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1. Extraction of valuable chemicals from food waste via computational solvent screening and experiments

   https://doi.org/10.1016/j.seppur.2023.123719  

   Gupta, Yagya; Bhattacharyya, Souryadeep; Vlachos, Dionisios G. (July 2023, Separation and purification technology)

   Vlachos, Dionisios G. (Ed.)

   About 1.3 billion tons of global food production end up in landfills and composting, leading to significant anthropogenic greenhouse gas (GHG) emissions. Extracting antioxidant and antimicrobial chemicals (flavonoids, phenolic acids, etc.) from food waste is an economically lucrative valorization strategy but is hindered by efficient solvent selection. Here we perform in silico high throughput screening to identify high solubility solvents for key phenolics and reveal >100+ higher-performing solvents than the traditional ethanol and methanol. Solubilities of nine shortlisted solvents are measured and found in reasonable agreement with model predictions. Analysis of the Conductor like Screening Model for Real Solvents (COSMO-RS) σ-profiles and Hansen Solubility Parameters reveals that polarity and hydrogen bonding make dimethylformamide (DMF) an excellent single solvent. We showcase the replacement of high-solubility toxic solvents with green mixtures and demonstrate the approach to potato peel waste. Our work provides a blueprint for solvent selection and generates new insights into extraction from food waste. 

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2. 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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3. 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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4. Thermophilic Anaerobic Digestion: Enhanced and Sustainable Methane Production from Co-Digestion of Food and Lignocellulosic Wastes

   https://doi.org/10.3390/en11082058  

   David, Aditi; Govil, Tanvi; Tripathi, Abhilash; McGeary, Julie; Farrar, Kylie; Sani, Rajesh (August 2018, Energies)

   This article aims to study the codigestion of food waste (FW) and three different lignocellulosic wastes (LW) (Corn stover (CS), Prairie cordgrass (PCG), and Unbleached paper (UBP)) for thermophilic anaerobic digestion to overcome the limitations of digesting food waste alone (volatile fatty acids accumulation and low C:N ratio). Using an enriched thermophilic methanogenic consortium, all the food and lignocellulosic waste mixtures showed positive synergistic effects of codigestion. After 30 days of incubation at 60 °C (100 rpm), the highest methane yield of 305.45 L·kg−1 volatile solids (VS) was achieved with a combination of FW-PCG-CS followed by 279.31 L·kg−1 VS with a mixture of FW-PCG. The corresponding volatile solids reduction for these two co-digestion mixtures was 68% and 58%, respectively. This study demonstrated a reduced hydraulic retention time for methane production using FW and LW. 

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5. Low-pressure hydrothermal processing for conversion of polystyrene into oils

   https://doi.org/10.1016/j.jece.2024.113836  

   Gentilcore, Clayton; Jin, Kai; Barzallo, Genesis; Vozka, Petr; Wang, Nien-Hwa_Linda (October 2024, Journal of Environmental Chemical Engineering)

   Global polystyrene (PS) waste accumulates at a rate of 28 million tons annually, while recycling rates stay at 1.3 %. PS degrades into microplastics, releasing various chemicals that affect ecosystems and human health. Conventional waste treatment methods are ineffective in reducing PS waste accumulation. This study developed batch low-pressure hydrothermal processing (LP-HTP) methods to convert PS to oils. Oil yields of 96–99 % were obtained with 1–2 % char and up to 2 % gas at average temperatures of 341–424°C for 19–75 minutes. Reversible reactions between monomers (C6-C9) and poly-aromatics (C10-C20+) were found to limit monomer yields. A two-step kinetic model accounting for the reversible reactions was developed. Temperature histories of the batch experiments were considered such that the estimated kinetic parameters were independent of reactor heating or cooling rates. The predicted yields of monomers and poly-aromatics agreed with experimental yields to within 6 %. The model predicted increasing monomer yields with decreasing PS loadings. This predictive model can aid future process optimization and scale-up. PS and polyolefins were co-processed to produce oils with 87 % yields and higher aromatic contents than oils produced from polyolefins alone. LP-HTP methods required no catalyst, had higher oil yields and less char formation than pyrolysis, and used much lower operating pressures and energy than supercritical water liquefaction. The methods also potentially have lower environmental impacts and 4.7 times higher energy recovery than incineration. The oils from LP-HTP, if separated into pure monomers, can be used as chemical feedstocks to achieve a circular use of hydrocarbons. 

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