Flocculation Aid Research Articles

Flocculation Behaviour of Polymer Brushes of Various Nanostructure

Dextran-graft-polyacrylamide copolymers with different backbone lengths and graft numbers have been tested as flocculation aids in model kaolin suspensions. According to the sedimentation rate and the final sediment volume the graft copolymers proved to be rather similar to the linear acrylamide homopolymer having similar molecular weight. According to the supernatant liquid clarity the copolymers are more effective flocculants than the linear polyacrylamide. The supernatant clarity is inversely related to the length of backbone between the grafts. Apparently, conformation of grafted chain is somewhat more expanded in the cases where the grafts are closely disposed. Due to an expanded macromolecular conformation the functional groups of these copolymers are more capable of capturing solid particles than those of linear acrylamide polymers.

Flocculation-ultrasonic assisted extraction and solid phase clean-up for determination of polycyclic aromatic hydrocarbons in water rich in colloidal particulate with high performance liquid chromatography and ultraviolet-fluorescence detection

In the present work, a simple method of sample preparation for the determination of polycyclic aromatic hydrocarbons (PAHs) in water rich in colloidal particulate was developed. The technique was mainly based on the effect of the flocculation of aluminum sulfate and the adsorption of the flocculation aid florisil. The method contained three steps: flocculation, ultrasonic extraction, and solid-phase extraction cleanup. Major parameters of the procedure were optimized with high performance liquid chromatography (HPLC) separation and ultraviolet-fluorescence detection. When 250 mL model sample containing 16 EPA PAHs was processed, the developed method provided detection limits in the range of 0.02–5 ng/L. Both spiked and non-spiked polluted river water samples rich in suspended particles and organic matters were analyzed. Recoveries and relative standard deviations for the 16 PAHs were in ranges of 86–94% and 3–13% ( n = 5), respectively.

Floc structural characteristics using conventional coagulation for a high doc, low alkalinity surface water source

Removal of natural organic matter (NOM) is well established using metal salt coagulants. In addition, flocculant aids are also commonly used to improve solid removal. The objectives of this paper is to describe the impacts of both NOM and polymer on floc structure. The study offeres a comparison of floc physical characteristics for coagulant precipitate flocs, organic-coagulant flocs and organic-coagulant-polymer flocs for optimum coagulant and polymer doses. A ferric sulphate-based coagulant was used as the primary coagulant and the polymer selected was a high molecular weight (MW) cationic polydiallyldimethylammonium chloride (polyDADMAC). Floc size, breakage, re-growth and settling characteristics were measured. Precipitate flocs were larger than organic flocs and had better settling characteristics when compared to NOM-coagulant flocs. When polymer was added, floc size and compaction was seen to further reduce. An explanation was offered in terms of the mode of flocculation involved. Floc breakage behaviour showed that polymer reduced the rate of floc degradation but did not greatly improve floc re-growth potential after breakage, which was generally poor for all of the suspensions.

The effect of polymeric flocculants on floc strength and filter performance

Polymeric flocculants are widely used throughout the water industry as flocculant aids, they are known to increase floc density and aid settlement in the clarification stage of the water treatment process. In this research, polymeric flocculants were used to improve floc strength prior to filtration on a dissolved air flotation (DAF) plant in an attempt to prevent filter breakthrough. A modified jar test procedure using a PDA (photometric dispersion analyser) optical flocculation monitor was developed in order to evaluate the system floc strength. Filtration trials were carried out on a pilot filter rig situated on a surface water treatment works in Yorkshire. The filter feed originated from the main plant filter channel. Filter performance was assessed by continuous online monitoring of effluent particle counts, turbidity and headloss over the period of the filter run. Results indicated that low doses of polymeric flocculants had a beneficial effect on filtered water quality, as measured by particle counts, turbidity, UV254 absorption and dissolved organic carbon (DOC). Polymeric flocculants also had the effect of extending filter run length. The modified jar test results indicated that the flocculants used improved the floc strength and enhanced reflocculation of the micro flocs present after the flotation process.

