Multi-component ion equilibria and transport in ion-exchange membranes.

At the interface between an ion-exchange membrane and a multi-electrolyte solution, charged species redistribute themselves to minimize the free energy of the system. In this paper, we explore the Donnan equilibrium of membranes with quaternary electrolyte (Na+/Mg2+/K+/Ca2+/Cl-) solutions, experimentally. The data was used to calculate the ion activity coefficients for six commercial cation-exchange membranes (CEMs). After setting one of the activity coefficients to an arbitrary value, we used the remaining (N-1) activity coefficients as fitting parameters to describe the equilibrium concentrations of (N) ionic species with a mean relative error of 3 %. At increasing solution ionic strengths, the equivalent ion fractions of monovalent counter-ions inside the membrane increased at the expense of the multivalent ones in alignment with the Donnan equilibrium theory. The fitted activity coefficients were employed in a transport model that simulated a Donnan dialysis experiment involving all four cations simultaneously. The arbitrary value assigned to one activity coefficient affects the calculated Donnan potential at the membrane interface. Nevertheless, this arbitrary value does not affect the prediction of the ion concentrations inside the membrane and consequently does not affect the modeled ion fluxes.

Influence of combined abiotic/biotic factors on decay of P. aeruginosa and E. coli in Rhine River water.

Understanding the dynamic change in abundance of both fecal and opportunistic waterborne pathogens in urban surface water under different abiotic and biotic factors helps the prediction of microbiological water quality and protection of public health during recreational activities, such as swimming. However, a comprehensive understanding of the interaction among various factors on pathogen behavior in surface water is missing. In this study, the effect of salinity, light, and temperature and the presence of indigenous microbiota, on the decay/persistence of Escherichia coli and Pseudomonas aeruginosa in Rhine River water were tested during 7 days of incubation with varying salinity (0.4, 5.4, 9.4, and 15.4 ppt), with light under a light/dark regime (light/dark) and without light (dark), temperature (3, 12, and 20 °C), and presence/absence of indigenous microbiota. The results demonstrated that light, indigenous microbiota, and temperature significantly impacted the decay of E. coli. Moreover, a significant (p<0.01) four-factor interactive impact of these four environmental conditions on E. coli decay was observed. However, for P. aeruginosa, temperature and indigenous microbiota were two determinate factors on the decay or growth. A significant three-factor interactive impact between indigenous microbiota, temperature, and salinity (p<0.01); indigenous microbiota, light, and temperature (p<0.01); and light, temperature, and salinity (p<0.05) on the decay of P. aeruginosa was found. Due to these interactive effects, caution should be taken when predicting decay/persistence of E. coli and P. aeruginosa in surface water based on a single environmental condition. In addition, the different response of E. coli and P. aeruginosa to the environmental conditions highlights that E. coli monitoring alone underestimates health risks of surface water by non-fecal opportunistic pathogens, such as P. aeruginosa. KEY POINTS: Abiotic and biotic factors interactively affect decay of E. coli and P. aeruginosa E.coli and P.aeruginosa behave significantly different under the given conditions Only E. coli as an indicator underestimates the microbiological water quality.

Biostimulation with oxygen and electron donors supports micropollutant biodegradation in an experimentally simulated nitrate-reducing aquifer.

The availability of suitable electron donors and acceptors limits micropollutant natural attenuation in oligotrophic groundwater. This study investigated how electron donors with different biodegradability (humics, dextran, acetate, and ammonium), and different oxygen concentrations affect the biodegradation of 15 micropollutants (initial concentration of each micropollutant = 50 µg/L) in simulated nitrate reducing aquifers. Tests mimicking nitrate reducing field conditions showed no micropollutant biodegradation, even with electron donor amendment. However, 2,4-dichlorophenoxyacetic acid and mecoprop were biodegraded under (micro)aerobic conditions with and without electron donor addition. The highest 2,4-dichlorophenoxyacetic acid and mecoprop biodegradation rates and removal efficiencies were obtained under fully aerobic conditions with amendment of an easily biodegradable electron donor. Under microaerobic conditions, however, amendment with easily biodegradable dissolved organic carbon (DOC) inhibited micropollutant biodegradation due to competition between micropollutants and DOC for the limited oxygen available. Microbial community composition was dictated by electron acceptor availability and electron donor amendment, not by micropollutant biodegradation. Low microbial community richness and diversity led to the absence of biodegradation of the other 13 micropollutants (such as bentazon, chloridazon, and carbamazepine). Finally, adaptation and potential growth of biofilms interactively determined the location of the micropollutant removal zone relative to the point of amendment. This study provides new insight on how to stimulate in situ micropollutant biodegradation to remediate oligotrophic groundwaters as well as possible limitations of this process.

