This study provided an overview of established and emerging nanomaterial (NM)-enabled processes and devices for water disinfection for both centralized and decentralized systems. In addition to a ...discussion of major disinfection mechanisms, data on disinfection performance (shortest contact time for complete disinfection) and energy efficiency (electrical energy per order; EEO) were collected enabling assessments firstly for disinfection processes and then for disinfection devices. The NM-enabled electro-based disinfection process gained the highest disinfection efficiency with the lowest energy consumption compared with physical-based, peroxy-based, and photo-based disinfection processes owing to the unique disinfection mechanism and the direct mean of translating energy input to microbes. Among the established disinfection devices (e.g., the stirred, the plug-flow, and the flow-through reactor), the flow-through reactor with mesh/membrane or 3-dimensional porous electrodes showed the highest disinfection performance and energy efficiency attributed to its highest mass transfer efficiency. Additionally, we also summarized recent knowledge about current and potential NMs separation and recovery methods as well as electrode strengthening and optimization strategies. Magnetic separation and robust immobilization (anchoring and coating) are feasible strategies to prompt the practical application of NM-enabled disinfection devices. Magnetic separation effectively solved the problem for the separation of evenly distributed particle-sized NMs from microbial solution and robust immobilization increased the stability of NM-modified electrodes and prevented these electrodes from degradation by hydraulic detachment and/or electrochemical dissolution. Furthermore, the study of computational fluid dynamics (CFD) was capable of simulating NM-enabled devices, which showed great potential for system optimization and reactor expansion. In this overview, we stressed the need to concern not only the treatment performance and energy efficiency of NM-enabled disinfection processes and devices but also the overall feasibility of system construction and operation for practical application.
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•Brief overview of NM-enabled processes and devices for water disinfection.•Evaluation of NM-enabled processes/devices based on performance and energy efficiency.•Applying contact time and electrical energy per order (EEO) for assessment of processes and devices.•Discussion of influencing factors on contact time and EEO for NM-enabled disinfection.•Summary of NMs recovery and electrode strengthening methods for practical application.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Summarized the over-growth risks of non-pathogenic CRB.•Presented the genus, sources and chlorine resistance of all the isolated CRB strains.•Demonstrated the lack of widely-accepted method to ...evaluate chlorine resistance.•Proposed a recommended evaluating method for chlorine resistance.•Proposed a quantitative definition of chlorine-resistant bacteria.
Chlorine-resistant bacteria (CRB) are commonly defined as bacteria with high resistance to chlorine disinfection or bacteria which can survive or even regrow in the residual chlorine. Chlorine disinfection cannot completely control the risks of CRB, such as risks of pathogenicity, antibiotic resistance and microbial growth. Currently, researchers pay more attention to CRB with pathogenicity or antibiotic resistance. The microbial growth risks of non-pathogenic CRB in water treatment and reclamation systems have been neglected to some extent. In this review, these three kinds of risks are all analyzed, and the last one is also highlighted. In order to study CRB, various methods are used to evaluate chlorine resistance. This review summarizes the evaluating methods for chlorine resistance reported in the literatures, and collects the important information about the typical isolated CRB strains including their genera, sources and levels of chlorine resistance. To our knowledge, few review papers have provided such systematic information about CRB. Among 44 typical CRB strains from 17 genera isolated by researchers, Mycobacterium, Bacillus, Legionella, Pseudomonas and Sphingomonas were the five genera with the highest frequency of occurrence in literatures. They are all pathogenic or opportunistic pathogenic bacteria. In addition, although there are many studies on CRB, information about chlorine resistance level is still limited to specie level or strain level. The difference in chlorine resistance level among different bacterial genera is less well understood. An inconvenient truth is that there is still no widely-accepted method to evaluate chlorine resistance and to identify CRB. Due to the lack of a unified method, it is difficult to compare the results about chlorine resistance level of bacterial strains in different literatures. A recommended evaluating method using logarithmic removal rate as an index and E. coli as a reference strain is proposed in this review based on the summary of the current evaluating methods. This method can provide common range of chlorine resistance of each genus and it is conducive to analyzing the distribution and abundance of CRB in the environment.