Nitrogen compounds removal from brackish water by electrodialysis at fixed electric potential and dynamic current density operations.

Nitrogen (N) compounds can occur in water resources from natural and anthropogenic activities. It is ideal that these contaminants be removed before water consumption. As water quality has been affected by increased salinity and pH variation, more advanced and robust technologies such as electrodialysis (ED) can be considered for simultaneous desalination and pollutant removal. In this context, the removal of N-species (NO3-, NO2-, NH4+, and CH4N2O) from brackish water by ED was investigated for different feed water quality, considering increased salinity (0 - 10g/L NaCl) and pH variation (3 - 11), under limit current density (LCD) at fixed electric potential condition. The applied electric potential (5 - 25V) under, at, and over the LCD at fixed electric potential and dynamic current density (DCD), as a percentage of LCD (0.4 - 1.2), were analyzed to improve the process. In addition, energy efficiency in the form of specific energy consumption (SEC) and current efficiency (CE) were assessed for ED at fixed electric potential and DCD. The results showed that, at extreme pH of the feed water, the removal of NO2- and NH4+ can be affected, while NO3-was the most stable compound with pH variation. An increase in feed water salinity just slightly impacted the removal of N-compounds, due to the similar characteristics of the ions in the water. The increase in electric potential at fixed electric potential or DCD increased the removal and molar flux of N-compounds. However, operating over the LCD increased the SEC of the ED process while changes in removal were not significant. DCD procedures resulted in higher CE and shorter run time of the experiments. Therefore, ED proved to be a suitable treatment technique to produce fresh water due to the selective removal of the studied ions, especially at 15V (fixed electrical potential) and 0.8 LCD (DCD) related to removal, molar flux, and run time to achieve guidelines.

Adsorption of glyphosate and metabolite aminomethylphosphonic acid (AMPA) from water by polymer-based spherical activated carbon (PBSAC).

Glyphosate (GLY) is the most commonly used herbicide worldwide, and aminomethylphosphonic acid (AMPA) is its main metabolite. Their occurrence in ground and surface waters causes diseases in humans, while complex physico-chemical properties hinder detection and effective removal. Polymer-based spherical activated carbon (PBSAC) can adsorb many micropollutants efficiently and, hence, overcome the shortfalls of conventional treatment methods. The static adsorption of a mixture of GLY and AMPA by PBSAC was investigated with varying PBSAC properties and relevant solution chemistry. The results show that PBSAC can remove 95% GLY and 57% AMPA from an initial concentration of 1 µg/L at pH 8.2. PBSAC properties (size, activation level, and surface charge) have a strong influence on herbicide removal, where surface area plays a key role. Low to neutral pH favors non-charge interactions and results in good adsorption, while higher temperatures equally enhance GLY/AMPA adsorption by PBSAC. The work demonstrated the effective removal of GLY to meet the European guideline concentration (0.1 µg/L), while AMPA could not be removed to the required level.

Organic matter interference with steroid hormone removal by single-walled carbon nanotubes - ultrafiltration composite membrane.

Composite adsorbent-ultrafiltration membranes for micropollutant removal are an interesting concept, although water matrix compounds, such as organic matter (OM), may interfere with micropollutant adsorption. To prevent this interference, the adsorbents such as single-walled carbon nanotubes (SWCNTs) can be deposited on the permeate side of an ultrafiltration membrane (UF) that can retain OM. In this study, the 'shielding' effect by different UF MWCOs of such an SWCNT-UF composite was evaluated for nine different types of OM. All nine OM types competed with 17ß-estradiol (E2) for adsorption to varying extents, and tannic acid (TA, 1.7 kDa) reduced E2 adsorption by SWCNT-UF most drastically. TA interference mechanisms included direct competition with hormones for adsorption sites, and indirect competition via TA-hormone interactions. TA was not fully retained by the composite membrane with an MWCO range of 3-100 kDa, resulting in ineffective shielding. In contrast, humic acid was mostly retained by the composite with low MWCO of 3-10 kDa and allowed high E2 adsorption. This study demonstrates that tailoring composite membranes by carefully choosing UF MWCO can prevent interference of OM types in micropollutant adsorption by permeate-side adsorbents.

Interactions between carbon-based nanoparticles and steroid hormone micropollutants in water.

