Chemical Engineering Journal

Industrial applications of microbial electrochemical systems will require regular maintenance shutdowns, involving inspections and component replacements to extend the lifespan of the system. Here, we examined the impact of such shutdowns on the performance of three electrode materials (i.e., platinized titanium, graphite, and nickel) as cathodes in a microbial electrochemical system that would be used for electromethanogenesis in power-to-gas applications. We focused on methane (CH4) production from hydrogen (H2) and carbon dioxide (CO2) using Methanothermobacter thermautotrophicus. We showed that the platinized titanium cathode resulted in high volumetric CH4 production rates and Coulombic efficiencies. Using a graphite cathode would be more cost-effective than using the platinized titanium cathode in microbial electrochemical systems but showed an inferior performance. The microbial electrochemical system with the nickel cathode showed improvements compared to the graphite cathode. Additionally, this system with a nickel cathode demonstrated the fastest recovery during a shutdown experiment compared to the other two cathodes. Fluctuations in pH and nickel concentrations in the catholyte during power interruptions affected CH4 production recovery in the system with the nickel cathode. This research enhances understanding of the integration of biological and electrochemical processes in microbial electrochemical systems, providing insights into electrode selection and operating strategies for effective and sustainable CH4 production.

A black precipitate produced by a sulfate reducing bacterium Cupidesulfovibrio sp. strain HK was investigated with multidisciplinary methods. X-ray diffraction (XRD) analysis revealed that the black precipitate was mackinawite. Cyclic voltammetry analysis showed the obvious redox peaks, and the biogenic mackinawite exhibited rechargeable properties. XRD analyses showed that the form of the rechargeable biogenic mackinawite (RBM-II) was changed by discharge and recharge treatments: Field-emission transmission electron microscope analyses revealed that lepidocrocite and amorphous iron oxide were appeared from mackinawite on discharged condition, and the three kinds of minerals were intermingled via the rechargeable treatments. Physicochemical parameters were changed regularly under the treatments, suggesting that discharge would be occurred by iron oxidation and sulfur reduction, and vice versa. These results indicated that dynamics of sulfur is important key process in rechargeable mechanism, supporting that a part of mackinawite was transformed to lepidocrocite and iron oxides, and vice versa. Microbial fuel cells (MFCs) equipped with lactate, strain HK-II and anode including RBM-II consumed lactate even under opened circuit conditions, after which MFCs generated higher current density at re-closed circuit conditions. These results demonstrated that the biogenic mackinawite is one of rechargeable materials and would play important roles in geomicrobiological reactions and biotechnology.

Genus Acidithiobacillus includes a group of Gram-negative Fe/S-oxidizing acidophilic chemolithotrophic bacteria that are extensively studied and used for biomining processes. Synthetic biology approaches are key means to study and improve their biomining performance. However, efficient genetic manipulations in Acidithiobacillus are still major bottlenecks. In this study, we report a simple and efficient pAFi system (CRISPR-dCas9) and a scarless pAF system (CRISPR-Cas9) for genetic manipulations in A. ferridurans JAGS. The pAFi system harboring both dCas9 and sgRNA was constructed based on pBBR1MCS-2 to knockdown HdrA and TusA genes, separately, of which the transcription levels were significantly downregulated by 48% and 93%, separately. The pAF system carrying pCas9-sgRNA-homology arms was constructed based on pJRD215 to delete HdrB3 gene and overexpress Rus gene. Our results demonstrated that the pAF system is a fast and efficient genome editing method with an average rate of 15-20% per transconjugant in one recombination event, compared to 10-3 and then 10-2 in two recombination events by traditional markerless engineering strategy. Moreover, with these two systems, we successfully regulated iron and sulfur metabolisms in A. ferridurans JAGS: the deletion of HdrB3 reduced 48% of sulfate production, and substitution overexpression of Rus promoter showed 8.82-fold of mRNA level and enhanced iron oxidation rate. With these high-efficient genetic tools for A. ferridurans, we will be able to study gene functions and create useful recombinants for biomining applications. Moreover, these systems could be extended to other Acidithiobacillus strains and promote the development of synthetic biology-assisted biomining. HighlightsO_LITwo shuttle vectors were constructed for Acidithiobacillus ferridurans C_LIO_LIAll-in-one pAFi (CRISPR-dCas9) and pAF (CRISPR-Cas9) systems were built up for gene knockdown and genome editing, separately C_LIO_LIThe transcription levels of HdrA and TusA were reduced 48% and 93% using pAFi system and thus suppressed sulfur oxidation C_LIO_LIHdrB3 deletion and Rus overexpression were achieved using pAF system and showed significant effects on sulfur and iron oxidation respectively C_LIO_LIOur pAF system facilitated genome editing in Acidithiobacillus ferridurans with high efficiency (15-20%) in less than 4 weeks C_LI

