Aerobic granular sludge is a promising wastewater treatment technology, but its practical application is still constrained by high aeration demand and limited operational stability. In this study, an algal-bacterial symbiotic granular sludge system was developed under Fe3O4@polyaniline-assisted cultivation and evaluated under reduced aeration conditions. Under illumination, algal-bacterial symbiosis was established in the system, and the dissolved oxygen concentration remained at 6.8-7.1 mg/L when the aeration intensity was reduced from 2.5 to 1.7 L/min. Fe3O4@polyaniline-assisted cultivation was beneficial for granulation and biomass retention during start-up, while the algal-bacterial system maintained stable carbon, nitrogen, and phosphorus removal under reduced aeration. Stoichiometric mass balance analysis indicated that bacterial metabolism remained the dominant estimated removal pathway, whereas the relative contribution of algae increased under reduced aeration. Microbial community analysis further showed that bacterial diversity was maintained, while algal proliferation increased at lower aeration intensity. This study offers an energy efficient algal-bacterial symbiotic granular sludge cultivation strategy, presenting a viable solution for sustainable wastewater treatment.

In recent years, CO2 capture and utilization (CCU) technologies have made significant advancements, propelled by the urgent need to mitigate climate change and reduce greenhouse gas emissions. This chapter summarizes the progress of the latest advancements in CO2 capture and utilization, with a particular emphasis on the development of low energy-consumption routes for capturing CO2 from flue gas and directly from the air. Additionally, this chapter explores a range of CO2 utilization approaches, which include thermocatalytic conversion, electrocatalytic conversion, photocatalytic conversion, as well as bioconversion. Each method is discussed in terms of its technical feasibility, materials, efficiency, and potential applications, providing a comprehensive overview of current research trends and the future potential of CO2 capture and utilization technologies.

While anaerobic digestion (AD) has been considered as a commonly used method for methane recovery from dairy wastewater, part of methane is lost as dissolved form (D-CH4) with the effluent, reducing overall efficiency of methane recovery and increasing greenhouse gas emissions. In this study, a hybrid system of microbial electrolysis cell (MEC) and AD was utilized to enhance the recovery of methane, the influence of organic loading rate, sludge concentration, particle size, and temperature on methane production and the D-CH4were investigated. The system recorded a 42.04% enhancement in the rate and an 18.13% enhancement in methane production at an applied voltage of 0.8V. Microbial analysis showed that voltage-dependent enrichment of Bacteroides and Methanobacterium species likely played a synergistic role in enhancing methanogenesis. The temperature was found to have the most desirable impact on the solubility of methane. The elevated temperatures could enhance microbial activity and methane production rates, which increase methane partial pressure in the liquid phase and thus elevate dissolved concentrations despite the decrease in solubility.

Conductive materials and electroactive microorganisms (EAM) are key factors on enhancing methane production in anaerobic digestion of waste actived sludge via the direct interspecies electron transfer (DIET). However, their combined impact on simultaneous methane production and phosphorus recovery remains unclear. The Fe2O3 and EAM were added together to synergistically improve anaerobic processes, resulting in a 1.53-fold increase in methane production and a remarkable 12.03-fold enhancement in phosphorus removal. The co-additon of Fe2O3 and EAM promoted Fe(III/II) redox cycling, increased enzyme activity, and enhanced electron transport system (ETS) functionality while enriching DIET-associated bacteria (e.g., Brooklawnia, Anaerolineae) and methanogens (Methanosarcina). Metagenomic analysis revealed the upregulated genes related to phosphorus and iron metabolism, ETS, and DIET-coupled electron bifurcation. Notably, Fe2O3 may act as an alternative to cytochromes and pili in mediating DIET in electron transfer processes.

The high-salinity rare earth industrial wastewater with complex inorganic ions (e.g., Na+, Cl-, F-, SO4 2-and La3+) has significant environmental threats if not efficiently desalinated. This paper employed a direct contact membrane distillation (DCMD) system based on commercially available polypropylene (PP) hollow fiber membranes for efficient desalination of rare earth industrial wastewater. Desalination performance and fouling characteristics of the membranes were investigated. Membrane flux was found to be greatly affected by feed temperature and flow rate. The concentrate reached 20-fold after 388 h of operation, and the membrane flux decreased by 83.48%. It was inferred that the decrease in flux was mainly due to inorganic scaling (NaCl, CaF2, La2(CO3)2(OH)2) and increased polarization effects. Although hydraulic and chemical cleaning (0.1% HCl) partially restored flux, repeated cleaning cycles resulted in irreversible fouling accumulation. This work demonstrates the feasibility of DCMD for the efficient treatment of high-salinity rare earth industrial wastewater.

