CO2 conversion to CH4 using Zero Valent Iron (ZVI) and anaerobic granular sludge: Optimum batch conditions and microbial pathways

Chemical and biological effects of zero-valent iron (ZVI) concentration on in-situ production of H2 from ZVI and bioconversion of CO2 into CH4 under anaerobic conditions

The conversion of carbon dioxide (CO2) to methane (CH4) is a strategy for sequestering CO2. Zero-valent iron (ZVI) has been proposed as an alternative electron donor for the CO2 reduction to CH4. In this study, the effects of ZVI concentrations on the abiotic production of H2 (without the action of microorganisms) in the first part and on the biological conversion of CO2 to CH4 using ZVI as a direct electron donor in the second part were examined. In the abiotic H2 production, the increase in the ZVI concentration from 16 to 32, 64, and 96 g/L was found to have positive effects on both the amounts of H2 generated and the rates of H2 production because the extent of ZVI oxidation positively correlates with increasing surface area. Nevertheless, the increase in ZVI concentration from 96 to 224 g/L did not benefit the H2 production because the ZVI dissolution was suppressed by the increasing aqueous pH above 10. In the bioconversion of CO2 to CH4 using ZVI as an electron donor, the main methanogenesis pathway occurred via hydrogenotrophic methanogenesis at pH 8.7-9.5 driven by the genus Methanobacterium of the class Methanobacteria. At ZVI concentrations of 64 g/L and above, the production of volatile fatty acid (VFA) became clear. Acetate was the main VFA, indicating the induction of homoacetogenesis at ZVI concentrations of 64 g/L and above. In addition, the presence of propionate as the second major VFA suggests the production of propionate from CO2 and acetate under conditions with high H2 partial pressure. The results indicated that the pathway for ZVI/CO2 conversion to CH4 was competitive between hydrogenotrophic methanogenesis and homoacetogenesis.

Treatment and recovery of phosphate from submerged anaerobic membrane bioreactor effluent using thermally treated biowaste and powder activated carbon

This study presents a novel treatment system using a submerged anaerobic membrane bioreactor (SAnMBR) followed by adsorption onto thermally treated biowaste, and ending with a final treatment using powdered activated carbon (PAC). Despite limited phosphate and ammonium ion removal during SAnMBR operation, thermally treated eggshell (EGSL) and seagrass (SG) received SAnMBR effluent and enhanced phosphate recovery, achieving removal rates of 71.8-99.9% and 60.5-78.0%, respectively. The SAnMBR achieved an 85% COD removal, which was slightly reduced further by biowaste treatment. However, significant further reductions in COD to 20.2 ± 5.2 mg/L for EGSL effluent and 57.0 ± 13.3 mg/L for SG effluent were achieved with PAC. Phytotoxicity tests showed the SAnMBR effluent after PAC treatment notably improved seed growth compared to untreated wastewater. In addition, volatile organic compounds (VOCs) were significantly reduced in the system, including common wastewater contaminants such as dimethyl disulfide, dimethyl trisulfide, phenol, p-cresol, nonanal, and decanal. Fractionation analysis of the solid fraction, post-adsorption from both synthetic and domestic wastewater, indicated that for SG, 77.3%-94% of the total phosphorus (TP) was inorganically bound, while for EGSL, it ranged from 94% to 95.3%. This study represents the first attempt at a proof-of-concept for simultaneous treatment of domestic wastewater and phosphorus recovery using this integrated system.

