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This investigation determined a feasible route to prepare hyperbranched polyesters involving citric acid (CA) and glycerol (GLC) monomers (CA-co-GLC) using a thermal polycondensation method. The synthesized copolymer was characterized using Fourier transform infrared spectroscopy (FT-IR), carbon-13 nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. The ability of CA-co-GLC to inhibit deposition of inorganic scales such as calcium carbonate was investigated under varying temperature and pH medium. The evaluation of inhibition efficiency (IE) was conducted using the static scale inhibition method. The mechanism of the inhibitor&rsquo, s action was investigated via growth solution analysis, measurement conductivity, and analysis of CaCO3 using FT-IR and scanning electron microscopy. The results obtained showed that the CA-co-GLC had good IE at an elevated temperature reaching 75% at 100 &deg, C, pH 7.5, and 10 ppm copolymer dose. Using the same dose, the IE reached 66% at 50 &deg, C and pH 10. The CA-co-GLC did not chelate Ca2+ in water, but led to a change in polymorphism, making it brittle and able to slip easily from the surface. Its action principally prevented the adhesion of calcium carbonate onto the surface.

International audience; In this study, hexafluoroalcohol-containing polyamide layer (HFAPA) was prepared on top of a conventional polyamide under-layer (REFPA) via sequential interfacial polymerization (SIP) to improve RO separation behavior, and the performance of the resulting bilayer membrane was thoroughly optimized by investigating the effect of cross-contamination in the SIP process. When several coupons of the polyamide bilayer membrane were prepared by SIP of MPD(aq), TMC(hx) and hexafluoroalcohol-containing diamine (HFAMDA)(aq) in the manner of subsequent membrane dipping, unreacted MPD monomer (mostly captured in the porous PSF support) carried over from the 1st interfacial reaction dissolved and accumulated in the 2nd aqueous solution as verified by UV spectroscopic analysis. The MPD contaminant then participated in the 2nd interfacial reaction, forming copolyamide with HFAMDA monomer onto the REFPA. Depending on the amount of MPD contaminant accumulated in the 2nd aqueous solution, the composition of the resulting co-polyamide in the top-layer varied, causing a significant variation of RO performance; the flux was gradually decreased with the increase of MPD contaminants while the salt rejection slightly increased (from 1st coupon toward 4th coupon). This result indicated that a trace amount of MPD contaminant may be necessary to maximize RO separation behavior. Through in-depth performance evaluation of polyamide bilayer membranes prepared by adding various known-amount of MPD into 2nd HFAMDA solution, and also by applying a frame process (2nd amine solution was applied only top surface of membrane) to eliminate uncontrollable MPD contamination, we have successfully demonstrated consistent RO performance, and identified an optimum material composition to provide superior separation performance. The bilayer membrane prepared by adding 1.2 mol% of MPD to the total amount of HFAMDA in the 2nd aqueous solution showed 99.8% NaCl rejection with the water flux of 45 LMH under the cross-flow filtration performed with 2000 ppm NaCl solution at 400 psi, 25 °C.

A novel thin film composite (TFC) membrane featuring a polyamide bilayer was prepared on a porous polysulfone support using sequential interfacial polymerization. A conventional polyamide membrane prepared using m-phenylenediamine (MPD) in water and trimesoyl chloride (TMC) in hexane via interfacial polymerization was subsequently immersed into an alkaline aqueous solution of a hexafluoroalcohol (HFA)-containing aromatic diamine (HFA-MDA) to form an HFA-substituted aromatic polyamide layer (HFAPA) on the surface of the conventional (or reference) polyamide layer (REFPA). Water contact angle (θw) measurements indicated that the surface of the membrane becomes much more hydrophobic (θw≅140°) after forming the additional HFAPA layer onto REFPA (θw≅78°) although cross-sectional TEM images showed no significant increment in film thickness. The HFAPA-on-REFPA bilayer membrane, which features a more hydrophobic surface than the conventional REFPA membrane, exhibited improved salt rejection (ca. 50% reduction in salt passage) with a small loss in water flux (ca. 8% reduction) compared to the REFPA membrane, resulting in an excellent combination of salt rejection and water flux. Moreover, higher boron rejection was also achieved using the bilayer membrane (HFAPA-on-REFPA) compared to the REFPA membrane.

