Overcoming Anaerobic Digestion Challenges of Biosolids Pyrolysis Liquid: Pretreatment and Organism Selection

Aqueous pyrolysis liquid (APL) is one product of wastewater sludge or biosolids pyrolysis and it is a high-COD solution with toxic chemicals that can be harmful to the environment. Presently, APL has no known use. One potential option is anaerobic digestion (AD) of APL for biogas and energy production. The challenge, however, is the presence of toxic compounds recalcitrant to anaerobic biodegradation such as methoxyphenols that can inhibit methane-producing microbes. In this study, two approaches were investigated to overcome this challenge: partially oxidizing inhibitory organics using ozone and employing an acclimated methanogenic seed culture that has previously degraded compounds similar to those in APL. Toxicity to methanogenic biomass decreased 30% when ozonated APL was fed to batch digesters with both acclimated and unacclimated digester seed cultures. Methane production significantly increased when the acclimated seed culture was employed and more than 80% of theoretical maximum methane was produced at the highest APL loading, whereas about 40% of theoretical maximum methane was generated with unacclimated seed culture. Both ozone pretreatment and employing acclimated biomass are promising approaches to improve anaerobic degradability of APL.