Construction of a mycelium sphere using a Fusarium strain isolate and Chlorella sp. for polyacrylamide biodegradation and inorganic carbon fixation

In the context of global demand for carbon reduction, the formation of inorganic carbon (IC) in the wastewater from oil flooding becomes a potential threat. In this study, Chlorella sp. and Fusarium sp. were used to assemble a fungal-algal pellet to degrade polyacrylamide (PAM) and fix IC in synthetic oil-flooding wastewater. The results showed that the combination of Chlorella sp. and Fusarium sp. was more effective at degrading PAM and removing carbon than a monoculture. With PAM as the sole nitrogen source, the degradation of PAM by the consortium was enhanced up to 35.17 ± 0.86% and 21.63 ± 2.23% compared with the monocultures of fungi or microalgae, respectively. The degradation of the consortium was significantly enhanced by the addition of an external nitrogen source by up to 27.17 ± 2.27% and 22.86 ± 2.4% compared with the monoculture of fungi or microalgae, respectively. This may depend on the effect of synergy between the two species. For the removal of IC from the water, the removal efficiency of the consortium was higher than that of the microalgae by 38.5 ± 0.08%, which may be attributed to the ability of the fungi to aid in the adsorption of nutrients and its assimilation by the microalgae. Therefore, the Fusarium-Chlorella consortium can effectively degrade PAM, while simultaneously fixing carbon, which provides a feasible scheme for the treatment and carbon neutralization of the wastewater that contains PAM.

Enhancing methane production from food waste with iron-carbon micro-electrolysis in a two-stage process

A two-stage process, consisting of a leach-bed reactor (LBR) and an up-flow anaerobic sludge blanket reactor (UASB), has been commonly adopted to improve food waste anaerobic digestion. However, its application is limited due to low hydrolysis and methanogenesis efficiencies. This study proposed a strategy of incorporating iron-carbon micro-electrolysis (ICME) into the UASB and recirculating its effluent to the LBR to improve the two-stage process efficiency. Results showed that the integration of the ICME with the UASB significantly increased the CH4 yield by 168.29%. The improvement of the food waste hydrolysis in the LBR mainly contributed to the enhanced CH4 yield (approximately 94.5%). The enrichment of hydrolytic-acidogenic bacterial activity, facilitated by the Fe2+ generated through ICME, might be the primary cause of the improved food waste hydrolysis. Moreover, ICME enriched the growth of hydrogenotrophic methanogens and stimulated the hydrogenotrophic methanogenesis pathway in the UASB, contributing partially to the enhanced CH4 yield.

Roles of zero-valent iron in anaerobic digestion: Mechanisms, advances and perspectives

With the rapid growth of population and urbanization, more and more bio-wastes have been produced. Considering organics contained in bio-wastes, to recover resource from bio-wastes is of great significance, which can not only achieve the resource recycle, but also protect the environment. Anaerobic digestion (AD) has been proved as one of the most promising strategies to recover bio-energy from bio-wastes, as well as to realize the reduction of bio-wastes. However, the conventional interspecies electron transfer is sensitive to environmental shocks, such as high ammonia, organic pollutants, metal ions, etc., which lead to instability or failure of AD. The recent findings have proved that the introduction of zero-valent iron (ZVI) in AD system can significantly enhance methane production from bio-wastes. This review systematically highlighted the recent advances on the roles of ZVI in AD, including underlying mechanisms of ZVI on AD, performance enhancement of AD contributed by ZVI, and impact factors of AD regulated by ZVI. Furthermore, current limitations and outlooks have been analyzed and concluded. The roles of ZVI on underlying mechanisms in AD include regulating reaction conditions, electron transfer mode and function of microbial communities. The addition of ZVI in AD can not only enhance bio-energy recovery and toxic contaminants removal from bio-wastes, but also have the potential to buffer adverse effect caused by inhibitors. Moreover, the electron transfer modes induced by ZVI include both interspecies hydrogen transfer and direct interspecies electron transfer pathways. How to comprehensively evaluate the effects of ZVI on AD and further improve the roles of ZVI in AD is urgently needed for practical application of ZVI in AD. This review aims to provide some references for the introduction of ZVI in AD for enhancing bio-energy recovery from bio-wastes.