Semi-artificial photosynthesis offers a promising route for converting CO2 into value-added chemicals. Herein, a novel self-assembled biohybrid of Methanosarcina barkeri and NH2-MIL-101(Fe) enables direct CO2-to-CH4 conversion, achieving a CH4 yield of 563.72 ± 23.75⋅μmol gcat-1 and nearly 100% selectivity. NH2-MIL-101 exhibits high CO2 adsorption without generating H2 as a by-product. The biohybrid showed enhanced light-harvesting, improved electron-hole separation, accelerated interfacial charge transfer, and increased abundance of membrane-bound redox-active mediators. Transcriptomic analysis revealed upregulation of key genes promoting methanogenesis via both hydrogenase- and cytochrome-dependent mechanisms. These findings demonstrate the potential of solar-powered, self-replicating biohybrid systems for efficient CO2-to-CH4 conversion.

Conversion of organic pollutants to biogas through anaerobic digestion has been considered as an effective way to recover energy from wastewater. However, the biogas produced typically contains over 30% of CO2, which significantly reduces its energy density. In this work, a biohybrid composite consisting of Methanosarcina barkeri and g-C3N4 (M. barkeri-g-C3N4) was synthesized to selectively convert CO2 in the biogas into CH4 under the light condition. The physicochemical and structural properties of the M. barkeri-g-C3N4 biohybrid were thoroughly characterized. Key factors influencing the biohybrid's performance on light-driven CH4 production were investigated, including g-C3N4 dosage, NaHCO3 concentration, pH, and cysteine concentration. A g-C3N4 concentration of 0.033 g/L, a pH of 7.02, a NaHCO3 concentration of 10 mM, and a cysteine concentration of 0.05 wt% were suggested as the optimal conditions. It was indicated that light-driven electrons can be used by M. barkeri for the conversion of CO2 to CH4. Additionally, the generated electrons can also be stored in the g-C3N4 semiconductor during light exposure and subsequently released in the dark to M. barkeri for CO2-to-CH4 conversion.

Urban composite non-point source (UCNPS) pollution has become a considerable source of basin pollution. Its control can generally be approached at the source and process levels; however, source and process control facilities face challenges in achieving high-efficiency control. To optimize the layout of source control facilities, two methods were developed in this study: 1) a Storm Water Management Model (SWMM)-group decision-making method for small-area basins and 2) a multi-objective optimization method for large-area basins. For process control of combined sewer overflow (CSO) pollution, methods based on the SWMM and ideal point theory were developed to determine the optimal CSO storage tank volume and the optimal interception ratio of the combined drainage systems. For process control of first-flush runoff (FFR) pollution in separate drainage systems, methods integrating SWMM simulations with empirical design formulas were proposed to determine the optimal volume and layout of FFR storage tanks. These methods were applied to develop high-efficiency source and process control schemes in two representative urban areas—Yongchuan and Jintan—in the Yangtze River Basin, China. The results indicated that by optimizing the layout of source control facilities, 12.44

Electrical currents can enhance biomass removal and methane production in anaerobic digesters, particularly where Methanosarcina species like Methanosarcina barkeri are active. To explore how M. barkeri acquires electrons from cathodes, M. barkeri was inoculated into methanol-fed reactors with applied cathodic potentials that either generated hydrogen (-1.0 V vs. Ag/AgCl) or did not (-0.6 V). Transcriptomic analysis revealed increased expression of genes tied to carbon metabolism and intracellular hydrogen cycling in-0.6 V cells. Transcripts for Vht and Frh hydrogenase genes were also more abundant in-0.6 V cells, and flux balance analysis confirmed Vht hydrogenases' importance in electron uptake. A mutant lacking vhtGAC genes showed delayed growth in reactors with-0.6 V cathodes but compensated by upregulating Fpo dehydrogenase genes. These findings shed light on how M. barkeri facilitates direct electron uptake (direct electron transfer [DET]) from cathodes and should help improve methane production in bioelectrochemical systems.

