Arrested methanogenesis digestion of high-strength cheese whey and brewery wastewater with carboxylic acid production

Competitive partitioning of denitrification pathways during arrested methanogenesis: Implications in ammonium recovery, N2O emission, and volatile fatty acid production

The complex interaction between nitrate (NO3-) reduction and fermentation is poorly understood when high levels of NO3- are introduced into anaerobic systems. This study investigated the competitive distribution between conventional denitrification (DEN) and dissimilatory nitrate reduction to ammonium (DNRA) during simultaneous denitrification and fermentation in arrested methanogenesis. Up to 62% of initial NO3- (200 mg-N/L) was retained as ammonium through DNRA at a chemical oxygen demand (COD)/N ratio of 25. Significant N2O emission occurred (1.7 - 8.0% of the initial NO3-) with limited carbon supply (≤1600 mg COD/L) and sludge concentration (≤3000 mg COD/L). VFA composition shifted predominantly towards acetic acid (>50%) in the presence of nitrate. A novel kinetic model was developed to predict DNRA vs. DEN partitioning and NO2- accumulation. Overall, NO3- input, organic loading, and carbon source characteristics independently and collectively controlled competitive DNRA vs. DEN partitioning.

Current Status and Prospects of Valorizing Organic Waste via Arrested Anaerobic Digestion: Production and Separation of Volatile Fatty Acids

Volatile fatty acids (VFA) are intermediary degradation products during anaerobic digestion (AD) that are subsequently converted to methanogenic substrates, such as hydrogen (H2), carbon dioxide (CO2), and acetic acid (CH3COOH). The final step of AD is the conversion of these methanogenic substrates into biogas, a mixture of methane (CH4) and CO2. In arrested AD (AAD), the methanogenic step is suppressed to inhibit VFA conversion to biogas, making VFA the main product of AAD, with CO2 and H2. VFA recovered from the AAD fermentation can be further converted to sustainable biofuels and bioproducts. Although this concept is known, commercialization of the AAD concept has been hindered by low VFA titers and productivity and lack of cost-effective separation methods for recovering VFA. This article reviews the different techniques used to rewire AD to AAD and the current state of the art of VFA production with AAD, emphasizing recent developments made for increasing the production and separation of VFA from complex organic materials. Finally, this paper discusses VFA production by AAD could play a pivotal role in producing sustainable jet fuels from agricultural biomass and wet organic waste materials.

Metagenomic insights into improving mechanisms of Fe0 nanoparticles on volatile fatty acids production from potato peel waste anaerobic fermentation

The management of potato peel waste (PPW) has been a challenge faced by the potato industry. This investigation assessed the feasibility of PPW for volatile fatty acids (VFAs) production via anaerobic fermentation, and investigated the impact of Fe⁰ nanoparticles (Fe⁰ NPs) supplementation on the VFAs production. It is found that PPW is a potential feedstock for producing VFAs, achieving a yield of 480.4 mg COD/g-vS Meanwhile, the supplementation of Fe⁰ NPs significantly promoted the VFAs productivity and quality. The higher enrichment of VFAs-producing bacteria, including Clostridium, Proteiniphilum, Fonticella and Pygmaiobacter, contributed to the promotion of the VFAs yield. Furthermore, metagenomic analysis revealed that the encoding genes responsible for carbohydrate metabolism (especially starch), membrane transport, glycolysis and the formation of acetic and butyric acids were remarkably up-regulated,which could be the essential reason for the enhanced metabolic activity and VFAs productivity. This work provides a promising strategy for recycling PPW.

Anaerobic digestate management, environmental impacts, and techno-economic challenges

Digestate is a nutrient-rich by-product from organic waste anaerobic digestion but can contribute to nutrient pollution without comprehensive management strategies. Some nutrient pollution impacts include harmful algal blooms, hypoxia, and eutrophication. This contribution explores current productive uses of digestate by analyzing its feedstocks, processing technologies, economics, product quality, impurities, incentive policies, and regulations. The analyzed studies found that feedstock, processing technology, and process operating conditions highly influence the digestate product characteristics. Also, incentive policies and regulations for managing organic waste by anaerobic digestion and producing digestate as a valuable product promote economic benefits. However, there are not many governmental and industry-led quality assurance certification systems for supporting commercializing digestate products. The sustainable and safe use of digestate in different applications needs further development of technologies and processes. Also, incentives for digestate use, quality regulation, and social awareness are essential to promote digestate product commercialization as part of the organic waste circular economy paradigm. Therefore, future studies about circular business models and standardized international regulations for digestate products are needed.

