Excessive Ozonation Stress Triggers Severe Membrane Biofilm Accumulation and Fouling.

The established benefits of ozone on microbial pathogen inactivation, natural organic matter degradation, and inorganic/organic contaminant oxidation have favored its application in drinking water treatment. However, viable bacteria are still present after the ozonation of raw water, bringing a potential risk to membrane filtration systems in terms of biofilm accumulation and fouling. In this study, we shed light on the role of the specific ozone dose (0.5 mg-O3/mg-C) in biofilm accumulation during long-term membrane ultrafiltration. Results demonstrated that ozonation transformed the molecular structure of influent dissolved organic matter (DOM), producing fractions that were highly bioavailable at a specific ozone dose of 0.5, which was inferred to be a turning point. With the increase of the specific ozone dose, the biofilm microbial consortium was substantially shifted, demonstrating a decrease in richness and diversity. Unexpectedly, the opportunistic pathogen Legionella was stimulated and occurred in approximately 40% relative abundance at the higher specific ozone dose of 1. Accordingly, the membrane filtration system with a specific ozone dose of 0.5 presented a lower biofilm thickness, a weaker fluorescence intensity, smaller concentrations of polysaccharides and proteins, and a lower Raman activity, leading to a lower hydraulic resistance, compared to that with a specific ozone dose of 1. Our findings highlight the interaction mechanism between molecular-level DOM composition, biofilm microbial consortium, and membrane filtration performance, which provides an in-depth understanding of the impact of ozonation on biofilm accumulation.

Membrane modification in enhancement of virus removal: A critical review.

Many waterborne diseases are related with viruses, and COVID-19 worldwide has raised the concern of virus security in water into the public horizon. Compared to other conventional water treatment processes, membrane technology can achieve satisfactory virus removal with fewer chemicals, and prevent the outbreaks of viruses to a maximal extent. Researchers developed new modification methods to improve membrane performance. This review focused on the membrane modifications that enhance the performance in virus removal. The characteristics of viruses and their removal by membrane filtration were briefly generalized, and membrane modifications were systematically discussed through different virus removal mechanisms, including size exclusion, hydrophilic and hydrophobic interactions, electronic interactions, and inactivation. Advanced functional materials for membrane modification were summarized based on their nature. Furthermore, it is suggested that membranes should be enhanced through different mechanisms mainly based on their ranks of pore size. The current review provided theoretical support regarding membrane modifications in the enhancement of virus removal and avenues for practical application.

Employing Visible Light To Construct Photoinitiated Polymerized Nanofiltration Membranes for High Permeation and Environmental Micropollutant Removal.

Improving the nanofiltration (NF) performance of membrane-based treatment is conducive to promoting environmental water recycling and addressing water resource depletion. Combinations of light, electricity, and heat with traditional techniques of preparing membranes should optimize membrane performance. Interfacial polymerization and photopolymerization were integrated to construct a photopolymerized thin-film composite NF membrane with a ridged surface morphology. Under visible light initiation, 2-acrylamido-2-methyl-1-propanesulfonic acid was crosslinked with the polyamide network. The control effects of light on the membrane surface and physicochemical properties were revealed via infrared thermal images and response surface methodology. To present the diffusion motion of piperazine molecules, molecular dynamics simulations were implemented. Through density functional theory simulations, the crosslinking mechanism of the photoinduced NF network was identified and verified. The surface physicochemical characteristics and perm-selectivity performance were systematically illustrated. The photopolymerized membrane outperformed the pristine in permeability and selective separation competence; without degradation of solute repulsion, the water permeation was enhanced to 33.5 L m-2 h-1 bar-1, 6.6 times that of the initial membrane. In addition, the removal of organic contaminants and antifouling capacities were improved. This work represents a novel lead for applying sustainable resources in constructing high-performance membranes for environmental challenges.

Nanofiltration Membranes with Salt-Responsive Ion Valves for Enhanced Separation Performance in Brackish Water Treatment: A Battle against the Limitation of Salt Concentration.