Fe30.4 has shown great potential for enhancing methanogenesis by facilitating direct interspecies electron transfer (DIET), thereby promoting efficient resource recovery from organic wastewater. However, its susceptibility to corrosion and loss under acidic anaerobic conditions limits its application. In this study, a core-shell structured Fe3O4@PPy was synthesized by coating Fe3O4 with polypyrrrole (PPy) to enhance its stability. The PPy shell effectively protected the Fe30.4 core from acidic corrosion, while leveraging the electrical conductivity of Fe30.4 and the electron transfer capacity of PPy to optimize DIET in the anaerobic wastewater treatment. At an optimal Fe304:PPy ratio of 1:1.5 and a dosage of 0.6 g/L, 31.9 % increase in methane production rate and a 21.8 % improvement in methane yield was achieved. Microbial community analysis revealed significant enrichment of both acidogenic bacteria and methanogenic archaea. Moreover, the key functional genes and enzymes related to electron transfer and methanogenesis were upregulated, indicating that Fe304@PPy enhanced electron transfer in methanogenesis process.

Correction for ‘Cellulose derived magnetic mesoporous carbon nanocomposites with enhanced hexavalent chromium removal’ by Bin Qiu et al., J. Mater. Chem. A, 2014, 2, 17454–17462, https://doi.org/10.1039/C4TA04040F.

Innovation in the molecular design of surfactants holds great potential for developing novel soft materials with unique properties. A surfactant with a long alkyl tail is expected to form giant aggregates with intriguing behavior. However, molecules with a large hydrophobic group often suffer from poor solubility in solutions, inhibiting the aggregation process. Herein, a new aspartame-based bicephalous anionic surfactant, disodium stearoyl-l-aspartyl-phenylalanine (C18-AP-2Na), has been synthesized. C18-AP-2Na showed excellent compatibility with the cationic surfactant cetyltrimethylammonium bromide (CTAB) and resulted in transparent viscoelastic mixed systems over a wide range of molar ratios and concentrations. Moreover, when CTAB and C18-AP-2Na were mixed with an equimolar charge ratio, the viscosity increased consistently from 61 mPa s (0.13 wt%) to an astonishing 14 000 Pa s (13.2 wt%). Cryo-TEM images revealed a network of extensively entangled wormlike micelles with cross-sectional diameters of 4-5 nm and lengths extending up to several micrometers at a C18-AP-2Na/CTAB molar ratio of 5 mM : 10 mM. The presence of long alkyl tails is the origin of wormlike micelle elongation. Different from other conventional anionic surfactants, C18-AP-2Na is distinguished by the amino acid unit near the head group. The extended molecular structure is not linear shaped. C18-AP-2Na is able to combine with CTAB molecules through electrostatic attractions while avoiding the too close contact of the alkyl tails. In this way, the formed ionic pairs remain hydrated in solutions instead of being precipitated. In addition, due to the strong attractions between the head groups of C18-AP-2Na and CTAB, the inorganic ions are ineffective to shield the head group charges. The viscosity of the mixed solutions remained nearly unchanged even with NaCl concentrations of up to 5%, demonstrating significant salt resistance. This work utilizes the advantages of the amino acid and develops stable cationic/anionic mixed solutions with strong viscoelasticity. The excellent compatibility as well as the strong salt resistance make the formulations promising for applications in oil recovery, cosmetic formulations, and the creation of smart materials. The self-assembly principles of surfactants demonstrated here also offer valuable insights for designing new viscoelastic systems and molecular structures.