Clay and oxide destabilization induced by mixed alum/macromolecular flocculation aids

The review points out typical differences and analogies of the bulk characteristics of aluminum ion complexed polyelectrolytes and of their adsorption behaviors when such systems were supplied to inorganic colloids such as oxides and clays. It reports some particular investigations that were carried out in aqueous media to determine (i) the nature of the interactions existing between clay or oxides, aluminum ions and polyelectrolytes and (ii) the effects on the interfacial characteristics and the colloid stability related to the relative concentrations of these different constituents. The investigations concerned the synthetic alumina/polyacrylic acid systems and the natural kaolinite/humic acid systems, as well as partly the mixed alumina/humic acid systems. Different adsorption features and destabilization kinetics were determined to develop within these systems. One of the main constraints of the investigation arose from the presence of three interacting components which developed amphoteric and amphipatic interactions, the latter being generated by the hydrophobic moieties induced by the aluminum ions/carboxylic acid groups ion-pairing. The investigations concerned the extent and the rate of transfer of hydrogen, aluminum ions and polyelectrolytes from the bulk solution to the solid surface. Electrical surface charge characteristics were expressed in terms of the zeta potential of the colloid/polymer complexes. The colloid stability of the systems was determined as a function of time at short and long terms. The variation as a function of time of the number and weight average masses was correlated with the variation with time of the zeta potential. All these systems were determined to reach the kinetic and thermodynamic equilibrium only slowly. Despite the fact that the supply of mixed coagulants provoked the initial aggregation and the subsequent fragmentation processes for both systems, the mechanisms responsible for the two processes were found to be different as revealed by comparatively investigating the synthetic and the natural systems. The fragmentation originated from the slow segregation process of positively and negatively charged groups for the natural kaolinite/humic acid systems, while the segregation process affected hydrophobic and hydrophilic moieties for the synthetic alumina/polyacrylic acid systems.

Decolorization of reactive dyes using inorganic coagulants and synthetic polymer

A coagulation/flocculation process was employed for the treatment of high concentration reactive dye wastewater. A polymer flocculant synthesized from cyanoguanidine and formaldehyde under acidic conditions was applied with inorganic coagulant (alum or ferric salt) for the dyeing wastewater. The flocculant was tested for synthetic wastewater containing four model reactive dyes (Black 5, Blue 2, Red 2 and Yellow 2) and real wastewater containing reactive dyes from a local dyeing industry. For the synthetic wastewater, the use of inorganic coagulant (1 g/L) alone achieved only 20% of color removal or less. However, with the aid of polymer flocculant, almost 100% of color removal was obtained. The dye removal efficiency increased as polymer dose increased and the efficiency was affected by solution pH and types of the used inorganic coagulant. The use of inorganic coagulant alone appeared little effective in the removal of reactive dyes from the real wastewater. However, alum/polymer and ferric salt/polymer combinations improved color removal up to 60% and 40%, respectively.

Performance evaluation of an inclined belt filter using coagulation/flocculation aids for the removal of suspended solids and phosphorus from microscreen backwash effluent

