Addition Of Ferric Chloride Research Articles

Performance Investigation of Pilot Study for Wastewater Reclamation Using Ferric Chloride as Coagulant

A pilot study was conducted to evaluate the efficiency of ferric chloride as coagulant agent on the long term performance to reverse osmosis membrane technology. The pilot unit comprised of 50m3/day pore controllable fiber (PCF) technology as a pre-treatment prior to RO for water reclamation from an effluent treatment plant based in Malaysia. The additions of ferric chloride ahead of PCF unit give high rejection of permeate quality after RO such as TSS, COD, alkalinity, and nitrite. However, there is deterioration of RO membrane performance after the pilot unit has been run continuously for 24 hours over 3 months. Average percentage reduction for parameters such as BOD5, COD, TDS, conductivity, and TSS for PCF-RO over 3 months operation is 51.12%, 70.01%, 68.36%, 68.39% and 69.17% respectively. Fouled RO membranes for both lines were analyzed using Fourier transform infrared (FTIR) spectroscopy and EDS coupled with scanning electron microscopy (SEM). EDS-SEM results showed that the foulants deposit on RO membrane for PCF-RO about 4.29-6.23µm and Fe element at 14.81% by the mean of weight. These imply that ferric chloride residual contribute to RO membrane fouling and thus affect the system stability and efficiency.

Optimization of phosphorus removal in secondary effluent using immersed ultrafiltration membranes with in-line coagulant pretreatment — implications for advanced water treatment and reuse applications

In-line addition of alum and ferric chloride was conducted at a hollow-fibre immersed ultrafiltration (UF) membrane pilot plant, using secondary effluent from a municipal wastewater treatment plant (WWTP) as the feed. The objective of such pretreatment was to remove phosphorus from the feed from an initial concentration of approximately 5 mg/L to below 0·3 mg/L. The simplified in-line coagulant addition process involved hydraulic mixing of the coagulant into the feed and subsequent flocculation, and a greatly reduced (12 – 14 min) flocculation time relative to conventional coagulation-flocculation-settling treatment. Both alum and ferric chloride effectively removed phosphorus to below the 0·3 mg/L threshold when applied as a pretreatment at optimized doses, both of which were below the WWTP’s current coagulant dose (as ferrous chloride). This simplified pre-treatment scheme provided consistent enhanced removal of phosphorus and organic compounds. These results suggest that simplified in-line coagulant addition in advance of immersed UF membranes enhances the ability to produce treated effluent suitable for water-reuse applications.

Graft copolymerization of thiophene onto polystyrene synthesized via nitroxide-mediated polymerization and its polymer − clay nanocomposite

A new strategy for graft copolymerization of thiophene onto a polystyrene (PSt) backbone by a multi-step process is suggested and the effects of an organoclay on the final properties of the graft copolymer sample are described. For this purpose, first poly(styrene-co-4-chloromethyl styrene) [P(St-co-CMSt)] was synthesized via nitroxide-mediated polymerization. Afterwards, the chlorine groups of P(St-co-CMSt) were converted to thiophene groups using the Kumada cross-coupling reaction and thiophene-functionalized PSt multicenter macromonomer (ThPStM) was synthesized. The graft copolymerization of thiophene monomers onto PSt was initiated by oxidized thiophene groups in the PSt chains after addition of ferric chloride (FeCl3), an oxidative catalyst for polythiophene synthesis, and FeCl3-doped polythiophene was chemically grafted onto PSt chains via oxidation polymerization. The graft copolymer obtained was characterized by 1H NMR and Fourier transform infrared spectroscopy, and its electroactivity behavior was verified under cyclic voltammetric conditions. Finally, PSt-g-PTh/montmorillonite nanocomposite was prepared by a solution intercalation method. The level of dispersion of organoclay and the microstructure of the resulting nanocomposite were probed by means of XRD and transmission electron microscopy. It was found that the addition of only a small amount of organoclay (5 wt%) was enough to improve the thermal stabilities of the nanocomposite.© 2013 Society of Chemical Industry

Depth filtration using novel fiber-ball filter media for the treatment of high-turbidity surface water

