Monolignol Potential and Insights into Direct Depolymerization of Fruit and Nutshell Remains for High Value Sustainable Aromatics.

The inedible parts of nuts and stone fruits are low-cost and lignin-rich feedstock for more sustainable production of aromatic chemicals in comparison with the agricultural and forestry residues. However, the depolymerization performances on food-related biomass remains unclear, owing to the broad physicochemical variations from the edible parts of the fruits and plant species. In this study, the monomer production potentials of ten major fruit and nutshell biomass were investigated with comprehensive numerical information derived from instrumental analysis, such as plant cell wall chemical compositions, syringyl/guaiacyl (S/G ratios, and contents of lignin substructure linkages (ß-O-4, ß-ß, ß-5). A standardized one-pot reductive catalytic fractionation (RCF) process was applied to benchmark the monomer yields, and the results were statistically analyzed. Among all the tested biomass, mango endocarp provided the highest monolignol yields of 37.1 % per dry substrates. Positive S-lignin (70-84 %) resulted in higher monomer yield mainly due to more cleavable ß-O-4 linkages and less condensed C-C linkages. Strong positive relationships were identified between ß-O-4 and S-lignin and between ß-5 and G-lignin. The analytical, numerical, and experimental results of this study shed lights to process design of lignin-first biorefinery in food-processing industries and waste management works.

The modified properties of sludge-based biochar with ferric sulfate and its effectiveness in promoting carbon release from particulate organic matter in rural household wastewater.

The scarcity of carbon sources presents a significant challenge for the bio-treatment of rural domestic wastewater (RDW). This paper presented an innovative approach to address this issue by investigating the supplementary carbon source through in-situ degradation of particulate organic matter (POM) facilitated by ferric sulfate modified sludge-based biochar (SBC). To prepare SBC, five different contents of ferric sulfate (0%, 10%, 20%, 25%, and 33.3%) were added to sewage sludge. The results revealed that the pore and surface of SBC were enhanced, providing active sites and functional groups to accelerate the biodegradation of protein and polysaccharide. During the 8-day hydrolysis period, the concentration of soluble chemical oxidation demand (SCOD) increased and peaked (1087-1156 mg L-1) on the fourth day. The C/N ratio increased from 3.50 (control) to 5.39 (25% ferric sulfate). POM was degraded the five dominant phyla, which were Actinobacteriota, Firmicutes, Synergistota, Proteobacteria, and Bacteroidetes. Although the relative abundance of dominant phyla changed, the metabolic pathway remained unchanged. The leachate of SBC (<20% ferric sulfate) was beneficial for microbes, but an excessive amount of ferric sulfate (33.3% ferric sulfate) could have inhibition effects on bacteria. In conclusion, ferric sulfate modified SBC holds the potential for the carbon degradation of POM in RDW, and further improvements should be made in future studies.

Acclimation of anaerobic fermentation microbiome with acetate and ethanol for chain elongation and the biochemical response.

Medium chain fatty acids (MCFAs) production is a promising method for resource recovery from organic wastes. In this study, the microbial community structure shift along the long-term acclimation experiment and the concomitant effect of H2 level on chain elongation performance was investigated. Chain elongation microbiome could be rapidly acclimated from traditional anaerobic fermentation consortia. Genera Caproiciproducens, Clostridium sensu stricto 12, Rummeliibacillus and Oscillibacter was found to be dominant during the operation. The H2 was accumulated in the headspace by increasing the ethanol input, which inhibited oxidation of caproate and butyrate immediately, while its inhibition effect on chain elongation was delayed. H2 level in the headspace was positively correlated to the MCFAs production related bacteria. However, too much H2 accumulated might be suppressive for MCFAs production in the long term. It might result from the thermodynamic barrier for discarding excess reducing equivalents under high H2 level, which further gave rise to ethanol accumulation in this system.

Roadmap from Microbial Communities to Individuality Modeling for Anaerobic Digestion of Sewage Sludge.

