Optimum Polymer Dose Research Articles

Optimization of a full-scale dewatering operation based on the rheological characteristics of wastewater sludge

Rheology is the science that deals with the flow and deformation of materials, and it has become an important tool in optimizing sludge dewatering. This study presents torque rheology data to illustrate two different methods for polymer optimization. The methods can be used to optimize the polymer dose and mixing intensity, as well as to select the best performing product among a number of candidate polymers. The first method is used for unconditioned sludges, and utilizes the peaks observed after the polymer injection. The second method is used for conditioned sludges and utilizes the entire torque-time rheograms. Both methods were tested at the lab- and full-scale at the Plum Island Water Reclamation Facility (Charleston, SC) using three different polymers. The methods were able to optimize the polymer dose and full-scale mixing, and reduce the polymer consumption by 50% at the treatment plant. This translates into major savings for the utility. Furthermore, the results indicate that the total shear intensity imparted to sludge during full-scale conditioning can be determined using torque rheology, and the jar-tester shear can be matched to the total shear based on the rheological characteristics of sludge. This information is essential to be able to simulate the full-scale mixing using a jar-tester and to precisely determine the optimum polymer dose. The results of this study indicate that well-defined rheological properties of sludge provide a reliable tool for the optimization of conditioning and dewatering operations at wastewater treatment plants.

Dissolved organic nitrogen removal during water treatment by aluminum sulfate and cationic polymer coagulation

Coagulation of three surface waters was conducted with aluminum salt and/or cationic polymer to assess dissolved organic nitrogen (DON) removal. Coagulation with aluminum sulfate removed equal or slightly lower amounts of DON as compared to dissolved organic carbon (DOC). At aluminum sulfate dosages up to 5 mg per mg DOC, the cationic polymer improved DON removal by an additional 15% to 20% over aluminum sulfate alone. At very high aluminum sulfate dosages (>8 mg aluminum sulfate per mg DOC), however, the cationic polymer addition negligibly increased DON removal. Molecular weight fractionation before and after coagulation experiments indicated that cationic polymer addition can increase the removal of all molecular weight fractions of DON with the highest molecular weight fraction (>10,000 Da) being preferentially removed. Results indicated that the DON added as part of the cationic polymer was almost completely removed at optimum aluminum sulfate and polymer doses.

Flocculation Mechanism Induced by Cationic Polymers Investigated by Light Scattering

Three cationic polymers with molecular weights and charge densities of 3.0 x 10(5) g/mol and 10%, 1.1 x 10(5) g/mol and 40%, and 1.2 x 10(5) g/mol and 100% were chosen as flocculants to aggregate silica particles (90 nm), under various conditions, including change in polymer dosage, particle concentration, background electrolyte concentration, and shear rate. The size and structure of flocs produced were determined using the static light scattering technique. On the basis of measurements of polymer adsorption and its effect on the zeta potential and floc properties, it has been found that the polymer charge density plays an important role in determining the flocculation mechanism. Polymers with a 10% charge density facilitate bridging, 40% charged polymers bring about either a combination of charge neutralization and bridging or bridging, depending on the polymer dosage, and polymers with the charge density of 100% induce electrostatic patch flocculation mechanism at the optimum polymer dosage and below but bring about bridging mechanism at the polymer dosage approaching the adsorption plateau value. Bridging aggregation can readily be affected by the particle concentration, and an increase in particle concentration results in the formation of larger but looser aggregates, whereas electrostatic patch aggregation is independent of particle concentration. The addition of a background electrolyte aids in bridging aggregation while it is detrimental to electrostatic patch aggregation. It has also been found that the effect of shear rate on the mass fractal dimension depends on polymer charge density.

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.

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.