Performance of the novel fiber-ball filter was investigated for the treatment of high-turbidity surface water. Impact of different operating parameters, such as coagulant type, coagulant dose and filtration velocity on the effluent turbidity, dissolved organic carbon (DOC) and head loss, as well as the particle removal characteristics were studied. The clean-bed filtration results showed that the fiber-ball filters had a great potential for the removal of turbidity matters. Addition of polymeric aluminum ferric chloride (PAFC) enhanced the removal of effluent turbidity and DOC, while the head loss was also increased. The effluent turbidity could be <0.5NTU and the removal efficiency of DOC was ∼16% when the PAFC was dosed at 12mg/L. The effluent turbidity and DOC increased slightly with increasing filtration velocities (30–50m/h) due to the greater drag forces resulted from higher filtration velocities. However, the head loss was also increased. The particle removal characteristics indicated that large particles were primarily removed in the top 30cm of the filter bed and the deep depth in the bottom 20cm played an important role in preventing the occurrence of turbidity breakthrough. It was also found that particles in the size larger than 2μm could be well removed by the fiber-ball filters, implying the potential application for the removal of protozoa like Cryptosporidium (3–15μm) to meet the desired requirement for drinking water treatment during depth filtration.

Occurrence and Biodegradation of Nonylphenol in the Environment

Nonylphenol (NP) is an ultimate degradation product of nonylphenol polyethoxylates (NPE) that is primarily used in cleaning and industrial processes. Its widespread use has led to the wide existence of NP in various environmental matrices, such as water, sediment, air and soil. NP can be decreased by biodegradation through the action of microorganisms under aerobic or anaerobic conditions. Half-lives of biodegradation ranged from a few days to almost one hundred days. The degradation rate for NP was influenced by temperature, pH and additions of yeast extracts, surfactants, aluminum sulfate, acetate, pyruvate, lactate, manganese dioxide, ferric chloride, sodium chloride, hydrogen peroxide, heavy metals, and phthalic acid esters. Although NP is present at low concentrations in the environment, as an endocrine disruptor the risks of long-term exposure to low concentrations remain largely unknown. This paper reviews the occurrence of NP in the environment and its aerobic and anaerobic biodegradation in natural environments and sewage treatment plants, which is essential for assessing the potential risk associated with low level exposure to NP and other endocrine disruptors.

Overcoming Membrane Performance Issues Resulting from Upstream Polymer and Ferric Chloride Addition

Overcoming Membrane Performance Issues Resulting from Upstream Polymer and Ferric Chloride Addition

Characterizing membrane foulants in MBR with addition of polyferric chloride to enhance phosphorus removal

The effect of polymeric ferric chloride (PFC) addition on phosphorus removal and membrane fouling were investigated in an anoxic/oxic submerged membrane bioreactor. The total phosphorus concentration in effluent averaged at 0.26mg/L with PFC addition of 10–15mg/L, while the rate of membrane fouling increased 1.6 times over the control MBR (without PFC addition). Three-dimensional excitation–emission matrix fluorescence spectroscopy and Gel Filtration Chromatography analysis indicated that soluble microbial byproduct-like materials and large molecules (MW>100kDa) were one of the main contributors of biofouling. Fourier transform infrared spectrum confirmed that the major components of the cake layer were proteins and polysaccharides materials. Scanning electron microscopy demonstrated that membrane surfaces were covered with compact gel layer formed by organic substances and Energy Dispersive X-ray analysis indicated that ferric metals were the most important inorganic pollutants. Consequently, soluble organic substances and dose of PFC should be controlled to minimize membrane fouling.

