Green Waste to Renewable Natural Gas by Pyrobiomethane: Anaerobic Codigestion of Pyrolysis Oil and Green Waste Sludge

Low temperature pyrolysis is an effective approach to convert municipal sludge biosolids from wastewater treatment plants (WWTPs) and green waste into bio-methane for power or fuel production in anaerobic digesters. In this study, anaerobically digested, municipal sludge biosolids and green waste were dried and processed with low temperature pyrolysis to produce biogas; also, the pyrolysis process produces bio-oil and biochar as co-products. The bio-oil was fed to sludge-fed anaerobic digesters, leading to increases in biogas production and volatile solids destruction with no adverse impact on the microbial consortium or digestion process. At a ratio expected at a typical WWTP pyrolyzing indigenous sludge, co-digesting sludge and bio-oil from biosolids resulted in a 25 percent increase in the biogas production rate and a 5-10 percent increase in the volatile solids destruction rate compared to the results from anaerobic digestion of sewage sludge alone. The biochar generated from the pyrolysis process condensed nutrients and reduced the feed to the pyrolyzer by 45-55 percent. Concentration of nutrients and mass reduction enhance the value of the solid end-product and reduce costs associated with transportation and hauling of solid residuals from WWTPs.