Search

The safety threat posed by Perfluoroalkyl acids (PFAAs) in drinking water is a growing concern. In this study, we loaded chitosan (CS) on granular activated carbon (GAC) to adsorb PFAAs, and we explored the role of nanobubbles in the adsorption process through experiments and density functional theory (DFT) calculations. Compared with GAC, we found that the use of the composite adsorbent (CS/GAC) enhanced the removal rate of perfluorooctanoic acid by 136% with the assistance of nanobubbles. PFAAs with different chain lengths have different adsorption mechanisms owing to surface activity differences. PFAAs with longer C-F chains can be directly enriched with amino groups on the CS or air-water interface on composite adsorbents. Additionally, PFAAs can be enriched with nanobubbles in solution to form nanobubble-PFAA colloids, which are adsorbed by protonated amino groups on CS through electrostatic interactions. We found that PFAAs with shorter C-F chains are less affected by nanobubbles, and DFT calculations indicated that the adsorption of short-chain PFAAs is mainly affected by electrostatic interactions. We also proved that the electrostatic interactions between CS and PFAAs are mainly derived from the abundant protonated amino groups.

The widespread use of perfluorooctanoic acid (PFOA) has rendered its frequent detection in wastewater. The tolerance and recovery of aerobic granular sludge (AGS) to PFOA were investigated in short-term (Phase I) and long-term (Phase II, operation strategy adjustment: shortening aeration time and prolonging anaerobic and anoxic time). Results showed that in Phase I, the performance of R2 reactor (0.05 mg/L PFOA) was slightly negatively affected, while 0.5 and 2.0 mg/L PFOA in R3 and R4 reactors significantly damaged the key enzyme activities of AGS, leading to deterioration of nutrients removal. TN and TP removal efficiencies decreased correspondingly from 79.3% to 78.3% on day 0-74.7% and 74.1% in R2 and 68.6% and 67.8% in R3 and 56.9% and 57.5% in R4 on day 7, respectively. In Phase Ⅱ, the key enzyme activities of AGS were obviously renewed dependent on operation strategy adjustment and AGS self-regulation. The performance of AGS in R2 (continuously dosing 0.05 mg/L PFOA) and R4 (stopping dosing PFOA) recovered quite good, while the long-term adverse effects of 0.5 mg/L PFOA on AGS in R3 were still more difficult to be alleviated. In end of Phase Ⅱ (69-97days), the average TN and TP removal efficiencies correspondingly reached 83.3% and 82.1% in R1 (control), 80.7% and 79.6% in R2, 76.4% and 74.3% in R3, and 79.0% and 78.3% in R4, respectively. Further analysis revealed that the effect of PFOA on proteins in extracellular polymeric substances (EPS) was greater than that on polysaccharides. Specifically, short-term dosage of PFOA mainly affected loosely bound EPS, while long-term dosage of PFOA affected tightly bound EPS. Although AGS is severely inhibited by short exposure to 2.0 mg/L PFOA (in R4), after the operation strategy adjustment, EPS content decreased, nutrient and oxygen transport channels of AGS were re-established, which contributed to the recovery of AGS.

Pipe material and residual chlorine are key factors for the drinking water distribution system, and understanding the biofilm ecosystem is vital for water quality safeguard. The aim of our study was to determine the influence of pipe materials (ductile iron, steel, polyethylene) and chlorination on the biofilm structure and microbial community, as shown by the physicochemical properties, extracellular polymeric substances (EPS) structural characteristics, bacterial community composition, and functional traits. EPS spatial properties were studied based on a semi-quantitative confocal laser scanning microscope (CLSM) description. Regarding the impact of chlorination, residule chlorine (1.0 ± 0.3 mg L

