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1. Comparative Fuel Yield from Anaerobic Digestion of Emerging Waste in Food and Brewery Systems

   https://doi.org/10.3390/en15041538  

   Herman, Tess ; Nungesser, Emily ; Miller, Kimberley E. ; Davis, Sarah C. ( February 2022 , Energies)

   Food waste (FW), a major part of the US waste stream, causes greenhouse gases within landfills, but there is an opportunity to divert FW to anaerobic digestion (AD) facilities that produce biogas and digestate fertilizer. The composition of FW inputs to AD determines the value of these products. This study provides insight into the effect of waste composition on the quality of AD products by first characterizing the biogas and digestate quality of anaerobically digested FW from four diets (paleolithic, ketogenic, vegetarian, and omnivorous), and then estimating the difference in biogas produced from codigested FW and brewery waste (BW). Waste feedstock mixtures were incubated in lab-scale bioreactors for 21 days with live inoculum. Biogas quality was monitored for 21–30 days in four trials. Samples were analyzed using a gas chromatograph for detection of methane (CH4) and carbon dioxide (CO2). The composition of the waste inputs had a significant impact on the quality of biogas but not on the quality of the digestate, which has implications for the value of post-AD fertilizer products. Wastes with higher proportions of proteins and fats enhanced biogas quality, unlike wastes that were rich in soluble carbohydrates. Codigestion of omnivorous food waste with carbon-rich agricultural wastes (AW) improved biogas quality, but biogas produced from BW does not necessarily improve with increasing amounts of AW in codigestion. 

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2. 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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3. Recovery of Energy and Carbon Dioxide from Craft Brewery Wastes for Onsite Use

   https://doi.org/10.3390/fermentation9090831  

   Rawalgaonkar, Dhanashree ; Zhang, Yan ; Walker, Selina ; Kirchman, Paul ; Zhang, Qiong ; Ergas, Sarina J. ( September 2023 , Fermentation)

   Interest in craft beers is increasing worldwide due to their flavor and variety. However, craft breweries have high water, energy, and carbon dioxide (CO2) demands and generate large quantities of high-strength waste and greenhouse gases. While many large breweries recover energy using anaerobic digestion (AD) and recapture CO2 from beer fermentation, little is known about the economic feasibility of applying these technologies at the scale of small craft breweries. In addition, compounds in hops (Humulus lupulus), which are commonly added to craft beer to provide a bitter or “hoppy” flavor, have been shown to adversely affect anaerobic microbes in ruminant studies. In this study, biochemical methane potential (BMP) assays and anaerobic sequencing batch reactor (ASBR) studies were used to investigate biomethane production from high-strength craft brewery waste, with and without hop addition. A spreadsheet tool was developed to evaluate the economic feasibility of bioenergy and CO2 recovery depending on the brewery’s location, production volume, waste management, CO2 requirement, energy costs, and hop waste addition. The results showed that co-digestion of yeast waste with 20% hops (based on chemical oxygen demand (COD)) resulted in slightly lower methane yields compared with mono-digestion of yeast; however, it did not significantly impact the economic feasibility of AD in craft breweries. The use of AD and CO2 recovery was found to be economically feasible if the brewery’s annual beer production is >50,000 barrels/year. 

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4. Reinforcement learning-based control for waste biorefining processes under uncertainty

   https://doi.org/10.1038/s44172-024-00183-7  

   Gao, Ji ; Wahlen, Abigael ; Ju, Caleb ; Chen, Yongsheng ; Lan, Guanghui ; Tong, Zhaohui ( February 2024 , Communications Engineering)

   Waste biorefining processes face significant challenges related to the variability of feedstocks. The supply and composition of multiple feedstocks in these processes can be uncertain, making it difficult to achieve economically feasible and sustainable waste valorization for large-scale production. Here, we introduce a reinforcement learning-based framework that aims to control these uncertainties and improve the efficiency of the process. The framework is tested on an anaerobic digestion process and is found to perform better than traditional control strategies. In the short term, it achieves faster target tracking with increased precision and accuracy, while in the long term, it shows adaptive and robust behavior even under additional seasonal supply variability, meeting downstream demand with high probability. This reinforcement learning-based framework offers a promising and scalable solution to address uncertainty issues in real-world biorefining processes. If implemented, this framework could contribute to sustainable waste management practices globally, making waste biorefining processes more economically viable and environmentally friendly.

    

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5. Modified Ceria for “Low‐Temperature” CO 2 Utilization: A Chemical Looping Route to Exploit Industrial Waste Heat

   https://doi.org/10.1002/aenm.201901963  

   Haribal, Vasudev Pralhad ; Wang, Xijun ; Dudek, Ryan ; Paulus, Courtney ; Turk, Brian ; Gupta, Raghubir ; Li, Fanxing ( September 2019 , Advanced Energy Materials)

   Efficient CO₂utilization is key to limit global climate change. Carbon monoxide, which is a crucial feedstock for chemical synthesis, can be produced by splitting CO₂. However, existing thermochemical routes are energy intensive requiring high operating temperatures. A hybrid redox process (HRP) involving CO₂‐to‐CO conversion using a lattice oxygen‐deprived redox catalyst at relatively low temperatures (<700 °C) is reported. The lattice oxygen of the redox catalyst, restored during CO₂‐splitting, is subsequently used to convert methane to syngas. Operated at temperatures significantly lower than a number of industrial waste heat sources, this cyclic redox process allows for efficient waste heat‐utilization to convert CO₂. To enable the low temperature operation, lanthanum modified ceria (1:1 Ce:La) promoted by rhodium (0.5 wt%) is reported as an effective redox catalyst. Near‐complete CO₂conversion with a syngas yield of up to 83% at low temperatures is achieved using Rh‐promoted LaCeO_4−x. While La improves low‐temperature bulk redox properties of ceria, Rh considerably enhances the surface catalytic properties for methane activation. Density functional theory calculations further illustrate the underlying functions of La‐substitution. The highly effective redox catalyst and HRP scheme provide a potentially attractive route for chemical production using CO₂, industrial waste heat, and methane, with appreciably lowered CO₂emissions.

    

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