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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 methane-producing microbes. This review presents information on APL and HTL-AP characterization and biodegradability. Feedstock composition and process operational parameters are major factors affecting APL and HTL-AP composition, subsequent toxicity, and degradability. Feedstocks with high nitrogen content as well as increased thermochemical processing temperature and retention time result in a more toxic aqueous liquid and lower methane yield. Dilution and low AD organic loading are required to produce methane. More comprehensive APL and HTL-AP chemical characterization is needed to adopt suitable treatment strategies. Pretreatments such as overliming, air stripping, partial chemical oxidation, adsorption, and solvent extraction of toxic constituents as well as co-digestion and microbial acclimatization successfully reduce toxicity and increase methane yield.
Saba Seyedi; Kaushik Venkiteshwaran; Daniel Zitomer. Current status of biomethane production using aqueous liquid from pyrolysis and hydrothermal liquefaction of sewage sludge and similar biomass. Reviews in Environmental Science and Bio/Technology 2020, 20, 237 -255.
AMA StyleSaba Seyedi, Kaushik Venkiteshwaran, Daniel Zitomer. Current status of biomethane production using aqueous liquid from pyrolysis and hydrothermal liquefaction of sewage sludge and similar biomass. Reviews in Environmental Science and Bio/Technology. 2020; 20 (1):237-255.
Chicago/Turabian StyleSaba Seyedi; Kaushik Venkiteshwaran; Daniel Zitomer. 2020. "Current status of biomethane production using aqueous liquid from pyrolysis and hydrothermal liquefaction of sewage sludge and similar biomass." Reviews in Environmental Science and Bio/Technology 20, no. 1: 237-255.
Pyrolysis can convert wastewater solids into useful byproducts such as pyrolysis gas (py-gas), bio-oil and biochar. However, pyrolysis also yields organic-rich aqueous pyrolysis liquid (APL), which presently has no beneficial use. Autocatalytic pyrolysis can beneficially increase py-gas production and eliminate bio-oil; however, APL is still generated. This study aimed to utilize APLs derived from conventional and autocatalytic wastewater solids pyrolysis as co-digestates to produce biomethane. Results showed that digester performance was not reduced when conventional APL was co-digested. Despite having a lower phenolics concentration, catalyzed APL inhibited methane production more than conventional APL and microbial community analysis revealed a concomitant reduction in acetoclastic Methanosaeta. Long-term (over 500-day) co-digestion of conventional APL with synthetic primary sludge was performed at different APL organic loading rates (OLRs). Acclimation resulted in a doubling of biomass tolerance to APL toxicity. However, at OLRs higher than 0.10 gCOD/Lr-d (COD = chemical oxygen demand, Lr = liter of reactor), methane production was inhibited. In conclusion, conventional APL COD was stoichiometrically converted to methane in quasi steady state, semi-continuous fed co-digesters at OLR ≤ 0.10 gCOD/Lr-d. Undetected organic compounds in the catalyzed APL ostensibly inhibited anaerobic digestion. Strategies such as use of specific acclimated inoculum, addition of biochar to the digester and pretreatment to remove toxicants may improve future APL digestion efforts.
Saba Seyedi; Kaushik Venkiteshwaran; Nicholas Benn; Daniel Zitomer. Inhibition during Anaerobic Co-Digestion of Aqueous Pyrolysis Liquid from Wastewater Solids and Synthetic Primary Sludge. Sustainability 2020, 12, 3441 .
AMA StyleSaba Seyedi, Kaushik Venkiteshwaran, Nicholas Benn, Daniel Zitomer. Inhibition during Anaerobic Co-Digestion of Aqueous Pyrolysis Liquid from Wastewater Solids and Synthetic Primary Sludge. Sustainability. 2020; 12 (8):3441.
Chicago/Turabian StyleSaba Seyedi; Kaushik Venkiteshwaran; Nicholas Benn; Daniel Zitomer. 2020. "Inhibition during Anaerobic Co-Digestion of Aqueous Pyrolysis Liquid from Wastewater Solids and Synthetic Primary Sludge." Sustainability 12, no. 8: 3441.
Wastewater resource recovery facilities produce wastewater solids that offer potential for energy recovery. This opinion article provides a perspective on state-of-the-art technologies to recover energy from sludge (unstabilized wastewater residual solids) and biosolids (stabilized wastewater solids meeting criteria for application on land). The production of biodiesel fuel is an emerging technology for energy recovery from sludge, whereas advancements in pretreatment technologies have improved energy recovery from anaerobic digestion of sludge. Incineration is an established technology to recover energy from sludge or biosolids. Gasification, and to a greater extent, pyrolysis are emerging technologies well-suited for energy recovery from biosolids. While gasification produces high-energy gases, pyrolysis has the benefit of producing biochar in addition to pyrolysis gas. Research on the use of pyrolysis liquids, however, must proceed to advance pyrolysis implementation efforts. Future research on improvements to dewatering and drying of sewage sludge and biosolids will help advance all technologies reviewed.
Zhongzhe Liu; Brooke K. Mayer; Kaushik Venkiteshwaran; Saba Seyedi; Arun S.K. Raju; Daniel Zitomer; Patrick J. McNamara. The state of technologies and research for energy recovery from municipal wastewater sludge and biosolids. Current Opinion in Environmental Science & Health 2020, 14, 31 -36.