Effect of Ferric Chloride Addition and Holding Time on Gravity Belt Thickening of Waste Activated Sludge

Phosphorus removal using ferric chloride (FeCl3) addition was demonstrated at the Egan Water Reclamation Plant. Concurrently, sludge thickening performance problems occurred in the gravity belt thickeners (GBTs). Blinding problems and polymer demand change were attributed to FeCl3 and long sludge holding times. Laboratory tests were conducted to gain insight to the GBT problems. Sludge holding time effects before polymer conditioning and thickening and prolonged contact of the solids with FeCl3 were evaluated via modified time-to-filter and blinding tests developed for this study. The tests assessed the sludge filterability under polymer and FeCl3 conditioning treatments and varying sludge holding and FeCl3 contact times. It was determined that fresh sludge was the easiest to thicken compared with sludge stored for any length of time. The FeCl3 improved thickening; however, when both the FeCl3 and polymer were used as conditioners, higher FeCl3 concentrations resulted in thickening inhibition compared with polymer alone.

A combined treatment of landfill leachate using calcium oxide, ferric chloride and clinoptilolite

The aim of this research was development of appropriate procedure for treatment of landfill leachate taken from old sanitary landfill Piskornica (Koprivnica, Croatia). Due to complex nature of the effluent a combined treatment approach was applied. Samples were treated with calcium oxide followed by ferric chloride and finally with clinoptilolite. The optimum amount of treating agents and contact time were determined. Application of calcium oxide (25 g/L, 20 min. contact time) resulted in the reduction of color, turbidity, suspended solids and ammonia for 94.50%, 96.55%, 95.66% and 21.60%, respectively, while the removal efficiency of Cr (VI), Fe, Ni, Cu, Zn and Pb was 75.00%, 95.34%, 56.52%, 78.72%, 73.02% and 100.00%, respectively. After addition of ferric chloride (570 mg Fe3+/L, 20 min. contact time) removal efficiency of color, turbidity, suspended solids and ammonia increased to 96.04%, 99.27%, 98.61%, and 43.20%, respectively. Removal of ammonia (81.60%) increased significantly after final adsorption onto clinoptilolite (25 g/L, 4 h contact time). Removal of COD after successive treatment with calcium oxide, ferric chloride and clinoptilolite was 64.70%, 77.40% and 81.00%, respectively.

Effects of ferric chloride on thermal degradation of γ‐oryzanol and oxidation of rice bran oil

The kinetics of γ-oryzanol degradation in antioxidant-stripped rice bran oil were investigated at 180°C for 50 h. Ferric chloride was added to the oil at different concentrations (0, 2.5, 5.0, and 7.5 mg/kg-oil) to determine the degradation reaction rate of γ-oryzanol and the extent of lipid oxidation (peroxide value and p-anisidine value). It was found that the losses of γ-oryzanol and its four components (cycloartenyl ferulate, 24-methylene cycloartanyl ferulate, campesteryl ferulate, and β-sitosteryl ferulate) could be described by a first-order kinetics model. The degradation rate constant, k, linearly increased (p < 0.05) with the ferric chloride concentration, and increased about 1.5 times when 7.5 mg/kg-oil ferric chloride was added. Ferric chloride addition also accelerated the lipid oxidation of rice bran oil significantly (p < 0.05). Practical applications: This paper describes the kinetic analysis of the degradation of γ-oryzanol, a major phytochemical in rice bran oil, at its frying temperature. The results indicated that iron in the form of ferric chloride accelerated both the degradation of γ-oryzanol and lipid oxidation.

Application of a combined biological and chemical system for the treatment of phosphorus-containing wastewater from the food industry

Coagulants can be dosed at different points during the wastewater treatment process to achieve phosphorous removal. Addition of metal coagulants on the aeration basin (simultaneous precipitation) involves lowest cost; however, inert solids reduce the volatile solids percentage which can be deleterious to the biological process. The general objective of the present study was to analyze the feasibility of P removal in a wastewater model system of the dairy industry using simultaneous precipitation in a laboratory-scale activated sludge reactor by addition of ferric chloride. Results showed that the addition of a high dose Fe:P (molar ratio)= 1.9-2.3:1 on the aeration basin of the reactor caused a progressive enrichment of the sludge with inorganic solids. This phenomenon, which involved a gradual deterioration of the environmental quality of the biological system, led finally to a strong decline of the reactor performance. The organisms associated to flocs (crawling ciliates and attached ciliates) were the more sensitive to these changes. A mathematical model allowed the estimation of the concentration of total fixed suspended solids as well as the decrease in the abundance of these organism groups as a function of time of Fe(III) application, considering the influent flow rate, the influent Fe concentration, and the waste flow rate of the sludge. The Shannon-Wiener diversity index and the sludge biotic index (SBI) can early predict the decreasing of the system performance due to metal salts overload. The simultaneous application of the proposed mathematical model and the biological indices guarantee a successful control of systems operated with phosphorous simultaneous precipitation by Fe(III).

