Which Micropollutants in Water Environments Deserve More Attention Globally?

Increasing chemical pollution of aquatic environments is a growing concern with global relevance. A large number of organic chemicals are termed as "micropollutants" due to their low concentrations, and long-term exposure to micropollutants may pose considerable risks to aquatic organisms and human health. In recent decades, numerous treatment methods and technologies have been proposed to remove micropollutants in water, and typically several micropollutants were chosen as target pollutants to evaluate removal efficiencies. However, it is often unclear whether their toxicity and occurrence levels and frequencies enable them to contribute significantly to the overall chemical pollution in global aquatic environments. This review intends to answer an important lingering question: Which micropollutants or class of micropollutants deserve more attention globally and should be removed with higher priority? Different risk-based prioritization approaches were used to address this question. The risk quotient (RQ) method was found to be a feasible approach to prioritize micropollutants in a large scale due to its relatively simple assessment procedure and extensive use. A total of 83 prioritization case studies using the RQ method in the past decade were compiled, and 473 compounds that were selected by screening 3466 compounds of three broad classes (pharmaceuticals and personal care products (PPCPs), pesticides, and industrial chemicals) were found to have risks (RQ > 0.01). To determine the micropollutants of global importance, we propose an overall risk surrogate, that is, the weighted average risk quotient (WARQ). The WARQ integrates the risk intensity and frequency of micropollutants in global aquatic environments to achieve a more comprehensive priority determination. Through metadata analysis, we recommend a ranked list of 53 micropollutants, including 36 PPCPs (e.g., sulfamethoxazole and ibuprofen), seven pesticides (e.g., heptachlor and diazinon), and 10 industrial chemicals (e.g., perfluorooctanesulfonic acid and 4-nonylphenol) for risk management and remediation efforts. One caveat is that the ranked list of global importance does not consider transformation products of micropollutants (including disinfection byproducts) and new forms of pollutants (including antibiotic resistance genes and microplastics), and this list of global importance may not be directly applicable to a specific region or country. Also, it needs mentioning that there might be no best answer toward this question, and hopefully this review can act as a small step toward a better answer.

Water Recovery from Advanced Water Purification Facility Reverse Osmosis Concentrate by Photobiological Treatment Followed by Secondary Reverse Osmosis.

Reverse osmosis (RO)-based desalination and advanced water purification facilities have inherent challenges associated with concentrate management and disposal. Although enhanced permeate recovery and concentrate minimization are desired, membrane scaling due to inorganic constituents, such as silica, calcium, phosphate, and iron, hinders the process. To solve this problem, a new diatom-based photobiological process has been developed to remove these scaling constituents by biological uptake and precipitation. In this study, RO concentrate samples were collected from a full-scale advanced water reclamation facility in California and were treated in 3.8 and 57 L photobioreactors inoculated with a brackish water diatom  Pseudostaurosira trainorii PEWL001 using light-emitting diode bulbs or natural sunlight as a light source. The photobiological treatment removed 95% of reactive silica and 64% of calcium and enabled additional water recovery using a secondary RO at a recovery rate up to 66%. This represents 95% overall recovery, including 85% recovery in the primary RO unit. In addition to the scaling constituents, the photobiological treatment removed 12 pharmaceuticals and personal care products, as well as N-nitrosodimethylamine, from RO concentrate samples primarily via photolysis. This novel approach has a strong potential for application to brackish water desalination and advanced water purification in arid and semiarid areas.

N-nitrosodimethylamine formation upon ozonation and identification of precursors source in a municipal wastewater treatment plant.

Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary influent, primary effluent, and secondary effluent of a wastewater treatment plant producing water destined for potable reuse. Results showed the most N-Nitrosodimethylamine (NDMA) production from primary effluent, and the recycle streams entering the primary clarifiers were identified as the main source of NDMA precursors. The degradation of aminomethylated polyacrylamide (Mannich) polymer used for sludge treatment was a significant cause of precursor occurrence. A strong correlation between NDMA formation and ammonia concentration was found suggesting an important role of ammonia oxidation on NDMA production. During ozonation tests in DI water using dimethylamine (DMA) as model precursor, the NDMA yield significantly increased in the presence of ammonia and bromide due to the formation of hydroxylamine and brominated nitrogenous oxidants. In addition, NDMA formation during ozonation of dimethylformamide (DMF), the other model precursor used in this study, occurred only in the presence of ammonia, and it was attributable to the oxidation of DMF by hydroxyl radicals. Filtered wastewater samples (0.7 µm) produced more NDMA than unfiltered samples, suggesting that ozone reacted with dissolved precursors and supporting the hypothesis of polymer degradation. Particularly, the total suspended solids content similarly affected NDMA formation and the UV absorbance decrease during ozonation due to the different ozone demand created in filtered and unfiltered samples.