Previous bioreactor studies achieved high volumetric n-caprylate (i.e., n-octanoate) production rates and selectivities from ethanol and acetate with chain-elongating microbiomes. However, the metabolic pathways from the substrates to n-caprylate synthesis were unclear. We operated two n-caprylate-producing upflow bioreactors with a synthetic medium to study the underlying metabolic pathways. The operating period exceeded 2.5 years, with a peak volumetric n-caprylate production rate of 190 {+/-} 8.4 mmol C L-1 d-1 (0.14 g L-1 h-1). We identified oxygen availability as a critical performance parameter, facilitating intermediate metabolite production from ethanol. Bottle experiments in the presence and absence of oxygen with 13C-labeled ethanol suggest acetyl-coenzyme A-based derived production of n-butyrate (i.e., n-butanoate), n-caproate (i.e., n-hexanoate), and n-caprylate. Here, we postulate a trophic hierarchy within the bioreactor microbiomes based on metagenomics, metaproteomics, and metabolomics data, as well as experiments with a Clostridium kluyveri isolate. First, the aerobic bacterium Pseudoclavibacter caeni and the facultative anaerobic fungus Cyberlindnera jadinii converted part of the ethanol pool into the intermediate metabolites succinate, lactate, and pyroglutamate. Second, the strict anaerobic C. kluyveri elongated acetate with the residual ethanol to n-butyrate. Third, Caproicibacter fermentans and Oscillibacter valericigenes elongated n-butyrate with the intermediate metabolites to n-caproate and then to n-caprylate. Among the carbon chain-elongating pathways of carboxylates, the tricarboxylic acid cycle and the reverse {beta}-oxidation pathways showed a positive correlation with n-caprylate production. The results of this study inspire the realization of a chain-elongating production platform with separately controlled aerobic and anaerobic stages to produce n-caprylate renewably as an attractive chemical from ethanol and acetate as substrates. Broader contextNext to renewable electric energy, carbon-based chemicals have to be produced sustainably and independently from fossil sources. To meet this goal, we must expand the portfolio of bio-based conversion technologies on an industrial scale to cover as many target chemicals as possible. We explore the bioprocess of chain elongation to provide medium-chain carboxylates that can function as future platform chemicals in the circular economy. The most valuable medium-chain carboxylate produced with chain elongation is n-caprylate (i.e., n-octanoate). This molecule with eight carbon atoms in a row (C8) is challenging to produce renewably for the chemical industry. Previous reports elucidated that elevated ethanol-to-acetate ratios, which are found in syngas-fermentation effluent, stimulated n-caprylate production. Until now, studies have suggested that chain elongation from high concentrations of ethanol and acetate is a fully anaerobic process. We refine this view by showing a trophic hierarchy of aerobic and anaerobic microbes capable of facilitating this process. Appropriate oxygen supplementation enables the synthesis of succinate, lactate, and pyroglutamate that permit high-rate chain elongation to n-caprylate under anaerobic conditions. Given these results, future research should focus on the segregated study of aerobic and anaerobic microbes to further enhance the process performance to produce n-caprylate renewably at an industrial scale.

