Ceramic membrane fouling mechanisms and control for water treatment

Membrane separation, as an important drinking water treatment technology, has wide applications. The remarkable advantages of ceramic membranes, such as chemical stability, thermal stability, and high mechanical strength, endow them with broader prospects for development. Despite the importance and advantages of membrane separation in water treatment, the technique has a limitation: membrane fouling, which greatly lowers its effectiveness. This is caused by organics, inorganic substances, and microorganisms clogging the pore and polluting the membrane surface. The increase in membrane pollution greatly lowers purification effectiveness. Controlling membrane fouling is critical in ensuring the efficient and stable operation of ceramic membranes for water treatment. This review analyzes four mechanisms of ceramic membrane fouling, namely complete blocking, standard blocking, intermediate blocking, and cake filtration blocking. It evaluates the mechanisms underlying ceramic membrane fouling and summarizes the progress in approaches aimed at controlling it. These include ceramic membrane pretreatment, ceramic membrane surface modification, membrane cleaning, magnetization, ultrasonics, and nanobubbles. This review highlights the importance of optimizing ceramic membrane preparation through further research on membrane fouling and pre-membrane pretreatment mechanisms. In addition, combining process regulations with ceramic membranes as the core is an important research direction for ceramic membrane-based water treatment.

Insight of chemical environmental risk and its management from the vinyl chloride accident

The combustion of vinyl chloride(VC)after the train derailment accident in Ohio,USA in February,2023 has caused widespread concern around the world.This paper tried to analyze several issues concerning the accident,including the appropriateness of the VC combustion in the emergency response in this accident,the meanings of so-called“controlled combustion”,the potential environmental risks caused by VC and combustion by-products,and follow-up work.In our view,this accident had surely caused environmental and health risks to some extent.Hence,a comprehensive environmental risk assessment is necessary,and then the site with risk should be comprehensively remediated,hazardous waste should be harmlessly treated as soon as possible.Finally,this accident suggests that further efforts should be taken to bridge the gap between chemical safety management and their environmental risk management.

Dissolved organic matter accelerates microbial degradation of 17 alpha-ethinylestradiol in the presence of iron mineral

Dissolved organic matter(DOM)and iron minerals widely existing in the natural aquatic environment can mediate the migration and transformation of organic pollutants.However,the mechanism of interaction between DOM and iron minerals in the microbial degradation of pollutants deserves further investigation.In this study,the mechanism of 17 alphaethinylestradiol(EE2)biodegradation mediated by humic acid(HA)and three kinds of iron minerals(goethite,magnetite,and pyrite)was investigated.The results found that HA and iron minerals significantly accelerated the biodegradation process of EE2,and the highest degradation efficiency of EE2(48%)was observed in the HA-mediated microbial system with pyrite under aerobic conditions.Furthermore,it had been demonstrated that hydroxyl radicals(HO·)was the main active substance responsible for the microbial degradation of EE2.HO·is primarily generated through the reaction between hydrogen peroxide secreted by microorganisms and Fe(II),with aerobic conditions being more conducive.The presence of iron minerals and HA could change the microbial communities in the EE2 biodegradation system.These findings provide new information for exploring the migration and transformation of pollutants by microorganisms in iron-rich environments.

Intake of tobacco nitrosamines of smokers in various provinces of China and their cancer risk:A meta-analysis

