Application of filtration in seawater and stormwater treatment

University of Technology, Sydney. Faculty of Engineering and Information Technology.Water scarcity is becoming a significant problem throughout the world and the creation of new sources of potable water has been a significant issue worldwide and as a consequence harvesting of stormwater and desalination have become two of the most vital and valuable alternative resources in many countries around the world. Membrane based separation systems (such as reverse osmosis) have been widely used to produce potable water. In membrane separation system membrane fouling is major problem which results in deterioration in membrane performance, lessens membrane life time and increases total cost to treatment plants. As a result, suitable pre-treatment is required which can significantly minimize fouling problems to membrane filtration technique. The main aim of this study was to assess relative performance of filtration systems as pretreatment to seawater and stormwater. The pre-treatment systems that were used in this study were deep bed filter (single medium and dual media), fibre filter and hybrid filter (fibre filter followed by media filter). They were assessed in terms of turbidity and organic matter removal, and head loss build-up. The efficiency of the filter as pre-treatment was evaluated in terms of Silt Density Index (SDI) and Modified Fouling Index (MFI). In this study, two different water sources were used (namely seawater and stormwater). Seawater was chosen mainly for its organic matter together with dissolved solids and stormwater was chosen for highly colloidal substances. Four representative pre-treatments were examined to find out their effectiveness as pre-treatment to different water sources (seawater and wastewater). Another attractive and environmentally friendly pre-treatment of biofilter was not studied in this research as there was concurrent research performed in our laboratory (Chinu et al. 2008) From the filter experimental results on seawater, it was found that the turbidity removal was high and all the deep bed filters produced more or less the same quality water. There was a slower buildup of head loss for coarser filter medium. The result showed that finer filter media (sand) and dual media filter with filtration velocity of 5 m/h exhibits 70% of turbidity removal efficiency. The high rate fibre filter used with in-line flocculation removed the 7080% of turbidity. The turbidity was decreased to 0.16 - 0.49 NTU by fiber filter. The pressure drop (AP) on fibre filter with and without in-line flocculation was 33 and 4 mbar respectively. The use of in-line flocculation improved the performance of these filters as measured by the MFI and SDI. After pre-treatment with contact flocculation-filtration and fibre filter the MFI and SDfo value reduced from 138-256 s/L2 to 0.77-2.95 s/L2 and from 7.40-8.75 to 2.4-4.8 respectively. On the other hand, the headloss development on dual media filter in hybrid filter system with in-line flocculation of influent seawater to the fibre filter was 11.0 cm. In addition, when different pre-treatment hybrid systems were operated at different filtration velocities (5 and 10 m/h), the MFI and SDfio was reduced to 1.4-3.6 s/L2 and 2.6-3 respectively. A post treatment of reverse osmosis (RO) after an inline- flocculation-dual media filtration showed lower normalized flux decline (J/Jo) (0.35 to 0.22 during the first 20 hours operation) while, seawater without any pre-treatment showed steeper flux decline (0.18 to 0.11 within 20 hours operation) of RO. The application of deep bed filters, fibre filter and hybrid filter as pre-treatment to stormwater was also experimentally investigated in detail. It was found that the removal efficiency for turbidity, suspended solids and TOC was found to be 95-98%, 99 % and 4060 % respectively at a flocculant dose of FeCf of 15 mg/L. The phosphorous removal efficiency was relatively good (up to70%). The removal efficiency for heavy metals such as Cd, Pb, Cr and Ni was found to be very low for all tested filtration systems because concentrations of these metals in the influent were also low. These filters can be used as a pre-treatment to micro/ultra filter. This is demonstrated through MFI measurements. The MFI was reduced from 750-950 s/L2 (for stormwater) to 15-9 s/L2 (for filtered effluent). Detailed submerged membrane filter experiments conducted with pre-treated water (after dual media filtration) showed that the membrane filter can successfully be used as posttreatment to in-line flocculation-filter at a sustainable flux of 10 L/m\h to remove the remaining solids and pathogens. An increase of air scouring in the membrane unit decreased the pressure development although it did not have any effect on increasing the critical flux beyond 10 L/irf.h

Membrane bio-reactor (MBR) : effect of operating parameters and nutrients removal