Utilizing brackish water resources has imposed a high requirement on the design and construction of nanofiltration membranes. To overcome the limitation of high salt concentration on the nanofiltration separation performance resulting from the weakened Donnan effect, a nanofiltration membrane with the effect of salt-responsive ion valves was developed by incorporating zwitterionic nanospheres into the polyamide layer (PA-ZNs). The interaction between the nanospheres and membranes at high salinity was revealed through a combination analysis from the perspectives of water transport model, positron annihilation spectroscopy, and solute rejection, contributing to the formation of the valve effect. The PA-ZNs membrane presented a breakthrough in overcoming the limitation of increased salt concentrations on nanofiltration separation performance, achieving a high selectivity of 105 for mono/multivalent anions. To reveal the role of the ion valve effect in ion transport through the membrane, the membrane conductance was determined at different salt concentrations, confirming channel-controlled transport at low salinity and ion valve-controlled transport at high salinity. Moreover, the main membrane separation mechanisms were systematically studied. The concept of salt-responsive ion valves may contribute to expanding the application of nanofiltration in brackish water treatment.

Fe(II)-Modulated Microporous Electrocatalytic Membranes for Organic Microcontaminant Oxidation and Fouling Control: Mechanisms of Regulating Electron Transport toward Enhanced Reactive Oxygen Species Activation.

Regulation of the fast electron transport process for the generation and utilization of reactive oxygen species (ROS) by achieving fortified electron "nanofluidics" is effective for electrocatalytic oxidation of organic microcontaminants. However, limited available active sites and sluggish mass transfer impede oxidation efficiency. Herein, we fabricated a conductive electrocatalytic membrane decorated with hierarchical porous vertically aligned Fe(II)-modulated FeCo layered double hydroxide nanosheets (Fe(II)-FeCo LDHs) in an electro-Fenton system to maximize exposure of active sites and expedite mass transfer. The nanospaced interlayers of Fe(II)-FeCo LDHs within the microconfined porous structure formed by its vertical nanosheets highly boost the micro/nanofluidic distribution of target pollutants to active centers/species, achieving accelerated mass transferability. Aliovalent substitution by Fe(II) activates in-plane metallics to maximize the available active sites and makes each Fe(II)-FeCo LDH nanosheet a geometrical nanocarrier for constructing a fast electron "nanofluidic" to accelerate Fe(II) regeneration in Fe(III)/Fe(II) cycles. As a result, the Fe(II)-FeCo LDHs exhibited improved reactivity in catalyzing H2O2 to •OH and 1O2. Accordingly, the membrane exhibited a higher atrazine degradation kinetic (0.0441 min-1) and degradation rate (93.2%), which were 4.7 and 2.1 times more than those of the bare carbon nanotube membrane, respectively. Additionally, the enhanced hydrophilic and strongly oxidized reactivity synergistically mitigated the organic fouling occurring in the pores and surface of the membrane. These findings clarify the activation mechanism of ROS over an innovative electrocatalytic membrane reactor design for organic microcontaminant treatment.

Mechanistic Insights of a Thermoresponsive Interface for Fouling Control of Thin-Film Composite Nanofiltration Membranes.

In spite of extensive research, fouling is still the main challenge for nanofiltration membranes, generating an extra transport resistance and requiring a larger operational pressure in practical applications. We fabricated a highly antifouling nanofiltration membrane by grafting poly(N-isopropylacrylamide) (PNIPAM) chains on a bromine-containing polyamide layer. The resulting membrane was found to have a double permeance compared to the pristine membrane, while the rejection of multivalent ions remained the same. In addition, PNIPAM chains yielded a better deposition resistance and adhesion resistance, thereby mitigating the increase of fouling and promoting the recovery of flux during the filtration and traditional cleaning stages, respectively. Moreover, PNIPAM chains shrank when the water temperature was above the lower critical solution temperature (LCST), indicating the formation of a buffer layer between the membrane and pollutants. The buffer layer would eliminate the membrane-foulant interaction energy, thus further enhancing the detachment of pollutants. This simple and efficient cleaning method could act as an enhanced cleaning procedure to remove irreversible fouling. This provides new insights into the fabrication of enhanced antifouling membranes using smart responsive polymer chains.