Improving microbial electrosynthesis could be one solution for transitioning towards sustainable chemical production, offering a pathway to convert CO2 into valuable commodities from renewable energy sources. Therefore, we examined the performance differences between liquid- and vapor-fed anode zero-gap bioelectrochemical cells for electromethanogenesis, utilizing a membrane electrode assembly to enhance mass and ohmic transport. Focusing on CH4 and H2 production, we compared two ion-exchange membranes with the liquid-fed anode system and selected the best performing ion-exchange membrane for the vapor-fed anode system. Liquid-fed anode systems did not show significant differences in volumetric CH production rates compared to vapor-fed anode systems, although the latter demonstrated advantages in reducing electrocatalyst degradation and maintaining stable cell voltages. The research underscores the need for further optimization to address performance losses and suggests potential for industrial applications of microbial electrosynthesis, highlighting the importance of catalyst protection.

High cathodic overpotential of the oxygen reduction reaction (ORR) in MFC carbon-based cathodes is one of the key barriers to the widespread adoption of the technology. Current Pt-based ORR catalysts are expensive. The use of novel and inexpensive catalysts as replacements for platinum is therefore desirable. In this study, nanomaterials were directly chemically synthesized on carbon microfiber electrodes to improve the performance of lake sediment inoculated MFCs. Nanomaterial of MnO2, MnO2/polyaniline (PANI), ZnO/NiO and ZnO/NiO/PANI attachments were directly chemically synthesized on the carbon material and used as cathode electrodes. The maximum power densities recorded for the different treatments were; MnO2 78.5 mW/m2, MnO2/PANI (Polyaniline) 141.6 mW/m2, ZnO/NiO 67.6 mW/m2, and ZnO/NiO/PANI 129.4 mW/m2. The current and poswer densities were more than six-fold higher in ZnO/NiO/PANI and MnO2/PANI nanoparticle modified cathodes compared to the control MFCs with no catalyst. Cyclic voltammetry (CV) and FTIR data and SEM images suggest that the nanoparticle attached carbon material is morphologically, chemically and electrochemically different from the controls with no nanomaterial attachment. The outcome of this study demonstrates that nanomaterials-incorporated carbon microfiber cathodes bring about significant enhancements to power densities and may potentially have applications in cost-effective MFCs.

his study investigates the performance of two Continuous Stirred Tank Reactors (CSTRs) with a focus on biogas yield, physicochemical parameters, and microbial dynamics. By integrating experimental observations with insights from recent literature, the research aims to elucidate the intricate relationships between reactor conditions, microbiome composition, and biogas production efficiency. Two substrates were used: a control substrate (SB1) and a protein-rich test substrate (SB2). The study monitored key parameters such as pH, Total Alkalinity of Carbonates (TAC), and volatile fatty acids (FOS), and analyzed the microbial communities using high-throughput sequencing. Results indicated significant temporal variations in pH, TAC, and nitrogen levels, with a declining FOS/TAC ratio. The introduction of SB2 led to increased biogas production and methane content, particularly at higher Hydraulic Retention Times (HRT). The study also high-lighted the role of specific microbial taxa in enhancing biogas quality. These findings contribute to the development of optimized strategies for sustainable biogas production and process control.