Application of Polyelectrolyte in Turbidity Removal from Surface Water

One of the most important treatment processes in surface water treatment plants is coagulation. Surface waters such as rivers and lakes contain suspended particles and turbidity. With the aid of coagulants, and by flocculation process, followed by sedimentation and filtration, these impurities can be removed from raw waters these days, besides conventional chemicals such as Alum and Ferric chloride, polymers are getting common. Polymers can be used as pretreatment and filter aids chemicals, also. There are some advantages in the usage of polymers, such as; higher sedimentation rate, lower price, better finished water quality, lower sludge volume produced, and a better sludge quality with respect to mineral coagulants. Of course some disadvantages are related to the polymers such as the monomers and residues in finished water which may be a health hazard. In this research, four different polymers for turbidity removal from raw waters were investigated. Raw water with turbidities of 200, 500, 700 and 1000 FTU were treated with optimum polymer dosage. The results showed that, polymers with small dosage can be used for water purification. In this regard it was found that Magnafloc LT27 has lowest dosage and better floc strength with respect to others.

The Control of Polymer Addition to Raw Waste Sludge Using Electrical Resistance Tomography – a Preliminary Study

AbstractThis paper presents the application of a monitor technique using electrical resistance tomography (ERT) for controlling the optimum polymer dosage for sludge dewatering. The content starts from introduction for characterization of a raw sewage sludge sample, including particle size distribution and volumetric solids concentration, and the conductivity properties of the sludge and the polymer used. The experimental results demonstrate that the different polymer doses mixed with raw sludge leads to a change of floc size and distribution, and further these changes can be monitored using ERT. The result of ERT measurement can be applied in determining the optimum polymer dosage in the water treatment, as a potential new technique.

Case Study I: Application of the Divalent Cation Bridging Theory to Improve Biofloc Properties and Industrial Activated Sludge System Performance—direct Addition Of Divalent Cations

The objectives of this study were to examine the application of the divalent cation bridging theory (DCBT) to improve settling, dewatering, and effluent quality in pilot-scale reactors and a full-scale system treating an industrial wastewater. This was accomplished by lowering the monovalent-to-divalent (M/D) cation ratio by direct divalent cation addition. Research has shown that the M/D ratio is a potential indicator for settling and dewatering problems at wastewater treatment plants, and M/D ratios above 2 have been associated with poor settling, dewatering, and effluent quality. The M/D ratio of the wastewater in this study ranged from 6 to 20. The cations studied were calcium and magnesium. Results showed that the addition of calcium improved floc properties compared to control reactors with no calcium addition. The reductions in sludge volume index, effluent chemical oxygen demand (COD), and effluent total suspended solids (TSS) were approximately 35, 34, and 55%, respectively, when the M/D ratio was decreased to approximately 2:1. In addition, the cake solids from a belt filter press simulator increased by 72% and the optimum polymer dose required for conditioning was reduced by 70% in the reactor fed the highest calcium concentration when compared to control reactors with no calcium addition. The addition of calcium also decreased the negative effect of high filamentous organism numbers. In general, the addition of magnesium (Mg2+) had similar effects on effluent quality and dewatering properties, although some differences were measured. A full-scale test using calcium addition was performed. Measurements of effluent quality and floc properties were performed before, during, and after the calcium (Ca2+) addition period. The average M/D ratio during these periods was 6.2, 4.6, and 14.0, respectively. The addition of Ca2+ decreased the effluent five-day biochemical oxygen demand, effluent TSS, and effluent COD. The increased Ca2+ concentration also improved dewatering measured by a decrease in specific resistance to filtration and capillary suction time. Overall, the addition of divalent cations to the pilot- and full-scale activated sludge systems improved floc properties and the data fit well with the DCBT.