The complexities of decision-making in food waste valorization: A critical review.

The efficient utilization of food waste (FW) resources through Food Waste Valorization (FWV) has received increasing attention in recent years. Various decision-making studies have been undertaken to facilitate FWV implementation, such as the studies on decision-making framework and FWV technology assessment. Food waste hierarchy is a widely discussed framework in FW management, but it was found too simplified and does not always contribute positively to environmental sustainability. Moreover, decision-making studies in FWV often focus on specific aspects of the food system and employ distinctive decision-making approaches, making it difficult to compare the results from different studies. Therefore, our literature review is conducted to provide a comprehensive understanding of FWV decision-making. This study identifies what decisions are needed, and three levels of decisions are revealed: system-level, FW stream-level, and FWV option-level. The assessment approaches and criteria used to support decision-making in FWV are also collected and analyzed. Building upon these findings, an hourglass model is synthesized to provide a holistic illustration of decision-making in FWV. This study untangles the complexities of FWV decision-making and sheds light on the limitations of current studies. We anticipate this study will make more people realize that FWV is a multidisciplinary issue and requires the collective participation of researchers, practitioners, policymakers, and consumers. Such collective engagement is essential to effectively address practical challenges and propel the transition of the current food system toward a more resource-efficient paradigm.

Hydroponic materials improve organic micropollutant removal in vertical flow constructed wetlands treating wastewater.

Unconventional substrata like activated carbon or clay beads can enhance micropollutant removal in constructed wetlands. However, hydroponic materials widely used in horticulture have not yet been investigated for their potential to remove micropollutants. In addition, potential effect of plant species other than reeds on micropollutant removal has not been sufficiently investigated. Therefore, a nature-based, post-treatment technology called improved vertical flow constructed wetlands (CW) with hydroponic (H) materials (CWH) was designed by employing cocopeat and mineral with ornamental plant species syngonium and periwinkle. A mesocosm CWH system was tested in a climate-controlled greenhouse for 550 days for its potential to remove frequently found micropollutants in wastewater, namely sulfamethoxazole, trimethoprim, diclofenac, erythromycin, carbamazepine, pyrimethanil, tebuconazole, pymetrozine, atrazine and DEET from wastewater effluent. The main focus was to understand the contribution of sorption, microbial degradation and phytoremediation on the removal of those micropollutants. It was found that cocopeat showed a capacity for sorbing micropollutants, ranging between 80 and 99% of the compounds added while less than 10% sorption was observed for mineral wool. Additionally moderate to high biological removal (25-60 µg of compound/kg dry weight of substratum/day) for most of the studied compounds was observed in all the cocopeat biotic groups. Furthermore, it could be stated that plants appear not to be an important factor for micropollutant removal. The observed differences in removal between the cocopeat and mineral wool systems could be explained by the difference in physico-chemical properties of the substrata, where cocopeat has a higher water holding capacity, moisture content, nutrient and organic matter content, and a higher intraparticle porosity and surface area. This study revealed notable removal of persistent and mobile micropollutants in cocopeat CWH, namely carbamazepine (80-86%) and diclofenac (97-100%). These results demonstrate the potential beneficial use of hydroponic materials as substratum in more advanced constructed wetlands designed to remove micropollutants.

Bioaugmentation has temporary effect on anaerobic pesticide biodegradation in simulated groundwater systems.