Nanofiltration Membranes with Octopus Arm-Sucker Surface Morphology: Filtration Performance and Mechanism Investigation.

Precisely tailoring the surface morphology characteristics of the active layers based on bionic inspirations can improve the performance of thin-film composite (TFC) membranes. The remarkable water adsorption and capture abilities of octopus tentacles inspired the construction of a novel TFC nanofiltration (NF) membrane with octopus arm-sucker morphology using carbon nanotubes (CNTs) and beta-cyclodextrin (ß-CD) during interfacial polymerization (IP). The surface morphology, chemical elements, water contact angle (WCA), interfacial free energy (ΔG), electronegativity, and pore size of the membranes were systematically investigated. The optimal membrane exhibited an enhanced water permeance of 22.6 L·m-2·h-1·bar-1, 180% better than that of the TFC-control membrane. In addition, the optimal membrane showed improved single salt rejections and monovalent/divalent ion selectivity and can break the trade-off effect. The antiscaling performance and stability of the membranes were further explored. The construction mechanism of the octopus arm-sucker structure was excavated, in which CNTs and ß-CD acted as arm skeletons and suckers, respectively. Furthermore, the customization of the membrane surface and performance was achieved through tuning the individual effects of the arm skeletons and suckers. This study highlights the noteworthy potential of the design and construction of the surface morphology of high-performance NF membranes for environmental application.

MXene Nanosheet Templated Nanofiltration Membranes toward Ultrahigh Water Transport.

The demand for thin-film composite (TFC) nanofiltration membranes with superior permeance and high rejection is gradually increasing for seawater desalination and brackish water softening. However, improving the membrane permeance remains a great challenge due to the formation of excrescent polyamide in the substrate pores and thick polyamide film. Herein, we fabricated a high-performance TFC nanofiltration membrane via a classical interfacial polymerization reaction on a two-dimensional lamellar layer of transition-metal carbides (MXene). The MXene layer promoted the absorption of the reactive monomer, and higher amine monomer concentration facilitated the self-sealing and self-termination of interfacial polymerization to generate a thinner outer polyamide film from 68 to 20 nm. The almost nonporous lamellar interface inhibited the formation of inner polyamide in the substrate pores. In addition, the MXene lamellar layer could be eliminated by mild oxidation after interfacial polymerization to avoid imparted additional hydraulic resistance. The resulting TFC membrane conferred a high rejection above 96% for Na2SO4 and excellent permeance of 45.7 L·m-2·h-1·bar-1, which was almost 4.5 times higher than that of the control membrane (10.2 L·m-2·h-1·bar-1). This research provides a feasible strategy for fabricating a high-performance nanofiltration membrane using two-dimensional nanosheets as a templated interface.

Comparison of pyrolysis process, various fractions and potential soil applications between sewage sludge-based biochars and lignocellulose-based biochars.

To deeply assess the feasibility of sewage sludge-based biochars for use in soil applications, this review compared sewage sludge-based biochars (SSBBs) with lignocellulose-based biochars (LCBBs) in terms of their pyrolysis processes, various fractions and potential soil applications. Based on the reviewed literature, significant differences between the components of SSBB and LCBB result in different pyrolysis behavior. In terms of the fractions of biochars, obvious differences were confirmed to exist in the carbon content, surface functional groups, types of ash fractions and contents of potential toxic elements (PTEs). However, a clear influence of the feedstock on labile carbon and polycyclic aromatic hydrocarbons (PAHs) was not observed in the current research. These differences determined subsequent discrepancies in the soil application potential and corresponding mechanisms. The major challenges facing biochar application in soils and corresponding recommendations for future research were also addressed. LCBBs promote carbon sequestration, heavy metal retention and organic matter immobilization. The application of SSBBs is a promising approach to improve soil phosphorus fertility, immobilize heavy metals and provide available carbon sources for soil microbes to stimulate microbial biomass. The present review provides guidance information for selecting appropriate types of biochars to address targeted soil issues.