We demonstrate a single chamber, 96-well plate based Microbial Fuel Cell (MFC). This invention is aimed at robust selection of electrogenic microbial community under specific conditions, (pH, external resistance, inoculum) that can be altered within the 96 well plate array. Using this device, we selected and multiplicated electrogenic microbial communities fed with acetate and lactate that can operate under different pH and produce current densities up to 19.4 A/m3 (0.6 A/m2) within 5 days past inoculation. Moreover, studies shown that Cu mobilization through PCB bioleaching occurred, thus each community was able to withstand presence of Cu2+ ions up to 600 mg/L. Metagenome analysis reveals high abundance of Dietzia spp., previously characterized in MFCs, but not reported to grow at pH 4, as well as novel species, closely related to Actinotalea ferrariae, not yet associated with electrogenicity. Microscopic observations (combined SEM and EDS) reveal that some of the species present in the anodic biofilm were adsorbing copper on their surface, probably due to the presence of metalloprotein complexes on their outer membranes. Taxonomy analysis indicated that similar consortia populate anodes, cathodes and OCP controls, although total abundances of aforementioned species are different among those groups. Annotated metagenomes showed high presence of multicopper oxidases and Cu-resistance genes, as well as genes encoding aliphatic and aromatic hydrocarbon-degrading enzymes. Comparison between annotated and binned metagenomes from pH 4 and 7 anodes, as well as their OCP controls revealed unique genes present in all of them, with majority of unique genes present in pH 7 anode, where novel Actinotalea spp. was present.

Microbial electrosynthesis is an emerging biosynthesis technology that produces value-added chemicals and fuels and, at the same time, reduces the environmental carbon footprint. However, constraints, such as low current densities and high inner resistance, disfavor this technology for industrial-scale purposes. The cathode performance has been strongly improved in recent years, while the anode performance has not been given enough attention despite its importance in closing the electric circuit. For traditional water electrolysis, O2 is produced at the anode, which is toxic to the anaerobic autotrophs that engage in microbial electrosynthesis. To overcome O2 toxicity in conventional microbial electrosynthesis, the anode and the cathode chamber have been separated by an ion-exchange membrane to avoid contact between the microbes and O2. However, ion-exchange membranes increase the maintenance costs and compromise the production efficiency by introducing an additional internal resistance. Furthermore, O2 is inevitably transferred to the catholyte due to diffusion and electro-osmotic fluxes that occur within the membrane. Here, we proved the concept of integrating carbon oxidation with sacrificial anodes and microbes to simultaneously inhibit the O2 evolution reaction (OER) and circumvent membrane application, which allows microbial electrosynthesis to proceed in a single chamber. The carbon-based anodes performed carbon oxidation as the alternative reaction to the OER. This enables microbial electrosynthesis to be performed with cell voltages as low as 1.8-2.1 V at 10 A{middle dot}m-2. We utilized Methanothermobacter thermautotrophicus {Delta}H in a single-chamber Bioelectrochemical system (BES) with the best performing carbon-based anode (i.e., activated-carbon anode with soluble iron) to achieve a maximum cathode-geometric CH4 production rate of 27.3 L{middle dot}m-2{middle dot}d-1, which is equal to a volumetric methane production rate of 0.11 L{middle dot}L-1{middle dot}d-1 in our BES, at a coulombic efficiency of 99.4%. In this study, Methanothermobacter thermautotrophicus {Delta}H was majorly limited by sulfur that inhibited electromethanogenesis. However, this proof-of-concept study allows microbial electrosynthesis to be performed more energy-efficiently and can be immediately utilized for research purposes in microbial electrosynthesis.

This study evaluates the performance of carbon monoxide dehydrogenase (codh) embedded strains in bench-scale microbial electrochemical systems (MES) for CO2 reduction to biofuels and biochemicals. CO2 fermentation efficiency was evaluated by comparing the wild-type Clostridium acetobutylicum (Wild), a negative control E. coli strain lacking the codh gene (NC-BL21), and engineered E. coli strain (Eng) alone and with IPTG induction (Eng+IPTG). Four electrochemical systems were used viz. Wild+E, NC-BL21+E, Eng+E, and Eng+IPTG+E, with a poised potential of 0.6 V applied to the working electrode. CO2 and bicarbonate were supplemented to a total inorganic carbon (IC) concentration of 40 g/L, with a retention time of 60 h. The engineered strains demonstrated enhanced metabolic performance compared to the wild-type and negative control strains, yielding a maximum formic acid concentration of 2.1 g/L and acetic acid concentration of 7.8 g/L under the Eng+IPTG condition. Ethanol yield was highest at 3.9 g/L under the Eng+IPTG+E condition, substantially exceeding the 2.4 g/L acetic acid yield observed in the wild-type strain. The engineered strains showed superior cumulative yields (0.4075 g/g), improved codh charge flux stability (60 vs. 5 for Wild), and upregulated expression of genes in the Wood-Ljungdahl pathway. Bioelectrochemical performance analysis demonstrated elevated reductive catalytic currents, enhanced CO2 reduction, and optimal charge transfer kinetics. This study highlights the effectiveness of genetic and process engineering, particularly codh overexpression and IPTG induction, in optimizing microbial electrosynthesis for biofuel and biochemical production from C1 gases.