Groundwater is the most important source for drinking water in The Netherlands. Groundwater quality is threatened by the presence of pesticides, and biodegradation is a natural process that can contribute to pesticide removal. Groundwater conditions are oligotrophic and thus biodegradation can be limited by the presence and development of microbial communities capable of biodegrading pesticides. For that reason, bioremediation technologies such as bioaugmentation (BA) can help to enhance pesticide biodegradation. We studied the effect of BA using enriched mixed inocula in two column bioreactors that simulate groundwater systems at naturally occurring redox conditions (iron and sulfate-reducing conditions). Columns were operated for around 800 days, and two BA inoculations (BA1 and BA2) were conducted in each column. Inocula were enriched from different wastewater treatment plants (WWTPs) under different redox-conditions. We observed a temporary effect of BA1, reaching 100% removal efficiency of the pesticide 2,4-D after 100 days in both columns. In the iron-reducing column, 2,4-D removal was in general higher than under sulfate-reducing conditions demonstrating the influence of redox conditions on overall biodegradation. We observed a temporary shift in microbial communities after BA1 that is relatable to the increase in 2,4-D removal efficiency. After BA2 under sulfate-reducing conditions, 2,4-D removal efficiency decreased, but no change in the column microbial communities was observed. The present study demonstrates that BA with a mixed inoculum can be a valuable technique for improving biodegradation in anoxic groundwater systems at different redox-conditions.

Influence of redox condition and inoculum on micropollutant biodegradation by soil and activated sludge communities.

Micropollutant biodegradation is selected by the interplay among environmental conditions and microbial community composition. This study investigated how different electron acceptors, and different inocula with varying microbial diversity, pre-exposed to distinct redox conditions and micropollutants, affect micropollutant biodegradation. Four tested inocula comprised of agricultural soil (Soil), sediment from a ditch in an agricultural field (Ditch), activated sludge from a municipal WWTP (Mun AS), and activated sludge from an industrial WWTP (Ind AS). Removal of 16 micropollutants was investigated for each inoculum under aerobic, nitrate reducing, iron reducing, sulfate reducing, and methanogenic conditions. Micropollutant biodegradation was highest under aerobic conditions with removal of 12 micropollutants. Most micropollutants were biodegraded by Soil (n = 11) and Mun AS inocula (n = 10). A positive correlation was observed between inoculum community richness and the number of different micropollutants a microbial community initially degraded. The redox conditions to which a microbial community had been exposed appeared to positively affect micropollutant biodegradation performance more than pre-exposure to micropollutants. Additionally, depletion of the organic carbon present in the inocula resulted in lower micropollutant biodegradation and overall microbial activities, suggesting that i) an additional carbon source is needed to promote micropollutant biodegradation; and ii) overall microbial activity can be a good indirect indicator for micropollutant biodegradation activity. These results could help to develop novel micropollutant removal strategies.

Seasonal variation in antibiotic resistance genes and bacterial phenotypes in swine wastewater during three-chamber anaerobic pond treatment.

Antibiotic resistance is a global public health concern. Antibiotic usage in pigs makes swine wastewater (SW) a reservoir for antibiotic resistance genes (ARGs). SW is usually stored and treated in a three-chamber anaerobic pond (3-CAP) in medium and small pig farms in northern China. However, the yet unexplored presence of ARGs in SW during 3-CAP treatment may result in ARGs spreading into the environment if farmers apply SW to farmland as a liquid organic fertilizer. This study investigated the profiles of and changes in ARGs in SW during its treatment in 3-CAP over four seasons and analyzed the correlation between ARGs and bacterial phenotypes, along with the physicochemical parameters of the water. The results revealed that ARG abundance decreased considerably after 3-CAP treatment in April (47%), October (47%), and December (62%) but increased in May (43%) and August (73%). The ARG copies in the influent and other SW samples increased significantly from 107 copies/mL in April to 109 copies/mL in October and were maintained in December. The increase in ARG abundance was not as rapid as the growth of the bacterial population, resulting in lower relative abundance in October and December. Bacterial communities possessed more sul1 and tetM genes, which were also positively correlated with mobile genetic elements. After the 3-CAP treatment, 16% of antibiotics and 60% of heavy metals were removed, and both had a weak correlation with ARGs. Predicted phenotypes showed that gram-positive (G+) and gram-negative (G-) bacteria have different capacities for carrying ARGs. G+ bacteria carry more ARGs than G- bacteria. This study revealed the persistence of ARGs in SW after 3-CAP treatment over different seasons. Applying SW in the proper month will mitigate ARG dissemination to the environment.

Improving suitability of urban canals and canalized rivers for transportation, thermal energy extraction and recreation in two European delta cities.