Settling behaviour of polymer flocculated water-treatment sludge I: analyses of settling curves

Abstract Settling behaviour of polymer conditioned water-treatment sludge was investigated in this study for the purpose of a better understanding of a so-called “CML30 method”, which was developed in previous study to evaluate the optimum polymer dosage in sludge conditioning. The “CML30 method” is on the basis of a 30 min settling test in 100 ml measuring cylinders. In this study, the series of settling tests in 100, 500 and 1000 ml measuring cylinders were, respectively, performed and the settling curves (interfacial height to dose and time) were the main focuses for presentation and analyses in great detail in this paper. According to the experimental data presented in this study, settling behaviour may be controlled by both the growth of large sized floc and progressively decreased viscosity. The “speed-up” phenomenon in small polymer dose range obviously enhances the settlement and plays a critical role for the settling set in a 100 ml measuring cylinder at a special dose and at the settling time interval 5–30 min. It is such special observation that leads to the success of so-called ad hoc “CML30 method”. However, sludge settling behaviour could be controlled by the formation of networked structure which is involved in excess polymer during the large range (say over 10 mg/l for the case tested) of polymer doses. The higher liquid viscosity values derived from excess polymer will increase the drag force for the resistance of the settlement. In addition, wall effects are likely to interplay with the internal networked structure in large dosed region.

Correlations between floc physical properties and optimum polymer dosage in alum sludge conditioning and dewatering

This paper aims to examine the correlations between floc physical properties, such as size, density, structure (in terms of fractal dimension) and optimum dosage in an alum sludge conditioning with organic polymer and also dewatering using an air pressure plate apparatus. Initially, optimum dosage was evaluated by a modified specific resistance to filtration (SRF). Thereafter, floc size, density and structure were examined in greater detail by means of an image analysis system. The results of this investigation reveal that: (1) polymer conditioning of alum sludge can result in a significant increase of floc size with a plateau to be reached in higher dosages; (2) higher floc effective densities are associated with larger doses; and (3) increased fractal dimensions are associated with increased dose, particularly in small dosages, this reflecting the increased compactness of floc structure. However, no direct correlation was found between floc physical properties and optimum dose both in conditioning and dewatering except for the weak correlation in floc size and optimum dosage.

Centrate viscosity for continuous monitoring of polymer feed in dewatering applications

The researchers have previously documented that minimum centrate or filtrate viscosity using batch measurement indicates the optimum polymer dose as determined by capillary suction time (CST) and solids recovery. This paper describes research conducted to test the use of continuous centrate viscosity measurements for polymer dose monitoring in the biosolids dewatering process. Initial results indicate that liquid stream viscosity must be measured on-site since filtrate samples in the overdosing range decrease in viscosity over several hours following sampling. A sensitive viscometer is required for continuous monitoring since the observed viscosity range is from 1 to 3 centipoise (cP). An international search for viscometer vendors showed that two types of viscometers could be used for this purpose: rotational and vibrational. Only data from rotational type viscometers were obtained for this paper. The viscometer was installed to continuously sample centrate from the centrifugation of anaerobic digested biosolids. Full-scale dose response experiments showed that minimum viscosity correlates with maximum cake solids measurements, and thus such viscometers can be used in monitoring and controlling polymer feed during dewatering. However, several modifications are required for such viscometers to withstand the demanding conditions in wastewater treatment plants. Use of viscosity for control of polymer dose requires use of a minimum value, necessitating a complex control algorithm.

Flocculation Mechanism of Suspended Particles Using the Hydrophilic/Hydrophobic Transition of a Thermosensitive Polymerx [Translated]<sup>†</sup>

We examined the flocculation of suspended particles using a thermosensitive polymer which undergoes a reversible hydrophilic/hydrophobic transition when heating or cooling its aqueous solution. As a thermosensitive polymer poly(N-isopropylacrylamide) (polyNIPAM), whose transition temperature is about 32°C, was used. Flocculation experiments were performed by the jar test using kaolin suspension. In the case of operating temperature lower than the transition temperature of poly-NIPAM, there was an optimum polymer dosage, and by dosing excessively kaolin particles were dispersed stably in the same manner as conventional polymeric flocculants. However, floc formation was observed by heating the suspension above the transition temperature under the excess polymer dosage. Furthermore, by cooling the floc-containing suspension down to below the transition temperature again, the flocs were disorganized to the particles. These phenomena show that the floc formation caused by heating to above the transition temperature is due to the hydrophobic interaction of polyNIPAM molecules adsorbed on the particles.† This report was originally printed in Kagaku Kogaku Ronbunshu, 26(5), 734-737 (2000) in Japanese, before being translated into English by KONA Editorial Committee with the permission of the editorial committee of the Soc. Chemical Engineers, Japan.

