[Show abstract][Hide abstract] ABSTRACT: Algae organic matter (AOM), including intracellular organic matter (IOM) and extracellular organic matter (EOM), are major membrane foulants in the treatment of algae-polluted water. In this study, the effects of EOM and IOM (at dissolved organic concentrations of 8 mg/L) on the fouling of a polyethersulfone ultrafiltration (UF) membrane were investigated using a dead-end down-flow UF unit. Changes in the membrane pore geometry and the interaction energy between the membrane and foulants were analyzed based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. The data (relative standard deviation within 10%) showed that UF was able to retain 57% and 46% of IOM and EOM respectively, while the corresponding membrane fluxes rapidly reduced to 28% and 33% of their respective initial values after a specific filtration volume of only 3.75 mL/cm2. The fouling model implied that cake formation was the major mechanism. Specifically, IOM foulant had a much greater free energy of cohesion (-59.08 mJ/m2) than EOM foulant (3.2 mJ/m2), leading to the formation of a compacted cake layer on the membrane surface. In contrast, small molecules of hydrophobic EOM tended to be adsorbed into the membrane pores, leading to significant reduction of the pore size and membrane flux. Therefore, the overall fouling rates caused by EOM and IOM were comparable when both of the above mentioned mechanisms were considered.
[Show abstract][Hide abstract] ABSTRACT: The draw solution is the driving force of the forward osmosis (FO) process; however, the solute loss of the draw solute to the feed side is a general, financial limitation for most applications. The anthropogenic amino acid ethylenediaminetetraacetic acid (EDTA) was investigated as a draw solution for FO. At concentrations of approximately 1.0 osmol/kg, EDTA demonstrated comparable water fluxes (Jv = 5.29 L/m(2) h) to the commonly used salt, NaCl (Jv = 4.86 L/m(2) h), and both produced better water fluxes than glucose (Jv = 3.46 L/m(2) h). EDTA showed the lowest solute loss with Js (reverse solute loss or solute leakage) = 0.54 g/m(2) h. The molecular weight, degree of ionisation and charge of EDTA played a major role in this efficiency and EDTA was therefore well rejected by the membrane, showing a low Js/Jv ratio of 0.10 g/L. Owing to the low solute loss of EDTA and its resistance to biodegradation, this compound has the potential to be used as a draw solute for FO during long periods without requiring much replenishment.
Water Science & Technology 11/2014; 70(10):1677-82. · 1.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Reverse osmosis (RO) systems for secondary effluent water reuse frequently encounter severe biofouling due to the high nutrient concentration in the RO feed water. Deployment of negatively charged tight ceramic ultrafiltration (UF) may restrict biofouling in RO by phosphate limitation, since the tight ceramic UF can reject dissolved phosphate by electrostatic interactions. However, the organic matter and cations can potentially impact phosphate rejection by tight ceramic UF. In this study, the effects of organic matter and Ca2+ on phosphate rejection by the 3 kDa tight ceramic UF membrane were investigated, using synthetic water containing natural organic matter (NOM) and effluent organic matter (EfOM), as well as secondary effluent water. Phosphate rejection was found to be linearly correlated to the zeta potential of the organics in the membrane feed water when the membrane was fouled by NOM. Furthermore, the EfOM-fouled membrane yielded higher phosphate rejection than the membrane fouled by the NOM due to additional adsorption of phosphate by the biopolymers. A preferential phosphate rejection was observed during effluent water filtration by the 3 kDa tight ceramic UF membrane.
Separation and Purification Technology 08/2014; 132:289–294. · 3.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The draw solution is the driving force in forward osmosis (FO) processes. The reverse solute leakage of the draw solution is however a major constraint due to cost and energy requirements when reconcentrating the solutes subsequent to the FO process. Several zwitterions as draw solutions (π≈24 bar and 7 bar) were systematically investigated to enhance the FO performance and minimise the solute loss. The highly soluble zwitterions: glycine, l-proline and glycine betaine demonstrated comparable water fluxes to NaCl (~5 L/m2 h), but with significantly lower solute loss (Js: 2.13±0.54 g/m2 h; 1.37±0.09 g/m2 h, 0.96±0.4 g/m2 h respectively and JsNaCl: 3.26±0.53 g/m2 h), which is advantageous for cost reduction. The physico-chemical properties, charge and size played a dominant role in the flux efficiencies. The Js/Jv ratios decreased with (i) a decrease in hydrophobicity and (ii) an increase in size. The FO mass transfer model verified the experimental investigations of the solute transport through the membrane.