Bioassay guided analysis coupled with non-target chemical screening in polyethylene plastic shopping bag fragments after exposure to simulated gastric juice of Fish.

In this study, fragments of polyethylene plastic bags were treated with simulated gastric juice of fish for 16 h. Following solid-phase extraction, methanol eluents caused acute toxicity to embryos and larvae of Japanese medaka. Chromatographic fractions (polar to more non-polar with numbers increasing) of the extract were evaluated for toxicity and estrogenic activity using medaka and an estrogen receptor (ER) cell-line. Fractions 6 and 9 had the highest estrogenic effects with relative hydrophobic chemicals. The vtg expression in fraction 6 was 22-fold higher than control, and the ER cellular response in fraction 9 was 8.5-fold higher than controls. Following non-target screening (NTS), several novel phthalates and phenols were identified in the above two fractions. Fractions 1 and 2 appeared to be primarily responsible for the acute toxicity observed with the whole extract. The hatching rate decreased to 36 % in fraction 2, and was not observed following exposure to fraction 1. NTS of these fractions indicated 635 and 808 entities, respectively, most without toxicity information. These results indicate plastic leachates from gastric juices of fish are complex mixtures of many compounds that can have acute reproductive and sublethal endocrine impacts in fish.

Applications of MXene-based membranes in water purification: A review.

Since MXenes (a new family of two-dimensional materials) were first produced in 2011, they have become very attractive nanomaterials due to their unique properties and the range of potential industrial applications. Numerous recent studies have discussed the environmental applications of different MXenes in adsorption, catalysis, and membranes. Only a limited number of MXene-based membrane studies have been published to date, and most have discussed only specific MXenes (i.e., Ti3C2Tx), a small number of solutes (e.g., dyes and inorganic salts), and laboratory-scale short-term experiments under limited water-quality and operational conditions. In addition, to our knowledge, there has been no review of MXene-membrane studies. It is therefore essential to assess the current status of understanding of the performance of these membranes in liquid separation and water purification. Here, a comprehensive literature review is conducted to summarize the current preparation techniques for MXene-based membranes and their applications, particularly in terms of environmental and industrial applications (e.g., water treatment and organic solvent filtration), and to direct future research by identifying gaps in our present understanding. In particular, this review focuses on several key factors, including the effects of preparation techniques on membrane properties, operational conditions, and compound properties that influence liquid separation during MXene-based membrane filtration.

Evaluation of a photocatalytic reactor membrane pilot system for the removal of pharmaceuticals and endocrine disrupting compounds from water.

A photocatalytic reactor membrane pilot system, employing UV/TiO(2) photocatalysis, was evaluated for its ability to remove thirty-two pharmaceuticals, endocrine disrupting compounds, and estrogenic activity from water. Concentrations of all compounds decreased following treatment, and removal followed pseudo-first-order kinetics as a function of the amount of treatment. Twenty-nine of the targeted compounds in addition to total estrogenic activity were greater than 70% removed while only three compounds were less than 50% removed following the highest level of treatment (4.24 kW h/m(3)). No estrogenically active transformation products were formed during treatment. Additionally, the unit was operated in photolytic mode (UV only) and photolytic plus H(2)O(2) mode (UV/H(2)O(2)) to determine the relative amount of energy required. Based on the electrical energy per order (EEO), the unit achieved the greatest efficiency when operated in photolytic plus H(2)O(2) mode for the conditions tested.

Assessment of online bacterial particle counts for monitoring the performance of reverse osmosis membrane process in potable reuse.

