Impact of pre-ozonation on disinfection by-product formation and speciation from chlor(am)ination of algal organic matter of Microcystis aeruginosa.

The increasing use of algal-impacted source waters is increasing concerns over exposure to disinfection byproducts (DBPs) in drinking water disinfection, due to the higher concentrations of DBP precursors in these waters. The impact of pre-ozonation on the formation and speciation of DBPs during subsequent chlorination and chloramination of algal organic matter (AOM), including extracellular organic matter (EOM) and intracellular organic matter (IOM), was investigated. During subsequent chlorination, ozonation pretreatment reduced the formation of haloacetonitriles from EOM, but increased the yields of trihalomethanes, dihaloacetic acid and trichloronitromethane from both EOM and IOM. While in chloramination, pre-ozonation remarkably enhanced the yields of several carbonaceous DBPs from IOM, and significantly minimized the nitrogenous DBP precursors. Also, the yield of 1,1-dichloro-2-propanone from IOM was decreased by 24.0% after pre-ozonation during chloramination. Both increases and decreases in the bromine substitution factors (BSF) of AOM were observed with ozone pretreatment at the low bromide level (50µg/L). However, pre-ozonation played little impact on the bromide substitution in DBPs at the high bromide level (500µg/L). This information was used to guide the design and practical operation of pre-ozonation in drinking water treatment plants using algae-rich waters.

Formation and speciation of disinfection byproducts during chlor(am)ination of aquarium seawater.

The chemistry associated with the disinfection of aquarium seawater is more complicated than that of freshwater, therefore limited information is available on the formation and speciation of disinfection byproducts (DBPs) in marine aquaria. In this study, the effects of organic precursors, bromide (Br-) and pre-ozonation on the formation and speciation of several typical classes of DBPs, including trihalomethanes (THM4), haloacetic acids (HAAs), iodinated trihalomethanes (I-THMs), and haloacetamides (HAcAms), were investigated during the chlorination/chloramination of aquarium seawater. Results indicate that with an increase in dissolved organic carbon concentration from 4.5 to 9.4 mg/L, the concentrations of THM4 and HAAs increased by 3.2-7.8 times under chlorination and by 1.1-2.3 times under chloramination. An increase in Br- concentration from 3 to 68 mg/L generally enhanced the formation of THM4, I-THMs and HAcAms and increased the bromine substitution factors of all studied DBPs as well, whereas it impacted insignificantly on the yield of HAAs. Pre-ozonation with 1 mg/L O3 dose substantially reduced the formation of all studied DBPs in the subsequent chlorination and I-THMs in the subsequent chloramination. Because chloramination produces much lower amounts of DBPs than chlorination, it tends to be more suitable for disinfection of aquarium seawater.

Effective and mechanistic insights into shale gas wastewater reverse osmosis concentrate treatment using ozonation-biological activated carbon process.

Reverse osmosis (RO) plays a pivotal role in shale gas wastewater resource utilization. However, managing the reverse osmosis concentrate (ROC) characterized by high salinity and increased concentrations of organic matter is challenging. In this study, we aimed to elucidate the enhancement effects and mechanisms of pre-ozonation on organic matter removal efficacy in ROC using a biological activated carbon (BAC) system. Our findings revealed that during the stable operation phase, the ozonation (O3 and O3/granular activated carbon)-BAC system removes 43.6-72.2 % of dissolved organic carbon, achieving a 4-7 fold increase in efficiency compared with that in the BAC system alone. Through dynamic analysis of influent and effluent water quality, biofilm performance, and microbial community structure, succession, and function prediction, we elucidated the following primary enhancement mechanisms: 1) pre-ozonation significantly enhances the biodegradability of ROC by 4.5-6 times and diminishes the organic load on the BAC system; 2) pre-ozonation facilitates the selective enrichment of microbes capable of degrading organic compounds in the BAC system, thereby enhancing the biodegradation capacity and stability of the microbial community; and 3) pre-ozonation accelerates the regeneration rate of the granular activated carbon adsorption sites. Collectively, our findings provide valuable insights into treating ROC through pre-oxidation combined with biotreatment.

Alleviating Ultrafiltration Membrane Fouling Caused by Effluent Organic Matter Using Pre-Ozonation: A Perspective of EEM and Molecular Weight Distribution.