Research Article: The Effect of Ferric Chloride Addition for Phosphorus Removal on Ultraviolet Radiation Disinfection of Wastewater

In light of the potential need for disinfection and nutrient removal at the Metropolitan Water Reclamation District of Greater Chicago's water reclamation plants (WRPs), the inhibitory effects of ferric chloride (FeCl3) on ultraviolet (UV) radiation disinfection was examined. Results of a 2007 preliminary study indicated that a 2-log reduction in fecal coliform (FC) concentrations for each WRP secondary effluent was achieved with a UV dose of 10 mJ/cm2 except for the John E. Egan (Egan) WRP, where FeCl3 addition in the aeration basin for phosphorus removal was being employed. A subsequent study examined the effect of Egan unfiltered (secondary) and filtered (final) effluent on UV disinfection in 2008 during FeCl3 application and 2009 upon cessation of FeCl3 application: FeCl3 addition and filtration had little effect on UV transmittance (UVT). However, with FeCl3 addition, secondary and final effluent had higher total iron and lower total phosphorus relative to the respective secondary and final effluent without FeCl3 addition. Final effluent with and without FeCl3 addition showed lower total suspended solids concentrations relative to secondary effluent. Collimated beam test results indicated that a higher UV dose was needed to achieve the desired log reductions with FeCl3 addition and secondary effluent. Therefore, filtration of the effluent may be required if FeCl3 addition for nutrient removal is used at WRPs that employ UV disinfection.

Performance and biological indicators of a laboratory-scale activated sludge reactor with phosphate simultaneous precipitation as affected by ferric chloride addition

Iron-base coagulants are widely used for the phosphorous removal from wastewaters. Coagulants may be applied on the secondary treatment (simultaneous precipitation); however, coagulant excess may alter the biological process. The objectives of this work were: (a) to study in a laboratory-scale activated sludge reactor, fed with a model wastewater system from the dairy industry, the feasibility of phosphorous removal by applying simultaneous precipitation using ferric chloride; (b) to assess the effect of different Fe:P (molar ratio) dose ranges: high = 1.9–2.3:1, mean = 1.5–1.9:1 and low = 1.0–1.4:1 on the reactor performance by measuring physical–chemical parameters (pH, COD, TSS, Fe, P), settling properties (DSVI, diluted sludge volume index) and abundance of filamentous microorganisms by microscopic observation; (c) to evaluate the effect of the coagulant on activated sludge microfauna (abundance and morphological–functional groups); (d) to assess the usefulness of these parameters as control tools. A high Fe:P ratio acted as shock load improving the soluble phosphorous and COD removal. Sludge settling properties were rapidly improved due to both a successful control of filamentous bulking and an increase in the flocs density. Prolonged application of high Fe(III) doses negatively affected the reactor performance; a Fe:P ratio = 1.5–1.9:1 achieved an acceptable effluent quality. Changes in the density of Chilodonella sp., Opercularia sp., Vorticella microstoma, Vorticella spp., Colpoda sp. and rotifers were analyzed as a function of the progressive enrichment of Fe(III) in the sludge. Crawling ciliates constituted the most sensitive group to changes in the activated sludge reactor environmental quality, becoming a potential biological indicator of Fe(III) overload.