Nitrosamines are a class of carcinogens which have been detected widely in food,water,some pharmaceuticals as well as tobacco.The objectives of this paper include reviewing the basic information on tobacco consumption and nitrosamine contents,and assessing the health risks of tobacco nitrosamines exposure to Chinese smokers.We searched the publications in English from“Web of Science”and those in Chinese from the“China National Knowledge Infrastructure”in 2022 and collected 151 literatures with valid information.The content of main nitrosamines in tobacco,including 4-(methylnitrosoamino)-1-(3-pyridyl)-1-butanone(NNK),N-nitrosonornicotine(NNN),N-nitrosoanatabine(NAT),N-nitrosoanabasine(NAB),total tobacco-specific nitrosamines(TSNA),and N-nitrosodimethylamine(NDMA)were summarized.The information of daily tobacco consumption of smokers in 30 provinces of China was also collected.Then,the intakes of NNN,NNK,NAT,NAB,TSNAs,and NDMA via tobacco smoke were estimated as 1534ng/day,591 ng/day,685 ng/day,81 ng/day,2543 ng/day,and 484 ng/day by adult smokers in30 provinces,respectively.The cancer risk(CR)values for NNN and NNK inhalation intake were further calculated as 1.44×10^(-5)and 1.95×10^(-4).The CR value for NDMA intake via tobacco smoke(inhalation:1.66×10^(-4))indicates that NDMA is similarly dangerous in tobacco smoke when compared with the TSNAs.In China,the CR values caused by average nitrosamines intake via various exposures and their order can be estimated as the following:smoke(3.75×10^(-4))>food(1.74×10^(-4))>drinking water(1.38×10^(-5)).Smokers in China averagely suffer 200%of extra cancer risk caused by nitrosamines in tobacco when compared with non-smokers.

Review on corrosion and corrosion scale formation upon unlined cast iron pipes in drinking water distribution systems

The qualified finished water from water treatment plants(WTPs) may become discolored and deteriorated during transportation in drinking water distribution systems(DWDSs), which affected tap water quality seriously. This water stability problem often occurs due to pipe corrosion and the destabilization of corrosion scales. This paper provides a comprehensive review of pipe corrosion in DWDSs, including corrosion process, corrosion scale formation, influencing factors and monitoring technologies utilized in DWDSs. In terms of corrosion process, corrosion occurrence, development mechanisms, currently applied assays, and indices used to determine the corrosion possibility are summarized, as well as the chemical and bacterial influences. In terms of scale formation, explanations for the nature of corrosion and scale formation mechanisms are discussed and its typical multilayered structure is illustrated. Furthermore, the influences of water quality and microbial activity on scale transformation are comprehensively discussed. Corrosion-related bacteria at the genus level and their associated corrosion mechanism are also summarized. This review helps deepen the current understanding of pipe corrosion and scale formation in DWDSs, providing guidance for water supply utilities to ensure effective measures to maintain water quality stability and guarantee drinking water safety.

Influence of pore structure on biologically activated carbon performance and biofilm microbial characteristics

Optimizing the characteristics of granular activated carbon(GAC)can improve the performance of biologically activated carbon(BAC)filters,and iodine value has always been the principal index for GAC selection.However,in this study,among three types of GAC treating the same humic acidcontaminated water,one had an iodine value 35%lower than the other two,but the dissolved organic carbon removal efficiency of its BAC was less than 5%away from the others.Iodine value was found to influence the removal of different organic fractions instead of the total removal efficiency.Based on the removal and biological characteristics,two possible mechanisms of organic matter removal during steady-state were suggested.For GAC with poor micropore volume and iodine value,high molecular weight substances(3500–9000 Da)were removed mainly through degradation by microorganisms,and the biodegraded organics(soluble microbial by-products,<3500 Da)were released because of the low adsorption capacity of activated carbon.For GAC with higher micropore volume and iodine value,organics with low molecular weight(<3500 Da)were more easily removed,first being adsorbed by micropores and then biodegraded by the biofilm.The biomass was determined by the pore volume with pore diameters greater than 100μm,but did not correspond to the removal efficiency.Nevertheless,the microbial community structure was coordinate with both the pore structure and the organic removal characteristics.The findings provide a theoretical basis for selecting GAC for the BAC process based on its pore structure.