Wastewater reclamation has gradually become an important way to cope with the global water crisis. Ultrafiltration plays an imperative part as a safeguard for the aim but is often limited by membrane fouling. Effluent organic matter (EfOM) has been known to be a major foulant during ultrafiltration. Hence, the primary aim of this study was to investigate the effects of pre-ozonation on the membrane fouling caused by EfOM in secondary wastewater effluents. In addition, the physicochemical property changes of EfOM during pre-ozonation and the subsequent influence on membrane fouling were systemically investigated. The combined fouling model and the morphology of fouled membrane were adopted to scrutinize the fouling alleviation mechanism by pre-ozonation. It was found that membrane fouling by EfOM was dominated by hydraulically reversible fouling. In addition, an obvious fouling reduction was achieved by pre-ozonation with 1.0 mg O3/mg DOC. The resistance results showed that the normalized hydraulically reversible resistance was reduced by ~60%. The water quality analysis indicated that ozone degraded high molecular weight organics such as microbial metabolites and aromatic protein and medium molecular weight organics (humic acid-like) into smaller fractions and formed a looser fouling layer on the membrane surface. Furthermore, pre-ozonation made the cake layer foul towards pore blocking, thereby reducing fouling. In addition, there was a little degradation in the pollutant removal performance with pre-ozonation. The DOC removal rate decreased by more than 18%, while UV254 decreased by more than 20%.

Effects of combined remediation of pre-ozonation and bioaugmentation on degradation of benzo[a]pyrene and microbial community structure in soils.

The combination technique of pre-ozonation and bioaugmentation is promising for remediating benzo[a]pyrene (BaP)-contaminated soil. However, little is known about the effect of coupling remediation on the soil biotoxicity, soil respiration, enzyme activity, microbial community structure, and microbial in the process of remediation. This study developed two coupling remediation strategies (pre-ozonation coupled with bioaugmentation by addition of polycyclic aromatic hydrocarbons (PAHs) specific degrading bacteria or activated sludge), compared with sole ozonation and sole bioaugmentation, to improve degradation of BaP and recovery of soil microbial activity and community structure. Results showed that the higher removal efficiency of BaP (92.69-93.19%) was found in coupling remediation, compared with sole bioaugmentation (17.71-23.28%). Meanwhile, coupling remediation significantly reduced the soil biological toxicity, promoted the rebound of microbial counts and activity, and recovered the species numbers and microbial community diversity, compared with sole ozonation and sole bioaugmentation. Besides, it was feasible to replace microbial screening with activated sludge, and coupling remediation by addition of activated sludge was more conducive to the recovery of soil microbial communities and diversity. This work provides a strategy of pre-ozonation coupled with bioaugmentation to further degrade BaP in soil by promoting the rebound of microbial counts and activity, as well as the recovery of species numbers and microbial community diversity.

Analysis of the evolution of ultra-filtered water quality in a drinking water distribution system by particle size distribution: Influence of pre-ozonation.

An experimental drinking water distribution system (DWDS) was used to evaluate the evolution of particle size distribution (PSD) and basic quality parameters of ultrafiltered water with or without pre-ozonation. An ultrafiltration (UF) module was set up, associated with a pre-ozonation system (3.7 g O3 /m3 ). The permeate was circulated in the DWDS (300 m; 0.9 m/s) with 0.4 mg/L of chlorine, and the analysis of the PSD was performed using a ß-variable mathematical model. A better control of membrane fouling was obtained with pre-ozonation, and PSD was necessary to observe water quality differences between permeates and in the DWDS. A decrease in particle concentration of 1.8 logarithms was obtained with the application of UF membranes, while a decrease of only 1.2 logarithms was obtained with pre-ozonation. The system without pre-ozonation showed a higher efficiency at removing smaller particles (around 2 µm), with the absence of particles larger than 23 µm during both stages. The PSD revealed a worsening of water quality in the DWDS with an increase of particles smaller than 5 µm during the application of UF membranes, while with pre-ozonation, all particle sizes analyzed increased their concentration. PRACTITIONER POINTS: Pre-ozonation led to a better control of membrane fouling, but a worsening of permeate quality according to particle size distribution. Pre-ozonation does not improve the turbidity, dissolved organic carbon or UV254 removal capacity of ultrafiltration during drinking water treatment. Particles size distribution reveals the deterioration of water quality in a drinking water distribution system better than turbidity or DOC. Ozone prior to ultrafiltration membranes led to a worsening of permeate quality, more significant in the drinking water distribution system.