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Attached microalgae cultivation could simplify the microalgae harvest process and reduce its associated cost, which has attracted much attention recently. In this paper, the reactor patterns, ...advantages, microalgae biomass productivity, influencing factors and the microalgae physicochemical properties in the attached microalgae cultivation was summarized to show the sketch of this novel microalgae cultivation. It was concluded that the attached microalgae cultivation is advantageous in achieving less water and space consumption, higher water treatment potential and higher biomass productivity compared with the traditional suspended microalgae cultivation. The accumulation of the attached microalgae biomass showed a linear increase with culture time with the largest productivity up to 20.7 g m−2 d−1. Chlorella and Scenedesmus were the top two species that have been studied in attached culture system. Cellulose acetate/nitrate membrane, polycarbonate membrane and cotton were the most popular materials used owing to their high hydrophilicity and wide availability. Flow rate, nutrients, light, CO2 and other factors could affect the attached microalgae productivity and the physicochemical property in a way different from the suspended microalgae, which were described in detail in this review. At last, some technical bottlenecks and the corresponding solvents in the attached microalgae were suggested.
•Attached cultivation could simplify microalgae harvest process and reduce its cost.•Attached microalgae showed a linear growth with the rate up to 20.7 g m−2 d−1.•Algae species, support media and nutrients affected attached microalgae growth.•Physicochemical property and their influence factors varied with culture patterns.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
In reverse osmosis (RO) system for wastewater reclamation, biofouling is an inevitable issue. Chlorine disinfection is commonly used in pretreatment to control biofouling. Some chlorine-resistant ...bacteria could survive after chlorine disinfection and the microbial community structure in feed water changes significantly, thus leading to the change of biofouling potential. In this study, the effect of chlorine disinfection on the biofouling of RO membrane was investigated using a laboratory cross-flow RO system. Chlorine disinfection inactivated most bacteria in feed water. However, during the operation of RO system, with the increase of chlorine dosage the flux decline became more severe after a period of operation. The final normalized flux after 21 days was 0.27, 0.26, 0.20, and 0.21 with 0, 1, 5, and 15 mg-Cl2/L chlorine as pretreatment, respectively. After the operation, the numbers of active bacteria in the foulants on the fouled membrane were on the same level regardless of the chlorine dosage, whereas the thickness of the foulants increased with the chlorine dosage significantly. Additionally, the higher total organic carbon concentration indicated more extracellular polymeric substances (EPS) in foulants. Microbial community structure analysis showed that the abundance and the species number of chlorine-resistant bacteria increased significantly with the chlorine dosage. Typical chlorine-resistant bacteria, including Methylobacterium, Pseudomonas, Sphingomonas, and Acinetobacter, were identified as significantly distinctive genera in the foulants after the pretreatment by 15 mg-Cl2/L chlorine. Compared with the bacteria without chlorine disinfection, these remaining bacteria produced more EPS with higher molecular weight, which could be the major contribution to more severe RO membrane fouling after chlorine disinfection.
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•Studied effect of chlorine disinfection on biofouling of reverse osmosis (RO) system.•Applied lab RO systems, multiple microscopy, gene sequencing and organic analysis.•Chlorine disinfection changed the microbial community structure in foulants.•Four dominant chlorine-resistant strains were found in foulants with 15 mg-Cl2/L.•Extracellular polymeric substance produced by these strains caused severe biofouling.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The oxygen evolution reaction (OER) has been explored extensively for reliable hydrogen supply to boost the energy conversion efficiency. The superior OER performance of newly developed non‐noble ...metal electrocatalysts has concealed the identification of the real active species of the catalysts. Now, the critical active phase in nickel‐based materials (represented by NiNPS) was directly identified by observing the dynamic surface reconstruction during the harsh OER process via combining in situ Raman tracking and ex situ microscopy and spectroscopy analyses. The irreversible phase transformation from NiNPS to α‐Ni(OH)2 and reversible phase transition between α‐Ni(OH)2 and γ‐NiOOH prior to OER demonstrate γ‐NiOOH as the key active species for OER. The hybrid catalyst exhibits 48‐fold enhanced catalytic current at 300 mV and remarkably reduced Tafel slope to 46 mV dec−1, indicating the greatly accelerated catalytic kinetics after surface evolution.
