In Situ Biogas Upgrading and Fertilizer Recovery in Anaerobic Digestion from Laminaria Hydrothermal Carbonization Process Water by Fe-Modified Hydrochar

Abstract

Hydrothermal carbonization (HTC) combined with anaerobic digestion (AD) is a cost-effective process to simultaneously treat biomass wastes for hydrochar production, energy recovery, and wastewater treatment. However, low fermentation efficiency and high carbon dioxide content in biogas are tricky problems of this process. This study developed a novel strategy based on Fe-modified hydrochar (Fe-HC) for in situ biogas upgrading and fertilizer recovery by AD of macroalgae Laminaria HTC process water. The daily yield and proportion of methane in biogas in the Fe-HC added reactor were 216.6 ± 13.1 mL/g COD fed and 90.3 ± 1.3%, respectively. The conductive Fe-HC increased relative abundances of Trichococcus and hydrogenotrophic methanogens (Methanosarcina and Methanobacterium) and promoted the electron transport system activity, heme c content in extracellular polymeric substances, and sludge granulation. These results implied the Fe-HC-promoted biogas upgrading might be ascribed to the enhancement of H 2 -mediated interspecies electron transfer, potential direct interspecies electron transfer, and trace FeCO 3 precipitation. The effluent from the Fe-HC supplemented reactor was rich in nutrients, including K + , I − , gibberellin (GA 3 ), etc., but low in human potential pathogenic bacteria and heavy metal content, indicating it had excellent potential as a fertilizer. This study provides an ecofriendly and sustainable strategy for energy and fertilizer recovery from macroalgae wastes.

Re-evaluating the Contribution of a Fe-Based Current Collector to Bioelectrochemical Methanogenesis: Role and Mechanisms

“…It has been reported that some microorganisms tended to absorb metal onto their cell surface through a number of proton- and metal-active surface functional groups such as amine and carboxyl groups . In addition, negatively charged exopolysaccharide around the surface cells also favored metal binding to form a stable three-dimensional structure …”

“…24 In addition, negatively charged exopolysaccharide around the surface cells also favored metal binding to form a stable threedimensional structure. 25 The elemental composition of the biofilm was further determined by X-ray photoemission spectroscopy (XPS). As shown in Table S2, an increment of N, O, and S content was detected with both electrodes compared to the raw carbon matrix, new elements of Ni, Fe, and P were present, especially on Bio FeCF.…”

Biochar Facilitated Direct Interspecies Electron Transfer in Anaerobic Digestion to Alleviate Antibiotics Inhibition and Enhance Methanogenesis: A Review

“…Hence, microbial aggregation contributes to the reinforcement of direct contact with syntrophic microbes, thereby further strengthening the DIET process [37]. Wang et al found that biochar increased the content of EPSs by 40.5% and excess EPSs facilitated the formation of a robust three-dimensional structure to accelerate the aggregation of sludge into granules [109]. The formation of granular sludge created a situation for the potential DIET process to develop.…”