Application of Ozonation-Biodegradation Hybrid System for Polycyclic Aromatic Hydrocarbons Degradation.

Creosote, a mixture of polycyclic aromatic hydrocarbons (PAHs), was and is a wood impregnate of widespread use. Over the years the accumulation of creosote PAHs in soils and freshwaters has increased, causing a threat to ecosystems. The combined ozonation-biodegradation process is proposed to improve the slow and inefficient biodegradation of creosote hydrocarbons. The impact of different ozonation methods on the biodegradation of model wastewater was evaluated. The biodegradation rate, the changes in chemical oxygen demand, and the total organic carbon concentration were measured in order to provide insight into the process. Moreover, the bacteria consortium activity was monitored during the biodegradation step of the process. The collected data confirmed the research hypothesis, which was that the hybrid method can improve biodegradation. The pre-ozonation followed by inoculation with a bacteria consortium resulted in a significant increase in the biodegradation rate. It allows for the shortening of the time required for the consortium to reach maximum degradation effectiveness and cell activity. Hence, the study gives an important and useful perspective for the decontamination of creosote-polluted ecosystems.

Moderate pre-ozonation coupled with a post-peroxone process remove filamentous cyanobacteria and 2-MIB efficiently: From bench to pilot-scale study.

The increasing frequency and intensity of taste- and odour-producing cyanobacteria in water sources is a growing global issue. Odour events caused by 2-methylisoborneol (2-MIB) mainly arising from filamentous cyanobacteria have been a very common problem in water supply. Removal rates of filamentous cyanobacteria and 2-MIB by conventional water treatment, such as coagulation, and disinfection treatment processes is low. Hence, a moderate pre-ozonation of cyanobacteria (with little cell damage) was proposed in this study as an enhanced coagulation step to remove filamentous cyanobacteria and intracellular 2-MIB effectively, while avoiding the release of intracellular 2-MIB. A post-peroxone (O3/H2O2) process was applied after sand filtration to degrade the residual dissolved 2-MIB. Results show that moderate pre-ozonation (0.2 mg/L O3 oxidation for 20 min) can substantially enhance the coagulation efficiency for algae, with low cell lysis and high cell viability. Furthermore, 2.0 mg/L O3 combined with 2.0 mg/L H2O2 can degrade the residual dissolved 2-MIB nearly 100% after 20 min reaction. Based on the optimal dosages, a 0.6 m3/h pilot system, including pre-ozonation, coagulation and sedimentation, sand filtration, and post-peroxone processes, was continuously run for 14 days, and it was found that the proposed process can effectively and stably remove filamentous cyanobacteria and 2-MIB.

Contrasting behaviors of pre-ozonation on ceramic membrane biofouling: Early stage vs late stage.

Pre-ozonation coupled with ceramic membrane filtration has been widely used to alleviate membrane fouling. However, information on the efficiency and underlying mechanism of pre-ozonation in the evolution of ceramic membrane biofouling is limited. Herein, filtration experiments with a synthesis wastewater containing activated sludge were conducted in a cross-flow system to evaluate the effects of pre-ozonation on ceramic membrane biofouling. Results of flux tests show that pre-ozonation aggravated biofouling at the early stage, but alleviated the biofouling at the late stage. In situ FTIR spectra show that the aggravated biofouling with pre-ozonation was mainly caused by the enhanced complexation between phosphate group from DNA and Al2O3 surface and the increased rigid of proteins' structure. At the early stage, more severe pore blockage further substantiated the higher permeate resistance. By contrast, more dead cells were observed on membrane surface at the late stage, indicating the prevention of biofouling development after long-term pre-ozonation. Additionally, the structures and compositions of cake layers at the early and late stages exhibited considerable differences accompanied by the variation in microbial community with the evolution of biofouling. Therefore, this work demonstrates the effectiveness of pre-ozonation in biofouling in long-term operation and provides mechanistic insights into the evolution of biofouling on ceramic membrane.

Molecular transformation of algal organic matter during sequential ozonation-chlorination: Role of pre-ozonation and properties of chlorinated disinfection byproducts.