As environmental regulations become more stringent, environmentally sound waste management and disposal practices are increasingly more important in all types of aquaculture. In many recirculation systems, microscreen filters are used to remove and concentrate the suspended solids from the process water, because they require minimal labor and floor space and can treat large flow rates of water with little head loss. These microscreen filters generate a separate solids waste stream that can be further concentrated to reduce the quantity and improve the quality of discharge water. A Belt Filter System, Hydrotech Model HBF537-1H, from Waste Management Technologies Inc., Baton Rouge, LA, USA was evaluated for rapid thickening of sludge from the backwash water of a microscreen filter. When used in conjunction with coagulation/flocculation aids, significant reduction of suspended solid and phosphorus are possible. Testing of the system was conducted using the backwash effluent of a microscreen filter that treated water discharged from several large-scale recirculating aquaculture production systems growing artic char and trout. The system was tested using only alum as the coagulant aid, using only a commercially available polymer as the flocculation aid and the two coagulation/flocculation aids in combination.Alum alone was moderately efficient in removing solids (82%), but was very efficient in sequestering reactive phosphorus (96%), with effluent concentrations less than 0.07mg/L-P at the highest alum dosage tested, 100mg/L. Several commercially available polymers used alone and at relatively low dosages (15mg/L) were very effective in removing suspended solids, with a removal rate averaging 96% and with an effluent TSS concentration of less than 30mg/L. The polymers were not as efficient as alum in removing reactive phosphorus, with a removal rate of approximately 40%. At the optimum combined dosage of alum (mg/L) and polymer (mg/L), the Inclined Belt Filter System increased the dry matter content of the sludge to approximately 13% solids, and reduced both the suspended solids and reactive phosphorus concentration of the effluent by 95 and 80%, respectively. The combination of coagulation/flocculation aids and the inclined belt filter show excellent potential to greatly reduce the volume of solids generated, and significantly reduce the concentration of suspended solids and phosphorus in discharged effluents. By eliminating the need for settling tanks or ponds, the leaching of nutrients (phosphorus, nitrogen) is minimized and the dewatered sludge is in a form for easy transport, storage, or disposal.

ENHANCED REMOVAL OF RESIDUAL ALUMINUM AND TURBIDITY IN TREATED WATER USING POLYMERS

This study investigated the possibility of reducing the residual aluminum (Al) in the treated water using polymers. Two raw waters (lake and river water) and three kinds of polymers (coagulant, flocculant, and filtration aids) were used for this purpose. This study found that coagulation at the high dose did not necessarily lead to the high concentration of the residual Al in the treated water. The coagulation efficacy was found more important in determining the residual Al than the coagulant dose. The use of a polymer enhanced the removal of turbidity as well as the residual Al. The coagulant aid removed the dissolved Al as well as the particulate Al by helping the coagulation and the solid-liquid separation. The flocculant aid and the filtration aid preferentially removed the particulate Al while helping the solid-liquid separation. The filtration aid reduced the residual Al substantially more effectively than the flocculant aid. The polyamine-based coagulant aid (FL) showed the better performance in reducing the residual Al and turbidity than DADMAC (WT). The cationic flocculant aid with weak charge density and the medium molecular weight (SC-020) showed the best performance in reducing the residual Al.

Application of guar gum as a flocculant aid in food processing and potable water treatment

Guar gum is a widely used ingredient in food processing industry. This work highlights the use of guar gum as a flocculant aid in potable water treatment. Current practice of using synthetic flocculants such as polyacryl-amide has raised controversies of acrylamide residues in water and thereby increasing health risk of the population. The flocculating effect of guar gum on the settling characteristics of flocs in a bench-scale potable water clarification process is presented in this work. Data from two experimental runs, namely, run A (guar gum and primary coagulant) and run B (primary coagulant only), were used to plot settling velocity distribution curves (SVDC). Observation of these curves revealed that guar gum increased the proportion of destabilised colloidal impurities settling above a stated minimum velocity. It was found that guar gum may be used along with alum to reduce raw water turbidity from 26.5 to 1.0. It may be concluded that guar gum can be used as a safer alternative to polyacrylamide in water treatment for drinking or food processing purposes.

Screening and evaluation of polymers as flocculation aids for the treatment of aquacultural effluents