The variations of disinfection byproduct (DBP) precursors and DBPs-associated toxic potencies were evaluated by ozonation, followed by a up-flow biological activated carbon (O3/UBAC) filter treating two reconstituted water samples, featuring either high bromide (105.3 μg/L) or dissolved organic nitrogen (0.73 mg N/L) concentration, respectively. Ozonation contributed to ∼20% decrease in dissolved organic carbon (DOC) concentration at a dosage of 0.7 mg of O3/mg of DOC, but no further reduction in DOC level was observed with an increased dose of 1.0 mg of O3/mg of DOC. When chlorine or preformed monochloramine was used as a disinfectant, UBAC process led to ∼40% reduction in the sum of detected DBP formation potential (FP) due to the removal of precursors at a feasible empty bed contact time of 15 min. The integrated effect of ozonation and UBAC biofiltration decreased the sum of DBP FP by ∼50% including halonitromethanes (THNMs), N-nitrosamines (NAs), and bromate, which increased in the effluent of ozonation. Chloramination produced less DBPs by weight as well as DBPs-associated additive toxic potencies than chlorination. The reduction in additive toxic potencies was generally lower than the removal efficiency of DBP FP after chlor(am)ination of treated waters by O3/UBAC, indicating that the removal of DBPs-associated additive toxic potencies should be focused to better understand on the residual risk to public health in controlling DBP precursors.

Novel pre-coagulation–sedimentation integrated with ultraviolet activated sodium percarbonate (SPC) (Fe(III)-UV/SPC) processes are promising methods for ultrafiltration (UF) pretreatment to ensure the safety of rural drinking water and mitigate UF membrane fouling. The process of surface water purification using the integrated coagulation-advanced oxidation processes (AOPs)-UF system relies on the idea that pre-coagulation can remove hydrophobic macromolecular organic compounds, thus facilitating the oxidation of hydrophilic molecules or medium-sized macromolecules to improve the utilization efficiency of free radicals in AOPs. Compared with the UV/SPC process, the removal rates of UV254 and DOC in the Fe(III)-UV/SPC process (Fe(III) = 0.1 mM, SPC = 0.5 mM) were increased from 87.39 % to 41.45 %–93.56 % and 52.51 %, respectively. Furthermore, the dosage of SPC was reduced from 0.75 mM in UV/SPC process to 0.5 mM due to effects of pre-coagulation. The free radical quenching experiment showed that a significant radical sink of reactions with organic contaminants was formed by •OH and CO3•- in the UV/SPC process, rather than a single specific radical. The destruction of the cake layer structure, reduction in contaminant concentration, and appearance of many permeable holes on the membrane surface were the main reasons for the alleviation of UF membrane fouling. Finally, the trans-membrane pressure and reversible membrane resistance decreased from 22.33 kPa to 3.68 × 1011 m−1 to 18.28 kPa and 0.93 × 1011 m−1, respectively. These results provide new insights into the behavior of membrane fouling control and offer technical references for the long-term stable operation of the UF process.

The raw water distribution systems (RWDSs) play key roles in urban water supply systems. The changes of disinfection byproducts (DBPs) precursors of trihalomethanes (THMs), haloacetic acids (HAAs) and halogenated acetaldehydes (HALs) in the RWDS in Taihu Basin were investigated by formation potentials. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) method and 454-pyrosequencing were employed to study the variation of molecular characteristics of low molecular weight-dissolved organic matter (LMW-DOM) and microbial communities of pipeline biofilms respectively, which played crucial roles in the variation of DBPs precursors. The results showed that both DBPs precursors and the molecular characteristics of LMW-DOM in the RWDS had changed. Moreover, the LMW-DOM could be an indicator due to the good positive correlation with precursors of HAAs and HALs. Specifically, the LMW-DOM showed continuous accumulation in the RWDS. The LMW-DOM tended to possess higher m/z and more CH2 or long alkyl chains while pre-chlorination controlled this trend. The LMW-DOM in the pre-chlorinated pipe section also possessed higher saturation. Additionally, lignins served as an important part of DBPs precursors and dominated the LMW-DOM. The microbial diversity decreased in the RWDS, and the abundance and diversity of the microbial community in the pre-chlorinated section were significantly lower than those in the no-chlorinated section. Finally, most DBPs precursors had positive correlation with dominant phylum and genus in RWDS. This study reveals variation of DBPs precursors, LMW-DOM and microbial pipeline biofilms as well, and provide important data for further research on raw water safety and stability in RWDSs.