Formation of unknown chlorinated disinfection byproducts (Cl-DBPs) during chlorination gradually raised great concern, and pre-oxidation was considered as an efficient method to minimize Cl-DBP formation. In this study, pre-ozonation of algal organic matter was investigated, to explore its impacts on Cl-DBP formation and acute toxicity during subsequent chlorination. With fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis, the conversion of algal organic matter in chlorination with/without pre-ozonation was tracked. The results show that pre-ozonation reduced the formation of trichloromethane (TCM), yet the species and intensity of unknown Cl-DBPs were significantly increased in subsequent chlorination. Meanwhile, the solution acute toxicity was higher in chlorination with pre-ozonation than in chlorination only. Besides, molecular properties of these unknown Cl-DBPs were further explored and featured. One-chlorine-containing DBPs were unsaturated high molecular-weight compounds with more CH2 structures, while two or three-chlorine-containing DBPs were mainly oxidized or saturated compounds. Of note, large amounts of one-chlorine-containing DBPs related to polycyclic aromatics and polyphenols compositions were generated, which may contribute to the high potential toxicity. Overall, the findings of this study could provide new insights into the impacts of pre-ozonation on the formation of unknown Cl-DBPs and potential toxicity during chlorination for actual application.

Can pre-ozonation be combined with gravity-driven membrane filtration to treat shale gas wastewater?

Low-cost gravity-driven membrane (GDM) filtration has the potential to efficiently manage highly decentralized shale gas wastewater (SGW). In this work, the feasibility of combining low dosage pre-ozonation with the GDM process was evaluated in the treatment of SGW. The results showed that pre-ozonation significantly increased the stable flux (372%) of GDM filtration, while slightly deteriorating the quality of the effluent water in terms of organic content (-14%). These results were mainly attributed to the conversion of macromolecular organics to low-molecular weight fractions by pre-ozonation. Interestingly, pre-ozonation markedly increased the flux (198%) in the first month of operation also for a GDM process added with granular activated carbon (GGDM). Nevertheless, the flux of O3-GGDM systems dropped sharply around the 25th day of operation, which might be due to the rapid accumulation of pollutants in the high flux stage and the formation of a dense fouling layer. Pre-ozonation remarkably influenced the microbial community structure. And O3-GDM systems were characterized by distinct core microorganisms, which might degrade specific organics in SGW. Furthermore, O3-GDM outperformed simple GDM as a pretreatment for RO. These findings can provide valuable references for combining oxidation technologies with the GDM process in treating refractory wastewater.

Formation and control of disinfection by-products from iodinated contrast media attenuation through sequential treatment processes of ozone-low pressure ultraviolet light followed by chlorination.

Different groups of disinfection by-products (DBPs) were studied through the degradation of iopamidol by the sequential oxidation process of ozone-low pressure ultraviolet light (O3-LPUV) followed by chlorination. This paper investigates the attenuation of iopamidol under this sequential treatment and the effect of chlorine contact time (30 min versus 3 days) to control the formation potential of DBPs: trihalomethanes (THMs), haloacetonitriles (HANs) and haloacetamides (HAMs). Thirty target DBPs among the 9 iodinated-DBPs (I-DBPs), were monitored throughout the sequential treatment. Results showed that O3-LPUV removed up to 99% of iopamidol, while ozone and LPUV alone removed only 90% and 76% respectively. After chlorine addition, O3-LPUV yielded 56% lower I-DBPs than LPUV. Increasing chlorine contact time resulted in higher concentrations of all DBP groups (THMs, HANs, and HAMs), with the exception of I-DBPs. One new iodinated-haloacetamide, namely chloroiodoacetamide (CIACM) and one iodoacetonitrile (IACN) were detected. These results suggest the iodine incorporated in iopamidol may be a precursor for iodinated-nitrogenous-DBPs, which are currently not well studied.

Trade-off control of organic matter and disinfection by-products in the drinking water treatment chain: Role of pre-ozonation.

