatile fatty acids promotion derived from sludge anaerobic digestion: Interrelating the affected steps with microbial metabolic regulation and adaptive responses

The massive use of zinc pyrithione (ZPT, as broad-spectrum bactericides) resulted in its high levels in waste activated sludge (WAS) and affected subsequent WAS treatment. This work revealed the effects of ZPT on the volatile fatty acids (VFAs) during WAS anaerobic digestion, in which VFAs yield was enhanced by approximately 6-9 folds (from 353 mg COD/L in control to 2526-3318 mg COD/L with low level of ZPT (20-50 mg/g TSS)). The ZPT occurred in WAS enabled the acceleration of solubilization, hydrolysis and acidification processes while inhibited the methanogenesis. Also, the low ZPT contributed to the enrichment of functional hydrolytic-acidifying microorganisms (e.g., Ottowia and Acinetobacter) but caused the reduction of methanogens (e.g., Methanomassiliicoccus and Methanothrix). Meta-transcriptomic analysis demonstrated that the critical genes relevant to extracellular hydrolysis (i.e. CLPP and ZapA), membrane transport (i.e. gltI, and gltL), substrates metabolisms (i.e. fadj, and acd), and VFAs biosynthesis (i.e. porB and porD) were all upregulated by 25.1-701.3% with low level of ZPT. Specifically, the ZPT stimulus on amino acids metabolism for VFAs transformation was prominent over carbohydrates. Moreover, the functional species enabled to regulate the genes in QS and TCS systems to maintain favorable cell chemotaxis to adapt the ZPT stress. The cationic antimicrobial peptide resistance pathway was upregulated to blunt ZPT with the secretion of more lipopolysaccharide and activate proton pumps to maintain ions homeostasis to antagonize the ZPT toxicity for high microbial activities, the abundance of related genes was up-regulated by 60.5 to 524.5%. This work enlightened environmental behaviors of emerging pollutants on WAS anaerobic digestion process with interrelations of microbial metabolic regulation and adaptive responses.

Comparison of anaerobic co-digestion of pig manure and sludge at different mixing ratios at thermophilic and mesophilic temperatures

The objective of this study is to assess the effects of the mixing ratio on the methane production and digestate dewaterability of co-digestion of pig manure (P) and sludge (S). Batch experiments were carried out at five different P/S mixing ratios at mesophilic and thermophilic temperatures. Compared to sludge anaerobic digestion, co-digestion of pig manure with sludge increased methane yield 83.0%-136.5% at mesophilic temperature and 31.3%-68.0% at thermophilic temperature. The normalized capillary suction time (NCST) and total solids (TS) of sediment (centrifugal dewatering) increased when pig manure proportion of substrate increased. The NCST at thermophilic temperatures (4.87-17.58 s g^-1-TSS) was higher than that at mesophilic temperatures (1.89-10.95 s g^-1-TSS). However, the TS of sediment was close at thermophilic and mesophilic temperatures. The results indicated that anaerobic co-digestion of pig manure and sludge at a proper mixing ratio (P/S = 2:1) provides a good choice for energy recovery and land utilization.

Bioenergy recovery from methanogenic co-digestion of food waste and sewage sludge by a high-solid anaerobic membrane bioreactor (AnMBR): mass balance and energy potential

To support smart city in terms of municipal waste management and bioenergy recovery, a high-solid anaerobic membrane bioreactor (AnMBR) was developed for sewage sludge (SeS) and food waste (FW) treatment in this study. COD mass balance showed that 54.1%, 66.9%, 73.5%, 91.4% and 93.5% of the COD input was converted into methane at the FW ratio of 0, 25%, 50%, 75% and 100%, respectively. The corresponding net energy balance was 13.6, 14.1, 17.1, 22.9 and 27.4 kJ/g-VS, respectively. An important finding of this investigation was that, for the first time, the relationship between net energy balance and carbon to nitrogen (C/N) ratio was revealed and the established sigmoid-type function was shown to be capable of predicting energy balance at different C/N ratios regardless of the region. The outcomes of this study show the potential of high-solid AnMBRs in SeS and FW treatment for supporting smart cities in the future.

Advanced methanogenic performance and fouling mechanism investigation of a high-solid anaerobic membrane bioreactor (AnMBR) for the co-digestion of food waste and sewage sludge

Disposal of the increasingly huge amounts of sewage sludge (SeS) has become an impending problem worldwide. To solve this problem, a high-solid anaerobic membrane bioreactor (AnMBR) was used for the anaerobic co-digestion (AcoD) of SeS and food waste (FW). This study investigated the effects of SeS ratio on the methanogenic performance of the AcoD with a gradual increase value from 0 to 25%, 50%, 75% and 100% (total solids based). The results showed that the highest methanogenic performance was achieved at mono FW digestion. As for the co-digestion, the optimal FW/SeS ratio for methanogenic performance was 75%:25% among all the mixing ratios. The COD based biogas yield and methane yield were 0.498 L-biogas/g-COD_fed and 0.295 L-CH₄/g-COD_fed at this optimal mixing ratio, which were 67.7% and 67.6% higher than those of the mono SeS digestion, respectively. The upgraded values were attributed to the improved hydrolysis ratio (by 8.14%) and the balanced carbon-to-nitrogen (C/N) ratio by co-digestion with FW, which synergistically stimulated methanogenesis ratio by 81.0%. The continuous membrane filtration property was investigated and four typical trans-membrane pressure (TMP) variation curves at different fouling degrees were determined. The membrane could sustainably operate at a flux of 6 L/m²/h (LMH) at the mixed liquor total solids (MLTS) concentration of 25 - 30 g/L. The combination of continuous membrane filtration property, particle size distribution of the mixed liquor and the external forces analysis was firstly applied to unravel the membrane fouling mechanism of a high-solid AnMBR. The result of this study will contribute to the establishment of an efficient FW and SeS treatment strategy.