Increasing 2 -Bio- (H2 and CH4) production from food waste by combining two-stage anaerobic digestion and electrodialysis for continuous volatile fatty acids removal

Relative contributions of mobility and partitioning to volatile fatty acid flux during electrodialysis

Economically valuable volatile fatty acids (VFAs) are sustainably produced via fermentation processes. To use VFAs downstream, they must be recovered using technologies like electrodialysis (ED). Solute transport properties (i.e., partition coefficient (K), diffusion coefficient (D), and permeability (P=KD)) govern flux in ED. Therefore, to advance understanding of VFA flux through anion exchange membranes (AEMs) in ED, we aimed to elucidate the relative contributions of VFA partitioning and mobility to their flux. Accordingly, for VFAs of different sizes (C1-C5) and inorganic anions (Cl-, Br-), we measured their fluxes during ED, permeabilities, and partition coefficients, and calculated the diffusion coefficients. We then evaluated the correlations between flux and transport properties and between transport properties and anion physicochemical properties. Results showed VFA flux had a strong correlation with permeability (R2=0.94, p<0.01), consistent with flux described by the Nernst-Planck equation. Further, while there was a negative correlation between VFA flux and partition coefficient (R2=0.46, p=0.21), there was a positive correlation between VFA flux and diffusion coefficient (R2=0.95, p<0.01) which showed VFA mobility governed VFA flux. We observed a negative correlation between VFA diffusion coefficient and carbon-chain length which was attributed to steric hindrance, and a positive correlation between partition coefficient and carbon chain-length which we attributed to hydrophobicity and polarizability. This work provides fundamental insight on interactions between VFAs and AEMs which affect anion flux during ED.

Enhancing acidification efficiency of vegetable wastes through heat shock pretreatment and initial pH regulation

Anaerobic digestion (AD) technology is a practical approach to alleviate severe environmental issues caused by vegetable wastes (VWs). However, its primary product is methane-rich biogas converted from the precursors (mainly volatile fatty acids, VFAs) after long fermentation periods, making traditional AD projects of low economic profits. Intervening in the methanogenesis stage artificially to produce high value-added VFAs can shorten the reaction time of the AD process and significantly improve profits, posing a promising alternative for treating VWs. Given this, this study applied heat shock (HS) pretreatment to inoculum to prevent methane production during AD and systemically investigated the effects of HS pretreatment and initial pH regulation on VFA production from VWs. The results showed that appropriate HS pretreatment effectively inhibited methane generation but promoted VFA accumulation, and VFA production was further enhanced by adjusting the initial pH to 8.0 and 9.0. The highest total VFA concentration of 14,883 mg/L with a VFA yield of 496.1 mg/gVS, 26.98% higher than that of the untreated group, was achieved at an initial pH 8.0 with HS pretreatment of 80 °C for 1 h. Moreover, pH regulation influenced the metabolic pathway of VFA production from VWs during AD, as butyrate was the dominant product at an initial pH of 6.0, while the increased initial pH improved the acetate proportion.

Role of Lactiplantibacillus paraplantarum during anaerobic storage of ear-removed corn on biogas production

To optimize the volatile fatty acid production for anaerobic fermentation, the ear-removed corn was ensiled without (control) or with Lactiplantibacillus plantarum (LP), Lacticaseibacillus paracasei (LC) and L. paraplantarum (LpP). Inoculation of LpP increased acetic acid content by 40%, and decreased butyric acid content by 38% in relative to control. Moreover, inoculation of LpP decreased the bacterial alpha diversity indices, while inherent species of Lentilactobacillus buchneri and L. hilgardii dominated the anaerobic fermentation. In particular, inoculation of LpP restricted the growth of yeasts and production of propionic acid at the early stage of storage, but continuously stimulated anaerobic fermentation, resulting in a higher maximal cumulative gas emissions of methane (by about 20 %) than that of LP and LC. Therefore, inoculation of LpP during anaerobic storage was favorable to produce intermediate metabolites (acetic acid) for subsequent biogas production of ear-removed corn.

Current Trends in Biological Valorization of Waste-Derived Biomass: The Critical Role of VFAs to Fuel A Biorefinery

The looming climate and energy crises, exacerbated by increased waste generation, are driving research and development of sustainable resource management systems. Research suggests that organic materials, such as food waste, grass, and manure, have potential for biotransformation into a range of products, including: high-value volatile fatty acids (VFAs); various carboxylic acids; bioenergy; and bioplastics. Valorizing these organic residues would additionally reduce the increasing burden on waste management systems. Here, we review the valorization potential of various sustainably sourced feedstocks, particularly food wastes and agricultural and animal residues. Such feedstocks are often micro-organism-rich and well-suited to mixed culture fermentations. Additionally, we touch on the technologies, mainly biological systems including anaerobic digestion, that are being developed for this purpose. In particular, we provide a synthesis of VFA recovery techniques, which remain a significant technological barrier. Furthermore, we highlight a range of challenges and opportunities which will continue to drive research and discovery within the field. Analysis of the literature reveals growing interest in the development of a circular bioeconomy, built upon a biorefinery framework, which utilizes biogenic VFAs for chemical, material, and energy applications.

