Coagulation Conditions Research Articles

Coagulation optimisation for NOM removal by direct filtration in clay aggregate filters

Optimisation of the coagulation step in a coagulation/direct filtration process in which filtration takes place in a lightweight expanded clay aggregates (Filtralite) filter is investigated. The water is high in NOM but low in turbidity, a situation frequently found in Norwegian lake water. Experimental studies in a pilot-scale direct filtration plant compare filtration efficiencies for different coagulants and coagulation conditions. Type of coagulant and coagulant dose are optimised as well as the pH of coagulation for four different coagulants. It is demonstrated that the biopolymer chitosan is a very interesting alternative coagulant in this particular process situation. Also poly-aluminium chloride (PAX) is superior to the traditional metal-salts, aluminium sulphate (ALG) and ferric chloride sulphate (JKL) in terms of turbidity and residual metal. Coagulation with ALG and JKL results in a certain floc-particle (turbidity) ‘leakage’ from the clay aggregate filter, while such ‘leakage’ is not equally evident when PAX and chitosan are used for coagulation.

Use of Total Suspended Solids in Characterizing the Impact of Spent Filter Backwash Recycling

Recycling of spent filter backwash water is a widely practiced residual management approach throughout the United States for drinking water utilities. The United States Environmental Protection Agency (USEPA), under the 1996 Safe Drinking Water Act Amendments, has recently proposed regulations governing the recycle of this waste stream. Considering this new regulation, a comprehensive study was conducted by researchers at Colorado State University, and a suspended solids mass balance model was developed to characterize the impact of backwash water recycling on the overall treatment process. Online particle count data indicated that certain recycle practices could impact the overall treatment process. Data from pilot-scale experiments showed that total suspended solids (TSS) is a useful tool for characterizing the impacts of the backwash recycle processes. TSS can be used to assess whether solids loading or suboptimal coagulation conditions are the cause of recycle related issues. For the study described here, filter breakthrough occurred at about the same total influent solids load, regardless of the manner in which backwash recycling was performed, indicating that recycle of backwash solids did not impact the overall treatment process.

Effects of prefluoridation on removal of particles and organic matter

For the past decade, US water utilities have been working to optimize their treatment processes to meet increasingly stringent regulations. Of the many unit processes employed in conventional treatment, water fluoridation appears to have been overlooked as a potential obstacle to effective compliance with the new requirements. A review of treatment plant schematics collected for the Information Collection Rule found that many utilities add fluoride to the process train at points where it can interfere with particle and natural organic matter (NOM) removal. In this research, bench‐ and pilot‐scale studies provided evidence that addition of fluoride to water prior to treatment with aluminum sulfate (alum) can severely affect removal of turbidity and NOM under enhanced coagulation conditions. Utilities disregarding these effects may face increased chemical costs, lower removal of organic matter and disinfection by‐product precursors, elevated concentrations of aluminum in the finished water, shorter filter run times, and the potential for turbidity breakthrough in filters.

Optimizing ferric sulfate coagulation of algae with streaming current measurements

This study sought to determine ferric sulfate coagulation conditions that lead to effective removal of algae by conventional gravity sedimentation. Using laboratory‐cultured Anabaena flos‐aquae spiked into natural water, charge titrations and jar tests were conducted to evaluate the effects of streaming current value, coagulation pH, and initial algae concentration on the removal of algae, turbidity, and natural organic matter. At pH 6, ferric sulfate doses corresponding to the point of zero charge (PZC), as determined by streaming current measurements, consistently produced low settled water algae concentrations when an anionic flocculant aid was added. In contrast, ferric sulfate coagulation at pH 7.0 and 7.5 was not effective for algae removal because the algae's surface charge could not be sufficiently neutralized. At pH 6 and the PZC, settled water algae concentrations, turbidity, and ultraviolet absorbance at 254 nm were similar for tests conducted at initial algae concentrations of 10,000 and 50,000 cells/mL, but a larger coagulant dose was required to reach the PZC at the higher initial algae concentration. Thus, adjusting coagulant doses based on streaming current value should be effective for maintaining settled water quality in plants that treat waters with rapidly varying influent algae concentrations and/or background water quality. Experiments conducted with a natural algae bloom sample confirmed that ferric sulfate coagulation at pH 6 and the PZC was effective for algae removal.