Ozone is a strong oxidant commonly used in drinking water treatment, but its role in the transformation/formation of organic matters (OMs) and disinfection by-products (DBPs) in the drinking water treatment chain had not been systematically studied. In this work the occurrence and building up of OMs, DBPs of trihalomethanes (THMs) and nitrosamines (NAs) during water purification steps under different pre-ozonation dosages have been studied through lab-scale and pilot-scale studies. Results indicated that 0-0.4 mg/L of pre-ozonation dosage could reduce organic load of following-up process steps but insufficient to control DBPs. Seasonal performances of a pilot plant indicated that the accumulation of DBPs was much less in summer than in winter. Furthermore the formation potential of NAs was higher in winter than summer when 0.4 mg/L pre-ozonation was dosed while the maximum removal efficiency of organic matter was found at a pre-ozonation dosage of 0.8 mg/L in summer. Finally a seasonal trade-off control strategy for both OMs and DBPs was proposed with an elucidated role of pre-ozonation in the drinking water treatment chain. This study provided working principles on optimizing pre-ozonation dosage and a seasonal control strategy for trade-off control of both OMs and DBPs in drinking water treatment plants.

Pre-ozonation for the mitigation of reverse osmosis (RO) membrane fouling by biopolymer: The roles of Ca2+ and Mg2.

Despite plenty of literatures focused on the application of pre-ozonation prior to membrane, it was still unclear about the role of divalent cations (Ca2+ and Mg2+) in reverse osmosis (RO) membrane fouling mitigation. In this study, ozone pre-treatment (0.10, 0.25 and 0.50 mg O3/mg DOC (dissolved organic carbon)) was employed to oxidize model biopolymer, which was represented by bovine serum albumin (BSA) and sodium alginate (SA) in the presence of Ca2+ and Mg2+ (0.5, 1.0 and 2.0 mM). Cross-flow filtration was conducted to investigate RO membrane fouling by concentration mode. The results showed that at appropriate ozone dose there were measurable changes in physicochemical properties of BSA and SA, including increases in particle size, hydrophilicity, density of negative charge and carboxylic groups. Pre-ozonation markedly alleviated RO fouling by BSA at ozone dose of 0.25 mg O3/mg DOC when Ca2+ and Mg2+ concentrations raised from 0.5 to 2.0 mM since the increase in electrostatic (EL) repulsion and decrease in hydrophobic (HP) interaction compensated the increase in divalent cation bridging. Similar results were obtained for SA fouling in the presence of Mg2+. In contrast, the effect of pre-ozonation on SA fouling strongly depended on the concentration of Ca2+. In brief, it mitigated SA fouling at 0.5 mM Ca2+, whereas accelerated irreversible fouling at higher Ca2+ concentration (1.0 and 2.0 mM) due to the overwhelming effect of divalent cation bridging compared to EL and HP interactions, as revealed by adsorption experiments (in-situ streaming potential measurement). Pre-ozonation shifted the fouling layer from compact to porous and weakened the adhesion forces between foulants and membrane (foulants) except for SA containing 1.0 and 2.0 mM Ca2+. This study may provide the guidance for the application of pre-ozonation prior to RO filtration.

Effects of microbubble pre-ozonation time and pH on trihalomethanes and haloacetic acids formation in pilot-scale tropical peat water treatments for drinking water purposes.

The high concentrations of dissolved organic matter (DOM), chloride, and bromide in tropical peat water have a significant impact on the formation of carcinogenic disinfection by-products (DBPs) such as trihalomethanes (THMs) and haloacetic acids (HAAs), especially during the chlorination process. Therefore, other pretreatment methods to effectively remove these harmful substances in the water during treatment are needed. The aim of this study was to determine the effects of microbubble pre-ozonation pH on the reduction of THM4 and HAA5 formed during the peat water treatment process and to determine the best conditions for microbubble pre-ozonation to reduce the formation of these two classes of DBPs. The microbubble pre-ozonation was conducted at a pH of 5.5, 7, and 8.5. Furthermore, the primary treatments applied after this pretreatment were coagulation and activated carbon adsorption before post-chlorine disinfection. The coagulation process using aluminum sulfate and activated carbon adsorption succeeded in reducing the formation of THM4 after chlorination, to a level below USEPA standards, but the concentration of HAA5 was still high. However, the use of microbubble pre-ozonation significantly reduced the formation of both classes of compounds during the chlorination process of the peat water. Also, the concentration of THM4 increased during the pre-ozonation process in all pH conditions, but HAA5 decreased except in alkaline state. Furthermore, the ideal conditions for microbubble pre-ozonation on peat water were at pH 7 (neutral) after 30 min, with the total THM4 concentration at 33.73 ± 0.40 µg/L, and that of HAA5 at 49.89 ± 0.09 µg/L, falling below the USEPA standard.