Critical challenges and technological breakthroughs in food waste hydrolysis and detoxification for fuels and chemicals production

Organic waste has increased as the global population and economy have grown exponentially. Food waste (FW) is posing a severe environmental issue because of mismanaged disposal techniques, which frequently result in the squandering of carbohydrate-rich feedstocks. In an advanced valorization strategy, organic material in FW can be used as a viable carbon source for microbial digestion and hence for the generation of value-added compounds. In comparison to traditional feedstocks, a modest pretreatment of the FW stream utilizing chemical, biochemical, or thermochemical techniques can extract bulk of sugars for microbial digestion. Pretreatment produces a large number of toxins and inhibitors that affect bacterial fuel and chemical conversion processes. Thus, the current review scrutinizes the FW structure, pretreatment methods (e.g., physical, chemical, physicochemical, and biological), and various strategies for detoxification before microbial fermentation into renewable chemical production. Technological and commercial challenges and future perspectives for FW integrated biorefineries have also been outlined.

Membrane-based technologies for biohydrogen production: A review

Overcoming the existing environmental issues and the gradual depletion of energy sources is a priority at global level, biohydrogen can provide a sustainable and reliable energy reserve. However, the process instability and low biohydrogen yields are still hindering the adoption of biohydrogen production plants at industrial scale. In this context, membrane-based biohydrogen production technologies, and in particular fermentative membrane bioreactors (MBRs) and microbial electrolysis cells (MECs), as well as downstream membrane-based technologies such as electrodialysis (ED), are suitable options to achieve high-rate biohydrogen production. We have shed the light on the research efforts towards the development of membrane-based technologies for biohydrogen production from organic waste, with special emphasis to the reactor design and materials. Besides, techno-economic analyses have been traced to ensure the suitability of such technologies in bio-H₂ production. Operation parameters such as pH, temperature and organic loading rate affect the performance of MBRs. MEC and ED technologies also are highly affected by the chemistry of the membrane used and anode material as well as the operation parameters. The limitations and future directions for application of membrane-based biohydrogen production technologies have been individuated. At the end, this review helps in the critical understanding of deploying membrane-based technologies for biohydrogen production, thereby encouraging future outcomes for a sustainable biohydrogen economy.

Intensification of Acidogenic Fermentation for the Production of Biohydrogen and Volatile Fatty Acids—A Perspective

Utilising ‘wastes’ as ‘resources’ is key to a circular economy. While there are multiple routes to waste valorisation, anaerobic digestion (AD)—a biochemical means to breakdown organic wastes in the absence of oxygen—is favoured due to its capacity to handle a variety of feedstocks. Traditional AD focuses on the production of biogas and fertiliser as products; however, such low-value products combined with longer residence times and slow kinetics have paved the way to explore alternative product platforms. The intermediate steps in conventional AD—acidogenesis and acetogenesis—have the capability to produce biohydrogen and volatile fatty acids (VFA) which are gaining increased attention due to the higher energy density (than biogas) and higher market value, respectively. This review hence focusses specifically on the production of biohydrogen and VFAs from organic wastes. With the revived interest in these products, a critical analysis of recent literature is needed to establish the current status. Therefore, intensification strategies in this area involving three main streams: substrate pre-treatment, digestion parameters and product recovery are discussed in detail based on literature reported in the last decade. The techno-economic aspects and future pointers are clearly highlighted to drive research forward in relevant areas.

The Impact of Family Members Serving as Village Cadres on Rural Household Food Waste: Evidence from China

Based on nationwide survey data from China, we used a fractional logit model for analysis and propensity score matching (PSM) to evaluate the impact of family members serving as village cadres on household food waste. We found that, first, one household in rural China wasted an average of 1.62% of total food per day; in particular, the waste of staple foods was the most serious, with 5.14% of rice wasted per day. Differences in economic development, the geographical environment and diet habits caused differences in food waste in various regions of China. Second, empirical analysis showed that family members serving as cadres significantly increased household food waste. Third, the PSM results showed that family members serving as village cadres significantly increased household food waste and the waste of rice products. Households with members serving as cadres wasted 1.98% of total foods and 7.15% of rice products, on average, while other households wasted only 1.22–1.55% of total foods and 3.55–4.74% of rice products, on average.

Effects of co-digestion of food waste, corn straw and chicken manure in two-stage anaerobic digestion on trace element bioavailability and microbial community composition

Co-digestion is known to effectively alleviate trace elements (TEs) deficiency in mono-substrates; however, the bioavailability of TEs is crucial for the stability of anaerobic digestion. Therefore, this study investigated the effects of co-digestion of food waste (FW), corn straw (CS) and chicken manure (CM) in two-stage anaerobic digestion on TEs bioavailability and microbial community composition. Various VS_FW:(VS_CS:VS_CM) ratios of 8:2, 7:3, 4:6, and 2:8 were evaluated in two-stage (group A, B, C, D) anaerobic digestion in which the VS_CS:VS_CM ratio was fixed at 3:1. Results showed that the highest hydrogen production of 106 mL/g VS and methane production co-efficiency of 125.3% was obtained in group A. Group A has a high close range of easily bioavailable TEs (32-64%) compared to other groups, especially the mono-substrate, where almost all TEs ranged between 10 and 36%. The increased relative abundance of the obligate hydrogenotrophic methanogens reflected a positive two-stage methane co-digestion efficiency.

Increased biological and cathodic hydrogen production using a novel integrated thermophilic fermenter and dual anion exchange membrane bioelectrochemical system

Many researchers are interested in utilizing renewable and sustainable energy made by exoelectrogenic bacteria during electrodialysis for the separation of minerals and organic matters from aqueous environments. The aim of this study was to develop a novel thermophilic fermenter and dual anion exchange membrane bioelectrochemical system for separating biohydrogen production inhibitors from the thermophilic fermenter and thereby increasing biological and cathodic hydrogen production by food waste and wastewater.•

Using this innovative system the biohydrogen production inhibitors were separated and nutrients (for example ammonium), alkalinity, buffering capacity and pH were preserved in the bioreactor at the same time, led to higher biological and cathodic hydrogen production.