Canals and canalized rivers form a major part of surface water systems in European delta cities and societal ambitions to use these waters increase. This is the first assessment of how suitability of these waters can improve for three important uses: transportation, thermal energy extraction (TEE) and recreation. We assess suitability with Suitability Indices (SIs) and identify which alterations in the water system are needed to improve SI scores in Amsterdam, The Netherlands, and Ghent, Belgium. The results show spatial variability in suitability scores. Current suitability for transportation is low (SI score = 1) to excellent (SI score = 4), for TEE fair (SI score = 2) to excellent (SI score = 4), and suitability for recreation is low (SI score = 1). Suitability could improve by enlarging specific waterway dimensions, increasing discharge and clarity, and by enhancing microbiological water quality. The same methodology can be applied to optimize designs for new water bodies and for more water uses.

Effect of electrolyte composition on electrochemical oxidation: Active sulfate formation, benzotriazole degradation, and chlorinated by-products distribution.

Electrochemical oxidation is an effective technique for treating persistent organic pollutants, which are hardly removed in conventional wastewater treatment plants. Sulfate and chloride salts commonly used and present in natural wastewater influence the electrochemical degradation process. In this study, the effect of electrolyte composition on the active sulfate species (SO4●⁻ and S2O82⁻) formation, benzotriazole degradation-a model organic compound, and chlorinated by-products distribution have been investigated while using a boron-doped diamond (BDD) anode. Different Na2SO4:NaNO3 and Na2SO4:NaCl ratios with constant conductivity of 10 mS/cm were used in the experiments and applied anode potential was kept constant at 4.3 V vs. Ag/AgCl. The electrogenerated SO4●⁻ and S2O82⁻ formation were faster in 10:1 and 2:1 Na2SO4:NaNO3 ratios than in the 1:0 ratio. The ●OH-mediated SO4●⁻ production has prevailed in 10:1 and 2:1 ratios. However, ●OH-mediated SO4●⁻ production has hindered the 1:0 ratio due to excess chemisorption of SO42⁻ on the BDD anode. Similarly, the faster benzotriazole degradation, mineralization, and lowest energy consumption were achieved in the 10:1 Na2SO4:NaNO3 and Na2SO4:NaCl ratio. Besides, chlorinated organic by-product concentration (AOX) was lower in the 10:1 Na2SO4:NaCl ratio but increased with the increasing chloride ratio in the electrolyte. LC-MS analysis shows that several chlorinated organic transformation products were produced in 0:1 to 2:1 ratio, which was not found in the 10:1 Na2SO4:NaCl ratio. A comparatively higher amount of ClO4⁻ was formed in the 10:1 ratio than in 2:1 to 0:1 ratio. This ClO4⁻ formation train evidence the effective ●OH generation in a sulfate-enriched condition because the ClO4⁻ formation is positively correlated to ●OH concentration. Overall results show that sulfate-enriched electrolyte compositions are beneficial for electrochemical oxidation of biorecalcitrant organic pollutants.

Selective pressure on microbial communities in a drinking water aquifer - Geochemical parameters vs. micropollutants.

Groundwater quality is crucial for drinking water production, but groundwater resources are increasingly threatened by contamination with pesticides. As pesticides often occur at micropollutant concentrations, they are unattractive carbon sources for microorganisms and typically remain recalcitrant. Exploring microbial communities in aquifers used for drinking water production is an essential first step towards understanding the fate of micropollutants in groundwater. In this study, we investigated the interaction between groundwater geochemistry, pesticide presence, and microbial communities in an aquifer used for drinking water production. Two groundwater monitoring wells in The Netherlands were sampled in 2014, 2015, and 2016. In both wells, water was sampled from five discrete depths ranging from 13 to 54 m and was analyzed for geochemical parameters, pesticide concentrations and microbial community composition using 16S rRNA gene sequencing and qPCR. Groundwater geochemistry was stable throughout the study period and pesticides were heterogeneously distributed at low concentrations (µg L-1 range). Microbial community composition was also stable throughout the sampling period. Integration of a unique dataset of chemical and microbial data showed that geochemical parameters and to a lesser extent pesticides exerted selective pressure on microbial communities. Microbial communities in both wells showed similar composition in the deeper aquifer, where pumping results in horizontal flow. This study provides insight into groundwater parameters that shape microbial community composition. This information can contribute to the future implementation of remediation technologies to guarantee safe drinking water production.