As environmental regulations become more stringent, environmentally sound waste management and disposal are becoming increasingly more important in all aquaculture operations. One of the primary water quality parameters of concern is the suspended solids concentration in the discharged effluent. For example, EPA initially considered the establishment of numerical limitations for only one single pollutant: total suspended solids (TSS). For recirculation systems, the proposed TSS limitations would have applied to solids polishing or secondary solids removal technology. The new rules and regulations from EPA (August 23, 2004) require only qualitative TSS limits, in the form of solids control best management practices (BMP), allowing individual regional and site specific conditions to be addressed by existing state or regional programs through NPDES permits. In recirculation systems, microscreen filters are commonly used to remove the suspended solids from the process water. Further concentration of suspended solids from the backwash water of the microscreen filter could significantly reduce quantity of discharge water. And in some cases, the backwash water from microscreen filters needs to be further concentrated to minimize storage volume during over wintering for land disposal or other final disposal options. In addition, this may be required to meet local, state, and regional discharge water quality. The objective of this research was an initial screening of several commercially available polymers routinely used as coagulation–flocculation aids in the drinking and wastewater treatment industry and determination of their effectiveness for the treatment of aquaculture wastewater. Based on the results of the initial screening, a further evaluation of six polymers was conducted to estimate the optimum polymer dosage for flocculation of aquaculture microscreen effluent and overall solids removal efficiency. Results of these evaluations show TSS removal was close to 99% via settling, with final TSS values ranging from as low as 10–17mg/L. Although not intended to be used for reactive phosphorus (RP) removal, RP was reduced by 92–95% by removing most of the TSS in the wastewater to approximately 1mg/L–P. Dosage requirements were fairly uniform, requiring between 15 and 20mg/L of polymer. Using these dosages, estimated costs range from $4.38 to $13.08 per metric tonne of feed.

Cadmium adsorption on hydrous aluminium (III) oxide: effect of adsorbed polyelectrolyte

Freshly precipitated hydrous oxides of Al (flocs) are important sorbents of heavy metal ions and are used in water treatment processes. The addition of chelating agents or polyelectrolytes can increase the efficiency of heavy metal removal by flocs. The polymer polyethylenimine is commonly used as a flocculant aid in water treatment and has been modified with phthalic acid. Adsorption studies have shown that the addition of millimolar concentrations of polyelectrolyte increases the removal of Cd ions from a 29.7 μM aqueous solution by aluminium flocs from ca. 40% to up to 75%. Experiments in which the pH was varied demonstrated that the observed enhancement of Cd adsorption is caused by a shift of the pH edge to lower pH values in the presence of polyelectrolyte. Maximum polyelectrolyte adsorption occurs between pH 6 and pH 7, corresponding to the point of enhanced Cd adsorption in the presence of polyelectrolyte. The enhancement of Cd adsorption observed below pH 7 is therefore likely to be due to the formation of a ternary surface complex. At pH values above pH 8 the polyelectrolyte forms a stable complex with Cd and Al ions in solution causing floc dissolution and decreased Cd adsorption.

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.

Application of Chemical Coagulation Aids for the Removal of Suspended Solids (TSS) and Phosphorus from the Microscreen Effluent Discharge of an Intensive Recirculating Aquaculture System

An evaluation of two commonly used coagulation–flocculation aids (alum and ferric chloride) was conducted to determine optimum conditions for treating the backwash effluent from microscreen filters in an intensive recirculating aquaculture system. Tests were carried out to evaluate the dosages and conditions (mixing and flocculation stirring speeds, durations, and settling times) required to achieve optimum waste capture. The orthophosphate removal efficiency for alum and ferric chloride were greater than 90% at a dosage of 60 mg/L. Optimum turbidity removal was achieved with a 60-mg/L dosage for both alum and ferric chloride. Both alum and ferric chloride demonstrated excellent removal of suspended solids from initial total suspended solid values of approximately 320 mg/L to approximately 10 mg/L at a dosage of 60 mg/L. Flocculation and mixing speed and duration played only a minor role in the removal efficiencies for both orthophosphates and suspended solids. Both coagulation–flocculation aids also exhibited excellent settling characteristics, with the majority of the floc quickly settling out in the first 5 min.

Performance of basaltic dust issued from an asphaltic plant as a flocculant additive for wastewater treatment

The feasibility of using basaltic dust as a flocculant additive or coagulant aid for wastewater treatment was assessed in this research. The experimental study was divided into two stages: 1) physicochemical characterisation of the basaltic dust by applying standardised techniques, and 2) evaluation of this material as flocculant additive for the coagulation-flocculation of wastewater treated for reuse. Coagulation-flocculation experiments were carried out in the laboratory with a mixture of industrial and municipal wastewater samples collected from two points of the final discharge of the Mexico City sewerage system. Aluminium sulphate and lime were used as coagulants and the basaltic dust as flocculant additive, by applying the jar-test technique. The results of the corrosivity, reactivity, explosiveness, toxicity, inflammability and biological risk tests indicated that this material is classified as a non-hazardous waste (according to the Mexican legislation, NOM-052-ECOL-1993). The density, oxide content and particle size values of basaltic dust were similar to those reported for the flocculant additive denominated activated silica. The jar test results showed a positive effect of basaltic dust over the effluent and sludge qualities, to the extent that coagulant doses can be reduced 30% (from 150 mg/L to 110 mg/L of Al2(SO4)3).

