Revealing the mechanism of novel nitrogen-doped biochar supported magnetite (NBM) enhancing anaerobic digestion of waste-activated sludge by sludge characteristics

Enhancing anaerobic digestion of sludge with dual-heteroatom-doped biochar derived from digested sludge: In-situ reuse of anaerobic residues for system self-circulation

The effectiveness of biochar as a promoter in the anaerobic digestion (AD) of complex organic matter is constrained by its limited surface reactive sites. However, heteroatom doping can enhance the surface functional groups and defect structures of biochar, improving its electron exchange capacity and potential to promote AD. Dual-heteroatom-doped biochar derived from digested sludge (DH-DSBC) focused on stimulating the acetogenic-methanogenic stage of sludge AD. The addition of DH-DSBC accelerated the utilization and conversion of organic matter in the AD system and increased the concentration of methanogenesis-related enzymes (coenzyme F420), ultimately boosting methane production by 52-60%. Additionally, the methane conversion rate increased by 60-69%. The enrichment of electroactive bacteria and Methanothrix (formerly Methanosaeta)/Methanosarcina suggests that DH-DSBC may facilitate direct interspecies electron transfer, as supported by the observed increase in sludge electrical conductivity and elevated electron transfer system activity. This study provides insights into the practical reuse of anaerobic residues in-situ and contributes to achieving self-circulation in AD systems.

Enhancing methane production in anaerobic digestion via improved electron transfer with dual-reaction-centers catalyst

The recovery of methane from waste-activated sludge and rice straw often encounters challenges due to inefficient electron transfer between microorganisms. To break through this bottleneck, a novel and effective strategy is urgently needed. Here, we propose adding dual reaction centers (DRCs) catalyst with electron-rich and electron-poor microregions into the anaerobic digestion (AD) system. Pigeon manure was transformed into a novel DRCs catalyst, Fe-PMC, through pyrolysis and doping. Our findings indicate that the micro-electric field on the surface of Fe-PMC effectively aggregated humic acid-like substances and increased sludge conductivity. Compared to the control group (0 mg/L), adding trace amounts of Fe-PMC (40 mg/L) significantly increased methane production by 27.45%. High-throughput sequencing analyses revealed that Fe-PMC enhanced the relative abundance of functional microorganisms, such as Geobacter (23.62%) and Methanobacterium (35.53%), thereby promoting methanogenic co-metabolism. Furthermore, functional genes associated with carbon dioxide reduction to methane and direct interspecific electron transfer were upregulated by 3.41%-297.66%. This study provides a valuable reference for recovering renewable energy from waste using DRCs catalysts.

Reversing inhibition to promotion in phenol-ammonium metabolism via algal-microbial fuel cell: Mechanisms of phenol-ammonium interaction and synergistic removal

Addressing the challenge of metabolic inhibition between phenol and ammonium in coal gasification wastewater (CGW), this study introduced a novel algal-microbial fuel cell (AMFC). It combined the advantages of electroactive bacteria and Synechocystis to achieve synergistic metabolism, establishing a cooperative mechanism for pollutant separation and enhanced transformation to achieve the mutual promotion of phenol and ammonium removal. Remarkably, raising phenol to 1500 mg COD/L boosted ammonium removal by 31.51 % in AMFC, due to a consistently higher potential difference than the control, which enhanced extracellular electron transfer (EET) via conductive nanowire and drove ammonium migration. Similarly, elevating ammonium concentration to 150 mg/L resulted in an 11.79 % increase in phenol removal efficiency, driven by superior solution conductivity and EET, as well as more electron acceptors (oxygen) from the algal cathode. This system challenged the conventional understanding of the antagonistic relationship between phenol and ammonium. Under high phenol conditions, the electroactive bacteria Clostridium sensu stricto 1 and Acinetobacter, Perlucidibaca formed a synergistic metabolic network, whereas Zoogloea, Ideonella, and other phenol-degrading bacteria were significantly enriched in high ammonium environments. The AMFC represented a breakthrough in reversing the metabolic inhibition between phenol and ammonium, providing a novel and energy-efficient strategy for treating complex industrial wastewater.