Modelling the thresholds of nitrogen/phosphorus concentration and hydraulic retention time for bloom control in reclaimed water landscape

The risks posed by algal blooms caused by nitrogen and phosphorus in reclaimed water used in urban water landscapes need to be carefully controlled.In this study,the combined effects of the nitrogen and phosphorus concentrations and the light intensity and temperature on the specific growth rates of algae were determined using Monod,Steele,and Arrhenius models,then an integrated algal growth model was developed.The algae biomass,nitrogen concentration,and phosphorus concentration mass balance equations were used to establish a new control model describing the nitrogen and phosphorus concentration and hydraulic retention time thresholds for algal blooms.The model parameters were determined by fitting the models to data acquired experimentally.Finally,the control model and numerical simulations for six typical algae and mixed algae under standard conditions were used to determine nitrogen/phosphorus concentration and hydraulic retention time thresholds for landscape water to which reclaimed water is supplied(i.e.,for a reclaimed water landscape).

Seasonal variations of microbial community and antibiotic resistome in a suburb drinking water distribution system in a northern Chinese city

Antibiotic resistance genes(ARGs)are an emerging issue for drinkingwater safety.However,the seasonal variation of ARGs in drinking water distribution systems(DWDS)is still unclear.This work revealed the tempo-spatial changes of microbial community,ARGs,mobile genetic elements(MGEs)co-occurring with ARGs,ARG hosts in DWDS bulk water by means of metagenome assembly.The microbial community and antibiotic resistome varied with sampling season and site.Temperature,ammonia,chlorite and total plate count(TPC)drove the variations of microbial community structure.Moreover,environmental parameters(total organic carbon(TOC),chlorite,TPC and hardness)shifted antibiotic resistome.ARGs and MGEs co-occurring with ARGs showed higher relative abundance in summer and autumn,which might be attributed to detached pipe biofilm.In particular,ARG-bacitracin and plasmid were the predominant ARG and MGE,respectively.ARG hosts changed with season and site and were more diverse in summer and autumn.In winter and spring,Limnohabitans and Mycobacterium were the major ARG hosts as well as the dominant genera in microbial community.In addition,in summer and autumn,high relative abundance of Achromobacter and Stenotrophomonas were the hosts harboring many kinds of ARGs and MGEs at site in a residential zone(0.4 km from the water treatment plant).Compared with MGEs,microbial community had a greater contribution to the variation of antibiotic resistome.This work gives new insights into the dynamics of ARGs in full-scale DWDS and the underlying factors.

Photosensitivity sources of dissolved organic matter from wastewater treatment plants and their mediation effect on 17α-ethinylestradiol photodegradation

Dissolved organic matter(DOM)from each treatment process of wastewater treatment plants(WWTPs)contains abundant photosensitive substances,which could significantly affect the photodegradation of 17α-ethinylestradiol(EE2).Nevertheless,information about EE2 photodegradation behavior mediated by DOM from diverse WWTPs and the photosensitivity sources of such DOM are inadequate.This study explored the photodegradation behavior of EE2 mediated by four typical WWTPs’DOM solutions and investigated the photosensitivity sources of DOM in the anaerobic-anoxic-oxic(A2/O)process.The parallel factor analysis identified three varying fluorescing components of these DOM,tryptophan-like substances or protein-like substances,microbial humuslike substances,and humic-like components.The photodegradation rate constants of EE2 were positively associated with the humification degree of DOM(P<0.05).The triplet state substances were responsible for the degradation of EE2.DOM extracted from the A2/O process,especially in the secondary treatment process had the fastest EE2 photodegradation rate compared to that of the other three processes.Four types of components(water-soluble organic matter(WSOM),extracellular polymeric substance,humic acid,and fulvic acid)were separated from the A2/O process DOM.WSOM had the highest promotion effect on EE2 photodegradation.Fulvic acid-like components and humic acid-like organic compounds in WSOM were speculated to be important photosensitivity substances that can generate triplet state substances.This research explored the physicochemical properties and photosensitive sources of DOM in WWTPs,and explained the fate of estrogens photodegradation in natural waters.