Particle size distribution in slaughterhouse wastewater before and after coagulation‐flocculation

AbstractSolid particles were removed from a slaughterhouse liquid effluent by physicochemical treatment (coagulation‐flocculation process) using aluminium sulfate as the coagulant, and activated silica, powdered activated carbon, precipitated calcium carbonate, polyacrylic acid, or anionic polyacrylamide as coagulant aids to improve the settling time.Once the optimal conditions of the coagulation‐flocculation process had been established (speed and time of stirring during flocculation, pH, coagulant and coagulant aid doses), the particle number and size distribution were measured before and after the addition of aluminium sulfate as the coagulant and the different coagulant aids, to determine the efficiency of the coagulation‐flocculation process. When aluminium sulfate was used without the coagulant aids, overall efficiency of particle removal was 87%. Use of powdered activated carbon, polyacrylic acid, or anionic polyacrylamide improved removal to values between 92 and 98%.

Evaluation of chemical coagulation–flocculation aids for the removal of suspended solids and phosphorus from intensive recirculating aquaculture effluent discharge

An evaluation of two commonly used coagulation–flocculation aids (alum and ferric chloride) was conducted for the supernatant overflow from settling cones used to treat the effluent from microscreen filters in an intensive recirculating aquaculture system. In addition to determining the effectiveness of these aids in removing both suspended solids and phosphorus, a systematic testing of the variables normally encountered in the coagulation–flocculation process was performed. Tests were carried out to evaluate the dosages and conditions (mixing and flocculation stirring speeds, durations, and settling times) required to achieve optimum waste capture. The orthophosphate removal efficiency for alum and ferric chloride were 89 and 93%, respectively, at a dosage of 90 mg/l. Optimum turbidity removal was achieved with a 60 mg/l dosage for both alum and ferric chloride. Both alum and ferric chloride demonstrated excellent removal of suspended solids from initial TSS values of approximately 100–10 mg/l at a dosage of 90 mg/l. Flocculation and mixing speed played only a minor role in the removal efficiencies for both orthophosphates and suspended solids. Both coagulation–flocculation aids also exhibited excellent settling characteristics, with the majority of the floc quickly settling out in the first 5 min.

Arsenic removal from drinking water by flocculation and microfiltration

Arsenic removal from drinking water is a major problem in many parts of the world. We have investigated arsenic removal by flocculation and microfiltration. Ferric chloride and ferric sulphate have been used as flocculants. The use of small amounts of cationic polymeric flocculants, as flocculation aids in the presence of ferric ions, has also been investigated. The results obtained here show that flocculation prior to microfiltration leads to significant arsenic removal in the permeate. Further, the addition of small amounts of cationic polymeric flocculants lead to significantly improved permeate fluxes during microfiltration. The residual turbidity, after flocculation and microfiltration, may be used as a guide to the level of arsenic removal. Since energy requirements for microfiltration are low and fluxes high, compared to other membrane processes such as reverse osmosis and nanofiltration, flocculation and microfiltration may be a cost effective method for arsenic removal from drinking water.