An irreversible phase transformation was tracked in situ from NiNPS to α‐Ni(OH)2. This result and potential‐dependent reversible conversion between α‐Ni(OH)2 and γ‐NiOOH prior to OER unveil the real active species of γ‐NiOOH in self‐reconstructed Ni‐based catalysts.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Water is essential for the sustainable development of human society. With the largest population and rapid economic development, water usage and treatment in China have grown tremendously in the past ...decades. In order to prevent water pollution, the standards for wastewater effluent discharge in China have been gradually developed and implemented since 1973. After the rapid development during over 40 years, numerous milestones have been achieved in terms of infrastructure coverage, standard and policy system establishment, and technological innovations. In this article, we reviewed the development history and the current status of the wastewater treatment in China, including the generation of wastewater, the construction of wastewater treatment plants (WWTPs), the overall treatment performance of WWTPs, as well as the developments in effluent discharge standards. In addition, we highlighted the challenges lying ahead in the aspects of influent concentration, sludge disposal and water reclamation. Based on the achievement and foundation built in the past, the new era of wastewater treatment of China is on the way, in which water reclamation, wastewater treatment in rural areas and resource/energy recovery from sludge are becoming the main tasks.
•The development history of wastewater treatment in China is reviewed.•The development process of wastewater discharge standards of China is summarized.•The treatment performance of WWTPs is evaluated according to discharge standards.•The future challenges in wastewater treatment of China is highlighted.•The main objectives in the new era of wastewater treatment in China is identified.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Using wastewater as resource for microalgal cultivation was seriously considered as a promising approach for sustainable biomass and lipid production. The proper selection of microalgal species is ...the foundation and key point to achieve this objective. This paper reviewed the recent status of microalgal cultivation in wastewater, including the characteristics of microalgal species used in recent studies, the performance of different microalgal species in different types of wastewater, the commonly-used isolation methods of microalgal species adaptable to the growth in wastewater, and the evaluation criteria of microalgal species. It was found that microalgal biomass and lipid production in wastewater were comparable to those in artificial culture medium, although most of the data was obtained in sterilized wastewater. Among all microalgal species involved in this review, Botryococcus braunii, Chlorella pyrenoidosa and Chlamydomonas reinhardtii showed superior performance in certain studies. However, no microalgal species has been demonstrated to meet all the requirements for large-scale biomass production in wastewater. Thus, the efforts on microalgal species isolation and characterization should still be promoted. On the basis of all the information, this review explored the limitations of recent studies and future research needs on this topic.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Pretreatment by high dosage of UV aggravated RO membrane fouling.•The organic matter amount in the foulants increased after UV disinfection.•The content of proteins and polysaccharides in foulants ...increased with high UV dosage.•Typical UV-resistant bacteria were selected in the foulants with high UV dosage.•Residual bacteria after UV disinfection secreted more amounts of EPS.