Understanding the transformation pattern of nitrogen (N) pollutants and its pathways in the prechlorinated raw water distribution system (PRWDS) is vital for controlling the stablitiy and safety of raw water qulity. This study investigated the N transformation, N functional genes and their correlations to find the N transformation pathways along the PRWDS. Results suggested that simultaneous nitrification, anaerobic ammonium oxidation and denitrification (SNAD) contribute to the N transformationin the PRWDS. Along the pipeline, anammox 16S rRNA (9.18 × 107–8.41 × 108 copies/g), limited by prechlorination, was the most abundant N functional genes and anammox process was the main pathway of ammonia nitrogen (NH4+-N). The decreasing NH4+-N was connected with Planctomycetes, Nitrospira and abundance of nxrA attributing to the joint effort of anammox and declined nitrification. The concentration of nitrate (NO3−-N) increasing at first and then decreasing, was correlated positively with Sphingomonas. because of the declined nitritication and increased denitrification. Besides, the NO3−-N→NO2−-N process was considered to be primary NO3−-N transformation pathways. Increases in the concentration of dissolved organic nitrogen (DON) and nitrite (NO2−-N) observed in the PRWDS had positive correlation with relative abundance of Pseudomonas. We believe that prechlorination shaped the particular bacterialcharacteristics in biofilms and influenced the N transformation pathways indirectly, resulting in the varying N transformation rules in PRWDSs. Moreover, systematic and extended research is particularly vital for determining the effects of changes in source water quality and environmental conditions on bacterial community structure and N conversion along PRWDSs.

The O3/BAC process has been widely used in drinking water treatment to improve the removal of dissolved organic matters (DOMs), including the precursors of nitrogenous disinfection byproducts (N-DBPs). In this study, the removal of N-DBP precursors by biological activated carbon (BAC) filters with different usage time of granular activated carbon (GAC) was investigated. Results showed that the BAC filter with 6 years of usage time of GAC (old BAC filter) had a poor performance in the removal of precursors of N-DBPs such as dichloroacetonitrile (DCAN; an average of only 4.7%), dichloroacetamide (DCAcAm), and trichloronitromethane (TCNM) when compared with the BAC filter with 1 year of usage time of GAC (new BAC filter). Particularly, the organic fraction >10 kDa and the percentage of autochthonous substances were increased in the effluent of the old BAC filter. The red shift of the fluorescence peaks was evident in the excitation–emission matrix spectrum of the effluent from the old BAC filter. The abiotic adsorption of precursors by the old BAC filter was less. In addition, less amino acids and polysaccharides were removed, but more amino sugars and proteins were produced because of microbial metabolism. The metabolism strength of the attached biofilm decreased with increased operation time of the BAC filter. The relative abundance of Sphingomonas significantly decreased in the biofilm of the old BAC filter. The diversity of microbial community in the old BAC filter was higher, but the equitability was lower than those of the new BAC filter. The less removal of N-DBP precursors by the old BAC filter was attributed to the changes in abiotic adsorption capacity and microbial metabolism properties, in which soluble microbial products played an important role.

The process parameters of the up-flow biological activated carbon filter (UBACF) were optimized in a pilot-scale trial for controlling the precursor of dichloroacetonitrile (DCAN), an emerging nitrogenous disinfection by-product. The experiments were performed using a central composite design (CCD) with the response surface methodology (RSM). The results showed that the removal efficiencies of formation potentials (FP) of DCAN increased from 28.9% to 64.4% with the optimized ozone dose, expansion rate of BAC and backwashing cycle, being scheduled to 1.52 mg/L, 27% and 9.5 d, respectively. Excitation and emission matrix (EEM) spectra indicated that the fluorescence peaks of aromatic protein (AP) and soluble microbial products-like (SMPs)-like region were weakened significantly in the effluent of improved process (IP) with optimization, which were main precursors of DCAN. The bacterial community before and after the optimization of UBACF was determined using the high-throughput sequencing technology. The class and genus of microorganism demonstrated that the IP had a more diverse microbial community and more even distribution of species in BAC filter. It was favor of the growth of Alphaproteobacteria, Bacilli and Betaproteobacteria attached to the BAC particles, which could biodegrade effectively the precursors of DCAN.