Removal of Cr(VI) Ions from Aqueous Solutions Using Poly 3-Methyl Thiophene Conducting Electroactive Polymers

This paper deals with a new application of poly 3-methyl thiophene synthesized chemically onto sawdust (termed as P3MTh/SD) as an effective adsorbent for removal of Cr(VI) ions from aqueous solutions using column system. Chemical synthesis of poly 3-methyl thiophene was performed by addition of ferric chloride (in chloroform) as oxidant to sawdust which had previously been soaked in monomer solution. All the sorption experiments were conducted using dynamic or column system at room temperature. The effect of important parameters such as pH and initial concentration on uptake of Cr(VI) was investigated. In order to find out the possibility of the regeneration and reuse of the exhausted adsorbent, desorption studies were also performed. The currently introduced adsorbent was found to be an efficient adsorbent for removal of highly toxic and hazardous Cr(VI) ions from aqueous solutions. As our breakthrough analysis has indicated, each gram of P3MTh/SD is able to remove more than 95% of Cr(VI)ions from 300 mL of Cr(VI) polluted solution with the initial concentration of 25 mg L−1 in column system. Sorption/desorption of Cr(VI) ions was found to be a highly pH dependent processes.

Effect of natural dissolved organic carbon on phosphate removal by ferric chloride and aluminum sulfate treatment of wetland waters

The use of wetlands for the removal of excess N and P has become widespread. Some sensitive P‐limited ecosystems, however, may require additional reductions in the concentration of P entering the system. It has been proposed that the treatment of wetlands through addition of ferric chloride or aluminum sulfate can augment the natural P removal mechanisms. However, high concentrations of natural dissolved organic matter may interfere with the removal of P by metal addition. We evaluated the doses of ferric chloride and aluminum sulfate necessary to reduce total P concentrations below 0.32 μM (10 μg/L) in water from the Northern Everglades, and we determined the effect of various concentrations (21, 38, and 60 mg/L) of natural dissolved organic carbon (DOC) on the removal of PO4 and total P. High concentrations of natural DOC inhibited both the short‐term removal of PO4 and the longer‐term removal of total P from the water column. Similar results were observed using 15 μM citric acid in an experiment to determine whether citric acid could effectively mimic the inhibition of phosphorus removal associated with natural DOC. Stoichiometry of these experiments indicates that the mechanism of natural DOC interference was not complexation of the metal ions by the DOC; we hypothesize that it could be adsorption to the terminal hydroxyl groups on a polynuclear Fe or Al colloid, effectively blocking the adsorption sites from a phosphate molecule. Also, the ability of citric acid to mimic the inhibitory effects also suggests that the results of the study are broadly applicable to wetland and other waters with high natural organic acid concentrations.

Optimization of phosphorus removal in secondary effluent using immersed ultrafiltration membranes with in-line coagulant pretreatment — implications for advanced water treatment and reuse applicationsA paper submitted to the Journal of Environmental Engineering and Science.

In-line addition of alum and ferric chloride was conducted at a hollow-fibre immersed ultrafiltration (UF) membrane pilot plant, using secondary effluent from a municipal wastewater treatment plant (WWTP) as the feed. The objective of such pretreatment was to remove phosphorus from the feed from an initial concentration of approximately 5 mg/L to below 0.3 mg/L. The simplified in-line coagulant addition process involved hydraulic mixing of the coagulant into the feed and subsequent flocculation, and a greatly reduced (12–14 min) flocculation time relative to conventional coagulation-flocculation-settling treatment. Both alum and ferric chloride effectively removed phosphorus to below the 0.3 mg/L threshold when applied as a pretreatment at optimized doses, both of which were below the WWTP’s current coagulant dose (as ferrous chloride). This simplified pre-treatment scheme provided consistent enhanced removal of phosphorus and organic compounds. These results suggest that simplified in-line coagulant addition in advance of immersed UF membranes enhances the ability to produce treated effluent suitable for water-reuse applications.