Biological models describing anaerobic digestion (AD) of sewage sludge have been widely applied to test various control and operation strategies. Anaerobic digestion model 1 (ADM1) provides a generic platform that includes the main processes of AD, excluding homoacetogenesis and the microbial structure. Homoacetogenic bacteria have been identified as important competitors for hydrogen consumption and acetate production. Although recent advances in meta-omics techniques have improved our characterization of AD microbial communities, conventional models treat functional groups as homogeneous and overlook the physiology and behavior of microbial individuality, limiting insights into mechanisms governing process performance. A novel microbial individuality model (MIM) that integrates kinetics, energetics, and agent-based modeling to describe a microbiome's behavior as heterogenic populations, including homoacetogenesis, was developed. The MIM was validated with two datasets from previous studies through daily biogas production, methane content, compound concentrations, and microbial relative abundance changes. The MIM identified the emergence of Methanosaeta at low concentrations of acetate. Moreover, this simulation supports experimental studies confirming that the overlooked homoacetogenesis is an important hydrogen sink in AD. Validated MIMs are expected to provide insights into syntrophic and competitive interactions among microbiomes in AD systems while testing different operational parameters in a virtual environment. The MIM offers a methodological framework to other biological treatment systems and their microbial community dynamics.

Biorefinery potential of chemically enhanced primary treatment sewage sludge to representative value-added chemicals - A de novo angle for wastewater treatment.

Chemically enhanced primary treatment (CEPT) is an emerging sewage treatment strategy due to its high efficiency and small land requirement. CEPT sludge can be easily dewatered and used for energy recovery through incineration. However, with large amount of reusable nutrients (40% organic carbon, 23% lipids, and 17% protein), the value of CEPT sludge may have been underestimated. In this study, the biorefinery potential of CEPT sludge has been proven via production of 28.9 g/L ethanol or 50.3 g/L lactic acid (LA) or 1.43 filter paper unit (FPU)/mL cellulase from 10 g of CEPT sludge experiment. Inhibition on cell growth and potential inhibitors from plasticizers, pharmaceuticals, and surfactants were determined. Nevertheless, production titer was not affected or performed even better than the non-inhibitors controls. CEPT sludge showed significant potential in biochemical conversion, and the related products may offer an opportunity to support wastewater treatment toward sustainability and carbon neutrality.

Genomic driven factors enhance biocatalyst-related cellulolysis potential in anaerobic digestion.

Anaerobic digestion (AD) is a promising technology to recover bioenergy from biodegradable biomass, including cellulosic wastes. Through a few fractionation/separation techniques, cellulose has demonstrated its potential in AD, but the performance of the process is rather substrate-specific, as cellulolysis bacteria are sensitive to the enzyme-substrate interactions. Cellulosome is a self-assembled enzyme complex with many functionalized modules in the bacteria which has been gradually studied, however the genomic fingerprints of the culture-specific cellulosome in AD are relatively unclear especially under processing conditions. To clarify the key factors affecting the cellulosome induced cellulolysis, this review summarized the most recent publications of AD regarding the fates of cellulose, sources and functional genes of cellulosome, and omics methods for functional analyses. Different processes for organic treatment including applying food grinds in sewer, biomass valorization, cellulose fractionation, microaeration, and enzymatic hydrolysis enhanced fermentation, were highlighted to support the sustainable development of AD technology.

Synergistic association between cytochrome bd-encoded Proteiniphilum and reactive oxygen species (ROS)-scavenging methanogens in microaerobic-anaerobic digestion of lignocellulosic biomass.

Intermittent (every other day) microaerobic [picomolar oxygen by oxidation-reduction potential (ORP) set at +25 mV above anaerobic baseline] digestion of lignocellulosic biomass showed higher digestibility and better stability at a high organic loading rate (OLR) of 5 g volatile solids (VS)/L/d than that under strict anaerobic conditions. However, the microbial mechanisms supporting the delicate balance under microaeration remain underexplored. On the basis of our previous findings that microbial communities in replicate experiments were dominated by strains of the genus Proteiniphilum but contained diverse taxa of methanogenic archaea, here we recovered related genomes and reconstructed the putative metabolic pathways using a genome-centric metagenomic approach. The highly enriched Proteiniphilum strains were identified as efficient cellulolytic facultative bacterium, which directly degraded lignocellulose to carbon dioxide, formate, and acetate via aerobic respiration and anaerobic fermentation, alternatively. Moreover, high oxygen affinity cytochromes, bd-type terminal oxidases, in Proteiniphilum strains were found to be closely associated with such picomolar oxygen conditions, which has long been overlooked in anaerobic digestion. Furthermore, hydrogenotrophic methanogenesis was the prevalent pathway for methane production while Methanosarcina, Methanobrevibacter, and Methanocorpusculum were the dominant methanogens in the replicate experiments. Importantly, the two functional groups, namely cellulolytic facultative Proteiniphilum strains and methanogens, encoded various antioxidant enzymes. Energy-dependent reactive oxygen species (ROS) scavengers (superoxide reductase (SOR) and rubrerythrin (rbr) were ubiquitously present in different methanogenic taxa in response to replicate-specific ORP levels (-470, -450 and -475 mV). Collectively, cytochrome bd oxidase and ROS defenders may play roles in improving the digestibility and stability observed in intermittent microaerobic digestion.