Biogas upgrading to methane and removal of volatile organic compounds in a system of zero-valent iron and anaerobic granular sludge

The current study presented a novel process of biogas upgrading to biomethane (higher than 97%) based on anaerobic sludge and zero-valent iron (ZVI) system. When ZVI was added into an aquatic system with anaerobic granular sludge (AnGrSl) under anaerobic abiotic conditions, H₂ was generated. Then, the H₂ and CO₂ were converted by the hydrogenotrophic methanogens to CH₄. Biogas upgrading to biomethane was achieved in 4 days in the AnGrSl system (50 g L^-1 ZVI, initial pH 5 and 20 g L^-1 NaHCO₃). In this system, when zero-valent scrap iron (ZVSI) was added instead of ZVI, a more extended period (21 days) was required to achieve biogas upgrading. X-ray diffraction (XRD) analysis revealed that the materials in a reactor with CO₂ or biogas headspace, exhibited a mixture of ferrite and the iron carbonate phase of siderite (FeCO₃), with the latter being the dominant phase. VOCs analysis in raw biogas (in the system of anaerobic sludge and ZVI) highlighted the reduction of low mass straight- and branched-chain alkanes (C₆-C₁₀). Also, H₂S and NH₃ were found to be substantially reduced when the anaerobic sludge was exposed to ZVI compared to the cases where ZVI was not added. This study found that simultaneously with biogas upgrading, VOCs, H₂S and NH₃ can be removed in a system of ZVI or ZVSI and AnGrSl under aquatic anaerobic conditions.

Sustainability and carbon neutralization trends in microalgae bioenergy production from wastewater treatment: A review

Reducing CO2 emissions using biomass is gaining popularity as an environmentally friendly strategy. Due to high growth rates, low production costs, and ability to withstand harsh conditions, microalgae have become quite popular. Microalgae may also undertake photosynthesis, converting CO2 and solar energy into sugar before becoming biomass, making them an excellent source of renewable and promising biofuels. CO2 sequestration and biofixation was utilized to compare the synthesis of biodiesel as a third-generation biofuel from various types of wastewater was also used as a source for the algal cultivation. This review article focuses on recent developments, research discoveries in the field of microalgal CO2 capture modification and the optimization of conversion efficiency. This review is intended to serve as a helpful and reference for the use of wastewater treatment with microalgae to collect CO2. The overarching objective of this study is to assist wastewater treatment systems in achieving carbon neutrality.

Membrane disruption boosts iron overload and endogenous oxidative stress to inactivate Escherichia coli by nanoscale zero-valent iron

The inactivation of microorganisms by nanoscale zero-valent iron (nZVI) was extensively reported, but what happens inside the cells is rarely explored. Herein, we revealed that nZVI caused the drastic increase of intracellular iron concentrations, which subsequently catalyzed the Haber-Weiss reaction to produce high levels of endogenous reactive oxygen species (ROSs) and inactivated E. coli cells by oxidative damage of DNA, evidenced by the significantly higher inactivation efficiencies of E. coli mutant strains deficient in iron uptake regulation and DNA repair than the parental strain. The intracellular iron levels, endogenous ROSs levels and the inactivation efficiencies of E. coli were positively correlated. The permeabilized cytomembrane due to the close contact between nZVI and E. coli was responsible for the iron overload. This work demonstrates experimentally for the first time that nZVI causes iron overload and endogenous oxidative stress to inactivate E. coli, thus deepening our knowledge of the nZVI antimicrobial mechanism.

Microbial Electrosynthesis Inoculated with Anaerobic Granular Sludge and Carbon Cloth Electrodes Functionalized with Copper Nanoparticles for Conversion of CO2 to CH4

Microbial electrosynthesis (MES) can sustainably convert CO₂ to products and significant research is currently being conducted towards this end, mainly in laboratory-scale studies. The high-cost ion exchange membrane, however, is one of the main reasons hindering the industrialization of MES. This study investigates the conversion of CO₂ (as a sole external carbon source) to CH₄ using membraneless MES inoculated with anaerobic granular sludge. Three types of electrodes were tested: carbon cloth (CC) and CC functionalized with Cu NPs, where Cu NPs were deposited for 15 and 45 min, respectively. During the MES experiment, which lasted for 144 days (six cycles), methane was consistently higher in the serum bottles with CC electrodes and applied voltage. The highest CH₄ (around 46%) was found in the second cycle after 16 days. The system’s performance declined during the following cycles; nevertheless, the CH₄ composition was twice as high compared to the serum bottles without voltage. The MES with Cu NPs functionalized CC electrodes had a higher performance than the MES with plain CC electrodes. Microbial profile analysis showed that the Methanobacterium was the most dominant genus in all samples and it was found in higher abundance on the cathodes, followed by the anodes, and then in the suspended biomass. The genus Geobacter was identified only on the anodes regarding relative bacterial abundance at around 6–10%. Desulfovibrio was the most dominant genus in the cathodes; however, its relative abundance was significantly higher for the cathodes with Cu NPs.