University of Technology Sydney. Faculty of Engineering and Information Technology.Membrane bio-reactor is an efficient, cost effective and reliable treatment process to produce high quality water from wastewater. In this study, a number of submerged membrane bio-reactors (SMBRs) experiments were conducted at different organic loading rates (OLRs) and fluxes (ranging from 2.5 - 40 L/m².h and corresponding hydraulic retention time of 10 - 1.5 h) to investigate their influence on organic and nutrient removal and on membrane fouling. A second set of experiment was also carried out with gradual increase of salt concentration in continuous MBR to assess its performances in this particular scenario (which may occur in coastal areas and in certain industries). The operation of MBRs at low HRT resulted in sudden rise of trans membrane pressure (TMP). The sudden development of TMP was minimized by introducing granular activated carbon (GAC) in MBR as suspended medium. The incorporation of GAC reduced TMP or total membrane resistance by 58% and also helped to remove an additional amount of dissolved organic matter. Further, a set of ion exchange adsorption study was conducted for the removal and recovery of the nutrients from the effluent of high rate MBR. The major findings are summarizes below. The increase of OLR, flux and salt concentration resulted in lower removal of organic and nutrients and also caused higher membrane fouling (i.e. increased transmembrane pressure (TMP) development). The removal efficiency of DOC decreased from 93 – 98 % to 45 - 60 % when the OLR increased from between 0.5 – 1.0 to 2.75 – 3.0 kg COD/m³d. Similarly the removal of ammonia decreased from 83–88% to less than 67% when the OLR was increased to 2.0 – 3.0 kg COD/m3d. The increase of flux (i.e. reducing of HRT) also resulted in 30 - 40 % lower removal of organics and nutrients. The removal of organic and nutrient decreased when the salt concentration was increased from 0 to 35 g/L. Based on the operating conditions of this study, the suspended media had less effect on nitrification but had an influence on organic removal. However, changing the operating parameters (such as increase of SRT) may improve nitrification rate. The increase of OLR and salt concentration resulted in higher membrane fouling. Similarly flux and aeration rate also played a major role in membrane fouling reduction. However, the effect of flux on the reduction of membrane fouling was much higher than that caused by aeration rate. A lower flux of 20 L/m² h produced 75 times more water than a higher flux of 40 L/m²h with an aeration rate of 0.6 m³/m² membrane area.h. The reduction of aeration rate from 1.5 to 1.0 m³/m² membrane area.h caused a sudden rise of TMP. The sudden rise of TMP can be minimized by incorporating the medium in suspension in the reactor (to induce surface scouring of the membrane). The incorporation of suspended medium prevented a sudden rise of TMP (total membrane resistance reduced by ~ 58%) by creating an extra shearing effect onto the membrane surface produced by suspended media. It reduced the deposition of particles on the membrane surface by scouring. The addition of GAC also adsorbed some organic matter prior to its entry to the membrane. Nevertheless it is also important to apply a sufficient aeration rate (in our case 1 m³/m² membrane area h) to maintain a good functioning of suspended media in MBR. The aeration helped in scouring and provision of oxygen to microorganisms and maintained the media in suspension. Additionally, the amount and sizes of the suspended medium played major role in fouling reduction. In this study, we found the concentration of suspended media of 2 g/L and GAC size of 300-600 μm was effective in reducing membrane fouling. Therefore a suitable amount and size of suspended medium needed depends on the flux and aeration (or air scour) rate used. The characteristics of organic matter of SMBRs effluent showed that a range of organic matter (such as amino acids, biopolymers, humics and fulvic acids type substances) was removed by the GAC both by scouring and adsorption mechanisms. A detailed organic matter characterization of membrane foulant, soluble microbial product and extracellular polymeric substances showed that bio-polymer together with humic acid and lower molecular neutral and acids were responsible for membrane fouling along with the deposition of floc particle onto the membrane surface. MBR usually removes both organic matter and nitrogen from water. However, the removal of nitrogen and phosphorus using a high rate MBR system is not sufficient. It is equally practical to remove nitrogen and phosphorus by physico-chemical processes as post-treatment such as ion exchange/ adsorption. In this study, different ion exchange materials such as purolite (A520E and A500P), hydrated ferric oxide (HFO) and zirconium (IV) hydroxides were used to remove nitrogen and phosphorus from MBR effluent. They all showed ~ 90% removal of nutrients. The nutrients captured on the ion exchanger were later recovered when the ion-exchange was regenerated