Effect of waterproof breathable membrane based cathodes on performance and biofilm microbiomes in bioelectrochemical systems.

A novel method for fabricating air-cathodes was developed by assembling an activated carbon (AC) catalyst together with a waterproof breathable membrane (WBM) and stainless steel mesh (SSM) to reduce manufacturing costs of bioelectrochemical systems (BESs). WBMs made of different materials were tested in the assembly, including a hybrid of polypropylene and polyolefin (PPPO), polyethylene (PE), and polyurethane (PU), and compared against poly tetrafluoroethylene (PTFE)-based cathodes. Results showed that the maximum power density of the activated carbon-stainless steel mesh-polyurethane (AC@SSM/PU) assembly was 2.03 W/m2 while that of conventional carbon cloth cathode assembly (Pt@CC/PTFE) was 1.51 W/m2. Compared to conventional cathode fabrication, AC@SSM/PU had a much lower cost and simpler manufacturing process. Illumina Miseq sequencing of 16S rRNA gene amplicons indicated that microbiomes were substantially different between anode and cathode biofilms. There was also a difference in the community composition between different cathode biofilms. The predominant population in the anode biofilms was Geobacter (38-75% relative abundance), while Thauera and Pseudomonas dominated the cathode biofilms. The results demonstrated that different types of air-cathodes influenced the microbial community assembly on the electrodes.

Energy-Efficient Single-Stage Nitrite Shunt Denitrification with Saline Sewage through Concise Dissolved Oxygen (DO) Supply: Process Performance and Microbial Communities.

Single-stage nitrite shunt denitrification (through nitrite rather than nitrate) with low dissolved oxygen (DO) supply is a better alternative in terms of energy-efficiency, short-footprint, and low C/N-ratio requirement. This study investigates the optimal DO level with temperature effect, with saline sewage at the fixed hydraulic and solids retention times of 8 h and 8 d, respectively. Moreover, 16S rRNA gene sequencing analysis corresponding with total nitrogen (TN) and chemical oxygen demand (COD) removals in each operating condition were performed. Results showed that DO of 0.3 mg/L at 20 °C achieved over 60.7% and over 97.9% of TN and COD removal, respectively, suggesting that such condition achieved effective nitrite-oxidizing bacteria inhibition and efficient denitrification. An unexpected finding was that sulfur-reducing Haematobacter and nitrogen-fixing Geofilum and Shinella were highly abundant with the copredominance of ammonia-oxidizing Comamonas and Nitrosomonas, nitrite-oxidizing Limnohabitans, and denitrifying Simplicispira, Castellaniella, and Nitratireductor. Further, canonical correspondence analysis (CCA) with respect to the operating conditions associated with phenotype prediction via R-based tool Tax4Fun was performed for a preliminary diagnosis of microbial functionality. The effects of DO, temperature, nitrite, and nitrate in various extents toward each predominant microbe were discussed. Collectively, DO is likely pivotal in single-stage nitrite shunt denitrification, as well as microbial communities, for energy-efficient saline sewage treatment.

Increasing ammonia recovery from high-level ammonium wastewater via adding sodium sulfate to prevent nitrogen generation in the cathode.

The high-level ammonium-nitrogen (NH4+-N) is a contaminant for aqueous environment but a potential hydrogen fuel. This study investigated an approach of increasing ammonia recovery via adding sodium sulfate of 0-1.5 M to prevent from nitrogen generation. The results of experiment tests, electrochemical analysis and MD simulation demonstrated that the added Na2SO4 assisted ammonium transport inhibited nitrogen gas generation in a certain concentration range. In electric double layer (EDL), with Na2SO4 concentration increasing, both the migration velocities of NH4+ and Na+ are accelerated for Na2SO4 of 0-0.25 M, whereas they are decelerated for concentrate Na2SO4 that 0.5 M). A thick layer formed by Na+ that imposed a fierce competitive adsorption blocked the migration of NH4+ and the transportation of electrons. The decrease of electrons and the accumulation of water molecules caused the potential drop in the EDL. 0.25 M Na2SO4 was the optimal concentration from the aspect of ion transports. The results obtained in this study can allow the manipulation of EDI capacity optimization.

Dark fermentation production of volatile fatty acids from glucose with biochar amended biological consortium.