Enhancing methanogenesis of anaerobic granular sludge by incorporating Fe/Fe oxides nanoparticles aided with biofilm disassembly agents and mediating redox activity of extracellular polymer substances

Anaerobic granular sludge (AGS) is a promising technology for organic wastewater treatment and energy recovery. In this study, three different kinds of Fe and Fe oxides nanoparticles (Fe₃O₄, Fe₂O₃ and ZVI) were tried to be incorporated into AGS through direct loading or aided with biofilm disassembly agents of norspermidine and D-tyrosine, which was aimed to enhance methane production capacity of AGS via increasing redox activity of extracellular polymer substance (EPS) and interspecies electron transfer. Despite the loading methods, incorporation of Fe and Fe oxides nanoparticles into AGS increased methane production capacity remarkably, with an enhancement of 36.49-85.17%, 20.37-204.95% and 189.71-243.32%, respectively, for the Fe₃O₄, Fe₂O₃ and ZVI loaded AGS. Pretreatment of AGS using biofilm disassembly agents helped to incorporate more Fe and Fe oxides into the inner structure of AGS, which further enhanced methane production capacity by 48.68% and 184.58%, respectively, for the Fe₃O₄ and Fe₂O₃ loaded AGS. Loading Fe and Fe oxides into AGS not only introduced exogenous conductive substances and Fe(III)/Fe(II) redox couples into EPS matrix of AGS, but also stimulated the production of redox active components of flavins and c-Cyts. All these factors may contribute to the reduced resistance of EPS, enhanced interspecies electron transfer and methane production capacity of AGS. This study provides a novel strategy and facile method to accelerate interspecies electron transfer and enhance methane production for matured AGS.

The role of iron-based nanoparticles (Fe-NPs) on methanogenesis in anaerobic digestion (AD) performance

Several strategies have been proposed to improve the performance of the anaerobic digestion (AD) process. Among them, the use of various nanoparticles (NPs) (e.g. Fe, Ag, Cu, Mn, and metal oxides) is considered one of the most effective approaches to enhance the methanogenesis stage and biogas yield. Iron-based NPs (zero-valent iron with paramagnetic properties (Fe⁰) and iron oxides with ferromagnetic properties (Fe₃O₄/Fe₂O₃) enhance microbial activity and minimise the inhibition effect in methanogenesis. However, comprehensive and up-to-date knowledge on the function and impact of Fe-NPs on methanogens and methanogenesis stages in AD is frequently required. This review focuses on the applicative role of iron-based NPs (Fe-NPs) in the AD methanogenesis step to provide a comprehensive understanding application of Fe-NPs. In addition, insight into the interactions between methanogens and Fe-NPs (e.g. role of methanogens, microbe interaction and gene transfer with Fe-NPs) beneficial for CH₄ production rate is provided. Microbial activity, inhibition effects and direct interspecies electron transfer through Fe-NPs have been extensively discussed. Finally, further studies towards detecting effective and optimised NPs based methods in the methanogenesis stage are reported.