Ultrathin Thin-Film Composite Polyamide Membranes Constructed on Hydrophilic Poly(vinyl alcohol) Decorated Support Toward Enhanced Nanofiltration Performance.

Traditional polyamide-based interfacial polymerized nanofiltration (NF) membranes exhibit upper bound features between water permeance and salt selectivity. Breaking the limits of the permeability and rejections of these composite NF membranes are highly desirable for water desalination. Herein, a high-performance NF membrane (TFC-P) was fabricated via interfacial polymerization on the poly(vinyl alcohol) (PVA) interlayered poly(ether sulfone) (PES) ultrafiltration support. Owing to the large surface area, great hydrophilicity, and high porosity of the PES-PVA support, a highly cross-linked polyamide separating layer was formed with a thickness of 9.6 nm, which was almost 90% thinner than that of the control membrane (TFC-C). In addition, the TFC-P possessed lower ζ-potential, smaller pore size, and greater surface area compared to that of the TFC-C, achieving an ultrahigh water permeance of 31.4 L m-2 h-1 bar-1 and a 99.4% Na2SO4 rejection. Importantly, the PVA interlayer strategy was further applied to a pilot NF production line and the fabricated membranes presented stable water flux and salt rejections as comparable to the lab-scaled membranes. The outstanding properties of the PVA-interlayered NF membranes highlight the feasibility of the fabrication method for practical applications, which provides a new avenue to develop robust polyamide-based NF desalination membranes for environmental water treatment.

Hybrid UF/NF process treating secondary effluent of wastewater treatment plants for potable water reuse: Adsorption vs. coagulation for removal improvements and membrane fouling alleviation.

Coagulation and adsorption are gradually adopted as pre-treatments to produce reclaimed potable water. However, previous researches on membrane fouling mechanisms were currently insufficient to minimize dual membrane fouling. This study aimed at investigating the effects of pre-coagulation and pre-adsorption on the removal performance and membrane fouling alleviation of dual membrane UF/NF process in treating secondary effluent from a wastewater treatment plant. The results indicated that both types of pretreatments conferred positive effects on organic membrane fouling removal of the UF process whereas diverse effects on NF process. Pre-coagulation could enhance the removal of nitrogen and phosphorus to contribute towards producing microbiologically-stable water. On the other hand, introduction of Al3+ reduced the removal efficiency of UF/NF systems on heavy metals. From the perspective of UF membrane fouling, two pretreatments employed could increase the flux of UF, but simultaneously aggravating irreversible membrane fouling. Hermia and Tansel models revealed an unstable cake filtration was caused by pre-coagulation and pre-adsorption. Both the models consistently demonstrated the rapid formation of cake filtration onto UF membrane surface. Interestingly, the powdered activated carbon (PAC) adsorption could significantly reduce cake layer fouling onto the surface of NF membrane, while pre-coagulation aggravated the NF fouling. These results are essential to developing robust, cost-effective and energy-efficient strategies based on membranes to produce reclaimed potable water.

Feasibility of sludge-based biochar for soil remediation: Characteristics and safety performance of heavy metals influenced by pyrolysis temperatures.