Deep bed filter as pre-treatment to stormwater

This paper presents the results of experiments on the application of dual media and single media deep bed filters as pre-treatments to stormwater. In-line flocculation-filtration experiments were conducted with dual and single media filter. The single filter media (80 cm) consisted of either anthracite or sand, and the dual media filter consisted of sand (40 cm at the bottom) and anthracite (40 cm on top). Filtration velocities of 5 m/h, 10 m/h and 15 m/h were examined. The removal efficiency for turbidity, suspended solids and TOC was found to be 95%, 99% and 30-45% respectively at a flocculant dose of FeCl3 of 15 mg/L. The anthracite filter media showed a lower head loss development (26 cm, operated at 5 m/h filtration velocity with FeCl3 dose of 5 mg/L). The removal efficiency for nitrogen was lower than phosphorus which was relatively good (up to 50%). The removal efficiency for heavy metals such as Cd, Pb, Cr and Ni was found to be very low for all tested filtration systems because concentrations of these metals in the influent were also low. This filter can be used as a pretreatment to a membrane filter as the modified fouling index was reduced from 750 s/L2 (for stormwater) to 15 s/L2 (for filtered effluent). Detailed submerged membrane filter experiments conducted with pre-treated water showed that the membrane filter can be successfully be used as post-treatment to in-line flocculant-filter at a sustainable flux of 10 L/m2.h to remove the remaining solids and pathogens. An increase of air scouring in the membrane unit decreased the pressure development although it did not have any effect on increasing the critical flux beyond 10 L/m2.h. © 2009 Desalination Publications

Removing rubidium using potassium cobalt hexacyanoferrate in the membrane adsorption hybrid system

© 2017 Elsevier B.V. Highly-priced rubidium (Rb) can be effectively extracted from seawater using potassium cobalt hexacyanoferrate (KCoFC) and ammonium molybdophosphate (AMP) adsorbents in the membrane adsorption hybrid system (MAHS). KCoFC (<0.075 mm), KCoFC (0.075–0.15 mm), and AMP (<0.075 mm) had Langmuir adsorption capacities of 145, 113, and 77 mg/g at pH 6.5–7.5, respectively. When KCoFC (<0.075 mm) at a dose of 0.2 g/L was initially added to 4 L of a solution containing 5 mg Rb/L in the MAHS and 25% of the initial dose was repeatedly added every hour, the amount of Rb removed remained steady at 90–96% for the experiment's 26 h duration. The removal of Rb by AMP under similar conditions was 80–82%. The cumulative Rb removed by KCoFC (<0.075 mm) in MAHS was only 33% reduced in the presence of high concentrations of other cations in synthetic seawater compared to that in solution containing only Rb. Approximately 30% of the adsorbed Rb was desorbed using 1 M KCl. When the desorbed solution was passed through a column containing resorcinol formaldehyde (RF), 35% of the Rb in the desorbed solution was adsorbed on RF. Furthermore 50% of the Rb adsorbed on RF was recovered by 1 M HCl leaching of the column. This sequence of concentration and separation of Rb in the presence of other cations in synthetic seawater is an efficient method for recovering pure Rb from real seawater and seawater reverse osmosis brine

A novel dual-layer bicomponent electrospun nanofibrous membrane for desalination by direct contact membrane distillation

In this study, a bicomponent nanofibrous composite membrane was fabricated by electrospinning and was tested for desalination by direct contact membrane distillation (DCMD). The nanofibrous membrane was composed of a dual-layered structure of poly(vinylidene fluoride-co-hexafluoropropylene) (PH) nanofibers and polyacrylonitrile (PAN) microfibers. Morphological characterization showed slightly beaded cylindrical PH nanofibers with porosity of about 90%. The contact angles of PH and PAN nano/microfibers were 150° and 100°, respectively. The nanofibrous membranes were tested by DCMD and a high water flux of 45 and 30Lm-2h-1 was obtained for distilled water and 35gL-1 NaCl solutions as feed, respectively using DL2 membrane (i.e., 25/75 PH/PAN thickness ratio). The present dual-layer membrane showed better flux performance compared to a commercial flat-sheet membrane. The results suggest the potential of the dual-layer nanofibrous membrane for DCMD applications. © 2014 Elsevier B.V