Electrochemical removal of amphoteric ions.

Several harmful or valuable ionic species present in seawater, brackish water, and wastewater are amphoteric, weak acids or weak bases, and, thus, their properties depend on local water pH. Effective removal of these species can be challenging for conventional membrane technologies, necessitating chemical dosing of the feedwater to adjust pH. A prominent example is boron, which is considered toxic in high concentrations and often requires additional membrane passes to remove during seawater desalination. Capacitive deionization (CDI) is an emerging membraneless technique for water treatment and desalination, based on electrosorption of salt ions into charging microporous electrodes. CDI cells show strong internally generated pH variations during operation, and, thus, CDI can potentially remove pH-dependent species without chemical dosing. However, development of this technique is inhibited by the complexities inherent to the coupling of pH dynamics and ion properties in a charging CDI cell. Here, we present a theoretical framework predicting the electrosorption of pH-dependent species in flow-through electrode CDI cells. We demonstrate that such a model enables insight into factors affecting species electrosorption and conclude that important design rules for such systems are highly counterintuitive. For example, we show both theoretically and experimentally that for boron removal, the anode should be placed upstream and the cathode downstream, an electrode order that runs counter to the accepted wisdom in the CDI field. Overall, we show that to achieve target separations relying on coupled, complex phenomena, such as in the removal of amphoteric species, a theoretical CDI model is essential.

WaterROUTE: A model for cost optimization of industrial water supply networks when using water resources with varying salinity.

Water users can reduce their impact on scarce freshwater resources by using more abundant regional brackish or saline groundwater resources. Decentralized water supply networks (WSN) can connect these regional groundwater resources with water users. Here, we present WaterROUTE (Water Route Optimization Utility Tool & Evaluation), a model which optimizes water supply network configurations based on infrastructure investment costs while considering the water quality (salinity) requirements of the user. We present an example simulation in which we determine the optimal WSN for different values of the maximum allowed salinity at the demand location while supplying 2.5 million m3 year-1 with regional groundwater. The example simulation is based on data from Zeeuws-Vlaanderen, the Netherlands. The optimal WSN configurations for the years 2030, 2045 and 2110 are generated based on the simulated salinity of the regional groundwater resources. The simulation results show that small changes in the maximum salinity at the demand location have significant effects on the WSN configuration and therefore on regional planning. For the example simulation, the WSN costs can differ by up to 68% based on the required salinity at the demand site. WaterROUTE can be used to design water supply networks which incorporate alternative water supply sources such as local brackish groundwater (this study), effluent, or rainwater.

Biostimulation is a valuable tool to assess pesticide biodegradation capacity of groundwater microorganisms.

Groundwater is the main source for drinking water production globally. Groundwater unfortunately can contain micropollutants (MPs) such as pesticides and/or pesticide metabolites. Biological remediation of MPs in groundwater requires an understanding of natural biodegradation capacity and the conditions required to stimulate biodegradation activity. Thus, biostimulation experiments are a valuable tool to assess pesticide biodegradation capacity of field microorganisms. To this end, groundwater samples were collected at a drinking water abstraction aquifer at two locations, five different depths. Biodegradation of the MPs BAM, MCPP and 2,4-D was assessed in microcosms with groundwater samples, either without amendment, or amended with electron acceptor (nitrate or oxygen) and/or carbon substrate (dissolved organic carbon (DOC)). Oxygen + DOC was the most successful amendment resulting in complete biodegradation of 2,4-D in all microcosms after 42 days. DOC was most likely used as a growth substrate that enhanced co-metabolic 2,4-D degradation with oxygen as electron acceptor. Different biodegradation rates were observed per groundwater sample. Overall, microorganisms from the shallow aquifer had faster biodegradation rates than those from the deep aquifer. Higher microbial activity was also observed in terms of CO2 production in the microcosms with shallow groundwater. Our results seem to indicate that shallow groundwater contains more active microorganisms, possibly due to their exposure to higher concentrations of both DOC and MPs. Understanding field biodegradation capacity is a key step towards developing further bioremediation-based technologies. Our results show that biostimulation has real potential as a technology for remediating MPs in aquifers in order to ensure safe drinking production.