Intensification of the ultrafiltration of real oil-contaminated (produced) water with pre-ozonation and/or with TiO2, TiO2/CNT nanomaterial-coated membrane surfaces.

In the present study, commercial PES, PVDF, PTFE ultrafilter membranes, and two different nanomaterial (TiO2 and TiO2/CNT composite)-covered PVDF ultrafilter membranes (MWCO = 100 kDa) were used for the purification of an industrial oil-contaminated (produced) wastewater, with and without ozone pretreatment to compare the achievable fouling mitigations by the mentioned surface modifications and/or pre-ozonation. Fluxes, filtration resistances, foulings, and purification efficiencies were compared in detail. Pre-ozonation was able to reduce the total filtration resistance in all cases (up to 50%), independently from the membrane material. During the application of nanomaterial-modified membranes were by far the lowest filtration resistances measured, and in these cases, pre-ozonation resulted in a slight further reduction (11-13%) of the total filtration resistance. The oil removal efficiency was 83-91% in the case of commercial membranes and > 98% in the case of modified membranes. Moreover, the highest fluxes (301-362 L m-2 h-1) were also measured in the case of modified membranes. Overall, the utilization of nanomaterial-modified membranes was more beneficial than pre-ozonation, but with the combination of these methods, slightly higher fluxes, lower filtration resistances, and better antifouling properties were achieved; however, pre-ozonation slightly decreased the oil removal efficiency.

Effect of pre-ozonation-enhanced coagulation on dissolved organic nitrogen in municipal wastewater treatment plant effluent.

Municipal wastewater treatment plant (WWTP) effluent is increasingly used as reclaimed water and as water sources for downstream areas. Effluent dissolved organic nitrogen (DON) is considered to be the precursor to nitrogen disinfection by-products (N-DBPs). Here, we investigated DON removal by pre-ozonation-enhanced coagulation and found that (1) pre-ozonation significantly enhanced the removal of DON, dissolved organic carbon (DOC), and UV254 by coagulation. (2) pH had an important impact on the pre-ozonation-enhanced coagulation. At lower pH, the removal of DON, DOC, and UV254 is higher. (3) As ozone dosage increased, zeta potential gradually increased, while dissolved calcium concentrations declined and there was a strong correlation between zeta potential and dissolved calcium concentrations. (4) Small (<6 kDa) molecular weight DON was dominant in the effluent. Hydrophilic and hydrophobic DON accounted for 58.5% and 30.8% of the total, respectively. (5) Coagulation reduced overall DBP formation potentials to less than 20%. In contrast, overall DBP formation potentials increased after ozonation. However, pre-ozonation-enhanced coagulation not only removed 71% DON, but also reduced overall DBP formation potentials by more than 40%. (6) 3-DEEM spectra indicated that DBP formation potentials and DON concentrations were related to three main peaks, which corresponded to tryptophan-based proteins, aromatic proteins, and fulvic acids.

Control of halophenol formation in seawater during chlorination using pre-ozonation treatment.

The reverse osmosis process is widely used for seawater desalination, whereas the pre-chlorination step for controlling membrane biofouling results in undesirable disinfection by-products, such as halophenols (HPs) which are not yet regulated but of increasing concerns. The formation and speciation of HPs during chlorination of three filtered seawater samples (SA, SB, and SC) with various phenol concentrations (0.25, 0.5, 1.0 mg/L) were evaluated. 4-Bromophenol (4-BrP), 2,4,6-trichlorophenol (2,4,6-TClP), 2,4-dibromophenol (2,4-DBrP), and 2,4,6-tribromophenol (2,4,6-TBrP) were identified during chlorination, with 2,4,6-TBrP as the predominant HP. Ozone as a common oxidant in water and wastewater treatment was subsequently applied to assess its effect in dissolved organic matter (DOM) and its ability of reducing HP precursors in the seawater samples. An initial ozone dose of 5 mg O3/L was capable of reducing dissolved organic carbon (DOC) in SA, and UV absorbance at 254 nm (UV254) in SB, whereas it induced an elevation of UV254 in SC. When ozone dose increased to 10 mg O3/L, the DOC and UV254 levels in all seawater samples were reduced. Ozone was more powerful on degrading DOM with molecular weight (MW) of near 1000 Da than those with MW of 20-100 Da, both of which composed the majority of DOM in the seawater samples. As determined by excitation emission matrix fluorescence spectroscopy, the most ozone-susceptible fraction of DOM was soluble microbial by-product-like substances, while the least was tryptophan-like aromatic proteins. Despite that the initial ozone of 5 mg O3/L was less effective in DOM degradation than the higher dose, it successfully degraded HP precursors. By pre-ozonation at 5 mg O3/L, no chlorophenol was detected during chlorination, and the mean reductions of the three bromophnols formed were above 92% in all seawater samples, with the reduction of 2,4,6-TBrP being the highest of 99.7, 99.6, and 99.1% in SA, SB, and SC, respectively.

