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1. Comparative assessment of pre‐ and inter‐stage hydrothermal treatment of municipal sludge for increased methane production

   https://doi.org/10.1002/wer.1523  

   Zhang, Chiqian ; Liu, Xiaoguang ; Wang, Qian ; Tang, Yuanzhi ; Pavlostathis, Spyros G. ( March 2021 , Water Environment Research)

   Hydrothermal treatment (HT) is a promising technology to enhance anaerobic digestion (AD) of municipal sludge. However, the capacity of pre‐ and inter‐stage HT (i.e., HT‐AD and AD‐HT‐AD, respectively) to enhance the digestibility of municipal sludge has not been sufficiently explored. This study compared the efficacy of pre‐ and inter‐stage HT performed from 90 to 185°C to enhance methane production from a mixture of primary sludge and waste activated sludge using mesophilic (35°C) biochemical methane potential tests. In both configurations, sludge solubilization increased with HT temperature. HT‐AD, and to a greater extent AD‐HT‐AD, increased the release of ammonium nitrogen. Even though HT at 185°C dramatically increased sludge solubilization, the overall specific methane yield with HT at 185°C was lower than or comparable to that at lower HT temperatures in the HT‐AD and AD‐HT‐AD configurations, respectively. Up to 155°C HT, the overall specific methane yield with the HT‐AD configuration was higher by 4.9%–8.3% compared to the AD‐HT‐AD configuration. However, when the HT energy was considered, compared to the control (i.e., AD of sludge without HT), the net energy gain (ΔE) decreased as the HT temperature increased, becoming negative at an HT of 185°C. The AD‐HT‐AD configuration resulted in a higher overall volatile solids destruction (by 8.1 to 20.1%). In conclusion, for municipal sludge with a relatively high ultimate digestibility, as was the case in this study, HT‐AD is preferable as it has a smaller footprint and is easier to operate than the AD‐HT‐AD configuration. However, given the significantly higher volatile solids destruction in the AD‐HT‐AD configuration, compared to the HT‐AD configuration, AD‐HT‐AD may be more beneficial considering post‐AD sludge handling processes.

   Hydrothermal treatment (HT) increased the rate and extent of methane production from municipal sludge mixture.

   155°C was the optimal temperature for either pre‐ or inter‐stage HT to increase biogas production.

   Pre‐ and inter‐stage HT resulted in comparable ultimate methane production.

   Pre‐stage HT is preferable to inter‐stage HT (smaller footprint, easier to operate).

   AD‐HT‐AD resulted in significantly higher volatile solids destruction compared to the HT‐AD configuration.

    

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2. Effect of removal of inhibitors on microbial communities and biogas yield of Jatropha curcas seeds during continuous anaerobic digestion

   https://doi.org/10.1016/j.jclepro.2023.139154  

   Haq, Abdul ; Malik, Ayesha ; Khan, Alam ; Weaver, Joseph E ; Wang, Ling ; Khan, Haji ; Khan, Samiullah ; Shah, Aamer Ali ; Ahmed, Safia ; Jamal, Asif ; et al ( November 2023 , Journal of Cleaner Production)

   Jatropha curcas seeds, as an abundant lignocellulosic biomass, offer a highly promising and ideal alternative for producing energy in the form of methane. Use of J. curcas seeds has the potential to significantly bolster the biofuel sector, fostering a more sustainable circular economy. In the current study, different fractions of processed J. curcas seeds were investigated for biogas production. J. curcas seed pressed cake, a by-product of biodiesel production, was subjected to methanolic extraction. The remaining solids, referred to as methanolic residues, yielded more biogas in batch experiments than pressed cake and residues from aqueous and n-hexane extractions. The compounds extracted with methanol inhibited hydrolysis and reduced biogas production by 35.5% compared to the same setup without extracts. In continuous reactors fed with methanolic residues, the highest biogas yield occurred at an organic loading rate (OLR) of 1 g VS L−1 day−1 and a hydraulic retention time (HRT) of 20 days. The relative abundance of acetogenic bacteria was higher in reactors fed with methanolic residues than in those fed with seed pressed cake, seed oil, and whole seed. Jatropha seed oil and whole seed did not inhibit methanogens. A higher relative abundance of methanogenic communities was observed in all reactors at HRT of 20 days compared to those at HRTs at 15 and 10 days. These findings can be used to increase biogas production during anaerobic digestion of J. curcas seed components and suggests a zero-waste biorefinery production route for value added compounds derived from the removal of biogas-inhibiting components. 