Mathematically formulated key performance indicators for design and evaluation of treatment trains for resource recovery from urban wastewater.

While urban wastewater infrastructure is aging and no longer adequate, climate change and sustainability are urging the transition from pollution management to resource recovery. Lacking evidence-based quantitative evaluation of the potential benefits and consequences of resource recovery from wastewater hinders the negotiation amongst stakeholders and slows down the transition. This study proposes mathematical formulations for technical, environmental, economic, and social key performance indicators (KPIs) that can be used to quantify the benefits and the risks of resource recovery. The proposed formulations are derived from the literature and validated with stakeholders. Each KPI is mathematically formulated at treatment train level by considering: (1) the characteristics of individual unit processes (UPs) in the treatment train (TT), (2) the context in which the TT is installed, and (3) the resources to be recovered. The mathematical formulations of the KPIs proposed in this study enable a transparent, consistent and informative evaluation of existing treatment trains, as well as support the (computer aided) design of new ones. This could aid the transition from urban wastewater treatment to resource recovery from urban wastewater.

DNA-SIP identification of phenanthrene-degrading bacteria undergoing bioaugmentation and natural attenuation in petroleum-contaminated soil.

DNA-stable isotope probing (SIP) with 13C labeled phenanthrene (PHE) as substrate was used to identify specific bacterial degraders during natural attenuation (NA) and bioaugmentation (BA) in petroleum contaminated soil. BA, with the addition of a bacterial suspension mixture named GZ, played a significant role in PHE degradation with a higher PHE removal rate (∼90%) than that of NA (∼80%) during the first 3 days, and remarkably altered microbial communities. Of the five strains introduced in BA, only two genera, particularly, Ochrobactrum, Rhodococcus were extensively responsible for PHE-degradation. Six (Bacillus sp., Acinetobacter sp., Xanthomonas sp., Conexibacter sp., Acinetobacter sp. and Staphylococcus sp.) and seven (Ochrobactrum sp., Rhodococcus sp., Alkanindiges sp., Williamsia sp., Sphingobium sp., Gillisia sp. and Massilia sp.) bacteria responsible for PHE degradation were identified in NA and BA treatments, respectively. This study reports for the first time the association of Xanthomonas sp., Williamsia sp., and Gillisia sp. to PHE degradation.

Effects of salinity on the treatment of synthetic petroleum-industry wastewater in pilot vertical flow constructed wetlands under simulated hot arid climatic conditions.

Petroleum-industry wastewater (PI-WW) is a potential source of water that can be reused in areas suffering from water stress. This water contains various fractions that need to be removed before reuse, such as light hydrocarbons, heavy metals and conditioning chemicals. Constructed wetlands (CWs) can remove these fractions, but the range of PI-WW salinities that can be treated in CWs and the influence of an increasing salinity on the CW removal efficiency for abovementioned fractions is unknown. Therefore, the impact of an increasing salinity on the removal of conditioning chemicals benzotriazole, aromatic hydrocarbon benzoic acid, and heavy metal zinc in lab-scale unplanted and Phragmites australis and Typha latifolia planted vertical-flow CWs was tested in the present study. P. australis was less sensitive than T. latifolia to increasing salinities and survived with a NaCl concentration of 12 g/L. The decay of T. latifolia was accompanied by a decrease in the removal efficiency for benzotriazole and benzoic acid, indicating that living vegetation enhanced the removal of these chemicals. Increased salinities resulted in the leaching of zinc from the planted CWs, probably as a result of active plant defence mechanisms against salt shocks that solubilized zinc. Plant growth also resulted in substantial evapotranspiration, leading to an increased salinity of the CW treated effluent. A too high salinity limits the reuse of the CW treated water. Therefore, CW treatment should be followed by desalination technologies to obtain salinities suitable for reuse. In this technology train, CWs enhance the efficiency of physicochemical desalination technologies by removing organics that induce membrane fouling. Hence, P. australis planted CWs are a suitable option for the treatment of water with a salinity below 12 g/L before further treatment or direct reuse in water scarce areas worldwide, where CWs may also boost the local biodiversity. Graphical abstract.

Applications of anodized TiO2 nanotube arrays on the removal of aqueous contaminants of emerging concern: A review.