Mini art review for zero valent iron application in anaerobic digestion and technical bottlenecks

Zero valent iron (ZVI) has been used extensively to control environmental pollution owing to its strong reducibility and low cost. Herein, we evaluate the impact of ZVI (iron scrap and ZVI powder with different scales) on anaerobic digestion (AD) reactor performance improvement and syntrophic relationship stimulation among various microbial groups in the methanogenesis process. In recent studies, ZVI addition significantly enhanced methane and volatile fatty acid (VFA) yields and alleviated excessive acidification, ammonia accumulation, and odorous gas production. Further, we reviewed the changes in enzyme activity and microbial metabolism after the addition of ZVI throughout the reaction process. Certain innovative technologies, such as bioelectrochemical system assistance and combined usage of conductive materials, may improve AD performance compared to the use of ZVI alone, the mechanism of which has been discussed from various viewpoints. Furthermore, the primary technical bottlenecks, such as poor mass transfer efficiency in dry AD and high ZVI dosage, have been illustrated, and syntrophic methanogenesis regulated by ZVI addition can be further studied by conducting theoretical research.

The performance of aerobic granular sludge for simulated swine wastewater treatment and the removal mechanism of tetracycline

In this study, aerobic granular sludge (AGS) cultivated in a sequencing batch reactor (SBR) was employed to investigate its ability on the decontamination of tetracycline (TC) from swine wastewater (SWW). The removal mechanism of TC by AGS was studied. Results showed that the AGS process could effectively remove chemical oxygen demand (COD), ammonium nitrogen (NH_{+ 4}-N), total phosphorus (TP), and TC during operation. The removal of TC by AGS was mainly due to adsorption and biodegradation, and the contribution rate of biodegradation increased after AGS adaptation to TC. Twenty-two by-products were detected during biodegradation of TC, and accordingly the degradation pathway of TC was speculated. Compared to the control reactor, the microbe diversity in different levels of classification was richer in the TC fed reactor according to the LefSe analysis. The results revealed that enzymes that participated in the metabolic pathway of microbial biodegradation of polycyclic aromatic compounds were enriched and may have played a key role in the biodegradation of TC.

In situ biogas upgrading and enhancement of anaerobic digestion of cheese whey by addition of scrap or powder zero-valent iron (ZVI)

Cheese whey is an easily biodegradable substrate with high organic matter that can be anaerobically digested to biogas; however, the process is often inhibited by excess acidification due to the presence of undissociated volatile fatty acids and requires considerable concentration of alkaline buffer. The current study investigates a new approach for biogas upgrading, and increase of total CH₄ in conjunction with buffering acidification by using zero-valent iron (powder and scrap metals at concentrations 25, 50, and 100 g/L) in anaerobic granular sludge and cheese whey under mesophilic batch conditions. During the first 2 cycles (total 34 days), a high performance was found in anaerobic bottles with 25 g/L powder zero valent iron (PZVI) and 50 g/L scrap zero valent iron (SZVI) since they had a higher total CH₄ production compared to anaerobic bottles free of ZVI, as well as 97% CH₄ composition in produced biogas compared to 74% CH₄ for anaerobic bottles free of ZVI. Under these conditions, no additional NaOH was added to anaerobic bottles with 25 g/L PZVI and 50 g/L SZVI to increase the pH and at the end of 2nd cycle the concentration of VFAs was substantially lower compared to the anaerobic bottles free of ZVI. However, no positive effects of ZVI in terms of alkaline buffer were found at the 3rd and 4th cycle probably due to ZVI inactivation outer surface layer. Based on the experimental findings (anaerobic bottles: (a) 25 g/L PZVI, (b) 50 g/L SZVI and (c) free of ZVI) an economic comparison for anaerobic digestion of cheese whey by large scale was contacted and pointed out that the best scenario was the anaerobic digestion by addition of 50 g/L SZVI, followed by anaerobic digestion free of ZVI and last was the anaerobic digestion by addition of 25 g/L PZVI. This study highlights a new proof of concept for in-situ biogas upgrading and alleviation of acidification by addition of 50 g/L SZVI or 25 g/L PZVI during anaerobic digestion of cheese whey.