The occurrence of micropollutants (MPs) including steroid hormones is a global environmental and health challenge. Carbon-based nanoparticles can be incorporated with water treatment processes to allow MP removal by adsorption. The aim was to compare the suitability of such nanoparticles (graphene, graphene oxide, carbon nanotubes and C60) to adsorb steroid hormones for later incorporation in membrane composites. All nanoparticles displayed fast kinetics; carbon nanotubes and graphene showed high adsorption capacities for hormones undeterminable in isotherm studies (over 10 mg/g). External surface adsorption appears to be the most prominent factor impacting adsorption performance. Structure, conformation, geometry and surface charge of nanoparticles can influence the accessibility of surface area through colloidal instability in aqueous solution. Mechanism inspection shows that adsorption initiates at long ranges (up to 10 nm) through hydrophobic and electrostatic interactions. At relatively short ranges (0.2-0.5 nm), adsorption is enhanced by π/π stacking, XH / π (X = C, O) interactions, van der Waals forces and hydrogen bonding. Both long- and short-range forces transporting hormones from the liquid bulk into the adsorbed phase could control the rate. With relatively short residence time required and high adsorption capacity, carbon nanotubes and graphene are promising for incorporation in a membrane composite.

Removal of Naturally Occurring Strontium by Nanofiltration/Reverse Osmosis from Groundwater.

Removal of naturally occurring strontium (Sr) from groundwater is vital as excessive exposure may lead to bone growth problems in children. Nanofiltration/reverse osmosis (NF/RO) is commonly used in groundwater treatment due to the high effectiveness and simple maintenance of these pressure driven membrane processes. In this research, a pilot-scale NF/RO system was used to desalinate a natural groundwater sample containing high Sr concentration (10.3 mg/L) and "old" groundwater organic matter (70.9 mg/L) from Esilalei in northern Tanzania to understand the removal of strontium by NF/RO. The impact of applied pressure (10-15 bar) and groundwater pH (3-12) on the membrane performance including permeate flux, strontium and total organic carbon (TOC) flux and removal was investigated. Increasing applied pressure was found to enhance the flux by increasing the driving force and enhance Sr and TOC removal by dilution effect (water flux higher than Sr passage). The alkaline pH caused severe flux decline likely due to membrane fouling and scaling, while it slightly enhanced Sr removal of RO membranes, but weakened the TOC removal. In contrast, acidic and neutral pH of groundwater enhanced TOC removal. These findings suggest that appropriately high applied pressure and acidic pH condition of groundwater are recommended to apply to the NF/RO membrane system in groundwater desalination to achieve better membrane performance.

Low pressure operated ultrafiltration membrane with integration of hollow mesoporous carbon nanospheres for effective removal of micropollutants.

An effective way to remove micropollutants is desirable for water purification. In this work, a dual-functional ultrafiltration (DFUF) membrane was fabricated by loading hollow mesoporous carbon nanospheres (HMCNs) into the finger-like support layer pores of the polymeric ultrafiltration (UF) membrane. The designed DFUF membrane combines the high selectivity of ultrafiltration that removes macromolecules based on size exclusion mechanism, and excellent adsorption capacity of HMCNs towards micropollutants in water. When tetracycline (TCN) and 17ß-Estradiol (E2) were selected as model micropollutants, corresponding 97 % and 94 % removal were achieved at a low pressure less than 0.15 bar and a flux of 50 and 64 L h-1 m-2 (estimated residence time less than 6 s), respectively. Moreover, simultaneous removal of multiple pollutants was demonstrated by filtering a mixture containing TCN and polyethylene glycols (PEG) 600 kDa macromolecules. Over a long filtration period (more than 60 h) that produced 3180 L/m2 of permeate, the TCN concentration reduced from 100 µg/L in the feed to less than 10 µg/L in the permeate. The above results indicate that the DFUF membrane is capable of removing the small molecular and macromolecular pollutants simultaneously at low pressure, and hence offers remarkable potential in water treatment applications.

Recycled and desalinated water: Consumers' associations, and the influence of affect and disgust on willingness to use.