Sorptive removal of phenolic endocrine disruptors by functionalized biochar: Competitive interaction mechanism, removal efficacy and application in wastewater

© 2017 Elsevier B.V. Sorptive removal of six phenolic endocrine disrupting chemicals (EDCs) estrone (E1), 17β-estradiol (E2), estriol (E3), 17α-ethynylestradiol (EE2), bisphenol A (BPA) and 4-tert-butylphenol (4tBP) by functionalized biochar (fBC) through competitive interactions was investigated. EDC sorption was pH dependent with the maximum sorption at pH 3.0–3.5 due to hydrogen bonds and π-π interactions as the principal sorptive mechanism. Sorption isotherm of the EDCs was fitted to the Langmuir model. Sorption capacities and distribution coefficient values followed the order E1 > E2 ≥ EE2 > BPA > 4tBP > E3. The findings suggested that EDC sorption occurred mainly through pseudo-second order and external mass transfer diffusion processes, by forming H-bonds along with π-π electron-donor–acceptor (EDA) interactions at different pH. The complete removal of ∼500 μg L−1 of each EDC from different water decreased in the order: deionised water > membrane bioreactor (MBR) sewage effluent > synthetic wastewater. The presence of sodium lauryl sulphonate and acacia gum in synthetic wastewater significantly suppressed sorption affinity of EDCs by 38–50%, hence requiring more fBC to maintain removal efficacy

Submerged membrane filtration adsorption hybrid system for the removal of organic micropollutants from a water reclamation plant reverse osmosis concentrate

© 2016 Elsevier B.V. Reverse osmosis (RO) is a widespread water treatment process utilised in water reuse applications. However, the improper discharge of RO concentrate (ROC) containing organic micropollutants such as pharmaceuticals into the environment may cause potential health risks to non-target species and particularly those in aquatic environments. A study was conducted using a submerged membrane-filtration/granular activated carbon (GAC) adsorption hybrid system to remove organic micropollutants from a water treatment plant ROC by initially adding 10 g GAC /L of membrane reactor volume with 10% daily GAC replacement. The percentage of dissolved organic carbon removal varied from 60% to 80% over an operation lasting 10 days. Removal of organic micropollutants was almost complete for virtually all compounds. Of the 19 micropollutants tested, only two remained (the less hydrophobic DEET 27 ng/L and the hydrophilic sulfamethoxazole 35 ng/L) below 80% removal on day 1, while five of the most hydrophobic micropollutants were detectable in very small concentrations ( 89%–> 99% being removed. High percentages of micropollutants were removed probably because of their high hydrophobicity or they had positive or neutral charges and therefore they were electrostatically adsorbed to the negatively charged GAC

Phosphate removal from water using an iron oxide impregnated strong base anion exchange resin

Removing phosphate from water is important as it causes eutrophication, which in turn has a harmful effect on aquatic life, resulting in a reduction in biodiversity. On the other hand, recovery of phosphate from phosphorus containing wastewater is essential for developing an alternative source of phosphorus to overcome the global challenge of phosphorus scarcity. Phosphate removal from aqueous solutions was studied using an iron oxide impregnated strong base anion exchange resin, Purolite FerrIX A33E in batch and fixed-bed column experiments. Phosphate adsorption in the batch study satisfactorily fitted to the Langmuir isotherm with a maximum adsorption capacity of 48mgP/g. In the column study, increase in inlet phosphate concentration (5-30 mgP/L), and filtration velocity (2.5-10 m/h) resulted in faster breakthrough times and increase in breakthrough adsorption capacities. Increase in bed height (3-19 cm) also increased adsorption capacity but the breakthrough time was slower. The breakthrough data were reasonably well described using the empirical models of Bohart-Adams, Thomas, and Yoon-Nelson, except for high bed heights. Phosphate adsorbed was effectively desorbed using 1M NaOH and the adsorbent was regenerated after each of three adsorption/desorption cycles by maintaining the adsorption capacity at >90% of the original value. Greater than 99.5% of the desorbed P was recovered by precipitation using CaCl2. © 2013 The Korean Society of Industrial and Engineering Chemistry