Current status of biomethane production using aqueous liquid from pyrolysis and hydrothermal liquefaction of sewage sludge and similar biomass

Abstract

Pyrolysis and hydrothermal liquefaction (HTL) are potential technologies for renewable energy production and waste valorization using municipal wastewater sewage sludge and other lignocellulosic biomass. However, the organic-rich aqueous pyrolysis liquid (APL) and HTL aqueous phase (HTL-AP) produced currently have no apparent use and are challenging to manage. Furthermore, the toxic organic compounds in them can be harmful to the environment. Anaerobic digestion (AD) may be a viable method to manage the liquids and recover energy in APL and HTL-AP in form of methane-rich biogas. Integrating thermochemical processes with AD could promote a circular economy by recovering resources and reducing environmental pollution. The challenge, however, is the presence of toxic compounds recalcitrant to anaerobic biodegradation such as phenols and nitrogen-containing organics that can inhibit methaneproducing microbes. This review presents information

Microbial valorization of underutilized and nonconventional waste streams

“…Hydrothermal liquefaction aqueous phase (HTL-AP) is the aqueous phase of waste generated from hydrothermal liquefaction processing of biomass to generate biofuel or biocrude at high temperatures and pressures (Skaggs et al., 2018 ). This waste contains toxic organic compounds such as alcohols, acids, ketones, aromatic compounds, and N-heterocyclic compounds and possesses a high COD, yet currently has no industrial use (Seyedi et al., 2020 ). While its toxicity poses a high challenge for valorization, reduction of treatment costs would be of enormous benefit.…”

“…While its toxicity poses a high challenge for valorization, reduction of treatment costs would be of enormous benefit. Anaerobic digestion is currently the main method of HTL-AP bioremediation, and has been reviewed recently (Seyedi et al., 2020 ).…”

“…HTL-AP at 20% was supplemented with mixed sugar hydrolysate to produce 21.6 g/l of TAL at the bioreactor scale. This study is one of few demonstrations of HTL-AP microbial valorization potential as the majority of literature is focused on improving microbial detoxification or AD strategies (Seyedi et al., 2020 ; Wang et al., 2021 ). Future work to expand the utility of this waste stream should involve further host strain engineering especially in the area of tolerance.…”

Anaerobic Co-Digestion of Products from Biosolids Pyrolysis – Implementation in ADM1

“…Pyrolysis gas contains varying amounts of H2, CO2, CO, CH4, and other C2+ gases, and has been successfully converted to biogas via anaerobic digestion (Luo and Angelidaki, 2012;Luo et al, 2013;Li et al, 2020;Torri et al, 2020). AD of pyrolysis liquids from various feedstocks has also been studied (Seyedi et al, 2020;Ghimire et al, 2021). Successful co-digestion of liquid and gaseous pyrolysis products in an industrial process might increase biogas production from initial feedstock, but it might also upset process behavior.…”

“…Results from Seyedi (2020) were not implemented in any AD model, but the data showed most success in reducing toxicity from biosolids pyrolysis liquid when using acclimated inoculum and a low loading rate (0.03 gCOD L -1 d -1 ) with correspondingly long solids retention time. Pyrolysis liquid from biosolids have different properties compared to liquid from lignocellulosic materials, such as much higher total ammonia nitrogen (TAN) content (Seyedi et al, 2019). In ADM1, inhibition from NH3 on acetate degrading organisms is modelled using a non-competitive reversible inhibition term (Eq.…”