Membrane fouling is a prominent problem that hinders the stable and efficient operation of the reverse osmosis (RO) system for wastewater reclamation. Previous studies showed that chlorine disinfection, which was commonly used in industrial RO systems as pretreatment, could lead to significant change in microbial community structure and resulted in serious biofouling. In order to prevent biofouling during wastewater reclamation, the effect of ultraviolet (UV) disinfection on RO membrane fouling was investigated and the mechanism was also revealed in this study. With the disinfection pretreatment by UV of 20, 40 and 80 mJ/cm2, the bacteria in the feed water were inactivated significantly with a log reduction of 1.11, 2.55 and 3.61-log, respectively. However, RO membrane fouling aggravated with higher UV dosage. Especially, in the group with the UV dosage of 80 mJ/cm2, the normalized RO membrane flux decreased by 15% compared with the control group after 19-day operation. The morphology of the fouled RO membranes indicated serious biofouling in all groups. The analysis on the microbial amount of the foulants showed that the heterotrophic plate counts (HPC) and ATP content on the fouled RO membranes with and without UV disinfection were at the same level. However, the total organic carbon content of the foulants with the UV dosage of 40 and 80 mJ/cm2 was significantly higher than the control group, with higher content of proteins and polysaccharides as indicated by EEM and FTIR spectrum. Microbial community structure analysis showed that some typical UV-resistant bacteria were selected and remained on the RO membrane after disinfection with high UV dosage, including. These residual bacteria after disinfection with high UV dosage showed higher extracellular polymeric substances (EPS) secretion compared with those without UV disinfection, and thus aggravated RO membrane fouling. Thicker EPS could decrease the transmission of UV rays, and thus bacteria with higher EPS secretion might be selected after UV disinfection.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Polysaccharides were usually considered as important organic compounds causing organic fouling of reverse osmosis (RO) membranes. In this study, the RO membrane fouling behaviors and mechanisms of 9 ...polysaccharides with different molecular weights and structures were studied. It was found that not the molecular weight but the molecular structure mainly influenced the fouling behavior. Straight-chain polysaccharides tended to cause slight and slow membrane fouling (final flux decline < 30% in 100 h), while branched-chain polysaccharides led to severe fouling (final flux decline > 50% in 50 h) and formed thicker foulant layers on membrane surfaces. The presence of Ca2+ could double and even triple the flux decline of straight-chain acid polysaccharides, but showed barely effect on branched-chain polysaccharides as well as neutral polysaccharides. The extended Derjaguin-Laudau-Verwey-Overbeek (XDLVO) theory revealed that attractive energy dominated the interaction between branched-chain polysaccharides and membranes. The addition of Ca2+ turned the repulsive interaction between straght-chain acid polysaccharides and membranes into attractive interaction, but showed no significant effect on neutral polysaccharides. The viscosity of straight-chain polysaccharides didn't increase with the polysaccharide concentrations, while that of branched-chain polysaccharides showed a positive relationship with mass concentrations. Ca2+ also enhanced the viscosity of straight-chain acid polysaccharides.
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•Polysaccharides with branched chains had high fouling potential with or without Ca2+.•Straight-chain polysaccharides showed slight fouling potential without Ca2+.•Ca2+ could aggravate membrane fouling of acidic straight-chain polysaccharides.•Studied the relationship between viscosity and fouling behaviors of polysaccharides.•Quantified and compared the fouling extent of representative polysaccharides.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Electrocatalytic water splitting is one of the most promising sustainable energy conversion technologies, but is limited by the sluggish electrochemical reactions. Inorganic nanomaterials have been ...widely used as efficient catalysts for promoting the electrochemical kinetics. Several approaches to optimize the activities of these nanocatalysts have been developed. The electronic structures of the catalysts play a pivotal role in governing the activity and thus have been identified as an essential descriptor. However, the underlying working mechanisms related to the refined electronic structures remain elusive. To establish the structure–electronic‐behavior–activity relationship, a comprehensive overview of the developed strategies to regulate the electronic structures is presented, emphasizing the surface modification, strain, phase transition, and heterostructure. Current challenges to the fundamental understanding of electron behaviors in the nanocatalysts are fully discussed.
Making split happen: Strategies to regulate electronic structures of materials to optimize their electrocatalytic activities in water splitting are summarized in this Review. The structure–electronic‐behavior–activity relationships are highlighted as well as current challenges on understanding the electronic behaviors.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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