Consolidated bioprocessing (CBP) of lignocellulosic biomass using cellulolytic microorganisms presents a promising sustainable and economical biomanufacturing platform where enzyme production, biomass hydrolysis, and fermentation to produce biofuels, biochemicals, and biomaterials occur in a single step. However, understanding and redirecting metabolism of microorganisms to be compatible with CBP to produce non-native metabolites are limited. In this study, we metabolically engineered a cellulolytic thermophile Clostridium thermocellum and demonstrated its compatibility with CBP integrated with a mild Co-solvent Enhanced Lignocellulosic Fractionation (CELF) pretreatment for conversion of hardwood poplar into short-chain esters (i.e., ethyl acetate, ethyl isobutyrate, isobutyl acetate, isobutyl isobutyrate) with broad use as solvents, flavors, fragrances, and biofuels. A recombinant C. thermocellum engineered with deletion of carbohydrate esterases and stable overexpression of a thermostable alcohol acetyltransferase improved the target esters production without compromised deacetylation activities. We discovered these esterases exhibited promiscuous thioesterase activities and their deletion improved ester production by increasing isobutanol flux and rerouting the native electron and carbon fermentative metabolism besides their known major function of ester degradation. The total ester production could be further enhanced up to 80-fold and the composition of short-chain esters could be modified by deleting lactate biosynthesis and/or CELF-pretreated poplar under different pretreatment conditions.

The enhanced biological phosphorus removal (EBPR) has been widely applied in treating domestic wastewater, while the performance on high-strength P wastewater is less investigated and the feasibility of coupling with short-cut nitrogen removal process remains unknown. This study first achieved the simultaneous high-efficient P removal and stable nitrite accumulation in one sequencing batch reactor for treating the synthetic digested manure wastewater. The average effluent P could be down to 0.8 {+/-} 1.0 mg P/L and the P removal efficiency was 99.5 {+/-} 0.8%. Candidatus Accumulibacter was the dominant polyphosphate accumulating organism (PAO) with the relative abundance of 14.2-33.1% in the reactor. Examination of the micro-diversity of Candidatus Accumulibacter using 16s rRNA gene-based oligotyping analysis revealed one unique Accumulibacter oligotype that different from the conventional system, which accounted for 64.2-87.9% of the total Accumulibacter abundance. The presence of high-abundant glycogen accumulating organisms (GAO) (15.6-40.3%, Defluviicoccus and Candidatus Competibacter) did not deteriorate the EBPR performance. Moreover, nitrite accumulation happened in the system with the effluent nitrite up to 20.4 {+/-} 6.4 mg N/L and the nitrite accumulation ratio was nearly 100% maintained for 140 days (420 cycles). Nitrosomonas was the dominant ammonia-oxidizing bacteria with relative abundance of 0.3-2.4% while nitrite-oxidizing bacteria were almost undetected (<0.1%). The introduction of extended anaerobic phase and high volatile fatty acid concentrations were proposed to be the potential selector forces to promote partial nitrification. This is the first study that combined EBPR with nitrite-accumulation for digested manure wastewater treatment, and it provided new sights in strategies to combine the EBPR and short-cut nitrogen removal via nitrite to achieve simultaneous nitrogen and phosphorus removal.