Journal of Membrane Science 06/2014; 460:82–90. · 4.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Amines show great potential for protecting steam-water cycles against corrosion, but their thermal stability is limited and acidic decomposition products are a concern due to increased corrosion risk. In this study, morpholine (hydro)thermolysis is simulated at boiler (352 °C, 17.5 MPa) and superheater (490 °C, 17.5 MPa) conditions with an experimental stainless steel flow reactor. Thermolysis under superheater conditions was more rapid than hydrothermolysis under boiler conditions. Organic acid anion decomposition products increased linearly over time, while the thermal decomposition of morpholine followed first order kinetics. Further experiments under superheater conditions were performed at 470, 490 and 510 °C, with pressures of 9.5, 13.5, and 17.5 MPa. With the kinetic rate constants for morpholine thermolysis in dry steam derived empirically, the activation energy of the decomposition reaction was 160.0 (±2.0) kJ/mol, the pre-exponential factor was e21.7 (±0.66) s–1, and the activation volume was 896 (±36) cm3/mol. This led to a model capable of predicting the observed pressure and temperature dependent thermolysis of morpholine under the investigated conditions. Care must be taken when using the model results to calculate morpholine stability in the SWC, because wall effects during (hydro)thermolysis require further investigation.
[Show abstract][Hide abstract] ABSTRACT: To efficiently adsorb micropollutants from surface water and groundwater by activated carbon, the concurrent natural organic matter (NOM) was removed by anionic exchange resin (AER) to reduce the adsorption competition. The studied AER showed a great affinity to the NOM fractions ‘humic substances’ and ‘building blocks’ measured by liquid chromatography with organic carbon detection. The overlapping adsorption isotherms of target compounds (atrazine and caffeine) in the presence of raw water and AER-treated water reflected an irrelevance of AER-removed NOM to site competition. Instead, it was likely the hydrophobic low molecular organics, refractory to AER treatment, competed with the target compounds. Microporous carbon, which contains higher amounts of small and secondary micropores, tended to have less site competition, and a lower dosage was required to achieve 90% removal of the target compounds. During fixed adsorber filtration, however, AER pretreatment slightly prolonged the breakthrough of most of the investigated micropollutants. This could be attributed to less pore blockage due to the lower contents of ‘humic substances’ and ‘building blocks’ in the background water.
Separation and Purification Technology 05/2014; · 3.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Research in the field of Forward Osmosis (FO) membrane technology has grown significantly over the last 10 years, but its application in the scope of wastewater treatment has been slower. Drinking water is becoming an increasingly marginal resource. Substituting drinking water for alternate water sources, specifically for use in industrial processes, may alleviate the global water stress. FO has the potential to sustainably treat wastewater sources and produce high quality water. FO relies on the osmotic pressure difference across the membrane to extract clean water from the feed, however the FO step is still mostly perceived as a "pre-treatment" process. To prompt FO-wastewater feasibility, the focus lies with new membrane developments, draw solutions to enhance wastewater treatment and energy recovery, and operating conditions. Optimisation of these parameters are essential to mitigate fouling, decrease concentration polarisation and increase FO performance; issues all closely related to one another. This review attempts to define the steps still required for FO to reach full-scale potential in wastewater treatment and water reclamation by discussing current novelties, bottlenecks and future perspectives of FO technology in the wastewater sector.
Water Research 04/2014; 58C:179-197. · 5.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Organic carbon breaks down in boilers by hydrothermolysis, leading to the formation of organic acid anions, which are suspected to cause corrosion of steam–water cycle components. Prediction of the identity and quantity of these anions, based on feedwater organic carbon concentrations, has not been attempted, making it hard to establish a well-founded organic carbon guideline. By using a batch-reactor and flow reactor, the influence of temperature (276–352 °C), retention time (1–25 min), concentration (150–2400 ppb) and an oxygen scavenger (carbohydrazide) on organic acid anion formation from organic carbon was investigated. By comparing this to data gathered at a case-study site, the validity of setups was tested as well. The flow reactor provided results more representative for steam–water cycles than the batch reactor. It was found that lower heating rates give more organic acid anions as degradation products of organic carbon, both in quantity and species variety. The thermal stability of the organic acid anions is key. As boiler temperature increases, acetate becomes the dominant degradation product, due to its thermal stability. Shorter retention times lead to more variety and quantity of organic acid anions, due to a lack of time for the thermally less stable ones to degrade. Reducing conditions (or the absence of oxygen) increase the thermal stability of organic acid anions. As the feedwater organic carbon concentration decreases, there are relatively more organic acid anions formed.