Safety of potable reuse can be enhanced by improved water quality monitoring techniques for assessing water treatment processes. This study evaluated the efficacy of online bacterial counting for continuous monitoring of reverse osmosis (RO) membranes to remove bacteria using real-time bacteriological commercial counters and an on-site pilot-scale RO system. Prior to on-site assessments, the online bacterial counting was verified by comparing the measurement of fluorescent particles in water with flow cytometry. During a seven day pilot test of RO treatment at a water reclamation plant, online bacterial counts in RO permeate were monitored below 15 counts/mL; whereas the bacterial counts in RO feed water were approximately 2500 to 10,000 counts/mL. Removal rates of bacterial counts ranged from 2.6 to 3.1-log (average = 2.9-log) by continuously monitoring bacterial removal. This is greater than a 2-log reduction frequently determined using other water quality surrogates (i.e., electrical conductivity). Overall, the continuous monitoring of bacteria in RO feed and permeate can be implemented without the addition of chemicals to provide near real-time bacterial counts to measure their reduction after RO treatment. This can be developed for continuous performance monitoring of the RO process, providing greater assurance of microbial water quality after RO treatment.

Organic matter removal and membrane fouling mitigation during algae-rich surface water treatment by powdered activated carbon adsorption pretreatment: Enhanced by UV and UV/chlorine oxidation.

In this work, UV and UV/chlorine (UV/Cl) were employed to enhance powdered activated carbon (PAC) adsorption pretreatment prior to ultrafiltration process for algae-contaminated surface water treatment. Their performance on membrane fouling mitigation and organic pollutant rejection was systematically evaluated. A comparative experiment was conducted under varying pollution degrees of algal extracellular organic matter (EOM) contamination in surface river water. The results indicated that UV/PAC and UV/Cl/PAC pretreatment effectively enhanced the removal of dissolved organic carbon (DOC) and UV-absorbing at 254 nm (UV254). The characteristics of feed water after pretreatments were investigated through apparent molecular-weight (MW) distribution and fluorescence parallel factor analysis (PARAFAC). In regard to membrane fouling mitigation, UV/Cl/PAC noticeably decreased reversible and irreversible fouling resistance simultaneously and UV/PAC preferred reducing reversible membrane fouling. Combined fouling modeling was operated to scrutinize the fouling mitigation mechanisms and standard pore blocking was proved to be dominant during the filtration process. Moreover, the UV/Cl and UV/Cl/PAC pretreatments were proved positive for emerging micropollutants degradation and disinfection by-products formation potential reduction. The results suggested that UV and UV/Cl are likely strategies to enhance the efficiency of PAC adsorption pretreatments prior to ultrafiltration during algae-contaminated water treatment.

Insight into Fe(II)/UV/chlorine pretreatment for reducing ultrafiltration (UF) membrane fouling: Effects of different natural organic fractions and comparison with coagulation.

Fe(II)/UV/chlorine was promoted as a pretreatment strategy for UF membrane to mitigate membrane fouling induced from different organic fractions. This treatment could be an emerging alternative prior to UF process attributed to the coupled role of oxidation and coagulation. To obtain a comprehensive understanding of fouling reduction, the influence of Fe(II)/UV/chlorine process on the characteristics of various feed solutions was inspected, including humic acid (HA), bovine serum albumin (BSA), sodium alginate (SA) and their mixture (HSB). The results suggested that Fe(II)/UV/chlorine process exhibited notable performance on membrane fouling control compared to Fe(II) coagulation alone. With the UV exposure of 720 mJ/cm2, the certain dose of Fe(II) and chlorine (15 µM and 2 mg/L) effectively prevented the rapid development of fouling caused by the single organic fractions and their mixture. And the increased dosage promoted the performance of membrane fouling mitigation. The reduction of organic loadings and characteristics change of feed water took the main responsibility for the fouling alleviation. The properties of membrane fouling and their correlation with feed water qualities were analyzed. The results and insight analysis were supposed to evaluate and predict the effectiveness of fouling control when the feed solutions were pretreated by Fe(II)/UV/chlorine process according to various compositions and characteristics of the organic fractions.

Reducing ultrafiltration membrane fouling during potable water reuse using pre-ozonation.