Electromethanogenesis refers to the process where methanogens utilize electrons derived from cathodes for the reduction of CO2 to CH4. Setting of low cathode potentials is essential for this process. In this study, we test if magnetite, an iron oxide mineral widespread in environment, can facilitate the adaption of methanogen community to the elevation of cathode potentials in electrochemical reactors. Two-chamber electrochemical reactors were constructed with inoculants obtained from a paddy field soil. We elevated cathode potentials stepwise from the initial -0.6 V vs standard hydrogen electrode (SHE) to -0.5 V and then to -0.4 V over the 120 days acclimation. Only weak current consumption and CH4 production were observed in the reactors without magnetite. But biocathodes were firmly developed and significant current consumption and CH4 production were recorded in the magnetite reactors. The robustness of electro-activity in the magnetite reactors was not affected with the elevation of cathode potentials from -0.6 V to -0.4 V. But, the current consumption and CH4 production were virtually halted in the reactors without magnetite when cathode potential was elevated to -0.4 V. Methanogens related to Methanospirillum were enriched on cathode surface of the magnetite reactors at -0.4 V, while Methanosarcina relatively dominated in the reactors without magnetite. Methanobacterium also increased in the magnetite reactors but stayed off electrodes in the culture medium at -0.4 V. Apparently, magnetite greatly facilitates the development of biocathodes, and it appears that with the aid of magnetite Methanospirillum spp. can adapt to high cathode potentials performing the efficient electromethanogenesis. IMPORTANCEConverting CO2 to CH4 through bioelectrochemistry is a promising approach for development of green energy biotechnology. This process however requires setting the low cathode potentials, which takes cost. In this study, we test if magnetite, a conductive iron mineral, can facilitate the adaption of methanogens to the elevation of cathode potentials. In the two-chamber reactors constructed using inoculants obtained from a paddy field soil, biocathodes were firmly developed in the presence of magnetite, whereas only weak electro-activity was observed in the reactors without magnetite. The elevation of cathode potentials did not affect the robustness of electro-activity in the magnetite reactors over the 120 days acclimation. Methanospirillum was identified as the key methanogens associated with cathode surface during the operation at relatively high potentials. The findings reported in this study shed a new light on the adaption of methanogen community to the elevated cathode potentials in the presence of magnetite.

Cell growth is a crucial biological property of cells, which plays key roles in several major biological processes including organ development, tissue repair and cancer development. It is of both scientific and medical significance to discover new strategies to modulate cell growth. Koisio technology is a novel technology that modulates the properties of water solely by physical approaches without additions of any external substances. In our current study we obtained the following findings regarding the effects of Koisio technology-modulated solutions on cell growth: First, compared with the lung fibroblast (L929) cell cultures cultured in normal media, the L929 cells cultured in Koisio technology-modulated media grew at approximately 20% higher speed; second, compared with the lung cancer cell cultures (LLC cells) cultured in normal media, the LLC cells cultured in Koisio technology-modulated media grew at approximately 9% lower speed; and third, compared with the telomere lengths of the L929 cells cultured in normal media, the L929 cells cultured in Koisio technology-modulated media had approximately 14% longer telomere length. Collectively, our study has provided the first evidence indicating that Koisio technology-modulated solutions affect differentially the growth of lung fibroblast cell cultures and that of lung cancer cell cultures. The capacity of the Koisio technology-modulated solutions to promote the growth of lung fibroblast cell cultures may result at least partially from its capacity to protect the telomere length.