Sludge-based biochars (SBB) were prepared to evaluate their physiochemical properties and safety performance for the possible application in soil amendments in this study. SBB were produced at the temperatures ranging from 300 to 900 °C at 200 °C intervals. Both the solid fraction and the soluble organic fraction of SBB were analyzed. The pyrolysis temperature was found to affect the characteristics of solid fraction of the SBB greatly, in terms of the pH, surface area and functional groups. The content and composition of dissolved organic matter in SBB were influenced evidently by pyrolysis temperatures, which was mainly comprised of humic-like compounds with the molecular weight in a range of 0.13-2.4 × 105 kDa. The safety performance of heavy metals in SBB at different temperatures were analyzed: (i) The bioavailable fractions (F1+F2+F3) of heavy metals significantly decreased from 91.65% to 9.44% for Cu, from 98.82% to 63.34% for Zn, from 97.91% to 52.11% for As, from 55.91% to 4.87% for Pb, from 78.20% to 12.50% for Cd, and from 73.51% to 9.57% for Cr when sludge was pyrolyzed to biochars at 900 °C.; (ii) Acid and alkaline conditions promoted the leaching of heavy metals from SBB. The luminescence inhibition of Vibrio fischeri was significantly decreased from 81.41% to 6.01% with the increasing pyrolysis temperatures. Compared with the raw sludge addition, the shoot length, root length and activities of soil microbes in sandy soil and loamy soil with pyrolyzed sludge under different pyrolysis temperatures were increased by 37.5-53.32%, 66.81-96.45%, 92.31-157.69% and 154.74-195.76%, respectively. The biotoxicity tests indicated the relatively safe and reliable performance of SBB. The study provided significant perspectives on the application of SBB as the potential soil amendments.

Incorporation of Cellulose Nanocrystals (CNCs) into the Polyamide Layer of Thin-Film Composite (TFC) Nanofiltration Membranes for Enhanced Separation Performance and Antifouling Properties.

To achieve greater separation performance and antifouling properties in a thin-film composite (TFC) nanofiltration membrane, cellulose nanocrystals (CNCs) were incorporated into the polyamide layer of a TFC membrane for the first time. The results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the successful formation of the CNC-polyamide composite layer. Surface characterization results revealed differences in the morphologies of the CNC-TFC membranes compared with a control membrane (CNC-TFC-0). Streaming potential measurements and molecular weight cutoff (MWCO) characterizations showed that the CNC-TFC membranes exhibited a greater negative surface charge and a smaller MWCO as the CNC content increased. The CNC-TFC membranes showed enhanced hydrophilicity and increased permeability. With the incorporation of only 0.020 wt % CNCs, the permeability of the CNC-TFC membrane increased by 60.0% over that of the polyamide TFC without CNC. Rejection of Na2SO4 and MgSO4 by the CNC-TFC membranes was similar to that observed for the CNC-TFC-0 membrane, at values of approximately 98.7% and 98.8%, respectively, indicating that divalent salt rejection was not sacrificed. The monovalent ion rejection tended to increase as the CNC content increased. In addition, the CNC-TFC membranes exhibited enhanced antifouling properties due to their increased hydrophilicity and more negatively charged surfaces.

Membrane Fouling and Rejection of Organics during Algae-Laden Water Treatment Using Ultrafiltration: A Comparison between in Situ Pretreatment with Fe(II)/Persulfate and Ozone.

In this study, in situ pretreatments with ozone and Fe(II)/persulfate were employed to suppress membrane fouling during the filtration of algae-laden water and to improve the rejection of metabolites. Both ozonation and Fe(II)/persulfate pretreatments negatively impacted the cell integrity, especially ozonation. Fe(II)/persulfate pretreatment improved the removal of dissolved organic carbon and microcystin-LR, but ozonation resulted in a deterioration in the quality of the filtered water. This suggests that the Fe(II)/persulfate oxidation is selective for organic degradation over cell damage. With ozonation, 2-methylisoborneol and geosmin were detected in the filtered water, and the irreversible fouling increased. The intracellular organic release and generation of small organic compounds with ozonation may be the reason for the increased membrane fouling. Fe(II)/persulfate oxidation substantially mitigated the membrane-fouling resistance at concentrations over 0.2 mM compared to the membrane-fouling resistance without oxidation. The combined effect of oxidation and coagulation is likely the reason for the excellent fouling control with Fe(II)/persulfate pretreatment. Membrane fouling during the filtration of algae-laden water is successively governed by complete-blocking and cake-filtration mechanisms. Ozonation caused a shift in the initial major mechanism to intermediate blocking, and the Fe(II)/persulfate pretreatment (>0.2 mM) converted the dominant mechanism into single-standard blocking.