A POSS derivative containing UV-curable methacrylate groups (methacryl-POSS) was used as a multi-functional cross-linker to form thin and durable hydrogel films with a hydrophilic comonomer, poly(ethylene glycol) methacrylate (PEGM), in the presence of photoinitiator. The water uptake of the crosslinked POSS–PEGM films was easily controlled from 8% to 90% by manipulating the weight ratio of methacryl-POSS and PEGM from 1:1 to 1:20. Further improvement in the water uptake was demonstrated by adding a sacrificial additive into the prepolymerization mixture of methacryl-POSS and PEGM. The addition of water soluble, non-crosslinkable polyethylene glycol (PEG) into a prepolymerization mixture and subsequent extraction of the PEG additive after UV-curing creates molecular-scale pores within the crosslinked film, resulting in significant increase in water uptake as well as water permeability of the film. The free standing film prepared from the prepolymerization mixture containing 1:20 weight ratio of methacryl-POSS and PEGM with 50 wt% PEG additive showed the highest water uptake (280%) and water permeability (130 L μm m−2 h−1 atm−1) among tested samples. PSF UF membranes coated with the highly water permeable, nanoporous POSS–PEGM materials showed excellent anti-fouling efficiency when tested in a cross-flow filtration system using an oil–water emulsion or a bovine serum albumin (BSA) solution as the feed. Molecular dye filtration studies conducted with a relatively dense POSS–PEGM material (MWCO

The present study explores for the first time, the effectiveness of photocatalytic oxidation of humic acid (HA) in the increasingly important highly saline water. TiO 2 (Degussa P25), TiO 2 (Anatase), TiO 2 (Rutile), TiO 2 (Mesoporous) and ZnO dispersions were used as catalysts employing a medium pressure mercury lamp. The effect of platinum loading on P25 and zinc oxide was also investigated. The zinc oxide with 0.3% platinum loading was the most efficient catalyst. The preferred medium for the degradation of HA using ZnO is alkaline, whereas for TiO 2 it is acidic. In addition, a comparative study of HA decomposition in artificial seawater (ASW) and natural seawater (NSW) is reported, and the surface areas and band gaps of the catalysts employed were also determined. A spectrophotometric method was used to estimate the extent of degradation of HA.

In the seawater desalination inorganic constituents (40,000–50,000 ppm) pose serious problems to multistage flash (MSF) process and more acutely to seawater reverse osmosis (SWRO) process which is also greatly influenced by organic content of (2–4 ppm). It is well-known that fouling on the RO membrane causes serious problems including (i) gradual decline of membrane flux thereby decreasing permeate production, (ii) an increase in ΔP thereby increasing the requirement of high pressure pump rating and (iii) degradation of membrane itself. The dissolved organic matter is not a single substance but a mixture of ill-defined aliphatic and aromatic compounds. Humic substance constitute major portion of total organics in seawater, thus to identify the nature, and compositional characteristic of such substance along with its estimation is of utmost importance to overcome the problems associated with fouling of RO membranes. Humic substances from Al-Jubail, Al-Khobar (Gulf Coast) and Jeddah (Red Sea Coast) were isolated and analyzed by different techniques, viz elemental analysis, UV-visible spectrometry, IR Spectrometry and fluorescence spectrometry. Method of isolation and purification of humic substance has been standardized to recover gram quantities. Two methods of quantitative estimation have also been developed. The first method involves estimation of humic substance from seawater by UV-visible spectrometer after isolation. In the second method, humic substance was determined using fluorescence technique by spectro-photofluorometer either after isolation and pre-concentration or directly in the seawater without isolation. The precision of methods in terms of percentage relative standard deviation for UV-visible method is 3.8% while for fluorescence method is 1.75%. Elemental composition, nature, IR spectra and concentration of humic substances of Al-Jubail and Al-Khobar are similar. However, humic substances from Jeddah differed in many respects including the composition. The remarkable deviation in elemental composition indicates that perhaps nature and origin of humic substances from Gulf and Red Sea coasts are different. High nitrogen, sulphur and hydrogen to carbon ratio indicate high bacterial activity in the Red Sea region.

A potential problem associated with the usage of chlorine as a biocide for drinking water is the formation of disinfection by-products (DBPs). Trihalomethanes (THMs), haloacetic acids (HAAs) and keto acids, for example, are some of the halogenated by-products which are health concerns due to their carcinogenic and mutagenic effects. Health organizations and other environmental agencies, e.g., WHO, USEPA, SASO, have regulated the maximum level for THMs and HAAs at 80μg/L and 60μg/L, respectively. This paper deals with the evaluation of formation potential for five haloacetic acids, viz., monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid and dibromoacetic acid in desalinated drinking water. The effect of chlorine concentrations, total organic carbon and bromide concentration on the formation potential of HAAs in seawater (feed to desalination plants), product water (from MSF), well water used for blending and blended water were studied. The concentration of haloacetic acids determined in drinking water and other streams was found to be very much below the maximum permissible level of 60μg/L. The study shows that the use of chlorine as a disinfectant for the products from desalination plants does not present any problems with respect to the formation of haloacetic acids and can be considered as a safe biocide for application in desalination processes.