3,4-Dihydroxybenzoate (protocatechuate, PCA) is a phenolic compound naturally found in edible vegetables and medicinal herbs. PCA is of interest in the chemical industry as a building block for novel polymers and has wide potential for pharmaceutical applications due to its antioxidant, anti-inflammatory, and antiviral properties. In the present study, we designed and constructed a novel Corynebacterium glutamicum strain to enable the efficient utilization of O_SCPLOWDC_SCPLOW-xylose for microbial production of PCA. The engineered strain showed a maximum PCA titer of 62.1 {+/-} 12.1 mM (9.6 {+/-} 1.9 g L-1) from O_SCPLOWDC_SCPLOW-xylose as the primary carbon and energy source. The corresponding yield was [Formula], which corresponds to 38 % of the maximum theoretical yield and is 14-fold higher compared to the parental producer strain on O_SCPLOWDC_SCPLOW-glucose. By establishing a one-pot bioreactor cultivation process followed by subsequent process optimization, the same maximum titer and a total amount of 16.5 {+/-} 1.1 g was reached. Downstream processing of PCA from this fermentation broth was realized via electrochemically induced crystallization by taking advantage of the pH-dependent properties of PCA. Since PCA turned out to be electrochemically unstable in combination with several anode materials, a threechamber electrolysis setup was established to crystallize PCA and to avoid direct anode contact. This resulted in a maximum final purity of 95.4 %. In summary, the established PCA production process represents a highly sustainable approach, which will serve as a blueprint for the bio-based production of other hydroxybenzoic acids from alternative sugar feedstocks.

Bakery waste is a promising feedstock for the circular economy; however, its use for producing medium-chain carboxylates (MCCs) via microbial chain elongation remains unexplored. This study investigated pretreatment, pertraction, and chain elongation strategies to convert bakery waste into n-caproate and n-caprylate. Bakery waste was mechanically and enzymatically processed, and different inocula were tested to optimize the conversion of the resulting glucose-rich solution into lactate and ethanol (intermediates). These intermediates were fed into continuous chain elongation systems, which operated for over 386 days at 37{degrees}C and pH 5.5. Results showed that 30-35% of bakery waste carbon was converted into n-caproate and 10-15% into n-caprylate. Enzymatic starch hydrolysis proved essential, and lactate was a superior intermediate for chain elongation compared to ethanol. A maximum volumetric MCC production rate of 131 mM C L-1 d-1 (0.1 g L-1 h-1) was achieved. This integrated approach, named "bakeraote," demonstrates an efficient pathway for valorizing bakery waste.

Sargassum spp. floods the Caribbean coastlines, causing damage to the local economy and environment. These macroalgae have a low methane yield that makes the anaerobic digestion (AD) process unviable, so low-cost pretreatments are required. This research investigated the efficiency of energy-saving pretreatments, such as water washing, that had not been evaluated for these species. The microbial communities involved in AD of the best and worst-performing systems were also analyzed by high-throughput sequencing. The results showed that water washing pretreatment modified the content of inorganic compounds, fibers, and C:N ratio and increased the methane yield by 38%. The bacterial phyla Bacteroidota, Firmicutes, and Thermotogota, as well as the archaea genera Methanosarcina, RumEn_M2, and Bathyarchaeia, dominated the microbial communities. This study is the first to show the microbial community structure involved in the AD of Sargassum spp. The pretreatments presented in this study may help overcome the previously reported limitations.

The plasic crisis is ominipresent, from littering macroplastic to reports that document plastic in every niche of this planet, including the human body. In order to achieve higher recycling quotas, especially of mixed plastic waste, pyrolysis seems to be a viable option. However, depending on the process parameters, plastic pyrolysis oil waste is encountered, which is difficult to valorize, due to the enormous spread of the molecules included. To reduce the molecular heterogeneity, we here artificially compounded, monitored, and optimized the performance of a bacterial consortium, which has the ability to tolerate organic pollutants and use them as energy and carbon sources for their own metabolic activity. The primary constituents of the here used plastic pyrolysis oil waste (PPOW) were alkanes and {varepsilon}-caprolactam. The bacterial community exhibited noteworthy efficacy in eliminating alkanes of diverse chain lengths ranging from 71% to 100%. Additionally, within 7-days, the microbial community demonstrated a removal efficiency surpassing 50% for various aromatic hydrocarbons, along with complete eradication of {varepsilon}-caprolactam and naphthalene. Besides, a back-propagation (BP) neural network method is applied to evaluate O2 consumption as a measure of microbial activity. The insights gained were used to build a model, which is able to predict O2 depletion in long-time experiments and other experimental conditions. The results are discussed in the context of a developing (open) circular plastic economy. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=105 SRC="FIGDIR/small/590079v1_ufig1.gif" ALT="Figure 1"> View larger version (35K): org.highwire.dtl.DTLVardef@628f68org.highwire.dtl.DTLVardef@b5274eorg.highwire.dtl.DTLVardef@1278ceaorg.highwire.dtl.DTLVardef@194887a_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightO_LISynthetic bacterial communities are used to remove plastic hydrolysis oil waste C_LIO_LIThe optimized biphase reaction system can remove the majority of pollutants C_LIO_LIThe biodegradation process can be monitored in a real-time bioprocess software C_LIO_LINeural network techniques are used to model and predict the removal process C_LI