Integrated ultrafiltration (UF) membrane technology has attracted extensive attention in drinking water treatment due to its excellent performance and small footprint. However, membrane modules normally are static in membrane tanks, which cause a gradual increase in the cake layer thickness over time, thus resulting in severe membrane fouling. To overcome this shortcoming, we report an effective strategy to regulate cake layer thickness by rotating the membrane module in the presence of flocs. The results showed that the cake layer thickness can be effectively reduced because of the floc looseness, resulting in the alleviation of membrane fouling. The higher the module rotation speed, the higher the flow velocity in the membrane tank and the larger the shearing force on the cake layer surface. As a result, the membrane fouling was considerably mitigated, and it was interesting that the pollutant removal efficiency was hardly influenced. With module rotation, we found that acid solutions displayed a better performance in removing pollutants (even low molecular weight pollutants) and alleviating membrane fouling compared to the alkaline conditions because of the smaller floc size, larger floc specific surface area, and higher floc positive charge. Additionally, an excellent UF membrane performance was also observed with the raw water taken from the South-North water in China. Collectively, this study demonstrated that floc-based cake layers can be effectively regulated with module rotation, which has a great potential in drinking water treatment application, particularly in small water plants.

A novel high-valent iron-oxo species (Fe(IV) = O) generated from Iron hexadecachlorophthalocyanine (FePcCl16)-mediated peroxymonosulfate (PMS) activation under visible light illumination for the degradation of a special group of compounds, indomethacine (IDM), containing methoxy, carboxyl, chloro, and amide groups was investigated. The experimental results indicate that Fe(IV) = O was able to selectively attack the carbonyl C–N bond on twisted amide groups, which exerts a strong toxic effect, and could therefore, effectively degrade and detoxify IDM and its byproducts. Twelve byproducts were identified by HPLC/MS/MS and calculation of frontier electron densities (FEDs), with all amide-group breakage products detected, and the possible pathways were deduced, which mainly consisted of Fe(IV) = O-induced cleavage of amide groups and radicals-induced reactions. Ecological risk assessment further confirmed a decrease in toxicity towards IDM degradation, which provides a promising Fe(IV) = O species for selective oxidation and detoxification of destabilized ground-state amides in drinking-water and wastewater treatment.

Sludge water was recycled using an ultrafiltration (UF) system. In order to control membrane fouling, three typical Fe(II)-activated peroxymonosulfate (PMS) processes: Fe(II)/PMS-UF (FPUF), 1/4Fe(II) × 4/PMS-UF (F4PUF) (adding Fe(II) in small increments four times), and Fe(II)/thiosulfate/PMS-UF (FTPUF) (adding Fe(II) after complexing with thiosulfate), were employed as UF pretreatments. Their mitigating effects of UF membrane fouling caused by sludge water are systematically discussed and compared. The results showed that FTPUF system had the best membrane fouling control effect. The F4PUF system was more suitable for long-term operation than FPUF due to its lower irreversible resistance. The pretreatments can effectively remove contaminants from sludge water through the dual effects of coagulation and oxidation. Specifically, coagulation removed most of the particles and macromolecular organic matter. Oxidation effectively decomposed fluorescent and UV-absorbing organic components, and reduced bacterial proliferation on the membrane surface. Concentrations of 2-methylisoborneol and geosmin in FPUF permeate were dramatically increased, which was mainly due to the rupture of algal cells in sludge water. Both adhesion force date and extended Derjaguin–Landau–Verwey–Overbeek theory indicated that the pretreatments significantly reduced interactions between the membrane–organic colloid and cake layer–organic colloid. In contrast, the stronger membrane–organic colloid interaction was a major contributor to membrane fouling. The mitigation of irreversible fouling was mainly attributed to the fact that oxidation enhanced the hydrophilicity of the organic colloids, thereby reducing the Lewis acid–base interaction energy. The results demonstrated the potential application of different Fe(II)-activated PMS processes as pretreatments for membrane fouling control during sludge water treatment.