Improving Biological Treatment of Real Bilge Wastewater With Zero Valent Iron and Activated Charcoal Addition

From the ships engine rooms a recalcitrant wastewater is produced called "bilge" which contains oil, metal working fluids, surfactants, and salinity. This study investigated the treatment of real bilge wastewater in short experiments using the following processes: (i) anaerobic digestion with granular sludge and ZVI addition for enhancement of methane production, (ii) activated charcoal addition to biological treatment (aerobic and anaerobic) for Chemical Oxygen Demand (COD) significant reduction and (iii) combination of ZVI and anaerobic charcoal addition for high performance treatment. The addition of ZVI in anaerobic sludge resulted in higher performance mostly in cumulative CH4 production. The microbial profile of anaerobic granular sludge exposed to ZVI was determined and Acetobacterium and Arcobacter were the most dominant bacteria genera. Activated charcoal achieved higher COD removal, compared to biological degradation (aerobic and anaerobic). The combination of the two mechanisms, activated charcoal and biomass, had higher COD removal only for aerobic biomass. The combination of ZVI and activated charcoal to anaerobic digestion resulted in higher CH4 production and significant COD removal in short contact time.

The bio-chemical cycle of iron and the function induced by ZVI addition in anaerobic digestion: A review

Zero-valent iron (ZVI) is known to be an additive in facilitating waste treatment and improving biogas production in anaerobic digestion (AD) systems. This review concentrates on the chemical cycle of iron as well as the function of the iron cycle in the removal of four kinds of pollutants: organic carbon, nitrogen, sulphur and phosphorus, which are commonly encountered in waste treatment. In recent studies, the addition of ZVI to an AD system promoted the in-situ production of CH₄ from CO₂, enabling carbon capture through biotechnology. Additionally, using iron-carbon microbial electrolytic cells in AD systems in order to accelerate electron transport, as well as specific pollutant degradation mechanisms, are illustrated in the present study. Particularly, the main factors affecting the removal efficiency of contaminants in a ZVI-AD system such as pH, VFA/ Alkalinity (ALK), oxidation-reduction potential and particle size are reviewed. According to the above characteristics, combined with technical model and economic analyses, an AD system based on ZVI was considered to be an economical, efficient and carbon-neutral pollutant treatment technology. Accordingly, Iron-based AD is suggested to be a promising and sustainable approach orientated to a circular economy, which may be applied to many waste treatments fields.

Performance and Microbial Community of Different Biofilm Membrane Bioreactors Treating Antibiotic-Containing Synthetic Mariculture Wastewater

The performance of pollutant removals, tetracycline (TC) and norfloxacin (NOR) removals, membrane fouling mitigation and the microbial community of three Anoxic/Oxic membrane bioreactors (AO-MBRs), including a moving bed biofilm MBR (MBRa), a fixed biofilm MBR (MBRb) and an AO-MBR (MBRc) for control, were compared in treating antibiotic-containing synthetic mariculture wastewater. The results showed that MBRb had the best effect on antibiotic removal and membrane fouling mitigation compared to the other two bioreactors. The maximum removal rate of TC reached 91.65% and the maximum removal rate of NOR reached 45.46% in MBRb. The addition of antibiotics had little effect on the removal of chemical oxygen demand (COD) and ammonia nitrogen (NH₄⁺-N)—both maintained more than 90% removal rate during the entire operation. High-throughput sequencing demonstrated that TC and NOR resulted in a significant decrease in the microbial diversity and the microbial richness MBRs. Flavobacteriia, Firmicutes and Azoarcus, regarded as drug-resistant bacteria, might play a crucial part in the removal of antibiotics. In addition, the dynamics of microbial community had a great change, which included the accumulation of resistant microorganisms and the gradual reduction or disappearance of other microorganisms under antibiotic pressure. The research provides an insight into the antibiotic-containing mariculture wastewater treatment and has certain reference value.

