Optimum Coagulation Conditions Research Articles

Enhanced Coagulation of Disinfection By-products Precursors in Istanbul Water Supply

During the chlorination of drinking water, chlorine reacts with natural organic matter (NOM) to produce disinfection byproducts (DBPs), such as trihalomethanes (THMs) and haloacetic acids (HAAs), which are believed to be harmful to human health. Enhanced coagulation is a DBPs precursor treatment technique with the objective of removing total organic carbon (TOC) to control DBPs formation in water. Scientifically, the removal of organic matter by coagulation depends on the TOC concentration, the chemical nature of the NOM, coagulant type, coagulant dosage, and coagulation pH. Currently, water treatment plants are practicing enhanced coagulation to further increase DBPs precursor removal. The focus of this study was to investigate enhanced coagulation of Terkos Lake Water (TLW) of Istanbul City. In this study, jar test experiments were conducted on TLW source to determine the effectiveness of enhanced coagulation for removal of DBPs surrogate parameters of total organic carbon (TOC), ultraviolet absorbance (UV254), and THM formation potential (THMFP). Jar tests results indicated that enhanced coagulation can increase the removal of DBPs precursors. To evaluate the coagulation performances, two different coagulants, aluminum and iron salts were used at different pH values to determine optimal coagulation conditions for surrogate parameters removal quantity.

Nano silica removal from IC wastewater by pre-coagulation and microfiltration

Microfiltration (MF) coupled with pretreatment by coagulation was adopted in the treatment of chemical mechanical polishing (CMP) wastewater from IC manufacturing plants, containing high concentrations of silica. Poly-aluminium chloride (PACl) was the coagulant, while the cationic polyacrylamide (PAA) was the flocculant aid. Preliminary tests were performed with the raw CMP wastewater in order to determine the optimal coagulation condition for subsequent microfiltration. Analysis of the particle size distribution shows that nearly all silica particles were enlarged from nano scale to at least 4 microm in diameter after the pre-treatment. The pre-treated wastewater was then filtered through a polytetrafluoroethylene (PTFE) membrane with a pore size 0.5 microm at a constant vacuum pressure. Trace amounts of PAA in addition to the PACl coagulation can effectively increases the permeate flux.

Performances de la coagulation ‐ floculation dans le traitement des effluents de seiche

Coagulation‐flocculation of the colloids particles present in the cuttlefish effluents was investigated using a coagulation step with aluminium sulphate (SA), followed by a flocculation step with starch, SiO, or MgO and then poly dimethyl ammonium chloride (PDMAC), in order to reduce the turbidity and chemical oxygen demand (COD). Kinetic aspects, adsorption equilibrium, pH and conductivity were studied in order to determine the optimum coagulation conditions and SA quantities. The addition of organic polymer as a flocculant agent gave a better performance than the use of salt alone with a reduction of 50% of the SA consumption. Polymer molecular weight of PDMAC and charge density of starch have been also investigated. The best result, which is 90% of removal rate in chemical oxygen demand (COD) and a turbidity value of 7 NTU was obtained with the combination using 165.5 mg l−1 of aluminium sulphate, 750 mg l−1 of MgO and 35 me l−1 of PDMAC 400000.

Regenerated cellulose films from NaOH/urea aqueous solution by coagulating with sulfuric acid

A series of novel regenerated cellulose (RC) films was prepared from cotton linters in 6 wt% NaOH/4 wt% urea aqueous solution by coagulating with 1–20 wt% sulfuric acid (H2SO4) aqueous for 1–20 min. Dependences of structure, morphology, light transmittance, mechanical properties, and water permeability of the films on the H2SO4 concentration and the coagulation time were investigated by using IR, UV–Vis, x-ray diffraction, scanning electron micrograph, tensile testing, membrane osmometry, etc. All of the films exhibited homogeneous porous structure on the surface, but different inner architectures for the various coagulation conditions. The tensile strength and breaking elongation of the films decreased with increasing H2SO4 concentration and the coagulation time, and the highest tensile strength (97 MPa) of the films was obtained by coagulating with 5 wt% H2SO4 for 2 min. The H2SO4 concentrations have significantly more influence on the structure and properties of the films than the coagulation time. The novel RC films displayed larger pore size and higher water permeability than those of RC films prepared from cellulose cuoxam, and the pore sizes could be adjusted by changing the H2SO4 concentration. This work provided an optimal coagulation condition for preparing RC films in the solvent system and scientific information for controlling the properties and pore sizes of the films.

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).

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.

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.

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.

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.

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.