PILOT TESTING OF DISSOLVED AIR FLOTATION (DAF) IN A HIGHLY EFFECTIVE COAGULATION-FLOCCULATION INTEGRATED (FRD) SYSTEM

Factors of pretreatment coagulation/flocculation units were studied using raw water of low temperature and low turbidity. Aluminum sulfate (AS) and selected polyaluminium chlorides (PACls) were all effective in the DAF process when used under favorable conditions of coagulant addition, coagulation, flocculation and flotation units. Compared with the AS coagulant, PACls, at lower dosage, could give the same effective performance even with shorter coagulation/flocculation time or lower recycle ratio during the treatment of cold water. This is attributed to the higher-charged polymeric Al species, and the lower hydrophilic and more compact flocculated flocs of PACl coagulant. Based on results of pilot experiments, the goal of FRD system can be achieved by combining a DAF heterocoagulation reactor with PACl coagulant (F), an efficient flocculation reactor (R), as well as an economical auto-dosing system (D).

Spider silk fibers spun from soluble recombinant silk produced in mammalian cells.

Spider silks are protein-based "biopolymer" filaments or threads secreted by specialized epithelial cells as concentrated soluble precursors of highly repetitive primary sequences. Spider dragline silk is a flexible, lightweight fiber of extraordinary strength and toughness comparable to that of synthetic high-performance fibers. We sought to "biomimic" the process of spider silk production by expressing in mammalian cells the dragline silk genes (ADF-3/MaSpII and MaSpI) of two spider species. We produced soluble recombinant (rc)-dragline silk proteins with molecular masses of 60 to 140 kilodaltons. We demonstrated the wet spinning of silk monofilaments spun from a concentrated aqueous solution of soluble rc-spider silk protein (ADF-3; 60 kilodaltons) under modest shear and coagulation conditions. The spun fibers were water insoluble with a fine diameter (10 to 40 micrometers) and exhibited toughness and modulus values comparable to those of native dragline silks but with lower tenacity. Dope solutions with rc-silk protein concentrations >20% and postspinning draw were necessary to achieve improved mechanical properties of the spun fibers. Fiber properties correlated with finer fiber diameter and increased birefringence.

Preliminary studies of the oxidation of arsenic(III) by potassium ferrate

Potassium ferrate was synthesized using ferric chloride, and its effects on the oxidation of arsenic(III) in water treatment were investigated. Under given coagulation conditions, the effects of several factors on arsenic oxidation efficiency were examined, which include the mole ratio of Fe(VI) and As(III) added in water and the time elapsed between the addition of potassium ferrate and the measurement of As(III) in treated water.

Innovation of conventional water treatment techniques in effluent reclamation

For reclamation of waste water treatment plant (wwtp) effluent, conventional water treatment techniques used in drinking water supply may be suitable. Earlier studies and experiments showed that the most promising cost-effective conventional techniques to polish wwtp effluent are coagulation and rapid multi-media filtration (direct filtration). In the past 4 years these techniques were tested in long term experiments on pilot scale (5-10 m3/h) at several waste water treatment plants in The Netherlands. For successful application of direct filtration for the removal of suspended solids and colloidal material careful consideration is needed with the coagulation conditions. However additional treatment is required to meet the standards for household and process water with respect to ammonium, colour, pathogens and (biodegradable) organic substances.

Controlling Cryptosporidium oocysts Using Conventional Treatment

Fourteen pilot‐scale tests were performed to assess the ability of conventional treatment to control Cryptosporidium oocysts and three surrogates: turbidity, total particle count, and aerobic endospores. Cryptosporidium oocysts were fed into the raw water at a target concentration of 106/L for 30–71 h in each test. The effects of coagulant type, coagulant dose, raw water quality, filter loading rates, and filter media were evaluated. Under optimal coagulation conditions, conventional treatment achieved more than 4‐log total Cryptosporidium removal, and surrogate log removals were conservative (low with respect to Cryptosporidium).

Cellulose/casein blend membranes from NaOH/urea solution

AbstractCellulose membranes and cellulose/casein blend membranes were successfully prepared from a new solvent system (6 wt % NaOH/4 wt % urea aqueous solution) by coagulation with a sulfuric acid aqueous solution. The structures and properties of the membranes were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), wide‐angle X‐ray diffraction, differential scanning calorimetry, and a tensile test. The experimental results showed that the suitable coagulation condition was 5 wt % H2SO4 for 5 min. When the casein content of the mixture was less than 15 wt %, the blend membranes were miscible because of the interactions between the hydroxyl groups of cellulose and the peptide bonds of casein. The blend membranes with 10 wt % casein had good miscibility, higher crystallinity, and the highest mechanical properties and thermal stability. In this case, the tensile strength and breaking elongation of the blend membranes were 109 MPa and 16%, respectively, and its pore size, obtained by SEM, was 290 nm, which suggests that the blend membranes provide a potential application for the field of separation technology. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3260–3267, 2001

Chitosan/gelatin microspheres prepared by modified emulsification and ionotropic gelation