[Show abstract][Hide abstract] ABSTRACT: Disinfection in swimming pools is often performed by chlorination, However, anthropogenic pollutants from swimmers will react with chlorine and form disinfection by-products (DBPs). DBPs are unwanted from a health point of view, because some are irritating, while others might be carcinogenic. The reduction of anthropogenic pollutants will lead to a reduction in DBPs. This paper investigates the continual release of anthropogenic pollutants by means of controlled sweat experiments in a pool tank during laboratory time-series experiments (LTS experiments) and also during on-site experiments (OS experiments) in a swimming pool. The sweat released during the OS and LTS experiments was very similar. The sweat rate found was 0.1-0.2 L/m(2)/h at water temperatures below 29 °C and increased linearly with increasing water temperatures to 0.8 L/m(2)/h at 35 °C. The continual anthropogenic pollutant release (CAPR) not only consisted of sweat, particles (mainly skin fragments and hair) and micro-organisms, but also sebum (skin lipids) has to be considered. The release of most components can be explained by the composition of sweat. The average release during 30 min of exercise is 250 mg/bather non-purgeable organic carbon (NPOC), 77.3 mg/bather total nitrogen (TN), 37.1 mg/bather urea and 10.1 mg/bather ammonium. The release of NPOC cannot be explained by the composition of sweat and is most probably a result of sebum release. The average release of other components was 1.31 × 10(9) # particles/bather (2-50 μm), 5.2 μg/bather intracellular adenosine triphosphate (cATP) and 9.3 × 10(6) intact cell count/bather (iCC). The pool water temperature was the main parameter to restrain the CAPR. This study showed that a significant amount of the total anthropogenic pollutants release is due to unhygienic behaviour of bathers.
Water Research 01/2014; 53C:259-270. · 5.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: TiO2/Ti composites were synthesized by the paint-thermal decomposition method, in which a titanium (Ti) substrate was used due to low impedance between the TiO2 film and Ti plate, providing a strong adhesion. Photoactive TiO2/Ti composites were further modified by an annealing treatment (500-750 °C). The structural evolution during annealing of the films was studied by XRD analysis. Morphology and microstructure characteristics were obtained by SEM and AFM measurements, respectively. The effects of photocatalytic (PC) activity and photoelectrocatalytic (PEC) activity were evaluated on the degradation of phenol in an aqueous solution and by the formation of hydroxyl radicals through a photoluminescence technique using terephthalic acid. It was found that the modified TiO2/Ti composite with an anatase-to-rutile ratio of 82/18 was optimal for both PC and PEC, which resulted in the highest efficiency when using solar light. The PEC degradation was 2.8 times higher than that of PC with the optimal mixture of anatase and rutile. The enhanced photocatalytic activity was derived from the synergistic effect between the modified TiO2/Ti composite electrode and an applied bias. The integration of the paint-thermal decomposition method with PEC technology with an applied bias of 1 V using solar light (UV300-400, 60 W/m2) showed promising degradation efficiencies for phenol (90%).
[Show abstract][Hide abstract] ABSTRACT: Research in the field of Forward Osmosis (FO) membrane technology has grown significantly over the last 10 years, but its application in the scope of wastewater treatment has been slower. Drinking water is becoming an increasingly marginal resource. Substituting drinking water for alternate water sources, specifically for use in industrial processes, may alleviate the global water stress. FO has the potential to sustainably treat wastewater sources and produce high quality water. FO relies on the osmotic pressure difference across the membrane to extract clean water from the feed, however the FO step is still mostly perceived as a “pre-treatment” process. To prompt FO-wastewater feasibility, the focus lies with new membrane developments, draw solutions to enhance wastewater treatment and energy recovery, and operating conditions. Optimisation of these parameters are essential to mitigate fouling, decrease concentration polarisation and increase FO performance; issues all closely related to one another. This review attempts to define the steps still required for FO to reach full-scale potential in wastewater treatment and water reclamation by discussing current novelties, bottlenecks and future perspectives of FO technology in the wastewater sector.
[Show abstract][Hide abstract] ABSTRACT: One of the main advantages of controlled struvite formation in digested sludge is an improvement in dewaterability of the digested sludge, which eventually leads to lower volumes of dewatered sludge that need to be transported. The effects of the control parameters for struvite formation, magnesium concentration and pH, on digested sludge dewaterability were investigated and are discussed in relation to the efficiency of struvite formation. Laboratory experiments with digested activated sludge were performed in a 20 L batch reactor. CO2 was stripped from the digested sludge using a bubble aerator and magnesium chloride was added to induce struvite formation. The dewaterability of the sludge was determined by gravity filtration tests. In the experiments, either the pH or the molar magnesium to phosphate ratio (Mg:PO4) was varied. The results confirm improved sludge dewaterability after struvite formation. Magnesium to phosphate ratios above 1.0 mol/mol did not further improve dewaterability. The addition of magnesium did not prevent the need for polymer addition for sludge dewatering. An increase in pH led to a deterioration in dewaterability. The best dewaterability results were found at the lowest pH value (pH = 7.0), while stirring the sludge instead of using the bubble aerator. At these settings, an orthophosphate removal of around 80% was achieved.
