High current densities in microbial electrolysis cells (MECs) result from the predominance of various Geobacter species on the anode, but it is not known if archaeal communities similarly converge to one specific genus. MECs were examined here on the basis of maximum methane production and current density relative to the inoculum community structure. We used anaerobic digester (AD) sludge dominated by acetoclastic Methanosaeta, and an anaerobic bog sediment where hydrogenotrophic methanogens were detected. Inoculation using solids to medium ratio of 25% (w/v) resulted in the highest methane production rates (0.27 mL mL⁻¹ cm⁻², gas volume normalized by liquid volume and cathode projected area) and highest peak current densities (0.5 mA cm⁻²) for the bog sample. Methane production was independent of solid to medium ratio when AD sludge was used as the inoculum. 16S rRNA gene community analysis using pyrosequencing and quantitative PCR confirmed the convergence of Archaea to Methanobacterium and Methanobrevibacter, and of Bacteria to Geobacter, despite their absence in AD sludge. Combined with other studies, these findings suggest that Archaea of the hydrogenotrophic genera Methanobacterium and Methanobrevibacter are the most important microorganisms for methane production in MECs and that their presence in the inoculum improves the performance.

To decrease the eutrophication caused by nitrogen (N) and phosphorus (P) in water, magnesium-modified corn stalk biochar (MgB) was prepared under the synergistic impact of the multi-pyrolysis temperatures and Mg²⁺ contents for the co-adsorption of ammonium (NH₄⁺-N) and phosphate (PO₄³⁻). The co-adsorption mechanism, slow-release performance and plant application of MgB were systematically studied. The results showed that pyrolysis temperatures (350–650 °C) and Mg²⁺(0–3.6 g/L) contents not only altered the physicochemical properties of biochar, but also significantly affected the adsorption efficacy of MgB. The adsorption of NH₄⁺-N and PO₄³⁻ was in accordance with Langmuir–Freundlich and pseudo-second-order kinetic models (Q_max = 37.72 and 73.29 mg/g, respectively). Based on the characteristics, adsorption kinetics and isotherms results, the adsorption mechanism was determined and found to mainly involve struvite precipitation, ion exchange, and surface precipitation or electrostatic attraction. Compared with the leaching performance of chemical fertilizers (CF), after adsorption of NH₄⁺-N and PO₄³⁻ (MgB-A), MgB had a more stable pH and lower conductivity. Leaching of NH₄⁺-N and PO₄³⁻ by MgB-A was controlled by both the diffusion mechanism and the dissolution rate of struvite and Mg-P. The excellent long-term slow-release performance and abundant Mg²⁺ of MgB-A promoted the growth of Zea mays L. and Lolium perenne L. Overall, this study suggested that MgB could realize a win–win outcome of struvite biochar-based fertiliser production and wastewater treatment.