Comparison of Hydrophilicity and Mechanical Properties of Nanocomposite Membranes with Cellulose Nanocrystals and Carbon Nanotubes.

The inherent properties of hydrophilicity and mechanical strength of cellulose nanocrystals (CNCs) make them a possible alternative to carbon nanotubes (CNTs) that may present fewer objections to application water-treatment membranes. In this work, the hydrophilicity and mechanical properties of CNCs and CNTs nanocomposite poly(ether sulfone) (PES) membranes were characterized and compared. Membrane pore geometry was analyzed by scanning electron microscopy (SEM). Overall porosity and mean pore radius were calculated based on a wet-dry method. Results showed that PES polymers were loosely packed in the top layer of both the CNC- and CNT-composite membranes (CNC-M and CNT-M). The porosity of the CNC-M was greater than that of the CNT-M. Membrane hydrophilicity, measured by water-contact angle, free energy of cohesion, and water flux, was increased through the addition of either CNCs or functionalized CNTs to an otherwise hydrophobic polymer membrane. The hydrophilicity of the CNC-M was greater than the CNT-M. In addition, the Young's modulus and tensile strength was enhanced for both the CNC-M and CNT-M. While smaller concentrations of CNTs were required to achieve an equal increase in Young's modulus compared with the CNCs, the elasticity of the CNC-composite membranes was greater.

Biofouling control by biostimulation of quorum-quenching bacteria in a membrane bioreactor for wastewater treatment.

Bacterial quorum quenching (QQ) has been shown to be effective in controlling biofouling in membrane bioreactors (MBRs) for wastewater treatment. However, the encapsulation of a sufficient level of QQ bacteria is complicated and difficult. In plant research, gamma-caprolactone (GCL), which is structurally similar to the quorum signal, N-acyl homoserine lactone (AHL), was successfully used to specifically stimulate AHL-degrading bacteria (biostimulation) in hydroponic systems to control blackleg and soft rot diseases in potato. In this study, the feasibility of enriching QQ bacteria from activated sludge by GCL was examined, and the effect of biostimulation on biofouling control in MBR treating domestic wastewater was investigated. The results showed that after enrichment with GCL, activated sludge could effectively degrade AHLs, and a QQ gene (qsdA) was augmented. The proposed biostimulation QQ strategy, by introducing and continuously dosing GCL, could significantly increase QQ activity, decrease AHL, control the secretion of extracellular polymeric substances (EPS), and thus, effectively control biofouling in an MBR. This biostimulation QQ strategy provides a more convenient option for biofouling control in MBR applications. Biotechnol. Bioeng. 2016;113: 2624-2632. © 2016 Wiley Periodicals, Inc.

Effect of solid retention time on membrane fouling in membrane bioreactor: from the perspective of quorum sensing and quorum quenching.

Solid retention time (SRT) is one of the most important operational parameters in membrane bioreactor (MBR), which significantly influences membrane fouling. It is widely recognized that SRT mainly changes biomass characteristics, and then, influences membrane fouling. Effect of SRT on quorum sensing (QS) in MBR, which could also influence fouling by coordinating biofilm formation, has not been reported. In this study, fouling, QS, soluble microbial products (SMP), and extracellular polymer substances (EPS) in MBRs operated under SRTs of 4, 10, and 40 days were investigated. The results showed that as SRT increased, the abundance of quorum quenching (QQ) bacteria increased, the quorum signal degradation activity of activated sludge increased, the concentrations of signal molecules in MBR decreased, the excretion of SMP and EPS decreased, and thus membrane biofouling was alleviated. Therefore, besides altering the biomass physiochemical properties, SRT also changed the balance between QS and QQ in MBR, and in this way, influenced membrane biofouling.

Towards a better hydraulic cleaning strategy for ultrafiltration membrane fouling by humic acid: Effect of backwash water composition.