Traditional water sources are increasingly coming under pressure from urbanization, population and industrial growth as well as climate variability and alternatives such as desalinated and recycled water will need to be considered in the future. However, available data indicate that consumers are apprehensive about these alternative water sources, with many reactions centered on disgust. It is not clear though, whether trait or state disgust is responsible for these disgust reactions. Secondly, the associations the public has with desalinated and recycled water are not well described, even though knowledge of these associations would provide the holistic understanding required for addressing perceptions. Using respondents from Australia and South Africa, therefore, this study investigated the associations people have with recycled and desalinated water, as well as the influence of affect, institutional trust, cultural/religious beliefs, water scarcity, and demographic variables, on willingness to use (WTU) these waters. The results show that whereas recycled water is associated with negative affect from notions of disgust, desalinated water is often thought of in terms of minerals, or as "simply water". We also found that affect was the most significant predictor, and that state disgust as well as trait disgust influenced WTU. Together these data suggest that disgust-related rejection of is likely due to the disgust elicited by the waters rather than disgust-proneness of individuals. It is plausible, therefore, that efforts to induce positive affect through making salient positive associations e.g. NEWater in Singapore, may increase WTU.

Steroid hormone micropollutant removal from water with activated carbon fiber-ultrafiltration composite membranes.

Short activated carbon fibers (ACF) with high surface area were fabricated via carbonization in N2 and activation in CO2 at high temperatures, with cellulose fibers as the raw materials. The obtained ACF were subsequently deposited into the support layer of a polyethersulfone (PES) ultrafiltration membrane by a facile filtration process to obtain the sandwich structured ACF-PES composite membrane. The hormone (17ß-estradiol, E2) adsorption kinetics and isotherm of ACF in static conditions, as well as E2 removal by filtration with the ACF-PES composite membrane were investigated. In static conditions, ACF rapidly and efficiently adsorbs E2 evidenced by a high removal of >97 %. The fitting of second order kinetics and linear (Henry) adsorption isotherm models indicated the availability of easily accessible adsorption sites. Besides, such efficient E2 adsorption was contributed by many interactions between E2 and ACF, namely hydrophobic interactions, hydrogen bonding and π-π stacking. The incorporation of ACF in a PES membrane resulted in a minor loss of filtration flux compared with the control membrane, but significantly improved E2 removal through adsorption pathway. With only 1.0 mg ACF incorporated (loading 2.0 g/m2), the composite membrane could reject 76 % of E2 from a 100 ng/L solution at a flux of 450 L/m2∙h, demonstrating that ACF-PES can overcome the permeability-selectivity trade-off of traditional UF membranes.

Removal of fluoride and natural organic matter from natural tropical brackish waters by nanofiltration/reverse osmosis with varying water chemistry.

In the context of decentralised brackish water treatment in development applications, the influence of water quality on membrane separation was investigated with real waters. High ionic strength (low net driving pressure) on fluoride (F) retention by nanofiltration (NF) and reverse osmosis (RO) was investigated over a wide pH range (2-12). Further, the influence of pH on the permeation of natural organic matter (NOM) fractions, in particular low molecular weight (LMW) neutrals, was elucidated. Natural and semi-natural waters from Tanzania with similar F concentrations of about 50 mg L-1 but varying NOM and inorganic carbon (IC) concentration were filtered with an NF and RO, namely NF270 and BW30. F retention by NF270 for the feed water with highest ionic strength and IC concentration was lower and attributed to charge screening. This parameter further reduced at high pH due to co-ions (F- and CO32-) interactions and combined (synergistic) effect of high salt concentration and pH on F. High NOM resulted in higher membrane zeta potential in comparison with low NOM natural water. However, there was no significant difference in F retention due to the fact that F retention enhancement was annulled by deposit formation on the membrane. The fraction of NOM found in NF/RO permeates was dominated by LMW neutrals. This was attributed to their size and uncharged nature, while their higher concentration at low pH remains unexplained. More humic substances (HS) of higher molecularity and aromaticity permeated the NF270 when compared with BW30, which can be explained with the different membrane molecular weight cut off (MWCO). The study highlights the complexity of treating tropical natural waters with elevated F and NOM concentrations. In order to develop appropriate membrane systems that will achieve optimal F and NOM removal, the influence of water quality parameters such as pH, NOM content, ionic strength and IC concentration requires understanding. Seasonal variation of water quality as well as operational fluctuations, which occur in particular when such treatment processes are operated with renewable energy, will require such challenges to be addressed. Further, given the high permeability of low molecular weight (LMW) organics significant permeate side fouling may be expected.

Renewable energy powered membrane technology: Impact of pH and ionic strength on fluoride and natural organic matter removal.