The O

N-nitrosodiethylamine (NDEA) is one of the emerging nitrogenous disinfection byproducts with probable cytotoxicity, genotoxicity, and carcinogenesis. Its potential toxicological effects have received extensive attention but remain to be poorly understood. In this study, changes in NDEA precursors in drinking water treatment process were studied using the trial of its formation potential (FP), and the toxicity induced by NDEA to adult zebrafish was investigated. NDEA FP in the raw water of Taihu Lake ranged from 46.9 to 68.3 ng/L. The NDEA precursors were removed effectively by O3/BAC process. Hydrophilic fraction and low-molecular-weight fraction (

Dichloroacetonitrile (DCAN) is one of nitrogenous disinfection by-products (N-DBPs) with strong cytotoxicity and genotoxicity. In this study, the formation potential (FP) of DCAN was investigated in the samples of six important water sources located in the Yangtze River Delta. The highest formation concentration of DCAN was 9.05 μg/L in the water sample taken from Taihu Lake with the lowest SUVA value. After the NOM fractionation, the conversion rate of hydrophilic fraction to DCAN was found the highest. Subsequently, a waterworks using Taihu Lake as water source was chosen to research the FP variations of DCAN in the treatment process and backwash water. The results showed that, compared to the conventional treatment process, O/biological activated carbon (BAC) process increased the removal efficiency of DCAN from 21.89% to 50.58% by removing aromatic protein and soluble biological by-products as main precursors of DCAN. The DCAN FP in the effluent of BAC filters using old granular activated carbon was higher than that in the influent and the DCAN FP of its backwash water was lower than that in raw water. In the backwash water of sand filters, the DCAN FP higher than raw water required the recycle ratio less than 5% to avoid the accumulation of DCAN.

The occurrence and removal of 39 selected pharmaceutical and personal care products (PPCPs) were investigated in an advanced drinking water treatment plant (ADWTP) around Taihu Lake. Fourteen of 39 targeted pharmaceuticals were detected in the raw water. After a series of purification processes, only indomethacin, caffeine and sulfamethoxazole were found in effluent, albeit at concentrations less than 2 ng L(-1). The results of principal component analysis suggested that three main purification processes, oxidation, coagulation combined with sedimentation and filtration combined with bio-degradation, influenced the removal performance of PPCPs. The ecotoxicological and human health risk assessment confirmed that drugs detected in effluent posed no potential toxicity and also suggested that two PPCPs (roxithromycin and sulfamethoxazole), especially sulfamethoxazole, should be seriously considered as candidates for regulatory monitoring and prioritization. Finally, the correlation between removal efficiency and risk quotient indicated that uniform removal efficiency for all PPCPs may not reflect an equal risk control in the ADWTP.

To evaluate the treatment capability of subsurface flow constructed wetland (SFCW) and the effect of salinity on the degradation of atrazine, the degradation of atrazine in SFCW was studied. Under the static condition, the degradation of atrazine in SFCW followed first-order kinetics: c = 0.09679 exp(−0.0396t) (c, residue concentration, mg l−1; t, retention time, d), with a half-life of approximately 17.5 days. The atrazine degradation kinetic functions were established for salinities of 1.5, 3.0, 5.0, 10.0 and 15.0 g l−1, respectively, which appeared to approach first-order kinetics. The effect of salinity on the atrazine treatment efficiency showed an exponential inhibition: ln k = 3.204 + 0.04991C (k, degradation constant; C, NaCl concentration, mg l−1). The attenuation of atrazine in SFCW cannot be a result of hydrolysis or sorption process. It was considered that some bacteria in the wetland system degraded atrazine into deethylatrazine (DEA) and deisopropylatrazine (DIA) and sequentially into CO2 and H2O. Salinity impacted on the growth of bacteria resulting in a switch of the microbial community. With the increase of salinity, Shannon–Wiener Diversity Index in the SFCW system declined. The relationship between atrazine degradation constant (k) and Shannon Index was established as shown in linear phase, y = −0.07286 + 0.0363x. The positive correlation between them indicated that microbial community played an important role in the atrazine degradation process.