As a routine measurement to alleviate membrane fouling, hydraulic cleaning is of great significance for the steady operation of ultrafiltration (UF) systems in water treatment processes. In this work, a comparative study was performed to investigate the effects of the composition of backwash water on the hydraulic cleaning performance of UF membranes fouled by humic acid (HA). Various types of backwash water, including UF permeate, Milli-Q water, NaCl solution, CaCl2 solution and HA solution, were compared in terms of hydraulically irreversible fouling index, total surface tension and residual HA. The results indicated that Milli-Q water backwash was superior to UF permeate backwash in cleaning HA-fouled membranes, and the backwash water containing Na(+) or HA outperformed Milli-Q water in alleviating HA fouling. On the contrary, the presence of Ca(2+) in backwash water significantly decreased the backwash efficiency. Moreover, Ca(2+) played an important role in foulant removal, and the residual HA content closely related to the residual Ca(2+) content. Mechanism analysis suggested that the backwash process may involve fouling layer swelling, ion exchange, electric double layer release and competitive complexation. Ion exchange and competitive complexation played significant roles in the efficient hydraulic cleaning associated with Na(+) and HA, respectively.

Effects of poly aluminum chloride dosing positions on the performance of a pilot scale anoxic/oxic-membrane bioreactor (A/O-MBR).

The effects of poly aluminum chloride (PACl) dosing positions on the performance of a pilot scale anoxic/oxic membrane bioreactor were investigated. PACl dosage was optimized at 19.5 mg Al2O3/L by jar test. Nutrients removal efficiencies and sludge properties were systematically investigated during periods with no PACl dosing (phase I), with PACl dosing in oxic tank (phase II) and then in anoxic tank (phase III). The results showed that total phosphorus removal efficiency increased from 18 to 88% in phase II and 85% in phase III with less than 0.5 mg P/L in effluent. Ammonia nitrogen removal efficiencies reached 99% in all phases and chemical oxygen demand removal efficiencies reached 92%, 91% and 90% in the three phases, respectively. Total nitrogen removal efficiency decreased from 59% in phase I to 49% in phases II and III. Dosing PACl in the oxic tank resulted in smaller sludge particle size, higher zeta potential, better sludge settleability and lower membrane fouling rate in comparison with dosing PACl in the anoxic tank.

Seasonal succession of phytoplankton community and its relationship with environmental factors of North Temperate Zone water of the Zhalong Wetland, in China.

A data set of phytoplankton community and environmental parameters in a hydrological integrity period, i.e. a poor water term, a medium term and a rich water term of North Temperate Zone climate, was analyzed in order to describe seasonal variation of phytoplankton community and its relationship with environmental variables in the Zhalong Wetland of China. The algal population of the Zhalong Wetland was not abundant, with a mean density of 5.08 × 10(7) cell/L (ranged from 4.54 × 10(7) cell/L in a poor term to 5.56 × 10(7) cell/L a medium term). However, its diversity was essentially limited to Cryptophyta, Bacillariophyta, Chlorophyta, Euglenophyta being the group with highest densities. There were considerable seasonal variations in phytoplankton composition. In general, the dominance of Bacillariophyceae was found in a medium term, which was higher than the other period (p < 0.05). The rich water period also showed Bacillariophyceae and Chlorophyta dominance while the phytoplankton was dominated by Cryptophyta erosa in a poor water term. 10 environmental variables, which were significant (p < 0.05) during the studied periods in one-way analysis of covariance, were selected to explore the relationship between phytoplankton structure and environmental factors by canonical correspondence analysis (CCA). The results of the CCA applied to the environmental factors indicated that water temperature (WT) and ammonia (NH3-N) significantly influenced the phytoplankton community (p < 0.05; Monte Carlo test of first constrained axis). Besides WT and NH3-N, the most discriminate physic-chemical variables were nitrite (NO2-N), suspend solid, nitrate (NO3-N), silicon dioxide (SiO2) and all the 10 physical-chemical parameters had a higher marginal effect and λA in the series of constrained CCAs though they were not significant.