Improving CH4 production and energy conversion from CO2 and H2 feedstock gases with mixed methanogenic community over Fe nanoparticles

To achieve methanogenic community optimization and improve the conversion efficiency of CO₂ to CH₄, Fe nanoparticles were used to promote the Methanothermobacter abundance in methanogens, which significantly increased the conversion efficiency of CO₂ and H₂ feedstock gases to CH₄ product. High-throughput 16S rRNA gene sequencing analysis revealed that Methanothermobacter abundance markedly increased from 7 to 16% when the Fe nanoparticles concentration increased from 0 to 1.5 g/L_R (the working volume in the bioreactor). Therefore, the CH₄ yield significantly promoted from 0.105 to 0.186 L/L_R. However, when the Fe nanoparticles concentration was further increased to 2 g/L_R, methanogenesis was inhibited due to toxic effects. The electron transfer constant k_app of anaerobic sludge increased by 32.8-fold to 5.77 × 10^-2 s^-1 when the Fe nanoparticles concentration increased from 0 to 1.5 g/L_R, which significantly promoted carbon conversion efficiency from 52.9 to 92.9% and energy conversion efficiency from 46.3 to 76.9%.

Enhanced 2,4,6-trichlorophenol degradation and biogas production with a coupled microbial electrolysis cell and anaerobic granular sludge system

A coupled microbial electrolysis cell - anaerobic granular sludge system (MEC-AGS) was established to explore the degradation efficiency of 2,4,6-trichlorophenol (TCP) with synchronous biogas production. Results showed that MEC-AGS yielded a higher proportion of CH₄ than MEC (83.8 ± 0.4% vs 82.0 ± 1.0%, P < 0.05) with sodium acetate (NaAc) as the only carbon source. Moreover, MEC-AGS had higher tolerance to the addition of TCP, with the highest TCP degradation efficiency of 45.5 ± 0.5% under 5 mg L^-1 of TCP addition in 24 h. Furthermore, microbial community structures were significantly changed based on community composition, hierarchical cluster and PCoA analysis, which proved that MEC-AGS favored the enrichment of dechlorination-related microbes such as Pseudomonas, Desulfovibrio and Longilinea, as well as their syntrophic bacteria of Anaerolineacea, Syntrophobacter, Arcobacter, etc. The coupled system provides a promising strategy for biogas production from wastewater with recalcitrant organics.

Impact of adding metal nanoparticles on anaerobic digestion performance - A review

Anaerobic digestion is the most widely adopted biological waste treatment processes with renewable energy production. The effects of adding metal nanoparticles (NPs) on improving digestion performance are well noted. This paper reviewed the traditional view on the cytotoxicity of NPs to living organisms and the contemporary view of mechanisms for enhancement in anaerobic digestion performance in the presence of metal NPs. The complicated interactions acquire further studies for comprehending the physical and chemical interactions of metal NPs to the constituent compounds and to the living cells, and the involvement of mechanisms such as direct interspecies electron transfer for better design and control of the "NP strategy" for anaerobic digestion performance enhancement.

Mechanism of oxytetracycline removal by aerobic granular sludge in SBR

In this study, oxytetracycline (OTC) as a target pollutant in swine wastewater was removed by aerobic granular sludge (AGS). The removal rate of 300 μg/L OTC in aerobic granular sludge sequencing batch reactor (AGSBR) increased to 88.00% in 33 days and maintained stable. The chemical oxygen demand (COD), ammonium nitrogen (NH₄⁺-N) and total phosphorus (TP) in wastewater were also efficiently removed. The removal of OTC mainly depended on the adsorption and biodegradation of AGS, and the biodegradation was increased obviously after AGS adaptation to OTC. The degradation products of OTC were analyzed by mass spectrometry. The analysis of metagenome sequencing revealed that the enzymes, such as glycosyl transferases (GTs), polysaccharide lyases (PLs) and auxiliary activities (AAs), may play an important role in the removal of OTC. The Lefse analysis showed that the Flavobacteriia, Flavobacteriales, Cryomorphaceae and Fluviicola were four kinds of microbes with significant difference in OTC feed reactor, which are considered to be drug-resistant bacteria in AGSBR. Furthermore, the dynamics of microbial community changed significantly at three levels, including the enrichment of drug-resistant microorganisms and the microorganisms that gradually reduced or even disappeared under the pressure of OTC.