Aerobic denitrifying bacteria have the potential for engineering applications due to the efficient nitrate removal capacity from wastewater. In this study, a novel aerobic denitrifying strain was isolated and identified as Achromobacter xylosoxidans GR7397 from the activated sludge of a wastewater treatment plant, which possessed efficient nitrate removal capacity. Moreover, the denitrification capacity and properties of the strain were investigated in the presence of nitrate as the only nitrogen source. Five denitrification reductases encoding genes were harbored by strain GR7397 determined by electrophoretic analysis of PCR amplification products, consisting of periplasmic nitrate reductase (NAP), nitrate reductase (NAR), nitrite reductase (NIR), nitrous oxide reductase (NOS), and nitric oxide reductase (NOR), demonstrating that the strain has a complete denitrification metabolic pathway. The optimum denitrifying condition of strain GR7397 included sodium acetate adopted as the electron donor, COD/TN ratio at 4, pH at 8, temperature at 30{degrees}C, under which condition, the nitrate removal rate reached 14.86 mg {middle dot} L-1 {middle dot} h-1 that the [Formula] concentration decreased from 93.90 mg/L to 4.73 mg/L within 6 h with no accumulation of nitrite. In addition, the bioaugmentation performance of strain GR7397 to enhance nitrate removal was evaluated to be effective and stabilized in a sequential batch reactor (SBR). The removal rate of [Formula] was the highest during each cycle with a range of 15.48-28.56 mg{middle dot}L-1{middle dot}h-1 in the SBR with inoculating 30% of the strain concentrate. The current research demonstrated that strain GR7397 has significant potential for application in enhancing nitrogen removal in wastewater treatment.

Plastics like polyethylene terephthalate (PET) have become an integral part of everyday life, yet plastic waste management remains a significant challenge. Enzymatic biocatalysis is an eco- friendly approach for recycling and upcycling of plastic waste. PET-hydrolyzing enzymes (PHEs) such as IsPETase, along with its engineered variants like FAST-PETase, demonstrate promising PET depolymerization capabilities at ambient temperatures. Whole-cell biocatalysts, displaying PHEs on their cell surface, offer high efficiency, reusability, and stability for PET depolymerization. However, their efficacy in fully breaking down PET is hindered by the necessity of two enzymes - PETase and MHETase. Current whole-cell systems either display only one PHE or struggle with performance when displaying larger passenger proteins like the MHETase-PETase chimera. In this work, we developed a Saccharomyces cerevisiae-based whole-cell biocatalyst system for complete PET depolymerization. Leveraging a cellulosome-inspired trifunctional protein scaffoldin displayed on the yeast surface, we immobilized FAST-PETase and MHETase, forming a multi-enzyme cluster. Our whole cell biocatalyst achieved complete PET depolymerization at 30{degrees}C, yielding 4.9 mM TPA in seven days with no intermediate accumulation. Furthermore, we showed improved PET depolymerization ability by binding FAST-PETase at multiple sites on the trifunctional scaffoldin. This breakthrough in complete PET depolymerization marks an essential step towards a circular plastic economy.