Effective treatment of high-concentration brewery wastewater through anaerobic digestion (AD) has always been a challenging issue. Enhancing direct interspecies electron transfer (DIET) was demonstrated to increase methane production during AD under high organic loading rate (OLR). Herein, the feasibility of enhancing DIET with the addition of riboflavin-loaded granular activated carbon (RF-GAC) as well as co-addition with Methanosarcina barkeri (Rf-GAC+M.barkeri) was investigated (M.barkeri is well-known to be capable of DIET with electroactive bacteria). During the whole process, the Rf-GAC and the Rf-GAC+M.barkeri group both achieved average COD removal rates above 97 %, which was 14 % higher than that of the control. The average methane production in the Rf-GAC group and the Rf-GAC+M.barkeri group respectively reached 0.334 ± 0.02 L(stp)/g COD and 0.345 ± 0.02 L(stp)/g COD, 1.35 and 1.39 times higher than the 0.247 ± 0.03 L(stp)/g COD reached by the control. The control reactor deteriorated at an OLR of 12 kg COD/(m3·d), whereas the Rf-GAC and the Rf-GAC+M.barkeri group maintained stable as the OLR reached as high as 17.5 kg COD/(m3·d) and the volatile fatty acids concentration was consistently below 10 mM. The RF-GAC performed better than Rf-GAC+M.barkeri in enriching Methanothrix, whose relative abundance was 60.6 % in the former group. Metabolic pathway analysis revealed the addition of RF-GAC upregulated genes related to DIET in Methanothrix species, including hdrA and fpoD. Furthermore, Methanothrix remained the dominant archaea even continuously inoculating pure strains of M.barkeri during the entire operational period. Pure culture experiments proved that GAC inhibited M.barkeri growth. The results of this study can be optimized for practical application of AD treating high-concentration brewery wastewater.

Conductive polyaniline (PANI) was employed to enhance volatile fatty acids (VFAs) production from anaerobic fermentation of waste activated sludge (WAS) in this work. The effects of conductivity, dosage, particle size, and pore structure of PANI on VFAs production were investigated. Results revealed the positive correlations between VFAs production and PANI conductivity and dosage, with an 8 g/L PANI dosage increasing butyrate yield by 144.73 %. Higher conductivity and specific surface area were found to promote the production of caproate and butyrate. Electrochemical analysis demonstrated the improved electron transfer in PANI-supplemented fermentation system. Microbial community analysis revealed the enrichment of Clostridium_sensu_stricto_12 and Clostridium_sensu_stricto_1, which are associated with acid-producing and chain-elongating. Metagenomic analysis further indicated that both the fatty acid biosynthesis (FAB) and reverse beta-oxidation (RBO) pathways contributed to VFAs production, while PANI supplementation upregulated key enzymes involved in the FAB pathway.

The low pH and intricate pollutants in Chinese liquor brewing wastewater (CLBW) pose significant challenges for effective anaerobic digestion (AD) treatment. Granular activated carbon (GAC) can facilitate direct interspecies electron transfer (DIET) and enhance the system's tolerance to high OLR and low pH. This study investigates a novel approach combining GAC addition and slight influent pH adjustment, which can enhance AD performance of CLBW with reduced alkali need. The synergistic effects and underlying mechanisms remain unclear. The results revealed that the reactor (R20-1), amended with 20 g/L GAC and the influent pH adjusted by adding 1 g NaOH/Linfluent, while the non-GAC reactor failed rapidly at an initial OLR of 3.4 kg COD/(m3 center dot d). Microbial community analysis revealed that Prevotella was enriched at 12.7 kg COD/(m(3)center dot d)), whereas Parabacteroides dominated at high OLRs > 15.9 kg COD/(m(3)center dot d). Key archaea such as Methanobacterium and Methanosaeta were predominant, with Methanocorpusculum and Methanobrevibacter enriched at high OLRs. Electroactive bacteria, particularly Syntrophomonas, were enriched in R20-1 but decreased at high OLRs. Moreover, genes involved in both DIET and acetate decarboxylation pathways assigned to Methanosaeta showed increased expression with GAC addition. This research provides valuable insights into microbial evolution, functional gene changes and the correlation relationships among environmental factors and microorganisms with increasing OLR, offering a more cost-saving and efficient strategy for treating high-strength organic and acidic wastewater compared to traditional AD methods.

