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To find a possible trade-off between effluent quality, sludge production, energy consumption and GHG emissions, this study monitored the carbon and nutrient removal and greenhouse gas (GHG) emissions in a membrane bioreactor (MBR) pilot plant with intermittent aeration (IA). The pilot plant was operated by alternating aerobic and anoxic conditions inside the biological reactor. Up to 98.2 % of carbon and 76.4 % of nitrogen were respectively remove through this MBR pilot plant with IA. The carbon footprint was equal to 2.4 kgCO 2eq m−3. Indirect emissions contributed the most to the carbon footprint (55.3 %), mainly due to energy consumption, despite the alterations in aeration during the pilot plant operation. The result of this study provides theoretical guidance for building the wastewater treatment plant in a sustainable way. [Display omitted] • MBR pilot plant aimed at carbon and nitrogen removal was monitored. • The pilot plant was operated under intermittent aeration conditions. • Excellent pollutants removal and low greenhouse gas production were obtained. • Sewage sludge production was in line with other MBR plants. • Carbon footprint was mainly debited to the energy consumption. [ABSTRACT FROM AUTHOR]

Microplastics (MPs) have attracted tremendous attention due to their widespread appearance in the environment and biota, and their adverse effects on organisms. Since plastics are substantially produced to meet human needs, primary and secondary MPs are extensively trapped in wastewater treatment plants, freshwater, drinking water, ocean, air, and soil. The serious MPs pollution calls for efficient treatment strategies Herein, we discuss three catalytic processes (photocatalysis, electrocatalysis, and biocatalysis) for the sustainable management of MPs, and the relevant catalytic mechanisms are clarified. For photocatalysis, three categories (organic, inorganic, hybrid) of photocatalysts are listed, with degradation efficiency of 23%–100%. Next, relative impact factors on photocatalysis, such as characteristics of MPs and photocatalysts, are discussed. Then, some promising electrocatalysts for the degradation/conversion of (micro)plastics and standard electrolyzer designs are briefly introduced. This electrocatalytic method has achieved over 77% of Faradaic efficiency. Next, potential organisms with abundant biocatalysts for degrading different types of MPs are reviewed. Advances in three bioremediation techniques including biositimulation, bioaugmentation, and biosurfactant are outlined. Lastly, perspectives are put forward to promote scientific development in solving environmental issues on MPs pollution in broad fields. This paper provides insights into the development of next-generation techniques for MPs pollution management in a sustainable manner. [Display omitted] • Mechanisms of MPs photo/electro/biocatalytic degradation are explained. • Current developments states of photo/electrocatalysts are illustrated. • The potential of microorganisms for enzymatic removing MPs is discussed. [ABSTRACT FROM AUTHOR]

Sulfur-containing substances in sewers frequently incur unpleasant odors, corrosion-related economic loss, and potential human health concerns. These observations are principally attributed to microbial reactions, particularly the involvement of sulfate-reducing bacteria (SRB) in sulfur reduction process. As a multivalent element, sulfur engages in complex bioreactions in both aerobic and anaerobic environments. Organic sulfides are also present in sewage, and these compounds possess the potential to undergo transformation and volatilization. In this paper, a comprehensive review was conducted on the present status regarding sulfur transformation, transportation, and remediation in sewers, including both inorganic and organic sulfur components. The review extensively addressed reactions occurring in the liquid and gas phase, as well as examined detection methods for various types of sulfur compounds and factors affecting sulfur transformation. Current remediation measures based on corresponding mechanisms were presented. Additionally, the impacts of measures implemented in sewers on the subsequent wastewater treatment plants were also discussed, aiming to attain better management of the entire wastewater system. Finally, challenges and prospects related to the issue of sulfur-containing substances in sewers were proposed to facilitate improved management and development of the urban water system. [Display omitted] • Transformation and emission of inorganic and organic sulfur components in sewers is reviewed. • Various strategies for mitigating sulfur-containing pollutants are critically discussed. • The measures imposed in sewers to control sulfur-containing pollutants inevitably impact WWTPs. • Current knowledge gaps and perspectives for the control and management of sulfur-containing substances are highlighted. [ABSTRACT FROM AUTHOR]