Unlocking anaerobic digestion potential via extracellular electron transfer by exogenous materials: Current status and perspectives

The efficiency of energy transfer among microorganisms presents a substantial hurdle for the widespread implementation of anaerobic digestion techniques. Nonetheless, recent studies have demonstrated that enhancing the extracellular electron transfer (EET) can markedly enhance this efficiency. This review highlights recent advancements in EET for anaerobic digestion and examines the contribution of external additives to fostering enhanced efficiency within this context. Diverse mechanisms through which additives are employed to improve EET in anaerobic environments are delineated. Furthermore, specific strategies for effectively regulating EET are proposed, aiming to augment methane production from anaerobic digestion. This review thus offers a perspective on future research directions aimed at optimizing waste resources, enhancing methane production efficiency, and improving process predictability in anaerobic digestion.

Integrated multi-omics with machine learning to uncover the intricacies of kidney disease

The development of omics technologies has driven a profound expansion in the scale of biological data and the increased complexity in internal dimensions, prompting the utilization of machine learning (ML) as a powerful toolkit for extracting knowledge and understanding underlying biological patterns. Kidney disease represents one of the major growing global health threats with intricate pathogenic mechanisms and a lack of precise molecular pathology-based therapeutic modalities. Accordingly, there is a need for advanced high-throughput approaches to capture implicit molecular features and complement current experiments and statistics. This review aims to delineate strategies for integrating multi-omics data with appropriate ML methods, highlighting key clinical translational scenarios, including predicting disease progression risks to improve medical decision-making, comprehensively understanding disease molecular mechanisms, and practical applications of image recognition in renal digital pathology. Examining the benefits and challenges of current integration efforts is expected to shed light on the complexity of kidney disease and advance clinical practice.

Simultaneous denitrification enhancement and sludge reduction based on novel suspended carrier modified using activated carbon and magnetite at low carbon/nitrogen ratio

A novel suspended carrier was prepared by sticking activated carbon (AC) and magnetite (Fe3O4) onto polypropylene slices. Although this carrier could not reverse the decreased denitrification capacity trends under anoxic conditions at an influent carbon/nitrogen (C/N) ratio of 2, it enhanced denitrification by stimulating sludge reduction and accelerating electron transfer to certain extent. The carrier stuck by mixed AC/Fe3O4 exhibited better performance in terms of sludge reduction, extracellular polymeric substances (EPS) secretion, and denitrification than that merely stuck by AC and Fe3O4 at an influent C/N ratio of 2. The carrier stuck by mixed AC/Fe3O4 increased the total nitrogen removal efficiency by 24.6 % ± 12.5 % in a 72-h denitrification batch experiment compared to the common polypropylene carrier. Moreover, the carrier improved EPS secretion and nitrogen metabolism and promoted the growth of Trichococcus and some denitrifying genera. This study provides a reference for the treatment of low C/N ratio sewage.

A review of microbial responses to biochar addition in anaerobic digestion system: Community, cellular and genetic level findings

The biochar is a well-developed porous material with various excellent properties, that has been proven with excellent ability in anaerobic digestion (AD) efficiency promotion. Current research is usually focused on the macro effects of biochar on AD, while the systematic review about the mechanisms of biochar on microbial behavior are still lacking. This review summarizes the effects and potential mechanisms of biochar on microorganisms in AD systems, and found that biochar addition can provide habitats for microbial colonization, alleviate toxins stress, supply essential nutrients, and accelerate interspecies electron transferring. Moreover, it also improves microbial community diversity, facilitates EPS secretion, enhances functional enzyme activity, promotes functional genes expression, and inhibits the antibiotic resistance genes transformation. Future research directions including biochar targeted design, in-depth microbial mechanisms revelation, and modified model development were suggested, which could promote the widely practical application of of biochar-amended AD technology.