SOLID–LIQUID SEPARATION OF FLUSHED SWINE MANURE WITH PAM: EFFECT OF WASTEWATER STRENGTH

Organic polymers are useful to increase separation of suspended solids and reduced carbon compounds from liquid swine manure. Along with the solids, there is a capture of the nutrients associated with small particles typical of these wastes. The combined effect increases the amount of materials available for value–added products, reduces the size of process units necessary to treat the liquid, and provides needed alternatives to land application. In this work, we evaluated the effect of solids strength typical of flushing systems on optimum polymer dose requirement and chemical use efficiency. Seven flush samples of varied strength were obtained two weeks apart during a three–month period in a feeder–to–finish operation (22.7 to 100 kg weight) in Bladen County, North Carolina. Treatments consisted of eight rates (0 to 140 mg L–1) of polyacrylamide (PAM) followed by screening. Manure samples were characterized for solids, nutrients, and oxygen–demanding compounds amenable for separation. Their concentration varied greatly: 0.4% to 2.5% total solids (TS), 0.1% to 1.6% total suspended solids (TSS), 5.9 to 31.3 g L–1 chemical oxygen demand (COD), 0.7 to 10.6 g L–1 biochemical oxygen demand (BOD5), 749 to 2442 mg total Kjeldahl (TKN) L–1, and 96 to 585 mg total phosphorus (TP) L–1. About 87% of P and 45% of N were organic forms, and 80% of TSS were volatile (VSS). Separation by screening alone was not effective; efficiencies were <20% TSS and VSS, <10% COD and BOD5, and <15% N and P. Mixing with PAM before screening substantially increased separation; efficiencies using 140 mg L–1 rate were 95% TSS and VSS, 69% COD, 59% BOD5, and 67% carbonaceous BOD5. Inorganic P and N were not reduced by treatment. However, PAM significantly enhanced removal of both organic P and N (92% and 85%, respectively). For every 100 g of TSS removed, there was a 1.32–g reduction of COD, 3.32–g reduction of organic P, and 7.26–g reduction of organic N. The N:P nutrient ratio was improved from 4.79 to 12.11, resulting in a more balanced effluent for crops. It was more economical to treat flushed manure with the higher strength. Changes in optimum PAM rate were small (70 to 110 mg L–1) and, consequently, polymer usage rate based on solids produced decreased significantly (from 5.34 to 0.75 g PAM/100 g dry solids separated) with increased wastewater strength. Therefore, reduction of total water volume to clean the houses can result in significant savings (about 700%) in total polymer cost. Chemical cost to capture 95% of the suspended solids was estimated to be $1.37 to $1.27 per finished pig for liquid waste containing 2% to 2.5% TS, respectively. Our results indicate that PAM technology can be enhanced for better liquid manure handling systems and associated management of nutrients.

Effects of solids concentration on activated sludge deflocculation, conditioning and dewatering

Optimum conditioning of activated sludge in terms of minimum CST was shown to correspond to the complete removal of turbidity, and the increase in turbidity with shear due to e.g. pumping is therefore expected to affect conditioning. The optimum polymer dosage was directly related to the turbidity of activated sludge after two minutes shear, and was considerably lower than the dosage required for charge neutralisation. The turbidity produced by shear increased more than is proportional with solids concentration and was directly related to the apparent viscosity. It is suggested that increasing solids concentration causes increased surface erosion when network structures are broken, and this causes increases in turbidity and required polymer dosage per solids mass. For Aby activated sludge, optimum polymer dosage per solids mass increased by 52% when the solids concentration was increased from 8.2 to 13.7 g SS/l. Modelling of the effect of solids concentration predicts even higher increases in required polymer dosage for higher solids concentrations. This means that reduced thickening prior to pumping and conditioning may be desirable when the hydraulic capacity of the dewatering device is sufficient. Similar trends were observed for an anaerobically digested sludge. For this sludge, reduction of turbidity with FeCl3 reduced the polymer demand.