Chitosan microspheres were prepared by an emulsion-phase separation technique without the use of chemical cross-linking agents; alternatively, ionotropic gelation was employed in a w/o emulsion. The possibility of three kinds of anions (tripolyphosphate, citrate and sulphate) to interact with chitosan was investigated by turbidimetric titration. The results indicate that there are electrostatic interactions between the above anions and chitosan in a certain region of solution pH(1.0-7.5 for sulphate/chitosan, 4.5-7.5 for citrate/chitosan and 1.9-7.5 for tripolyphosphate/chitosan), that is related to the natural characteristics of the anions. Out of the pH region where anions interact with chitosan, no microspheres were formed. However, even in the pH region where anions can interact with chitosan, only irregular microparticles were obtained in the case of the conventional emulsification and ionotropic gelation method, while spherical microspheres with diameters in the range of tens of microns were obtained when a modified process was employed. The key point of the modified process is the introduction of gelatin and allowing the ionic crosslinking process of chitosan/gelatin w/o emulsions to take place under coagulation conditions at a low temperature. The surface of sodium sulphate cross-linked chitosan/gelatin and sodium citrate cross-linked chitosan/gelatin microspheres was very smooth, but large gaps were observed on the surface of tripolyphosphate/chitosan microspheres. The increase of stirring speed led to a decrease in diameter and a narrowing in size distribution.

Conventional and optimized coagulation for NOM removal

Bench‐ and full‐scale experiments were conducted to evaluate the optimal coagulation conditions for removal of total organic carbon and disinfection by‐products.The evaluation of 16 sites with optimized coagulation (optimizing the pH of coagulation and then the coagulant dosage) provides an assessment of this coagulation technique and illustrates its capabilities to meet the requirements of the Disinfectants/Disinfection By‐products (D/DBP) Rule. Jar tests were used to determine the effectiveness of optimized coagulation for the removal of organic carbon, DBP precursors, particles, and turbidity when supernatant results were compared with conventional (baseline) treatment. Jar‐test results indicate that optimized coagulation can enhance the removal of organic carbon and DBP precursors.

Liquid-liquid phase separation during polysulfone membrane preparation

The cloud point curves for a ternary system of PSf/NMP/water were determined by a titration method at 15 ‡C, 30 ‡C, 45 ‡C and 60 ‡C. A small amount of water (3–10 wt% water) was needed to achieve liquid-liquid phase separation and the temperature effect was not significant. The vitrification composition for the ternary system of PSf/NMP/water was determined by DSC measurements for various compositions. Cross-sectional membrane morphologies were examined by SEM (Scanning Electron Microscope) and surface morphologies by AFM (Atomic Force Microscope) varying the parameters including polymer concentration and bath compositions. It was observed that there were two different modes of phase separation during the formation of polysulfone membrane when the coagulation conditions were varied.

Effect of Coagulation Conditions on Membrane Filtration Characteristics in Coagulation−Microfiltration Process for Water Treatment

In a coagulation−microfiltration (MF) hybrid process, membrane permeability and permeate water quality were investigated in conjunction with coagulation mechanisms under two kinds of dead-end (e.g....

Optimizing enhanced coagulation for DOC removal with ultrafiltration membrane separation using response surface methods and particle trajectory analysis

An enhanced coagulation study was conducted on bench scale to determine the optimal coagulation condition in terms of pH and coagulant dose for DOC removal by response surface method. 22 factorial design was performed to obtain the optimal coagulation condition of pH = 6.0 and alum dose = 50.4mg/l. A membrane separation experiment with ultrafiltration unit was conducted with the selected conditions of pH and alum dose around the optimal coagulation condition. Flux change, DOC removal efficiency, and turbidity removal efficiency were measured to see the performance of membrane separation. The particle trajectory model suggested by Altena and Belfort was used to analyze the relationship between the size of particles formed by enhanced coagulation and the fouling of ultrafiltration membrane processes, with simulation of the experimental conditions used in this study. The flux of PM30 ultrafiltration membrane was strongly affected by particle size formed in coagulation pretreatment rather than DOC removal rate.

A novel approach to prepare tripolyphosphate/chitosan complex beads for controlled release drug delivery

A novel approach was developed to improve the mechanical strength of tripolyphosphate (TPP)/chitosan beads prepared under coagulation condition at 4°C in the presence of gelatin. Cross-sectional analysis indicated that the beads had a homogeneous crosslinked structure, as a result the beads were strengthened greatly (the mechanical strength increased more than ten times). Furthermore sodium alginate (a polyanion) can interact with cationic chitosan on the surface of these TPP/chitosan beads to form polyelectrolyte complex film for the improvement of the drug sustained release performances. The loading efficiency of model drugs (brilliant blue and FITC-dextran) in these beads was very high (more than 90%). Crosslinking time, TPP solution pH and other preparation factors had an effect on the drug release performance of beads. The release period of brilliant blue (a poor water soluble dye) was more than 2-months at a fairly constant rate in 0.9% NaCl, 10 mM PBS pH 7.4. However, for FITC-dextran (a water soluble polysaccharide) only 1–2 days in the same conditions. It seems that TPP/chitosan bead prepared by the novel method is a promising formulation for drug delivery.