Coagulation rate studies of spinnable chitosan solutions

The coagulation properties of some mixtures of 5% chitosan in 2% aqueous acetic acid were investigated with the goal of determining the optimal coagulation conditions for the spinning of chitosan fibers. The chitosan was characterized and found to possess a deacetylation value of 84.9 ± 0.2%. Molecular weight of the chitosan was also measured; based on intrinsic viscosity, the Mv value was 7.73 × 105 g mol−1, and based on high-pressure liquid chromatography, the Mw value was 1.14 × 105 g mol−1. Solutions of 5% chitosan/2% acetic acid were prepared, filtered, and extruded through a large-diameter hole syringe into coagulation baths of varying composition that were all strongly basic in nature, at least a pH of 12 or greater. For each coagulant, time was varied from between 22 s and 2 minutes at room temperature. A second set of experiments was conducted where the temperature was varied from 20°C to 70°C at a constant time of 45 s. In a third set of experiments, using a 1M NaOH coagulant, different chitosans were also analyzed. Throughout all of the experiments, a distinct moving boundary between coagulated and uncoagulated polymer was observed within the cylindrical-shaped polymer fibers. Using a series of equations based on Fick's 2nd Law, a straight line relationship has been demonstrated between boundary motion and time and between boundary motion and temperature for each coagulant tested. The activation energy for each coagulant was also determined. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 117–127, 1997

Dyeing wastewater treatment by activated sludge process with a polyurethane fluidized bed biofilm

In case of the porous polyurethane fluidized bed biofilm-activated sludge process followed by a coagulation process(the FBAS-C process), 75% CODMn was removed by treating with the biological FBAS process in the loading range of 0.16∼0.32 kgCODMn/kgVSS·day. The biomass yield and microbial decay coefficients were 0.42 kg MLSS/kgBOD and 0.11 day−1, respectively. The optimum coagulation conditions for the effluent of the FBAS process were at pH 6 and 600mg/L alum dosage. Consequently, 92% of total CODMn removal efficiency was observed in the FBAS-C process. Meanwhile, in case of a coagulation process followed by the porous polyurethane fluidized bed biofilm-activated sludge process(C-FBAS process). the raw dyeing wastewater was treated at pH 6 in the presence of 1,000 mg/L alum and, continuously, the effluent coagulated wastewater was treated by the FBAS process in the loading range of 0.09∼0.19 kg CODMn/kgVSS·day. Removal efficiency of CODMn in the biological process, FBAS, was 82%. The biomass yield and microbial decay coefficient in the C-FBAS process were similar to those in the FBAS-C process. The final effluent CODMn was about 65 mg/L in both tested processes, the FBAS-C and C-FBAS. However, the FBAS-C process illustrated better treatibility than C-FBAS in terms of the total sludge production, since the former produced about 20% less sludge than the latter.

Coagulation-filtration of a secondary effluent by means of pre-hydrolyzed coagulants

Jar tests were applied to a secondary effluent in order to determine optimal conditions for coagulation. The metal salts Al2(SO4)3, AlCl3 and FeCl3 were used as coagulants, and their efficiency under various degrees of pre-hydrolysis was examined. The variables under examination were the dose of the coagulant, the degree of pre-hydrolysis, B=[OH−]/[Me+3], and the pH at two different levels (pH=5.5 and pH=7.5). The efficiency of the various coagulants was evaluated for the removal of turbidity, phosphorous, COD and UV absorbance at 254 nm. The results showed that as far as turbidity removals are concerned, pre-hydrolysis of the aluminum and ferric chloride coagulants at values of B equal to 0.5 to 1 gave optimal results. However, for phosphorous removal, the higher the degree of pre-hydrolysis, the lower the removal of phosphorous. No remarkable differences were observed for the removal of organic matter measured as COD, while alum gave the best results for the reduction in UV absorbance at 254 nm. Direct filtration of the effluent showed that the coagulant dose required was an order of magnitude lower than that required for coagulation. 35 cm of filter bed were sufficient for effective filtration. All coagulants performed well, increasing the degree of turbidity removal as compared to the absence of coagulants. The lowest headloss rate was observed when alum was used, while the highest headloss rate, almost three times as much, when the aluminum chloride coagulants were used (with and without pre-hydrolysis). Ferric coagulants, with or without pre-hydrolysis, demonstrated intermediate headloss rates.

Coagulation-filtration of a secondary effluent by means of pre-hydrolyzed coagulants

Jar tests were applied to a secondary effluent in order to determine optimal conditions for coagulation. The metal salts A12(SO4)3), AIC13 and FeCl3 were used as coagulants, and their efficiency under various degrees of pre-hydrolysis was examined. The variables under examination were the dose of the coagulant, the degree of pre-hydrolysis, B=[OH-]/[Me+3], and the pH at two different levels (pH=5.5 and pH=7.5). The efficiency of the various coagulants was evaluated for the removal of turbidity, phosphorous, COD and UV absorbance at 254 nm. The results showed that as far as turbidity removals are concerned, pre-hydrolysis of the aluminum and ferric chloride coagulants at values of B equal to 0.5 to 1 gave optimal results. However, for phosphorous removal, the higher the degree of pre-hydrolysis, the lower the removal of phosphorous. No remarkable differences were observed for the removal of organic matter measured as COD, while alum gave the best results for the reduction in UV absorbance at 254 rim. Direct filtration of the effluent showed that the coagulant dose required was an order of magnitude lower than that required for coagulation. 35 cm of filter bed were sufficient for effective filtration. All coagulants performed well, increasing the degree of turbidity removal as compared to the absence of coagulants. The lowest headloss rate was observed when alum was used, while the highest headloss rate, almost three times as much, when the aluminum chloride coagulants were used (with and without pre-hydrolysis). Ferric coagulants, with or without pre-hydrolysis, demonstrated intermediate headloss rates.