New diesel waste purification technology from Kemira Metalkat

Following pretreatment and enzymatic hydrolysis of lignocellulosic biomass within a biorefinery, the residual solids are often present in high concentration and have a wide particle size distribution. These solids, which can be difficult to remove from solution, can have a detrimental impact on downstream fermentations and separations. Here we show that polyelectrolyte flocculating agents can be used to enhance the solid–liquid clarification of a lignocellulosic biomass (Ponderosa Pine) hydrolyzate. Due to the negative zeta potential of Ponderosa Pine solids following pretreatment and enzymatic hydrolysis, flocculation with cationic polymers provided the largest flocs, which quickly settled out of solution. Adding Kemira flocculant C1592 up to 1000 mg/L created larger flocs; however, a higher dosage (5000 mg/L) resulted in solids re-dispersing into solution. It was estimated that a greater than 12-fold improvement in throughput with a scroll decanting centrifuge could be obtained when using flocculant, or that an approximately 40-fold higher flux could be obtained for a vacuum filtration operation. The addition of 100 mg/L of C1592 showed optimal suspended solids removal of the clarified solution (<0.1% w/w suspended solids) and the highest sugar recovery (up to 83% without washing). In all cases, the percentage of suspended solids remaining following either centrifugation or filtration was at least an order of magnitude lower with the aid of flocculant. The presence of residual polymer in solution did not affect the downstream ethanol productivity of a Saccharomyces cerevisiae fermentation.

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.

Effectiveness of coagulants and coagulant aids for the removal of filter-clogging Synedra

Research Article| May 01 2001 Effectiveness of coagulants and coagulant aids for the removal of filter-clogging Synedra Hang-Bae Jun; Hang-Bae Jun 1Department of Environmental Engineering, Chungbuk National University, CheongJu, Korea Search for other works by this author on: This Site PubMed Google Scholar Young-Ju Lee; Young-Ju Lee 1Department of Environmental Engineering, Chungbuk National University, CheongJu, Korea Search for other works by this author on: This Site PubMed Google Scholar Byung-Du Lee; Byung-Du Lee 2Department of Water Supply Operation & Maintenance, KOWACO, Taejon, Korea Search for other works by this author on: This Site PubMed Google Scholar Detlef R. U. Knappe Detlef R. U. Knappe 3Department of Civil Engineering, North Carolina State University, Raleigh, NC 27695-7908, USA Phone: 919-515-8791 Fax: 919-515-7908; E-mail: knappe@eos.ncsu.edu Search for other works by this author on: This Site PubMed Google Scholar Journal of Water Supply: Research and Technology-Aqua (2001) 50 (3): 135–148. https://doi.org/10.2166/aqua.2001.0013 Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Share Icon Share Twitter LinkedIn Tools Icon Tools Cite Icon Cite Permissions Search Site Search nav search search input Search input auto suggest search filter All ContentAll JournalsThis Journal Search Advanced Search Citation Hang-Bae Jun, Young-Ju Lee, Byung-Du Lee, Detlef R. U. Knappe; Effectiveness of coagulants and coagulant aids for the removal of filter-clogging Synedra. Journal of Water Supply: Research and Technology-Aqua 1 May 2001; 50 (3): 135–148. doi: https://doi.org/10.2166/aqua.2001.0013 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex The occurrence of Synedra spp. in the source water of the CheongJu water treatment plant (South Korea) decreased filter run times of rapid sand filters to below 5 hours. During the filter-clogging episode, full-scale Synedra removal by coagulation with polyaluminium hydrogen chloride silicate (PAHCS), flocculation and sedimentation ranged from 20 to 70%. To reduce filter clogging, strategies needed to be developed to improve the coagulation of Synedra. Jar test results showed that alum was more effective for Synedra removal than polyaluminium chloride (PACl), PAHCS and ferric chloride. At the optimum alum dose, Synedra removal in jar tests reached 88%. The addition of flocculant aids (Na- and Mg-alginate; nonionic and anionic polymers) in conjunction with alum did not improve Synedra removal. In contrast, the addition of cationic polymer in conjunction with alum improved Synedra removal to 99%. Analysis of floc with scanning electron microscopy (SEM) and light microscopy showed that the cationic polymer addition led to the formation of larger, stronger, and denser floc. More effective charge neutralization and the formation of interparticle bridges as a result of the cationic polymer addition can explain the improved incorporation of Synedra cells into settleable floc. coagulation, diatoms, filter clogging, polymers, sedimentation This content is only available as a PDF. © IWA Publishing 2001 You do not currently have access to this content.