Long-term alkaline volatile fatty acids production from waste streams: Impact of pH and dominance of Dysgonomonadaceae

Alkaline co-fermentation of primary sludge and external organic waste (OW) was studied to elucidate the influence of substrate ratios and long-term system robustness and microbial community dynamics using batch and semi-continuous reactors. Volatile fatty acid (VFA) production increased with increasing OW fraction in the substrate due to synergistic effects of co-degradation. VFA production at pH 10 increased up to 30,300 mgCOD/L (yield of 630 mg COD/gVS_fed) but reduced over time to ≈10,000 mgCOD/L. Lowering pH to 9 led to the restoration of VFA production with a maximum of 32,000 mg COD/L (676 mg COD/g VS_fed) due to changes in microbial structure. VFA was composed mainly of acetic acid, but propionic acid increased at pH 9. The microbial community was dominated by Bacillaceae (34 ± 10%) and Proteinivoracales_uncultured (16 ± 11%) at pH 10, while Dysgonomonadaceae (52 ± 8%) was enriched at pH 9. The study demonstrated a zero-waste strategy that turns organic wastes into bio-based products.

Microbial communities for valorizing biomass using the carboxylate platform to produce volatile fatty acids: A review

The carboxylate platform employs a diverse microbial consortium of anaerobes in which the methanogens are inhibited. Nearly all biomass components are digested to a mixture of C1-C8 monocarboxylic acids and their corresponding salts. The methane-arrested anaerobic digestion proceeds readily without needing to sterilize biomass or equipment. It accepts a wide range of feedstocks (e.g., agricultural residues, municipal solid waste, sewage sludge, animal manure, food waste, algae, and energy crops), and produces high product yields. This review highlights several important aspects of the platform, including its thermodynamic underpinnings, influences of inoculum source and operating conditions on product formation, and downstream chemical processes that convert the carboxylates to hydrocarbon fuels and oxygenated chemicals. This review further establishes the carboxylate platform as a viable and economical route to industrial biomass utilization.

Anaerobic digestion beyond biogas

Anaerobic digestion (AD) is a matured technology for waste (water) remediation/stabilization and bioenergy generation in the form of biogas. AD technology has several inherent benefits ranging from generating renewable energy, remediating waste (water), and reducing greenhouse gas emission to improving health/hygiene and the overall socio-economic status of rural communities in developing nations. In recent years, there has been a paradigm shift in applications of AD technology beyond biogas. This special issue (SI) entitled, "Anaerobic Digestion Beyond Biogas (ADBB-2021)," was conceptualized to incorporate some of the recent advances in AD in which the emphasis is beyond biogas, such as anaerobic biorefinery, chain elongation, treatment of micropollutants, toxicity and system stability, digestate as biofertilizer, bio-electrochemical systems, innovative bioreactors, carbon sequestration, biogas upgrading, microbiomes, waste (water) remediation, residues/waste pre-treatment, promoter addition, and modeling, process control, and automation, among others. This VSI: ADBB-2021 contains 53 manuscripts (14 critical reviews and 39 research). The key findings of each manuscript are briefly summarized here, which can serve as a valuable resource for AD researchers to learn of major advances in AD technology and identify future research directions.

Sustainable valorization of meat processing wastewater with synergetic eutectic mixture based purification of R-Phycoerythrin from porphyrium cruentium

Wastewater effluent from meat processing industries are enriched with nutrients but remain underutilized. Therefore, an efficient method was administered by employing this resource for the cultivation of Porphyreum cruentium. The cultured biomass was exposed to a one-step disruption and selective purification method using a protic deep eutectic solvent to obtain a commercially significant pigment, R-Phycoerythrin (R-PE). Six protic deep eutectic solvents (pDES) were synthesized and their thermophysical activity determined. A synergy between microwave and cavitation (MACE-DLPME) has been achieved for the effective recovery of these membrane proteins. The addition of pDES provides the selective medium for the concentration of R-PE. Optimization of the MACE-DLPME method yields 95.9% (w/w) of R-PE. Preparative size exclusion chromatography resulted in (28 µg/g) of R-PE. Further ultra-purification by anion exchange chromatography enhances the purity fold of R-PE to 125. The resulting ultrapure fraction exhibits enhanced anti-platelet activity (1.56 mg/g ascorbic acid equivalent).