Iron Depleted Erythropoiesis: Slow but Effective

Iron deficiency affects billions worldwide, and anemia develops when iron stores become insufficient to maintain normal erythropoiesis. However, iron depleted erythropoiesis is incompletely understood. In this study, an ex vivo model of iron depleted erythropoiesis was developed using dosed titrations of the iron chelator deferoxamine (DFO) in CD34+ cell cultures. All experiments were performed in triplicate with cells from three separate donors. Hemoglobinization and expression patterns of erythroid markers (GPA/CD71) demonstrated minimal changes in DFO supplemented medium. DFO caused dose-related suppression of cell counts after 14 days (20uM DFO: 42% reduction, 30uM DFO: 86% reduction, 40uM DFO: 96% reduction of cell counts compared to 0uM DFO controls). Cultures supplemented with 30uM DFO were used for subsequent studies, and the DFO-mediated effects were completely reversed by addition of 30uM ferric chloride. To investigate whether apoptosis caused the reduction in cell counts, surface Annexin V was measured by flow cytometry. No significant increases in levels of apoptosis among the proliferating erythroblasts were detected (Annexin V positive cells; 0uM DFO 6.2 ± 0.95%, 30uM DFO 9.0 ± 1.55%, p = 0.058). Analyses of p53 protein quantitation and p53 DNA-binding activity further suggested that the suppression of cell counts by iron chelation was not due to p53 related apoptosis. In the absence of apoptosis or maturation arrest, we hypothesized that the growth suppressing effects of DFO were not due to ineffective erythropoiesis. To test this hypothesis, a recently-discovered marker of ineffective erythropoiesis named GDF15 (Tanno et al. Nat. Med. 2007) was measured in the culture supernatants, and no increase was detected (GDF15 concentration per 1×104 cells: 0uM DFO; 79.7 ± 4.4 pg, 30uM; 43.9 ± 4.3 pg). In the clinic, serum GDF15 levels from 17 blood donors with significantly reduced ferritin and iron saturation (279 ± 98 pg/ml) were not increased when compared to serum GDF15 levels in 17 healthy volunteers with normal iron parameters (410 ± 119 pg/ml). To determine if cell cycling, instead of apoptosis, caused the reduction in cell counts, carboxyfluorescein diacetate succinimidyl diester (CFSE) staining studies were performed during the first and second weeks of culture. CFSE is an intracellular fluorescent stain, the intensity of which halves with each cell division. Three or four fewer erythroblast cell divisions were detected in 30uM DFO during the 14-day culture period when compared to controls. Based upon the reduction in cell divisions, it was estimated that the average cell cycle time was prolonged by 40–70% in DFO. Propidium iodide analyses additionally demonstrated changes in the cell cycle kinetics including a significant reduction in the percentage of S-phase erythroblasts at the peak phase of proliferation (30uM DFO: 37.0 ± 1.8% vs. control: 48.7 ± 3.4%, p = 0.0063). These results suggest that iron depletion inhibits the overall growth of erythroblasts by prolonging the cell cycle rather than causing apoptosis or maturation arrest. Due to the large amount of iron required for hemoglobin production, slower cell cycles may facilitate effective erythropoiesis by allowing extra time for uptake when extracellular iron is scarce.

Biotransformation of arsenic species by activated sludge and removal of bio-oxidised arsenate from wastewater by coagulation with ferric chloride

The potential of activated sludge to catalyse bio-oxidation of arsenite [As(III)] to arsenate [As(V)] and bio-reduction of As(V) to As(III) was investigated. In batch experiments (pH 7, 25 °C) using activated sludge taken from a treatment plant receiving municipal wastewater non-contaminated with As, As(III) and As(V) were rapidly biotransformed to As(V) under aerobic condition and As(III) under anaerobic one without acclimatisation, respectively. Sub-culture of the activated sludge using a minimal liquid medium containing 100 mg As(III)/L and no organic carbon source showed that aerobic arsenic-resistant bacteria were present in the activated sludge and one of the isolated bacteria was able to chemoautotrophically oxidise As(III) to As(V). Analysis of arsenic species in a full-scale oxidation ditch plant receiving As-contaminated wastewater revealed that both As(III) and As(V) were present in the influent, As(III) was almost completely oxidised to As(V) after supply of oxygen by the aerator in the oxidation ditch, As(V) oxidised was reduced to As(III) in the anaerobic zone in the ditch and in the return sludge pipe, and As(V) was the dominant species in the effluent. Furthermore, co-precipitation of As(V) bio-oxidised by activated sludge in the plant with ferric hydroxide was assessed by jar tests. It was shown that the addition of ferric chloride to mixed liquor as well as effluent achieved high removal efficiencies (>95%) of As and could decrease the residual total As concentrations in the supernatant from about 200 μg/L to less than 5 μg/L. It was concluded that a treatment process combining bio-oxidation with activated sludge and coagulation with ferric chloride could be applied as an alternative technology to treat As-contaminated wastewater.