Wastewater reclamation has increasingly become popular to secure potable water supply. Low-pressure membrane processes such as microfiltration (MF) and ultrafiltration (UF) play imperative roles as a barrier of macromolecules for such purpose, but are often limited by membrane fouling. Effluent organic matter (EfOM), including biopolymers and particulates, in secondary wastewater effluents have been known to be major foulants in low-pressure membrane processes. Hence, the primary aim of this study was to investigate the effects of pre-ozonation as a pre-treatment for UF on the membrane fouling caused by EfOM in secondary wastewater effluents for hydrophilic regenerated cellulose (RC) and hydrophobic polyethersulfone (PES) UF membranes. It was found that greater fouling reduction was achieved by pre-ozonation for the hydrophilic RC membrane than the hydrophobic PES membrane at increasing ozone doses. In addition, the physicochemical property changes of EfOM, including biopolymer fractions, by pre-ozonation were systemically investigated. The classical pore blocking model and the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theories were employed to scrutinize the fouling alleviation mechanism by pre-ozonation. As a result, the overarching mechanisms of fouling reduction were attributed to the following key reasons: (1) Ozone degraded macromolecules such as biopolymers like proteins and polysaccharides into smaller fractions, thereby increasing free energy of cohesion of EfOM and rendering them more hydrophilic and stable; (2) pre-ozonation augmented the interfacial free energy of adhesion between foulants and the RC/PES membranes, leading to the increase of repulsions and/or the decrease of attractions; and (3) pre-ozonation prolonged the transition from pore blocking to cake filtration that was a dominant fouling mechanism, thereby reducing fouling.

N-nitrosodimethylamine (NDMA) formation during ozonation of wastewater and water treatment polymers.

N-Nitrosodimethylamine (NDMA) formation by ozonation was investigated in the effluents of four different wastewater treatment plants destined for alternative reuse. Very high levels of NDMA formation were observed in wastewaters from treatment plants non operating with biological nitrogen removal. Selected experiments showed that hydroxyl radical did not have a significant role in NDMA formation during ozonation of wastewater. Furthermore, ozonation of three different polymers used for water treatment, including polyDADMAC, anionic polyacrylamide, and cationic polyacrylamide, spiked in wastewater did not increase the NDMA formation. Effluent organic matter (EfOM) likely reduced the availability of ozone in water able to react with polymers and quenched the produced ·OH radicals which limited polymer degradation and subsequent NDMA production. Excellent correlations were observed between NDMA formation, UV absorbance at 254 nm, and total fluorescence reduction. These data provide evidence that UV and fluorescence surrogates could be used for monitoring and/or controlling NDMA formation during ozonation.

Association of drinking-water source and use characteristics with urinary antimony concentrations.

Environmental factors, such as storage time, frequency of bottle reuse and temperature, have been shown to facilitate antimony (Sb) leaching from water- and food-packaging materials. The globally escalating consumption of water packaged in Sb-containing bottles, such as that of polyethylene terephthalate (PET), could increase human daily Sb doses. This study set out to investigate the relationship between drinking-water source, use characteristics, and urinary Sb concentrations (U-Sb) accompanied with survey responses of a healthy (n=35) Cypriot participant pool. One spot urine sample was collected during administration of questionnaire, while a second spot urine sample was collected from the same individual about 7 days later. Urinary and water Sb concentrations were measured with an inductively coupled plasma mass spectrometer. Survey responses showed that bottled water summed over various volumes and plastic types, such as polycarbonate and PET contributed to an average 61% of daily water consumption. Water sources such as tap, mobile stations (explained in a following section), and well water contributed to 24%, 14%, and 2% of an individual's daily water consumption pattern, respectively. Average daily potable water use of both bottled and tap water by individuals consisted of 65% drinking-water, while the remaining 35% was water used for preparing cold and hot beverages, such as, tea, coffee, and juices. A significant (P=0.02) association between per capita water consumption from PET bottles and urinary creatinine-unadjusted concentrations was observed, but this relationship did not remain after inclusion of covariates in a multivariate regression model. In the creatinine-adjusted regression model, only gender (female) was a significant (P<0.01) predictor of U-Sb, after adjusting for several covariates. It is proposed that consumption data collection on various water uses and sources among individuals could perhaps decrease the uncertainty associated with derivations of acceptable daily Sb intakes.