Recovery of methane and adding value to the digestate of biomass produced by high rate algal ponds or waste activated sludge, used to treat brewery effluent

There is an opportunity to anaerobically digest the sludge or algal biomass generated from the activated sludge (AS) and high rate algal pond (HRAP) brewery effluent treatment processes to produce methane, allowing the recovery of the carbon into a valuable product, prior to its disposal. This study evaluated the use of HRAP and AS waste biomasses for methane production during anaerobic digestion (AD), documented its efficiency, and described the digestate (waste) that was produced from the AD process. Brewery effluent grown algal and waste activated sludge (WAS) biomasses are suitable feed stocks for anaerobic digesters and this trial suggests that this process can be exploited commercially. It is recommended to operate WAS and algae fed anaerobic digesters at a total solids feeding rate of 1-2 g/l(reactor)/d and a hydraulic retention time of 17 days. The biogas yield of algal and WAS substrates was similar (Student t-test p > 0.05) with an average gas production of 241 mL/g volatile solids fed. Biogas from algae fed digesters had a significantly higher methane content (64.73 +/- 0.81 %) and lower carbon dioxide content (22.94 +/- 0.24 %) when compared to WAS fed digesters (60.08 +/- 0.18 % and 27.37 +/- 0.43 % respectively) due to it being a less oxidised substrate. The water quality parameters of the digestate from both WAS and algae fed digesters were similar (Student t-test p > 0.05) and has the potential to be used as a fertiliser in agriculture. The quality of this digestate as a fertiliser and its impact on the receiving soil needs to be researched.

Automated summary

There is potential to anaerobically digest sludge and algal biomass from brewery effluent treatment processes to produce methane. The study evaluated the use of waste biomasses for methane production and recommended operating anaerobic digesters at specific feeding rates. Algal-fed digesters showed higher methane content and lower carbon dioxide content compared to waste activated sludge-fed digesters, making it a promising substrate for biogas production.