Removal of Arsenic from High Ionic Strength Solutions: Effects of Ionic Strength, pH, and preformed versus in situ formed HFO

Arsenic sorption to hydrous ferric oxide (HFO) is an effective treatment method for removing dissolved arsenic from fresh drinking water sources. However, detailed information is limited regarding arsenic removal from solutions of high ionic strength such as brackish groundwater, seawater, or high-pressure membrane process residuals. Bench-scale treatment experiments were conducted exploring arsenic removal from simple solutions with ionic strengths ranging from 0.008 to 1.5 M by addition of ferric chloride followed by solid/liquid separation (microfiltration or ultrafiltration). Arsenic removal from these solutions during in situ iron precipitation was approximately 90% at Fe:As molar ratios of 10 to 15 and > 95% for Fe:As molar ratios greater than 20. Arsenic removal at iron doses of 10(-6) to 10(-4) mol-Fe/L improved when pH was lowered from 8 to less than 6.5 at ionic strength 0.2 M; this improvement was not as significant at ionic strength 0.7 M. Arsenic removal diminished when alkalinity was increased from 400 to 1,400 mg/L as calcium carbonate; however, arsenic removal at the higher alkalinity improved when pH was lowered from approximately 8 to less than 7. Arsenic removal with preformed HFO solids and subsequent microfiltration was significantly less than that observed with in situ HFO precipitation. Increased removal by in situ precipitation compared to that of preformed solids is explained by an increased number of adsorption sites due to uptake during iron oxy-hydroxide polymerization as well as an increase in surface area resulting in diminished surface charge effects. Model simulations of arsenic uptake by in situ precipitation adequately captured these effect by changing the model parameters used to model arsenic uptake by preformed HFO, specificallythe total number of surface sites and surface area.

Autopsy of high-pressure membranes to compare effectiveness of MF and UF pretreatment in water reclamation

A pilot-plant study was designed to compare the effectiveness of microfiltration (MF) and ultrafiltration (UF) as pretreatment for high-pressure membranes in reclamation of biologically treated wastewater effluent. Granular media, filtered secondary effluent from a full-scale wastewater treatment plant, was fed to MF and UF units that operated in parallel. Each of these filtrates served as the feedwater to two reverse osmosis (RO) units and one nanofiltration (NF) unit that operated in parallel. The decline in specific flux was substantially lower for high-pressure membranes receiving UF than MF pretreatment over the course of each of four pilot plant runs that lasted from 1 to 7 weeks. The removal of organic matter as measured by dissolved organic carbon (DOC) was somewhat higher by UF than MF pretreatment (about 15% by UF compared with 11% by MF). Addition of ferric chloride ahead of the UF unit, but not ahead of the MF unit, may account for this additional removal of organic matter. However, the additional DOC removal appeared insufficient to explain the differential in foulant accumulation between high-pressure membranes receiving UF and MF pretreatment. Extensive autopsy analyses of these high-pressure membranes showed from 35% to 56% less organic carbon on those receiving UF rather than MF pretreatment. A more specific indicator of a differential in organic fouling was the accumulation of polysaccharides and this showed from 27% to 38% less on UF- than on MF-pretreated membranes. Yet another possible source of foulants is inorganic material given that the inorganic and organic weight percentages were nearly equal (56% vs. 44%) on the membrane surface. One specific source was aluminum added for phosphorus removal. Less fouling of high-pressure membranes pretreated by UF than MF could be due to the following: (1) a small, but very important, colloidal fouling fraction may have passed through MF but was rejected by UF pretreatment; (2) organic fouling was not related to organics in either the MF or UF filtrates but rather to organics that are generated in situ by microbial activity on the membrane surface; and/or (3) less passage of colloidal Al–P that carried over from secondary wastewater treatment.