The presence of contaminants of emerging concern (CECs) in various water bodies and the associated threats to eco-system and human society have raised increasing concerns. To fight against such a problem, TiO2 photocatalysis is considered to be a powerful tool. In recent decades, TiO2 nanotube array (TNA) fabricated by electrochemical anodization emerged as a viable immobilized catalyst and its applications on CECs removal have gained a considerable amount of research interest. We herein present a critical review on the development of TNA and its applications on the removal of aqueous CECs. In this work, the CECs removal in different TNA based processes, the CECs removal mechanisms, the role of TNA properties, the role of operational parameters, and the role of water matrices are discussed. Moreover, perspectives on the current research progress are presented and recommendations on future research are elaborated.

Removal of organic compounds from cooling tower blowdown by electrochemical oxidation: Role of electrodes and operational parameters.

The reuse of cooling tower blowdown (CTBD) in the cooling tower itself requires CTBD deionization and a pre-treatment before deionization to remove organic compounds (OCs) that induce membrane fouling. This study assesses the potential of electrochemical oxidation (EO) with a boron-doped diamond (BDD) and a Ti/RuO2 mixed-metal oxide (MMO) anode for CTBD pre-treatment. Also, the influence of the applied current density (j), initial pH, hydrodynamic conditions, and supporting electrolyte on the process performance was evaluated. Results show that COD and TOC removal were 85 and 51%, respectively, with the BDD-anode; however, they were 50 and 12% with MMO-anode at a j-value of 8.7 mA cm-2 and neutral pH. An increased j-value increased the COD and TOC removal; however, different pHs, hydrodynamic conditions, and the addition of supporting electrolytes had a minor impact on the removal with both anodes. Liquid chromatography-organic carbon detection analysis showed that the OC in CTBD mainly consisted of humic substances (HS). EO with the BDD-anode resulted in 35% HS mineralization, while the rest of the HS were partially oxidized into low molecular weight compounds and building blocks. However, HS mineralization was limited with the MMO-anode. The mineralization and oxidation were accompanied by the formation of organic and inorganic chlorinated species. These species increased the toxicity to Vibrio fischeri 20-fold compared to the initially low-toxic CTBD. Thus, EO with a BDD-anode is a promising pre-treatment technology for the removal of OCs before CTBD deionization, but measures to minimize the chlorinated species formation are required before its application.

Pilot-scale hybrid constructed wetlands for the treatment of cooling tower water prior to its desalination and reuse.

Cooling towers are responsible for a large part of the industrial fresh water withdrawal, and the reuse of cooling tower water (CTW) effluents can strongly lower industrial fresh water footprints. CTW requires desalination prior to being reused, but various CTW components, such as total organic carbon (TOC), conditioning chemicals and total suspended solids (TSS) hamper physico-chemical desalination technologies and need to be removed from the CTW. A cost-efficient and robust pre-treatment is thus required, which can be provided by constructed wetlands (CWs). The present study is the first study that determined the CTW pre-treatment efficiency of hybrid-CWs and the impact of winter season and biocides in the CTW on the pre-treatment efficiency. The most efficient CW flow type and dominant removal mechanisms for CW components hampering physico-chemical desalination were determined. Subsurface flow CWs removed PO43-, TSS and TOC as a result of adsorption and filtration. Vertical subsurface flow CWs (VSSF-CW) excelled in the removal of benzotriazole as a result of aerobic biodegradation. Horizontal subsurface flow CWs (HSSF-CW) allowed the denitrification of NO3- due to their anaerobic conditions. Open water CWs (OW-CWs) did not contribute to the removal of components that hamper physico-chemical desalination technologies, but do provide water storage options and habitat. The biological removal processes in the different CW flow types were negatively impacted by the winter season, but were not impacted by concentrations of the biocides glutaraldehyde and DBNPA that are relevant in practice. For optimal pre-treatment, a hybrid-CW, consisting of an initial VSSF-CW followed by an OW-CW and HSSF-CW is recommended. Future research should focus on integrating the hybrid-CW with a desalination technology, e.g. reverse osmosis, electrodialysis or capacitive ionization, to produce water that meets the requirements for use as cooling water and allow the reuse of CTW in the cooling tower itself.