• Enrichment of comammox Nitrospira in a mainstream SBR in the step-feeding mode. • Candidatus Nitrospira nitrosa was the dominant (∼95 %) comammox species enriched. • Identification of K NH4 -N and K O2 for enriched comammox bacteria-dominant sludge. • Floccular sludge enriched with comammox Nitrospira possessed low N 2 O and NO yields. The discovery of complete ammonium oxidation (comammox) has subverted the traditional perception of two-step nitrification, which plays a key role in achieving biological nitrogen removal from wastewater. Floccular sludge-based treatment technologies are being applied at the majority of wastewater treatment plants in service where detection of various abundances and activities of comammox bacteria have been reported. However, limited efforts have been made to enrich and subsequently characterize comammox bacteria in floccular sludge. To this end, a lab-scale sequencing batch reactor (SBR) in the step-feeding mode was applied in this work to enrich comammox bacteria through controlling appropriate operational conditions (dissolved oxygen of 0.5 ± 0.1 g-O 2 /m3, influent ammonium of 40 g-N/m3 and uncontrolled longer sludge retention time). After 215-d operation, comammox bacteria gradually gained competitive advantages over counterparts in the SBR with a stable nitrification efficiency of 92.2 ± 2.2 %: the relative abundance of Nitrospira reached 42.9 ± 1.3 %, which was 13 times higher than that of Nitrosomonas , and the amoA gene level of comammox bacteria increased to 7.7 ± 2.1 × 106 copies/g-biomass, nearly 50 times higher than that of conventional ammonium-oxidizing bacteria. The enrichment of comammox bacteria, especially Clade A Candidatus Nitrospira nitrosa , in the floccular sludge led to (i) apparent affinity constants for ammonium and oxygen of 3.296 ± 0.989 g-N/m3 and 0.110 ± 0.004 g-O 2 /m3, respectively, and (ii) significantly low N 2 O and NO production, with emission factors being 0.136 ± 0.026 % and 0.023 ± 0.013 %, respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

Engineering robust non-noble metal electrocatalysts towards efficient impure water (e.g., seawater, wastewater) oxidation is a prospective approach to achieve carbon neutrality via accelerating green hydrogen energy development. Herein, a NiCo layered double hydroxides (LDH)/NiFe LDH composite (NiCo-LDH/NiFe-LDH) was developed for oxygen evolution reaction (OER) via a hydrothermal process-electrodeposition method. The optimal NiCo-LDH/NiFe-LDH-30 composite only needed an overpotential (η) of 240 mV to drive 100 mA/cm2 in alkalized freshwater, with a low Tafel slope of 16.6 mV/dec and good stability for over 90 h. Further analyses suggested that the strong interface interaction between NiCo-LDH and NiFe-LDH accelerated the oxygen gas bubble evolution and boosted interfacial charge transfer, and the formed built-in electric field and higher oxidation state species (metal oxyhydroxides) contributed to the high intrinsic catalytic activity. The NiCo-LDH/NiFe-LDH-30 composite also held excellent OER activities in different impure water environments, including alkaline 0.5 M NaCl solution (η 100 = 333 mV), alkaline lake water (η 100 = 345 mV), and alkaline wastewater treatment plant (WWTP) effluent (η 100 = 320 mV). More importantly, the potential effects of Cl− and CO 3 2− in impure water were revealed during the OER process. This work elaborates on the role of built-in electric field and the strong coupling interaction in composite catalysts, which pave the way for the design of cost-effective catalysts with excellent adaptability in different water environments. [Display omitted] • NiCo-LDH/NiFe-LDH composite showed strong electronic coupling interaction. • Hybridizing NiCo-LDH with NiFe-LDH led to fast interfacial electron transfer. • NiCo-LDH/NiFe-LDH exhibited prominent OER performance in different water matrices. • Built-in electric field enhanced OER activity and stability of NiCo-LDH/NiFe-LDH. [ABSTRACT FROM AUTHOR]