Acrylonitrile-maleic anhydride copolymer membrane (I): effects of casting conditions

The effects of casting conditions, including casting solution (composition and temperature) and coagulation conditions (pre-evaporation time, temperature and concentration of coagulation bath) on the structure and performance of acrylonitrile–maleic anhydride copolymer membrane have been investigated. The results showed that the water flux decreased gradually while the rejection of bovine serum albumin (BSA) decreased as the concentration of copolymer increased. When the total solid concentration was kept unchanged, the water flux increased with additive polyvinylpyrrolidone (PVP), the rejection did not decrease until the ratio of PVP/copolymer was 60%. When the content of copolymer in the casting solution was kept constant, the water flux decreased rapidly while the rejection increased a little (compared with the case of no additive) as the ratio of PVP/copolymer increased. As to the temperature of casting solution, the water flux had a maximum at 45 °C and the rejection had a maximum and a minimum at 45 and 55 °C, respectively. The water flux had a maximum value when the pre-evaporation time was 40 sec. The rejection of BSA was almost unchanged when the pre-evaporation time was less than 40 sec. and then decreased and reached a minimum value at 60 sec. As the temperature of coagulation bath increased, the water flux reached a maximum at 35 °C while the rejection increased uniformly. With increasing the concentration of DMSO in the coagulation bath, the water flux decreased gradually and got to a minimum at 50 wt% as the concentration of dimethylsulfoxide in the coagulation bath increased, but no apparent effect on the rejection was observed. Copyright © 2000 John Wiley & Sons, Ltd.

Removal of Humic Substances by UF and NF Membrane Systems

This paper deals with the removal efficiency and mechanisms of humic substances contained in a river water by ultrafiltration (UF) and nanofiltration (NF) membranes. UF membranes with molecular weight cut-off (MWCO) of 50 kDa to 200 kDa can remove only large molecular size humic substances (LMSHS). Even in the UF membranes operated under the cross-flow mode, the LMSHS were accumulated on the membrane surface, because the back transport velocity of LMSHS is always smaller than that of the permeate flux. Precoagulation enhanced the removal of humic substances effectively. The optimum coagulation conditions for removing the humic substances in the UF membranes was the same as that in the conventional coagulation/flocculation/sedimentation process. The vibration action increased the removal efficiency of humic substances in the NF membrane process. Strong shear produced by the vibration diffused away the humic substances from the membrane surface to the bulk water, therefore the accumulation of humic substances on/near the membrane surface, i.e. formation of cake and concentration polarization boundary layers, is prohibited.

Enhanced Coagulation: US Requirements and a Broader View

Enhanced Coagulation is a new regulatory requirement in the United States aimed at removing TOC by coagulation thereby controlling formation of disinfection byproducts. Coagulation principles are summarized for alum coagulation of natural organic matter (NOM). Negatively charged NOM creates a coagulant demand for positively charged Al species resulting in a stoichiometric relationship between the alum dosage and the raw water DOC that is pH dependent. The paper addresses coagulation with a broader view than Enhanced Coagulation, termed multiple objective coagulation. In general the objectives include: 1) to maximize particle and turbidity removals by downstream solid-liquid separation, 2) to maximize TOC and DBP precursor removals, 3) to minimize residual coagulant, 4) to minimize sludge production, and 5) to minimize operating costs. Optimum coagulation conditions are those that maximize pathogen removals, produce low turbidities and particle counts, and minimize residual Al. It is shown, for treatment of waters of low alkalinity, that the optimum alum dosage selected to minimize UV absorbance with strict pH control produced excellent treatment for turbidity, pathogens, and NOM. Full scale plant data are used to demonstrate a dual coagulation strategy of alum and cationic polymer that reduces sludge production and overall operating costs compared to alum alone.

Surface structure and phase separation mechanism of polysulfone membranes by atomic force microscopy

Atomic force microscopy (AFM) was used to investigate the surface of polysulfone (PSf) membranes. The AFM method provides information on both size and shape of pores or cavities on the surface as well as the roughness of the skin. The pore sizes obtained from AFM observation were found to be more accurate than those obtained from scanning electron microscopy (SEM) since the potential of altering the pore structure of the membrane during sample preparation was eliminated. It was observed that two different modes of phase separation existed during the formation of PSf membrane when the coagulation conditions were varied.