Enhancing biogas biological upgrading from kitchen wastewater by anaerobic digestion: integrated CSTR-TBR reactor with modified nZVI addition

This study developed an innovative strategy for enhancing biogas upgrading from kitchen wastewater by using extracellular polymeric substance-modified nanoscale zero-valent iron (EPS10-nZVI10) in an integrated continuous stirred tank reactor and trickle bed reactor (CSTR-TBR). The EPS10-nZVI10 composite served as a highly efficient in-situ H2 source, effectively overcoming limitations of conventional nZVI such as agglomeration and passivation. The integrated CSTR-TBR system with gas circulation achieved simultaneous biogas production and in-situ upgrading, significantly enhancing CO2/H2 mass transfer and conversion efficiency. The optimal performance was observed at the highest EPS10-nZVI10 dosage, yielding a remarkable CH4 content of 98.90 % and an average daily methane production of 363.75 mL/g COD, which was 2.08-fold of control. System stability was confirmed through low VFAs, alkalinity, and reduced ORP. Hydrogenotrophic methanogenesis was promoted, as evidenced by coenzyme F420 relative activity reaching 96.72 %. Microbial community analysis demonstrated selective enrichment of Firmicutes and Chloroflexi, along with Methanomassiliicoccus and Methanobacterium. This approach offers an effective and sustainable route for biogas upgrading and organic waste resource recovery.