Increased biogas production and salinity tolerance in continuous AD systems using marine aquaculture sludge as substrate

Marine aquaculture sludge is a significant side stream from the aquaculture industry and represents a promising substrate for biogas production. In this study, the performance of two lab-scale continuous biogas reactors was investigated when feeding increased amounts of marine aquaculture sludge (MAS) in mix with cow manure (CM) over a period of 340 days. The MAS volume was gradually increased from 20% to 100%, increasing the biogas yield from approx. 200 to 400 mL/g COD/d. The content of NaCl in the feedstock was 25 g/L when feeding 100% MAS. Microbial community analysis (16S rRNA gene amplicon sequencing) revealed that most archaeal OTUs detected at high MAS loading were associated with acetoclastic Methanothrix and Methanosarcina genera. Increasing the MAS load was associated with reduced microbial diversity, yet no distinct MAS-specific species emerged as key drivers in the recovered microbial community. Our results highlight the great potential of MAS as a substrate for biogas production and the possibility to establish biogas systems with salinity conditions corresponding to sea water. • Sea water salinity marine aquaculture sludge (MAS) was used as substrate for biogas production. • Biogas yield increased from ∼200 to 400 mL/g COD/day with elevated MAS content. • MAS with ∼25 g/L NaCl supported stable methane production in lab-scale reactors. • Microbial community established salt tolerance approaching sea level salinity and shifted toward acetoclastic methanogens at higher MAS loading.