Real water pH and ionic strength vary greatly, which influences the performance of membrane processes such as nanofiltration (NF) and reverse osmosis (RO). Systematic variation of pH (3-12) and ionic strength (2-10g/L as total dissolved solids (TDS)) was undertaken with a real Tanzanian water to investigate how water quality affects retention mechanisms of fluoride (F) and natural organic matter (NOM). An autonomous solar powered NF/RO system driven by a solar array simulator was supplied with constant power from a generator. An open NF (NF270) and a brackish water RO (BW30) membrane were used. A surface water with a very high F (59.7mg/L) and NOM (110mgC/L) was used. Retention of F by NF270 was <20% at pH <6, increased to 40% at pH6, and 60-70% at pH7-12, indicating a dominance of charge repulsion while being ineffective in meeting the guideline of 1.5mg/L. Increase in ionic strength led to a significant decline in retention of F (from 70 to 50%) and electrical conductivity (from 60 to 10%) by NF270, presumably due to charge screening. In contrast, BW30 retained about 50% of F at pH3, >80% at pH4, and about 99% at pH >5, due to the smaller pore size and hence a more dominant size exclusion. In consequence, only little impact of ionic strength increase was observed for BW30. The concentration of NOM in permeates of both NF270 and BW30 were typically <2mg/L. This was not affected by pH or ionic strength due to the fact that the bulk of NOM was rejected by both membranes through size exclusion. The research is carried out in the context of providing safe drinking water for rural and remote communities where infrastructure is lacking, and water quality varies significantly. While other studies focus on energy fluctuations, this research emphasises on feed water quality that affects system performance and may alter due to a number of environmental factors.

Adsorption of steroid micropollutants on polymer-based spherical activated carbon (PBSAC).

Removal and interaction mechanisms of four different steroid micropollutants, estrone (E1), estradiol (E2), progesterone (P) and testosterone (T) were determined for different types of polymer-based spherical activated carbon (PBSAC). Higher than 90% removal and significantly faster kinetics compared to conventional granular activated carbon (GAC) were observed, while performance was comparable with powdered activated carbon (PAC). No influence of pH in the range 2-12 was determined, while the presence of humic acid (HA) reduced both the removal and the kinetic by up to 20%. PBSAC was characterized in terms of morphology and material properties. The low oxygen content was identified as the main cause for the high performance observed. This was attributed to the enhancement of the hydrophobic effect between PBSAC and hormones and the reduced interactions between PBSAC and water. The ratio of micropollutant size (∼0.8nm) and average pore size (1-2nm) proved ideal for both micropollutant adsorption and HA exclusion. The homogenous size, spherical shape and surface smoothness of PBSAC did not influence adsorption negatively and make PBSAC a very promising sorbent for a vast range of applications, in particular for the removal of micropollutants in water treatment applications.

Estradiol Uptake in a Combined Magnetic Ion Exchange - Ultrafiltration (MIEX-UF) Process During Water Treatment.

BACKGROUND: Estrogens and their synthetic analogues are widely used as pharmaceuticals. Upon oral administration these drugs are eventually excreted via urine. The persistence of these pharmaceuticals and inefficient removal by water treatment lead to accumulation in surface water and effluents with negative effects for aquatic life and human health. METHODS: In this study, the uptake of estradiol by a combined magnetic ion exchange resin - ultrafiltration process (MIEX-UF) was investigated. This is a relatively common process used in drinking water treatment for the removal of natural organic matter. However, uptake of micropollutants, such as steroidal pharmaceuticals, may occur as a side effect of water treatment due to the high affinity for polymeric materials. To elucidate the mechanism governing estradiol partitioning between water, resin and membrane, the influence of different parameters, such as pH, humic acid concentration and membrane molecular-weight-cut-off (MWCO) was studied. RESULTS: Humic acid concentration and pH affected estradiol uptake most. At pH 11 the most significant increase of estradiol uptake was observed for MIEX-UF process (30 ng/g corresponding to 80%) compared with individual UF (17 ng/g corresponding to 12%). The presence of humic acid slightly reduced estradiol uptake at pH 11 (about 55%) due to competition for the ion exchange binding sites. CONCLUSION: Results demonstrated that the uptake of estradiol, which is amongst the most potent EDCs detected in surface water, in the MIEX-UF process can reach significant quantities (30 ng/g of resin) leading to uncontrolled accumulation of this micropollutant during drinking water treatment. This study gives a novel contribution in the understanding the mechanism of the unanticipated accumulation of pharmaceuticals, such as estradiol, in the drinking water treatment process.