Molecular ecological networks reveal the spatial-temporal variation of microbial communities in drinking water distribution systems

Microbial activity and regrowth in drinking water distribution systems is a major concern for water service companies.However,previous studies have focused on the microbial composition and diversity of the drinkingwater distribution systems(DWDSs),with little discussion on microbial molecular ecological networks(MENs)in different water supply networks.MEN analysis explores the potentialmicrobial interaction and the impact of environmental stress,to explain the characteristics of microbial community structures.In this study,the random matrix theory-based network analysis was employed to investigate the impact of seasonal variation including water source switching on the networks of three DWDSs that used different disinfection methods.The results showed that microbial interaction varied slightly with the seasons but was significantly influenced by different DWDSs.Proteobacteria,identified as key species,play an important role in the network.Combined UV-chlorine disinfection can effectively reduce the size and complexity of the network compared to chlorine disinfection alone,ignoring seasonal variations,which may affect microbial activity or control microbial regrowth in DWDSs.This study provides new insights for analyzing the dynamics of microbial interactions in DWDSs.

One representative water supply system in China with nitrosamine concern: Challenges and treatment strategies

Four sampling campaigns were conducted in two years to understand the fluctuation of N-Nitrosamines(NAs) and their precursors in one drinking water treatment plant(DWTP) in East China in different seasons.This water supply system has been facing several nitrosamine challenges related with source water, including the switch of water source,high concentration of ammonium, formed NAs and NA formation potential(FP) in source water.Besides, the use of ozonation in the DWTP and chloramination in networks will increase the NDMA concentration in tap water.To address these challenges, the biopretreatment was applied in this DWTP to decrease the concentration of ammonium and NAs.The following biological activated carbon(BAC) will neutralize the nitrosamine increase brought by ozonation.The use of free chlorine in disinfection process will also decrease the NDMA formation compared with chloramination.The results will benefit other cities in China and other countries with similar impacted water sources.

Optimization and modeling of coagulation-flocculation to remove algae and organic matter from surface water by response surface methodology

Seasonal algal blooms of Lake Yangcheng highlight the necessity to develop an effective and optimal water treatment process to enhance the removal of algae and dissolved organic matter (DOM). In the present study, the coagulation performance for the removal of algae, turbidity, dissolved organic carbon (DOC) and ultraviolet absorbance at 254 nm (UV254) was investigated systematically by central composite design (CCD) using response surface methodology (RSM). The regression models were developed to illustrate the relationships between coagulation performance and experimental variables. Analysis of variance (ANOVA) was performed to test the significance of the response surface models. It can be concluded that the major mechanisms of coagulation to remove algae and DOM were charge neutralization and sweep flocculation at a pH range of 4.66–6.34. The optimal coagulation conditions with coagulant dosage of 7.57 mg Al/L, pH of 5.42 and initial algal cell density of 3.83 × 106 cell/mL led to removal of 96.76%, 97.64%, 40.23% and 30.12% in term of cell density, turbidity, DOC and UV254 absorbance, respectively, which were in good agreement with the validation experimental results. A comparison between the modeling results derived through both ANOVA and artificial neural networks (ANN) based on experimental data showed a high correlation coefficient, which indicated that the models were significant and fitted well with experimental results. The results proposed a valuable reference for the treatment of algae-laden surface water in practical application by the optimal coagulation-flocculation process.

PPCPs in a drinking water treatment plant in the Yangtze River Delta of China: Occurrence,removal and risk assessment

The occurrence and removal of 39 targeted pharmaceuticals and personal care products(PPCPs)from source water,through a drinking water treatment plant(DWTP)to the water supply station,were investigated around the central part of Yangtze River Delta in China using both grab sampling and continuous sampling.Totally 24 of the 39 targeted PPCPs were detected in raw water,and 12 PPCPs were detected in the finished water.The highest observed concentration was enrofloxacin(85.623 ng/L)in raw water.Removal efficiencies were remarkably negative correlated with log Kow(r =– 0.777,p < 0.01)after calibration control of concentration,indicating that more soluble PPCPs are easier to remove by the combined process(prechlorination and flocculation/precipitation),the concentration level also had a great impact on the removal efficiency.The normal process in the pilot DWTP seems to be ineffective for PPCPs control,with the limited removal efficiency of less than 30% for each step: pre-chlorination,flocculation and precipitation,post-chlorination and filter.There were notable differences between the data from continuous sampling and grab sampling,which should be considered for different monitoring purposes.The chlorination and the hydrolytic decomposition of PPCPs in the water supply pipe may attenuate PPCPs concentration in the pipeline network.The PPCPs examined in the effluent of DWTP do not impose a potential health risk to the local consumers due to their RQ value lower than 0.00067.