The recovery of phosphorus (P) through vivianite crystallization offers a promising approach for resource utilization in wastewater treatment plants. However, this process encounters challenges in terms of small product size and low purity. The study aimed to assess the feasibility of using quartz sand as a seed material to enhance P recovery and vivianite crystal characteristics from anaerobic fermentation supernatant. Various factors, including seed dosage, seed size, Fe/P ratio, and pH, were systematically tested in batch experiments to assess their influence. Results demonstrated that the effect of seed enhancement on vivianite crystallization was more pronounced under higher seed dosages, smaller seed sizes, and lower pH or Fe/P ratio. The addition of seeds increased P recovery by 4.43% in the actual anaerobic fermentation supernatant and also augmented the average particle size of the recovered product from 19.57 to 39.28 μm. Moreover, introducing quartz sand as a seed material effectively reduced co-precipitation, leading to a notable 12.5% increase in the purity of the recovered vivianite compared to the non-seeded process. The formation of an ion adsorption layer on the surface of quartz sand facilitated crystal attachment and growth, significantly accelerating the vivianite crystallization rate and enhancing P recovery. The economic analysis focused on chemical costs further affirmed the economic viability of using quartz sand as a seed material for P recovery through vivianite crystallization, which provides valuable insights for future research and engineering applications. [Display omitted] • Quartz sand as seed material increased P recovery in anaerobic fermentation supernatant. • Seed-induced vivianite crystallization was enhanced at higher seed doses, smaller seed sizes, and lower pH or Fe/P ratios. • Quartz sand as seed material improved vivianite purity through reduced co-precipitation. • Quartz sand as seed material for vivianite crystallization was economically feasible. [ABSTRACT FROM AUTHOR]

[Display omitted] • The study firstly reviews MCFAs production from sewage sludge fermentation. • MCFAs synthesis can be suppressed by competitive metabolisms and sludge hydrolysis. • Competition and cooperation among microbes co-exist in sludge CE system. • Pretreatments and semi-/conductive materials are the main reinforcement strategies. • Pretreatments are efficient to impede byproducts formation and avoid BES dosing. Huge sludge volumes and increased energy demands are the main challenges faced by wastewater treatment plants (WWTPs) currently, while it stimulates organics transformation and carbon recovery from sludge treatment process. Due to higher energy density and greater hydrophobicity, medium-chain fatty acids (MCFAs) exhibit easier extraction and more widespread application than traditional short-chain fatty acids (SCFAs). Therefore, MCFAs synthesis from sewage sludge via chain elongation (CE) has recently attracted growing attention in anaerobic open culture fermentation. Nevertheless, a comprehensive and systematic review focused on MCFAs synthesis from sludge is not available so far. This study provides a critical review on sewage sludge-derived MCFAs synthesis. The metabolic pathways, potential influencing factors, and cooperative and competitive relationships among various microorganisms are first elucidated to understand the mechanisms, limitations, and microbial interactions involved in MCFAs production via open culture fermentation of sludge. Unfortunately, MCFAs synthesis from sewage sludge is mainly hampered by low organics accessibility, inferior electron transfer efficiency and presence of competitive microbes. To foster sludge degradation and high-value MCFAs production, various techniques based on pretreatment and facilitation of electron transfer have recently been proposed, which are comprehensively reviewed with the corresponding mechanisms meticulously discussed. Ultimately, knowledge gaps and new opportunities for sludge-derived MCFAs production are prospected. This review will offer theoretical and technological guidelines for the subsequent investigations and future engineering applications of MCFAs production from sewage sludge. [ABSTRACT FROM AUTHOR]

[Display omitted] • Short-term FA and FNA treatment on FN sludge instantly reduce N 2 O at all DO levels. • The dependency of N 2 OR on DO was altered by exposing FN sludge to high FNA. • Short-term exposure of PN sludge to high FNA abolished N 2 O production. • FNA treatment on sludge led to 3.5% more cost, while FA treatment saved 2% cost. The potentials of using endogenous free ammonia (FA) and free nitrous acid (FNA) as nitrous oxide (N 2 O) mitigators were investigated in treatment of both mainstream and sidestream wastewater. Although the N 2 O emission factor of a sidestream partial-nitritation (PN) reactor (averaged 1.70 % ± 0.39 %, n = 30) was about 2.4 times higher than a mainstream full-nitrification (FN) reactor (averaged 0.72 % ± 0.24 %, n = 30) (P < 0.01), one-hour exposure of PN sludge to 1.5 mg HNO 2 -N/L FNA could virtually abolish N 2 O emission. As for FN sludge, both 45 mg NH 3 -N/L FA and 0.015 mg HNO 2 -N/L FNA successfully mitigated N 2 O production at varying dissolved oxygen (DO) levels (50 % vs 61 %), while 1.5 mg HNO 2 -N/L FNA not only reduced more N 2 O (92 %) but also altered the N 2 O dependency on DO. Both FNA and FA sludge treatment were effective N 2 O mitigation strategies with FNA toward the end of carbon neutrality and FA being more economically appealing (2 % cost saving). [ABSTRACT FROM AUTHOR]