[Show abstract][Hide abstract] ABSTRACT: Literature shows that water demand forecasting models which use water demand as single input, are capable of generating a fairly accurate forecast. However, at changing weather conditions the forecasting errors are quite large. In this paper three different forecasting models are studied: an Adaptive Heuristic model, a Transfer/-noise model, and a Multiple Linear Regression model. The performance of the models was studied both with and without using weather input, in order to assess the possible performance improvement due to using weather input. Simulations with the models showed that when using weather input the largest forecasting errors can be reduced by 11%, and the average errors by 7%. This reduction is important for the application of the forecasting model for the control of water supply systems and for anomaly detection.
[Show abstract][Hide abstract] ABSTRACT: This study mainly focused on the adsorption of 2-methylisoborneol (2-MIB) and geosmin (GSM) form water onto a new type of adsorbent (attapulgite) (ATP) and thermally modified attapulgite (T-ATP). The adsorption isotherm and the adsorption kinetics of GSM onto T-ATP were studied in batch experiments. Meanwhile, the effect of temperature and pH on the removal efficiency and the absorbed amount of GSM and 2-MIB was also investigated. Experimental results show that the optimal concentrations of adsorption of GSM and 2-MIB onto ATP and T-ATP were both 1 g/L. The adsorption of GSM onto T-ATP better followed pseudo-second-order model. Freundlich isotherm fit the experimental data (the adsorption of GSM onto T-ATP) better than Langmuir isotherm. Besides, the best operational condition of adsorption of GSM and 2-MIB onto ATP and T-ATP was at lower temperature (5°C) and under neutral pH (6.5 ∼ 7.5). Although the adsorption of GSM onto T-ATP was nonspontaneous, it was an exothermic reaction, in terms of the thermodynamic parameters (positive of ΔG° and negative of ΔH° and ΔS°). The weak adsorption reaction could take place by simply raising shaking speeds.
Desalination and water treatment 01/2014; 52. · 0.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This paper reports on the direct ability of two positively charged organic polyelectrolytes (natural-based and synthetic) to reduce the atrazine concentration in water. The adsorption study was set up using multiple glass vessels with different polymer dosing levels followed by ultrafiltration with a 1 kDa membrane. The addition of polymers exhibited a capability in reducing the atrazine concentration up to a maximum of 60% in surface-to-volume ratio experiments. In the beginning, the theoretical L-type of the isotherm of Giles' classification was expected with an increase in the dosage of the polymer. However, in this study, the conventional type of isotherm was not observed. It was found that the adsorption of the cationic polymer on the negatively charged glass surface was necessary and influential for the removal of atrazine. Surface-to-volume ratio adsorption experiments were performed to elucidate the mechanisms and the polymer configuration. The glass surface area was determined to be a limiting parameter in the adsorption mechanism.
[Show abstract][Hide abstract] ABSTRACT: Phosphate limitation has been reported as an effective approach to inhibit biofouling in reverse osmosis (RO) systems for water purification. The rejection of dissolved phosphate by negatively charged TiO2 tight ultrafiltration (UF) membranes (1 kDa and 3 kDa) was observed. These membranes can potentially be adopted as an effective process for RO pre-treatment in order to constrain biofouling by phosphate limitation. This paper focuses on electrostatic interactions during tight UF filtration. Despite the larger pore size, the 3 kDa ceramic membrane exhibited greater phosphate rejection than the 1 kDa membrane, because the 3 kDa membrane has a greater negative surface charge and thus greater electrostatic repulsion against phosphate. The increase of pH from 6 to 8.5 led to a substantial increase in phosphate rejection by both membranes due to increased electrostatic repulsion. At pH 8.5, the maximum phosphate rejections achieved by the 1 kDa and 3 kDa membrane were 75% and 86%, respectively. A Debye ratio (ratio of the Debye length to the pore radius) is introduced in order to evaluate double layer overlapping in tight UF membranes. Threshold Debye ratios were determined as 2 and 1 for the 1 kDa and 3 kDa membranes, respectively. A Debye ratio below the threshold Debye ratio leads to dramatically decreased phosphate rejection by tight UF membranes. The phosphate rejection by the tight UF, in combination with chemical phosphate removal by coagulation, might accomplish phosphate-limited conditions for biological growth and thus prevent biofouling in the RO systems.
Water Research 01/2014; 48(1):498-507. · 5.32 Impact Factor