Emerging contaminant control:From science to action

Since the concept of emerging contaminants(ECs)was first proposed in 2001,the global scientific research of ECs has developed rapidly.In the past decades,great progress has been achieved in the scientific research of ECs in China,including the establishment of EC analysis method system,the evaluation of the pollution status,pollution characteristics and environmental risk of ECs in typical regions of China,and establishment of EC control technology system.Continuous progress in scientific research of ECs promoted China’s action on EC control.It is planned that the environmental risk of ECs will be generally controlled by 2035 in China.Priority ECs should be screened for environmental management.Although great efforts have been made,the EC control in China still faces tremendous challenges.It is necessary to bridge the gap between scientific research and decision-making management.Based on the science and technology study,various measures such as engineering,policy management and public participation should be combinedly adopted for EC control.

Insight into fluorescence properties of 14 selected toxic single-ring aromatic compounds in water:Experimental and DFT study

Various single-ring aromatic compounds in water sources are of great concern due to its hazardous impact on the environment and human health.The fluorescence excitation-emission matrix(EEMs)spectrophotometry is a useftil method to identify organic pollutants in water.This study provides a detailed insight into the fluorescence properties of the 14 selected toxic single-ring aromatic compounds by experimental and theoretical analysis.The theoretical analysis were done with Time-Dependent Density Functional Theory(TD-DFT)and B3LYP/6-31G(d,p)basis set,whereas,Polarizable Continuum Model(PCM)was used to consider water as solvent.The selected compounds displayed their own specific excitation-emission(Ex/Em)wavelengths region,at Ex<280 nm and Em<340 nm,respectively.Whereas the theoretical Ex/Em was observed as.Ex at 240 nm-260 nm and Em at 255 nm-300 nm.Aniline as a strong aromatic base has longer Em(340 nm)than alkyl,carbonyl,and halogens substituted benzenes.The lone pair of electrons at amide substituent serves as a 7r-electron contributor into the aromatic ring,hence increasing the stability and transition energy,which results in longer emission and low quantum yield for the aniline.The fluorescence of halogenated benzenes illustrates an increase in the HOMO-LUMO energy gap and a decrease in quantum yield associated with atomic size(F>Cl>Br>I).In this study the theoretical results are in line with experimental ones.The understanding of fluorescence and photophysical properties are of great importance in the identification of these compounds in the water.

Potential shift of bacterial community structure and corrosion-related bacteria in drinking water distribution pipeline driven by water source switching

As a result of pollution in the present water sources,cities have been forced to utilize cleaner water sources.There are few reports regarding the potential shift of bacterial community structure driven by water source switching,especially that of corrosion-related bacteria.Three types of finished water were used for simulation,the polluted source water from the Qiantang and Dongtiaoxi Rivers(China)was replaced by cleaner water from Qiandao Lake(China).Here,we discussed the transition effects through three simulated reactors.The bacterial characteristics were identified using the highthroughput sequencing and heterotrophic plate count method.It was observed that the level of culturable bacteria declined by 2–3 orders of magnitude after water source switching.The bacterial community released from the pipeline reactor was significantly different under different finished water,and it exhibited large variation at the genus level.Porphyrobacter(58.2%)and Phreatobacter(14.5%)clearly replaced Novosphingobium,Aquabacterium,and Cupriavidus as new dominant genera in system A,which could be attributed to the lower carbon and nitrogen content of the new water source.Although corrosion-inhibiting bacteria decreased after switching,they still maintained dominant in three reactors(6.6%,15.9%,and 19.7%).Furthermore,potential opportunistic pathogens such as Sphingomonas were detected.Our study shows that after transition to a high quality water source,the total culturable bacteria released was in a downtrend,which leads to a great reduction in the risk of bacterial leakage in the produced drinking water.