To combat the scaling problems in multistage flash (MSF) desalination plants, either mineral acids or scale control additives (SCAs) are used. Scaling phenomena from acid is controlled by adjusting pH and total alkalinity and requires stoichiometric amounts while SCAs act non-stoichiometrically by threshold effect or crystal distortion effect. Antiscalant dose rates in brine are found to vary from plant to plant. Efficiency of SCA could be influenced by its chemical nature, plant configuration and design, heat transfer rates and its surface and antiscalant reaction with brine constituents. The study was carried out to understand the varied dose rate and the role of some of the brine chemical constituents on the efficiencies of antiscalants. Experiments conducted with a bench-top system by simulating the MSF conditions at 95°C with brine and performance of SCA were evaluated using the threshold effect technique. Performance or efficiency of two SCAs, viz., polyphosphonate based (PPN) and polymaleic acid based (PMA) were evaluated in the presence of traces of copper, chromium, nickel, molybdenum and iron, which are present in the brine as corrosion products. Effects of humic substances, particulates, and chlorine which is used as biocide, are also evaluated. Results of bench-top studies revealed that Cu, Fe, and Cr do have a detrimental effect on the performance of two SCAs (PPN and PMA), while Mo and Ni do not have an adverse effect. Humic substances and particulates also do not have significant effect. However, chlorination of SCA does reduce the performance of SCA.

Salt carry-over due to excessive foaming in a multistage flash (MSF) distiller and detrimental foaming in the deaerator section have been reported in the Saline Water Conversion Corporation (SWCC) of Saudi Arabia and other desalination plants. The application of a suitable antifoaming agent has prevented distillate contamination and improved release of dissolved oxygen in the deaerator section, thus improving the operating efficiency of MSF plants. The developer of a polyoxypropylene glycol-based antifoaming agent collaborated with SWCC in carrying out trial runs to show that their product was as effective and economical as the one currently being used (a polyglycol blend in a hydrocarbon solvent) in SWCC plants. Trial tests were carried out at laboratory, pilot and commercial plant levels. Miscibility of this agent in water was determined initially in the laboratory, followed by field trial runs in an MSF pilot plant and the commercial plants of Al-Jubail I and II. Foam control, non-interference with antiscalant performance, distillate purity and stability at a low dose rate over a wide range of temperatures were some of the important criteria evaluated during testing of this antifoaming agent. During MSF plant runs, distillate conductivity and dissolved oxygen level in the feed were regularly monitored and found within the acceptable limits. Compatibility of this agent with antiscalant was also assessed. Heat transfer and plant performance data were found satisfactory confirming that this agent did not exhibit any adverse effect on the antiscalant used in Al-Jubail plants. Results of laboratory and field trial runs of this antifoaming agent are discussed.

Scale control additives (SCA) or antiscalants are used in multistage flash desalination plant to prevent fouling problems. Effective dose rates of some of these SCA are found to vary from plant to plant. Efficiency of antiscalants could be influenced by its chemical nature, plant configuration and design, heat transfer rate and its surface and antiscalant reaction with brine constituents. To understand the variation in concentration of SCA and effect of brine constituents on efficiency of SCA, some bench top experiments at 95°C with brine were conducted using the threshold effect technique. Two SCA, a polyphosphonate based (PPN) and polymaleic acid based (PMA) were used for these evaluations. The effect of Fe3+, Fe2+, Fe2O2. Fe(OH)3, and rust on efficiency of SCA was determined. The threshold effect method, which measures the total alkalinity and calcium content of supernant to evaluate efficiency of SCA, was found to be an effective technique. Recycled brine constituents and corrosion products, especially Fe and its various chemical forms affect the efficiency of SCA at 2 ppm concentration and at 95°C in 1.4 times concentrated seawater brine. Various chemical hydrated and hydroxylated forms of Fe present in brine, viz., Fe3+(H2O)6, Fe(OH)3, Fe2+, Fe2O3, rust, etc., all showed detrimental effect on efficiency of SCA. Among all the species of iron, Fe(OH)3, reduced the efficiency of SCA by maximum of 40%. Among the two antiscalants, PPN showed 10–12% better efficiency in the presence of various iron species compared to PMA under similar bench top experimental conditions. The effect of brine constituents on PMA was more pronounced compared to PPN perhaps due to better complexing ability of the former.

We report the first systematic study on the photocatalytic oxidation of humic acid (HA) in artificial seawater (ASW). TiO(2) (Degussa P25) dispersions were used as the catalyst with irradiation from a medium-pressure mercury lamp. The optimum quantity of catalyst was found to be between 2 and 2.5 gl(-1); while the decomposition was fastest at low pH values (pH 4.5 in the range examined), and the optimum air-flow, using an immersion well reactor with a capacity of 400 ml, was 850 ml min(-1). Reactivity increased with air-flow up to this figure, above which foaming prevented operation of the reactor. Using pure oxygen, an optimal flow rate was observed at 300 ml min(-1), above which reactivity remains essentially constant. Following treatment for 1 h, low-salinity water (2700 mg l(-1)) was completely mineralised, whereas ASW (46000 mg l(-1)) had traces of HA remaining. These effects are interpreted and kinetic data presented. To avoid problems of precipitation due to change of ionic strength humic substances were prepared directly in ASW, and the effects of ASW on catalyst suspension and precipitation have been taken into account. The Langmuir-Hinshelwood kinetic model has been shown to be followed only approximately for the catalytic oxidation of HA in ASW. The activation energy for the reaction derived from an Arrhenius treatment was 17 (+/-0.6) kJ mol(-1).