AMA StyleZhongzhe Liu, Brooke K. Mayer, Kaushik Venkiteshwaran, Saba Seyedi, Arun S.K. Raju, Daniel Zitomer, Patrick J. McNamara. The state of technologies and research for energy recovery from municipal wastewater sludge and biosolids. Current Opinion in Environmental Science & Health. 2020; 14 ():31-36.
Chicago/Turabian StyleZhongzhe Liu; Brooke K. Mayer; Kaushik Venkiteshwaran; Saba Seyedi; Arun S.K. Raju; Daniel Zitomer; Patrick J. McNamara. 2020. "The state of technologies and research for energy recovery from municipal wastewater sludge and biosolids." Current Opinion in Environmental Science & Health 14, no. : 31-36.
Past plastic management practices have resulted in pollution. An improved management scenario may involve adding used bioplastic to anaerobic digesters to increase methane for renewable energy. In this work, effects of polyhydroxybutyrate (PHB) bioplastic anaerobic co-digestion with synthetic primary sludge on operation and microbial communities were investigated. Co-digesters treating sludge were co-fed 20% untreated or pretreated (55 °C, pH 12) PHB. Pretreament resulted in shorter lag (5 d shorter) before methane production increased after co-digestion. At steady-state, co-digesters converted 86% and 91% of untreated and pretreated PHB to methane, respectively. Bacterial communities were different before and after bioplastic co-digestion, whereas no archaeal community change was observed. Relative abundance of 30 significant bacteria correlated with methane production and lag following PHB addition. No previously known PHB degraders were detected following PHB co-digestion. Microbial communities in anaerobic digesters treating synthetic primary sludge are sufficiently capable of co-digesting PHB to produce additional methane.
Kaushik Venkiteshwaran; Nicholas Benn; Saba Seyedi; Daniel Zitomer. Methane yield and lag correlate with bacterial community shift following bioplastic anaerobic co-digestion. Bioresource Technology Reports 2019, 7, 100198 .
AMA StyleKaushik Venkiteshwaran, Nicholas Benn, Saba Seyedi, Daniel Zitomer. Methane yield and lag correlate with bacterial community shift following bioplastic anaerobic co-digestion. Bioresource Technology Reports. 2019; 7 ():100198.
Chicago/Turabian StyleKaushik Venkiteshwaran; Nicholas Benn; Saba Seyedi; Daniel Zitomer. 2019. "Methane yield and lag correlate with bacterial community shift following bioplastic anaerobic co-digestion." Bioresource Technology Reports 7, no. : 100198.
Aqueous pyrolysis liquid (APL) is a high-COD byproduct of wastewater biosolids pyrolysis that is comprised of numerous complex organic compounds and ammonia nitrogen (NH3-N). One potential beneficial use of APL is as a co-digestate to produce more biogas in anaerobic digesters. However, some APL organics and NH3-N are known to inhibit methane-producing microbes. Autocatalytic pyrolysis which uses previously-produced biochar as a catalyst during biosolids pyrolysis, increases energy-rich py-gas while eliminating bio-oil production and reducing COD concentration in the APL (catalyzed APL). However, the catalyzed APL still has a high organic strength and no suitable treatment strategies have yet been identified. In this study, the methane production yields and methanogenic toxicity of non-catalyzed and catalyzed APLs were investigated. Both non-catalyzed and catalyzed APLs were produced at 800°C from a mix of digested primary and raw waste activated sludge from a municipal water resource reclamation facility. Using the anaerobic toxicity assay, APL digester loading rates higher than 0.5 gCOD/L for non-catalyzed and 0.10 gCOD/L for catalyzed APL were not sustainable due to toxicity. The IC50 values (APL concentration that inhibited methane production rate by 50%) for non-catalyzed and catalyzed APLs were 2.3 and 0.3 gCOD/L, respectively. Despite having significantly fewer identified organic compounds catalytic APL resulted in higher methanogenic toxicity than non-catalytic APL. NH3-N was not the main inhibitory constituent and other organics in APL, including 3,5-dimethoxy-4-hydroxybenzaldehyde, 2,5-dimethoxybenzyl alcohol, benzene, cresol, ethylbenzene, phenols, styrene, and xylenes as well as nitrogenated organics (e.g., benzonitrile, pyridine) ostensibly caused considerable methane production inhibition. Future research focused on pretreatment methods to overcome APL toxicity and the use of acclimated biomass to increase methane production rates during APL anaerobic digestion or co-digestion is warranted.
Saba Seyedi; Kaushik Venkiteshwaran; Daniel Zitomer. Toxicity of Various Pyrolysis Liquids From Biosolids on Methane Production Yield. Frontiers in Energy Research 2019, 7, 1 .
AMA StyleSaba Seyedi, Kaushik Venkiteshwaran, Daniel Zitomer. Toxicity of Various Pyrolysis Liquids From Biosolids on Methane Production Yield. Frontiers in Energy Research. 2019; 7 ():1.
Chicago/Turabian StyleSaba Seyedi; Kaushik Venkiteshwaran; Daniel Zitomer. 2019. "Toxicity of Various Pyrolysis Liquids From Biosolids on Methane Production Yield." Frontiers in Energy Research 7, no. : 1.