Effects of adding biochars on dark fermentation production of volatile fatty acids (VFAs) from glucose were investigated. Nine biochars were synthesized and applied, together with an activated carbon, as the testing amendment to enhance preferable fermentation. Biochars were porous materials with internal pores and excess surface functional groups, which would lead to enrichment of acetate over butyrate in the VFA production. Biochar coconut and biochar longan shell showed excess functional groups and high bulk internal crystallinity, presented 109.6% and 71.8% enrichments of acetate production, respectively. The syntrophic growth of fermentative bacteria and homoacetogens on biochar surfaces via direct interspecies electron transfer mechanism was assumed to interpret the noted enhanced acetate production. The excess functional groups on biochar surface to facilitate biofilm development and the high crystallinity of biochar bulk to ease electron transfer favored the production of acetate.

A Standardized Stoichiometric Life-Cycle Inventory for Enhanced Specificity in Environmental Assessment of Sewage Treatment.

In recent years, many life-cycle assessments (LCAs) have been applied to the field of sewage treatment (ST). However, most LCAs lack systematic data collection (DC) and processing methods for inventories of conventional ST (CST), much less for recently developed technologies. In addition, the use of site-generic databases results in LCAs that lack the representativeness and understanding of the regional environmental impacts and trade-offs between different impact categories, especially nutrient enrichment and toxicity-related categories. These shortcomings make comparative evaluation and implementation more challenging. In order to assist in the decision-making process, a novel stoichiometric life-cycle inventory (S-LCI) for ST was developed. In the S-LCI, biochemical pathways derived from elemental analyses combined with process-engineering calculations enable steady-state comparison of the water, air, and soil emissions of any sewage and sludge sample treated through the ST configurations analyzed herein. The DC required for the estimation of the foreground data for a CST is summarized in a 41-item checklist. Moreover, the S-LCI was validated for CST by comparing the S-LCI with actual ST plant operations performed in Hong Kong. A novel energy-derived ST inventory is developed and compared here with the CST. The resulting inventories are ready to be integrated into the SimaPro software for life cycle impact assessment as illustrated by the case study. Using the S-LCI not only helps to standardize the DC and processing, but it also enhances the level of specificity by using sample characterization and site-specific data. The EcoInvent database, which contains a single sample characterization per Swiss and global average ST plant class could be expanded by using the S-LCI.

Multi-agent simulation regulated by microbe-oriented thermodynamics and kinetics equations for exploiting interspecies dynamics and evolution between methanogenesis, sulfidogenesis, hydrogenesis and exoelectrogenesis.

Multi-agent simulation (MAS) regulated by microbe-oriented thermodynamics and kinetics equations were performed for exploiting the interspecies dynamics and evolution in anaerobic respiration and bioelectrochemical systems. A newly-defined kinetically thermodynamic parameter is recognized microbes as agents in various conditions, including electron donors and acceptors, temperature, pH, etc. For verification of the MAS, the treatment of synthetic wastewater containing glucose and acetate was evaluated in four 25°C laboratory-scale reactors with different electron acceptors and cathode materials that had potential for methanogenesis, hydrogenesis, sulfidogenesis and exoelectrogenesis. Within 1000 h operation, the reactors performance and microbial structures using 16S rRNA sequencing matched with the MAS, suggesting acetoclastic exoelectrogenesis predominance (Geobacter). After 2400 h, MAS observed the co-existence of acetoclastic methanogenesis and acetoclastic and propionate exoelectrogenesis, as was reported previously. Such microbial evolution from the short-term to long-term operation likely resulted from the glucose-driven propionate. The MAS developed is applicable in a wide range of complex engineering and natural ecosystems.

A review on the bioenergetics of anaerobic microbial metabolism close to the thermodynamic limits and its implications for digestion applications.

The exploration of the energetics of anaerobic digestion systems can reveal how microorganisms cooperate efficiently for cell growth and methane production, especially under low-substrate conditions. The establishment of a thermodynamically interdependent partnership, called anaerobic syntrophy, allows unfavorable reactions to proceed. Interspecies electron transfer and the concentrations of electron carriers are crucial for maintaining this mutualistic activity. This critical review summarizes the functional microorganisms and syntroph partners, particularly in the metabolic pathways and energy conservation of syntrophs. The kinetics and thermodynamics of propionate degradation to methane, reversibility of the acetate oxidation process, and estimation of microbial growth are summarized. The various routes of interspecies electron transfer, reverse electron transfer, and Poly-ß-hydroxyalkanoate formation in the syntrophic community are also reviewed. Finally, promising and critical directions of future research are proposed. Fundamental insight in the activities and interactions involved in AD systems could serve as a guidance for engineered systems optimization and upgrade.