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3. Isoprene Production from Municipal Wastewater Biosolids by Engineered Archaeon Methanosarcina acetivorans

   https://doi.org/10.3390/app11083342  

   Carr, Sean ; Aldridge, Jared ; Buan, Nicole R. ( April 2021 , Applied Sciences)

   Wastewater biosolids are a promising feedstock for production of value-added renewable chemicals. Methane-producing archaea (methanogens) are already used to produce renewable biogas via the anaerobic treatment of wastewater. The ability of methanogens to efficiently convert dissolved organic carbon into methane makes them an appealing potential platform for biorefining using metabolic engineering. We have engineered a strain of the methanogen Methanosarcina acetivorans to produce the volatile hemiterpene isoprene in addition to methane. The engineered strain was adapted to grow in municipal wastewater through cultivation in a synthetic wastewater medium. When introduced to municipal wastewater the engineered methanogens were able to compete with the indigenous microorganisms and produce 0.97 mM of isoprene (65.9 ± 21.3 g per m3 of effluent). The production of isoprene in wastewater appears to be dependent on the quantity of available methanogenic substrate produced during upstream digestion by heterotrophic fermenters. This shows that with minimal adaptation it is possible to drop-in engineered methanogens to existing wastewater environments and attain value-added products in addition to the processing of wastewater. This shows the potential for utilizing methanogens as a platform for low-cost production of renewable materials without expensive feedstocks or the need to build or adapt existing facilities. 

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4. Anaerobic Digestion of Food Waste, Brewery Waste, and Agricultural Residues in an Off-Grid Continuous Reactor

   https://doi.org/10.3390/su13126509  

   Miller, Kimberley E. ; Herman, Tess ; Philipinanto, Dimas A. ; Davis, Sarah C. ( June 2021 , Sustainability)

   Small-scale anaerobic digestion (AD) can be an effective organic waste management system that also provides energy for small businesses and rural communities. This study measured fuel production from digestions of single and mixed feedstocks using an unheated, 2 m3 digester operated continuously in a temperate climate for over three years. Using local food waste, brewery waste, grease waste, and agricultural residues, this study determined that small-scale AD co-digestions were almost always higher yielding than single feedstocks during psychrophilic operation and seasonal temperature transitions. Agricultural residues from Miscanthus x giganteus had the greatest impact on biomethane production during co-digestion (4.7-fold greater average biogas %CH4), while mesophilic digestion of brewery waste alone produced the most biogas (0.76 gCH4 gVS−1 d−1). Biogas production during the transition from mesophilic to psychrophilic was temporarily maintained at levels similar to mesophilic digestions, particularly during co-digestions, but biogas quality declined during these temperature shifts. Full-time operation of small-scale, unheated AD systems could be feasible in temperate climates if feedstock is intentionally amended to stabilize carbon content. 

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5. OPPORTUNITIES FOR USING NUCLEAR MICROREACTORS FOR WASTEWATER TREATMENT, HYDROGEN PRODUCTION, AND AMMONIA PRODUCTION

   https://doi.org/10.1615/TFEC2024.icc.050659  

   Strine, Bailey ; Pakkebier, Jack ; Parameswaran, Prathap ; Derby, Melanie M ( January 2024 , Begellhouse)

   In 2021, the White House proposed a 50-52% reduction in greenhouse gas emissions by the year 2030; therefore, there is significant interest in energy sources and processes that reduce carbon dioxide emissions. This paper presents a sensitivity analysis of a nuclear microreactor-powered design for concurrent hydrogen (H2) and ammonia (NH3) production, with a focus on wastewater treatment plant applications. Wastewater with organic materials (e.g., municipal wastewater, swine lagoon waste, and food waste) are the analyzed feedstocks. The system integrates the anaerobic digestion of wastewater sludge with a Brayton cycle-based power generation unit heated by the microreactor. Using empirical data and an analytical model, the paper investigates the system's response to variations in key operational parameters. The sensitivity analysis explores the influence of parameters such as the chemical oxygen demand of the feedstock, compressor isentropic efficiency, and reactor temperature and pressure on H2 and NH3 production rates, Brayton cycle efficiency, and carbon dioxide emissions. Highlights from this analysis show a nonlinear dependence for Brayton efficiency on reactor temperature, the proportionality of ammonia and hydrogen production on chemical oxygen demand values, the major impact of compressor isentropic efficiency, and the minimal response from changing the pressure of steam methane reforming. These results signify opportunities to improve the system and ultimately lead to lowered greenhouse gas emissions. 

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