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[Display omitted] • The roles of biochar on microbial growth and activity were systematically analyzed. • Biochar improved the microbial community diversity and population. • Biochar enhanced cellular enzyme activity and accelerated electron transfer. • Biochar promoted functional gene expression and regulated metabolic pathway. • Biochar targeted design to achieve high microbial activity in AD were suggested. 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. [ABSTRACT FROM AUTHOR]

The addition of biochar is a promising strategy to improve methane production via strengthening direct interspecies electron transfer (DIET) in anaerobic digestion (AD) field. In this study, a novel oil sludge biochar (OSBC) prepared at 500/600/700 °C was used to investigate its dosage effects on performances of sewage sludge AD. The characterization results indicated that OSBC prepared at 600 °C had highest electron accepting and donating capacity, meanwhile, it also contained moderate functional groups such as C O, which were in favor of methane production. Therefore, the highest accumulative methane yield (143.96 mL (g VS)−1) accompanying with the fast consumption of volatile fatty acids (VFAs) was achieved at dosage of 1.2 g. Additionally, the conductivity and enzyme activity (electron transport system activity and coenzyme F420) of AD with OSBC addition were also enhanced. Microbial community structures manifested that the potential syntrophic microbes including archaea Methanothrix , Methanospirillum , and bacteria Comamonas , Petrimonas and Syntrophomonas were enriched by OSBC due to its large surface area and microelement such as iron, and contributed to the improved methane production. The results suggested that OSBC exhibited excellent practical application potential in enhancing anaerobic sewage sludge treatment and biogas productivity. [Display omitted] • Oil sludge biochar prepared at 600 °C had highest electron accept/donate capacity. • Functional groups and iron of biochar were responsible for increasing CH 4 yield. • Oil sludge biochar improved the conductivity and enzyme activity of digesters. • IHT and DIET processes were promoted by oil sludge biochar from microbial perspective. [ABSTRACT FROM AUTHOR]

Strengthening direct interspecies electron transfer (DIET), via adding conductive materials, is regarded as an effective way for improving methane productivity of anaerobic digestion (AD). Therein, the supplementation of combined materials (composition of biochar and iron-based materials) has attracted increasing attention in recent years, because of their advantages of promoting organics reduction and accelerating biomass activity. However, as far as we known, there is no study comprehensively summarizing the application of this kind combined materials. Here, the combined methods of biochar and iron-based materials in AD system were introduced, and then the overall performance, potential mechanisms, and microbial contribution were summarized. Furthermore, a comparation of the combinated materials and single material (biochar, zero valent iron, or magnetite) in methane production was also evaluated to highlight the functions of combined materials. Based on these, the challenges and perspectives were proposed to point the development direction of combined materials utilization in AD field, which was hoped to provide a deep insight in engineering application. [ABSTRACT FROM AUTHOR]

[Display omitted] • The preparation methods influenced properties of biochar used in CWs. • Biochar addition improved transformation of pollutants in CWs via various pathways. • Biochar addition significantly enhanced common and emerging pollutants removal in CWs. • A novel Fe-C micro-electrolysis substrates boosted treatment performance of CWs. Traditional constructed wetlands (CWs) still face tremendous challenges, including low nitrogen removal, unstable operation, undesired refractory substances degradation and poor reoxygenation capacity, in their practical applications. Recently, biochar has been regarded as a promising alternative substrate in CWs to enhance pollutants removal via inner environment adjustment, plants growth facilitating and biotoxins adsorption. Based on VOSviewer analysis, this study comprehensively summarizes the mechanisms, application, and performances of biochar addition in CWs. First, physicochemical properties of biochar, including pore sizes/pore volumes, surface aeras, functional groups and chemical compositions, with different preparation methods were comparatively analyzed. Then, the mechanisms and applications of (modified) biochar in CWs and its improving effects on typical pollutants (such as nitrogen, phosphorus, complex organics and heavy metals) removal were summarized. Moreover, the mechanisms and strengthened effect of novel Fe-C micro-electrolysis substrates on pollutants reduction in CWs was also elucidated. Finally, the prospectives and challenges were proposed to offer a deep insight in biochar for its engineering application in CWs. [ABSTRACT FROM AUTHOR]