Dyeing wastewater treatment by activated sludge process with a polyurethane fluidized bed biofilm

In case of the porous Polyurethane fluidized bed biofilm-activated sludge process followed by a coagulation process(the FBAS-C process), 75% CODMn was removed by treating with the biological FBAS process in the loading range of 0.16–0.32 kgCODMn/kgVSS · day. The biomass yield and microbial decay coefficients were 0.42 kg MLSS/kgBOD and 0.11 day−1, respectively. The optimum coagulation conditions for the effluent of the FBAS process were at pH 6 and 600mg/L alum dosage. Consequently, 92% of total CODMn removal efficiency was observed in the FBAS-C process. Meanwhile, in case of a coagulation process followed by the porous Polyurethane fluidized bed biofilm-activated sludge process(C-FBAS process), the raw dyeing wastewater was treated at pH 6 in the presence of 1,000 mg/L alum and, continuously, the effluent coagulated wastewater was treated by the FBAS process in the loading range of 0.09 – 0.19 kg CODMn/kgVSS · day. Removal efficiency of CODMn in the biological process, FBAS, was 82%. The biomass yield and microbial decay coefficient in the C-FBAS process were similar to those in the FBAS-C process.The final effluent CODMm was about 65 mg/L in both tested processes, the FBAS-C and C-FBAS. However, the FBAS-C process illustrated better treatability than C-FBAS in terms of the total sludge production, since the former produced about 20% less sludge than the latter.

Studies on Coagulation Process of Soymilk in "Tofu" and "Kori-tofu" Manufacture. Part 6. Relationships of Coagulation Characteristics and Properties of "Kori-tofu" in a Controlled Soymilk Coagulation System.

A controlled coagulation system applying torque measurement was developed in order to investigate the related factors. From the characteristic rise of torque curve, proper amounts of coagulant could be determined automatically. The coagulated soymilk reacted with steadily added calcium chloride by this system, molded to intermediate and then frozen and dried to final product kori tofu. The optimum coagulation conditions were precisely examined at the various reaction conditions of concentration of soymilk, reaction temperature, and concentration of coagulant. The relationships between the torque changes and the properties of tofu and kori-tofu were also investigated.Through a series of coagulation and pressing experiments with this new system, following results were obtained. (1) Determination of the required amount of coagulant as well as the on-off control of stirring of soymilk are performed automatically. (2) The optimum initial concentration of soymilk was around 5% from the view point of water holding capacity of the dried kori-tofu. (3) The higher temperature, between 54 and 70°C, shortened the pressing time, hardened the tofu curd in one hand and decreased the water holding capacity of kori-tofu in the other. The optimum temperature was 60 to 65°C. (4) The optimum concentration of calcium chloride was around 10mM in the present experimental conditions.These findings contributed to the semi-automated processing and the products of fine properties.

Non‐spinneret formation and functional properties of fibrous texturates based on a liquid two‐phase system water‐casein‐field bean protein isolate

AbstractThe effects of pH, calcium chloride concentration and coagulation temperature on sol‐fraction yield during the formation of fibrous texturates from casein, field bean protein isolate (FBPI) and their mixtures have been studied. The optimal coagulation conditions in terms of least sol‐fraction yield were pH 7.0, 0.04 M calcium chloride and 100 °C. These conditions allow one to avoid neutralization and numerous washings of the texturates. Also studied were functional properties of texturates with varied content of the protein components as well as organoleptic properties of fish products in which 20% of fish was replaced with the texturates. Due to the effect of texturates the general acceptability of the products will be improved and the losses during cooking will be reduced.

Chorioretinal adhesion after argon laser photocoagulation.

A technique for examining chorioretinal adhesion in vitro investigated the strength of the adhesion resulting from photocoagulation. The adhesion was reduced only within the first days following photocoagulation, returned to normal by the third day and became enhanced at the fourth day, much earlier than previously supposed. Optimal adhesion and enhanced adhesion resulted only when the coagulation intensities used were sufficient to produce clearly visible lesions that became pigmented subsequently; second, best adhesion was produced with spot-diameters of 200 microns and greater; third, even under optimal coagulation conditions, single barriers were not able to resist extensive forcing, even when the exposures were confluent; fourth, only double barriers, consisting of two rows of exposures, were consistently able to withstand prolonged forcing. The best treatment for retinal tears is a double barrier of large, high-intensity coagulation spots, which affords enhanced adhesion after four days.

Effect of Ionic Environment and Temperature on the Coagulation of Color‐Causing Organic Compounds With Ferric Sulfate

In an earlier paper, a direct relationship between the color of a raw water and the optimum conditions required to remove that color were shown. By the use of extensive mobility determinations correlated with jar tests, the optimum conditions for color removal from soft surface waters were found to be a function of the raw water color. The work reported here should serve to expand the usefulness of these relationships, as it elucidates the effect of ionic environment and temperature on the optimum coagulation conditions.