Date of Award
Master of Science (MS)
Civil and Environmental Engineering
McNamara, Patrick J.
Pyrolysis is a process to treat biosolids and recover energy. During pyrolysis, conversion of organic matter to energy-rich products yields biochar, py-gas, and pyrolysis liquids (aqueous phase and non-aqueous bio-oil). The aqueous pyrolysis liquid (APL), is a high-COD liquid with no apparent use that contains polycyclic aromatic hydrocarbons and nitrogen-containing compounds. One potential beneficial use of APL is as a co-digestate to produce more biogas for renewable energy from anaerobic digesters at municipal water resource recovery facilities. Some of the organics in APL may be converted to biomethane via anaerobic digestion under proper conditions. However, some APL organics are known to inhibit methane-producing microbes. Biosolids APL can also contain high concentrations of NH3-N that inhibit methane production. In this study, sustainable, unacclimated anaerobic digester organic loading rates for APL from biosolids pyrolysis were determined using anaerobic toxicity assays (ATA). APL loading rates higher than 0.5 gCOD/L for non-catalyzed APL and 0.10 g COD/L for catalyzed APL were not sustainable due to toxicity. By means of pretreatment by NH3-N air stripping, the potential toxicity exerted from NH3-N was decreased considerably (>80%). NH3-N was not the main inhibitory constituent and other organic constituents in APL caused considerable inhibition of methane production. In subsequent testing, continuous co-digestion of APL and synthetic wastewater primary sludge was performed while digester function and microbial community composition changes were evaluated. During quasi steady state operation, digesters that received catalyzed APL exhibited greater inhibition of methane production than digesters fed non-catalyzed APL. However, NH3-N stripping in non-catalyzed APL increased methane production rate; additional methane production was observed when non-catalyzed aerated APL was co-digested (1.5 ± 1.7 mL/day extra methane). Shifts in the Archaeal community composition in inhibited digesters (received catalyzed APL) versus uninhibited digesters (control digesters and digesters received non-catalyzed APL) was observed. The archaeal genus Methanosaeta dominated in uninhibited digesters, whereas in inhibited digesters hydrogenotrophic Methanobrevibacter was dominant and growth of acetate-consuming Archaea (i.e., Methanosaeta) was inhibited. Inhibited digesters had distinctly different Bacterial community composition from those in uninhibited digesters and Clostridium was the dominant Bacterial genus in all digesters. Results suggested that the microbes started to acclimate to the catalyzed APL; however, using an already acclimated biomass may be more efficient. A future study using acclimated biomass by bioaugmentation could be used to prove this hypothesis.