Microbial community analysis in biologically active filters exhibiting efficient removal of emerging contaminants and impact of operational conditions.

In biologically active filters (BAFs), microorganisms acclimated on the media surface are the key players responsible for removing organic water contaminants. In this study, next generation sequencing by Illumina MiSeq was used to characterize the microbial community structures in the influent, effluent, and media of a set of bench-scale BAFs that have been demonstrated with high removal efficiency (>75%) of 16 contaminants of emerging concern (CECs), which include a variety of pharmaceuticals (e.g., sulfamethoxazole and ibuprofen), X-ray contrast agent (i.e., iopromide), and pesticides (e.g., atrazine) that are prevalently found in municipal waste streams. Proteobacteria and Planctomycetes were the most abundant phyla in filter media, while the influent and effluent samples were dominated by Proteobacteria, Actinobacteria, and Chlamydiae. Factorial and principal component analysis revealed microbial structures in the media were significantly affected by the operation conditions, including media type (GAC versus dual media anthracite sand), EBCT (10 versus 18 min), and pre-ozonation. Detrended correspondence analysis demonstrated media materials predominantly governed the structures of the acclimated biofilm in BAFs as they provide direct attachment surface. This is in line with the higher microbial activity and better treatment performance exhibited by GAC BAFs compared to the dual media BAFs, corroborating the importance of filter media selection to promote the acclimation of active and robust biofilm for efficient CEC removal. Principal component analysis revealed the significant influence from ozonation, which does not only break down CECs, but also stimulates microbes that grow on the ozonation products. Partial canonical correlation analysis further proved the shaping of biofilm communities on the BAF media is more associated with media type and ozonation compared to EBCT. Putative CEC degraders are predicted based on their dominance in the media and degradation capabilities reported in previous literature. This is the first study to examine the relationship between the microbial community structure and the BAF operating parameters, which are both aligned with the treatment performance exhibited by the BAFs.

Comparison of micropollutants' removal performance between pre-ozonation and post-ozonation using a pilot study.

Despite the strong oxidizing ability of ozone, pre-ozonation has seldom been employed for the purpose of micropollutant removal in drinking water utilities. In this paper, the possibility of using pre-ozonation instead of post-ozonation for the removal of micropollutants was explored because of the lower risk of forming carcinogenic bromate. A 1.0 m3/h pilot system was utilized to compare the efficacy of pre- and post-ozonation in the removal of bulk organic pollutants as well as micropollutants, including typical odor-causing compounds, pharmaceuticals, and typical pesticides, from one source water (Huangpu River) characterized by the occurrence of various micropollutants. Both pre-ozonation and post-ozonation could achieve similar water purification performance under an ozone dose of 1.5 mg/L, in terms of bulk water quality parameters like CODMn (66% in combination with biological activated carbon (BAC) treatment, compared to 62% with the pre-ozonation-BAC combination) or micropollutants including 27 pharmaceuticals (85% in combination with BAC compared to 87% with the pre-ozonation-BAC combination) and 25 pesticides (72% in combination with BAC compared to 61% with the pre-ozonation-BAC combination). Pre-ozonation exhibited slightly better odorant removal performance (100% in combination with BAC compared to 92% with the post-ozonation-BAC combination); however, post-ozonation generated approximately 6.0 µg/L bromate at an ozone dose of 2.0 mg/L, while pre-ozonation did not form bromate even at an ozone dose as high as 3.0 mg/L. So pre-ozonation in combination with BAC might be a solution for the removal of micropollutants from source water with high bromate formation risk. The results of this study will be helpful for the optimization of ozonation processes in the water supply industry.