Fish sludge as a co-substrate in the anaerobic digestion of municipal sewage sludge- maximizing the utilization of available organic resources

Abstract

The thriving of on-land based aquaculture at Norway's western region is to provide higher amounts of discharges to handle sustainably. Utilizing the sludge generated as a co-digestion substrate at already existing biogas plants treating sewage sludge may contribute to higher yields and improved nutrient recirculation. For this study, both wet and dried fish sludge samples were tested as co-substrates on the digestion of sewage sludge in semi-continuous bench-scale reactors. Additions of 30% in volatile solids (VS) of fish sludge gave a 35% methane production increase at mesophilic conditions. In thermophilic conditions the same addition caused process inhibition due to high ammonia levels obtained. Addition of up to 20% VS of dried fish sludge provided an increase between 30–50% in the yield. Fish sludge was verified as a promising co-substrate to increase the yield. However, heavy metals accumulation during the process caused the downgrading of the digested biomass as soil conditioner.

Keywords

• Aquaculture
• Fish sludge
• Sewage sludge
• Methane production
• Phosphorus
• Heavy metals