Excess sludge management is a restrictive factor for the development of municipal wastewater treatment plants. The addition of metabolic uncouplers has been proven to be effective in sludge reduction. However, the long-term effect of metabolic uncoupler o-chlorophenol (oCP) on the biological wastewater treatment system operated in anaerobic-oxic mode is still unclear. To this end, two parallel reactors operated in anaerobic-oxic mode with and without 10 mg/L of oCP addition were investigated for 91 days. The results showed that 56.1 ± 2.3% of sludge reduction was achieved in the oCP-added system, and the nitrogen and phosphorus removal ability were negatively affected. Dosing oCP stimulated the formation of microbial products and increased the DNA concentration, but resulted in a decrease in the electronic transport activity of activated sludge. Microbial community analysis further demonstrated that a significant reduction of bacterial richness and diversity occurred after oCP dosing. However, after stopping oCP addition, the pollutant removal ability of activated sludge was gradually increased, but the sludge yield, as well as species richness and diversity, did not recover to the previous level. This study will provide insightful guidance on the long-term application of metabolic uncouplers in the activated sludge system. [Display omitted] • Sludge reduction of 56.1% was achieved in the o-chlorophenol (oCP)-added system. • oCP addition stimulated the microbial products formation of activated sludge. • The species richness and diversity were reduced with oCP addition. • The sludge yield, as well as species richness and diversity, did not recover after stopping oCP addition. [ABSTRACT FROM AUTHOR]

• Wastewater and sludge treatment changes MPs morphology, sizes and chemical properties. • Changes in the intrinsic properties of MPs can affect their transport and distribution patterns. • The physicochemical properties of MPs affect coexisting pollutants and leaching behavior, leading to changes in ecological risk. • Need for further field-studies to address physicochemical-related environmental risk. Microplastics (MPs) have been frequently detected in effluent wastewater and sludge in wastewater treatment plants (WWTPs), the discharge and agricultural application of which represent a primary source of environmental MPs contamination. As important as quantitative removal is, changes of physicochemical characteristics of MPs (e.g., shapes, sizes, density, crystallinity) in WWTPs are crucial to their environmental behaviors and risks and have not been put enough attention yet. This review is therefore to provide a current overview on the changes of physicochemical characteristics of MPs in WWTPs and their corresponding environmental risks. The changes of physicochemical characteristics as well as the underlying mechanisms of MPs in different successional wastewater and sludge treatment stages that mainly driven by mechanical (e.g., mixing, pumping, filtering), chemical (e.g., flocculation, advanced oxidation, ultraviolet radiation, thermal hydrolysis, incineration and lime stabilization), biological (e.g., activated sludge process, anaerobic digestion, composition) and their combination effects were first recapitulated. Then, the inevitable correlations between physicochemical characteristics of MPs and their environmental behaviors (e.g., migration, adsorption) and risks (e.g., animals, plants, microbes), are comprehensively discussed with particular emphasis on the leaching of additives and physicochemical characteristics that affect the co-exist pollutants behavior of MPs in WWTPs on environmental risks. Finally, knowing the summarized above, some relating unanswered questions and concerns that need to be unveiled in the future are prospected. The physicochemical properties of MPs change after passing through WWTP, leading to subsequent changes in co-contaminant adsorption, migration, and toxicity. This could threaten our ecosystems and human health and must be worth investigating. [Display omitted] [ABSTRACT FROM AUTHOR]