The incorporation of in situ crystallization of vivianite (Fe3(PO4)28H2O) in an enhanced biological phosphorus removal (EBPR) process using an Fe-retrofitted University of Cape Town wastewater treatment process coupled with a membrane bioreactor is shown to be a highly effective strategy to improve the efficiency and stability of phosphorus removal during wastewater treatment over a 400-day trial period. Iron-mediated phosphorus removal (IPR)-driven by iron redox cycling and phase transformations in anaerobic-aerobic chambers-enhances polyphosphate synthesis/hydrolysis activity by polyphosphate-accumulating organisms (PAOs) with the synergy of IPR and EBPR in adsorbing phosphorus, increasing the efficiency of phosphorus removal to 90% during long-term operation. An essential decrease in the contribution of EBPR to final phosphorus removal as a result of the introduction of IPR reduced the requirement for a carbon source either from influent or via supplementation and also reduced the need for discharge of a phosphorus-rich sludge, thereby substantially decreasing the cost of phosphorus removal and the associated carbon emissions. In addition, phosphorus immobilization via the IPR pathway enables the recovery of this element in the form of separable vivianite granules, which aligns with the evolving role of WWTPs as resource recovery facilities.

Even after biological treatment, white liquor wastewater still contains residual nitrogen. The residual nitrogen poses a risk of eutrophication when the reclaimed water is used to recharge rivers. This study utilized a dualchamber microbial electrolysis cell to enhance nitrogen removal from nitrate-rich effluent, which originated from the biological treatment in the cathode chamber. By applying an external voltage and using highconcentration liquor wastewater as the carbon source for the anode, the denitrification efficiency was improved. When optimizing the parameters of the cathode chamber with the total nitrogen removal rate as the index, it was determined that a sludge inoculation amount of 10 %, an applied voltage of 0.2 V, a salinity of 0.5 g/L in the wastewater, and a C/N ratio of 2.5 resulted in a total nitrogen concentration of 4.1 mg/L in the effluent from the cathode chamber of the microbial electrolytic cell, achieving a removal rate of 80 %. The application of voltage effectively enriched denitrifying bacteria such as Cloacibacterium and Thermomonas in the cathode chamber, enhanced the abundance of genes related to nitrogen metabolism, and strengthened the collaborative nitrogen removal pathways of hydrogen-autotrophy and heterotrophy in the cathode chamber. This enabled efficient and thorough nitrogen removal from domestic wastewater.

Conductive materials are known to enhance methane production in anaerobic treatment process by facilitating direct interspecies electron transfer (DIET). However, the role of the porous structure of conductive materials in electron transfer remains underexplored. Polyaniline (PANI) was used as conductive materials in this study due to its easily controlled porosity, investigating how surface area and pore size affect methane production. It was demonstrated that the porosity of PANI is an important factor affecting methane production by anaerobic sludge. Methane production rate of 41.2 mL/h was achieved with the high-porosity PANI, which was similar to 73.2% higher than the control group. The porous PANI enhanced the electric field in the anaerobic sludge, facilitating the enrichment of electrogenic bacteria and archaea. In the anaerobic system supplemented with porous PANI, the maximum accumulation of acetic acid reached 3.72 mM. The abundance of electroactive bacteria Clostridium involved in DIET increased by 2.13-fold, while the abundance of electroactive archaea Methanosaeta and Methanobacterium, which also participate in DIET, rose by 1.55-fold. The porous structure of PANI promotes DIET and enhances aceticlastic methanogenesis.

Conductive materials enhance methane production in anaerobic wastewater treatment by facilitating direct interspecies electron transfer (DIET) between exoelectrogenic bacteria and methanogens. The electron transfer rate from exoelectrogenic bacteria is a critical factor that affects methane production efficiency. However, understanding how the three-dimensional (3D) structure of conductive materials influences this process remains challenging, primarily due to the difficulties in precisely tailoring their forms. In this study, polyaniline (PANI), a flexible conductive polymer, was synthesized in various shapes to match the 3D configurations of exoelectrogenic bacteria, aiming to optimize DIET and enhance methane production. The results revealed that granular PANI outperformed sheets form, increasing methane yield and rates, on average, by 13.6% and 9.0%, respectively. Micrometer-scale PANI particles exhibited superior DIET promotion versus millimeter/centimeter counterparts,with particle-cell alignment significantly enriching exoelectrogenic microbial consortia. Monte Carlo and molecular dynamics simulations demonstrated that the electron diffusion distance from bacterial donor to micrometer-scale PANI was significantly shortened by 450%-475% than centimeter, with Met79 and imine identified as key electron transfer sites at the cytochrome C/PANI interface. This study advances our understanding of the role of conductive materials in anaerobic wastewater treatment while offering practical guidelines for developing high-efficiency methanogenic systems through rational material architectonics.