Optimising polymer use in alum sludge conditioning: an ad hoc test

The paper describes two test procedures for gaining insight into the optimum polymer dose for conditioning an alum sludge prior to dewatering. The first method centres on a development of theory used to estimate the specific resistance to filtration (SRF) using the standard Buchner funnel test. The second is an ad hoc test (termed the ‘CML30 test’) which provides a simple means for treatment works operatives to gauge the optimum dose; it focuses on a particular type of alum sludge and there are no claims concerning its wider utility. Standard filtration theory has been developed to take account of the hydraulic resistance of the filter medium arising from clogging phenomena in overdose conditions. The modified theory yields an adjusted filtration resistance, namely SRF adj , which refers solely to the filtration behaviour of the cake. The CML30 test is based on 30 min settlement in a 100 ml measuring cylinder. With increasing dose, there exists a minimum interfacial height at a dose which coincides with the minimum in the SRF adj trend; this is regarded as an optimum and shows proportionality with the solids concentration. Simplified theory is presented to explain the settling behaviour.

Effectiveness of tannins obtained from valonia as a coagulant aid for dewatering of sludge

For evaluating the tannin (natural polyelectrolyte) and AN913 (synthetic anionic polyelectrolyte) as a coagulant aid for treating raw water to remove suspended matter the tannin or AN913 was added to the synthetic water sample which was stirred and then allowed to settle. After a settled time a sample of the supernatant liquid was removed and its turbidity determined. For use as sludge conditioners the optimum polymer dose was determined. Formed sludge dewatering investigated for optimum pH and optimum dose of coagulant and coagulant aids. The sludge filterability was determined by specific resistance measurements. Tannin and Al 2(SO 4) 3 together gave a significant improvement comparing with Al 2(SO 4) 3 only. As coagulant aids, tannin was more effective than AN913.

Clogging of filter medium by excess polymer during alum sludge filtration

Lab-scale studies of the conditioning of an alum sludge by an anionic polymer showed that the excess polymer can lead to clogging of the filter medium, thereby increasing its resistance. Tests showed that medium resistance (R m) behaved as R m= αe βv in which α and β coefficients and V is the volume of filtrate. Standard dewatering theory for the Specific Resistance to Filtration was modified to take account of this behavior. The modified theory shows that failure to take proper account of the characteristics of the medium resistance can distort the estimate of the cake resistance and can provide a misleading view of the optimum polymer dosage. The study also indicated that a simple test based on the moisture content of the sludge sediment can be used as a means of gauging an optimum polymer dosage.

CHEMICAL TREATMENT OF ANIMAL MANURE FOR SOLID-LIQUID SEPARATION

Chemical treatment of animal manure with metal salts and/or organic polymers can be an effective means ofenhancing solid-liquid separation efficiencies of sedimentation basins and mechanical separators. A detailed laboratorystudy on the use of two metal salts as coagulants and five cationic polyacrylamide polymers as flocculants for treating swineand dairy manure is reported in this article. Metal salts (ferric chloride and aluminum sulfate) were found to be effective incoagulating the suspended particles in the manure and enhancing the settling rate of manure solids. Highly charged cationicpolyacrylamide polymers were effective in flocculating the manure particles and improving the solids removal efficiency byscreening. The optimum polymer dosage was linearly related to the total solids content of manure. The amount of thepolymer required was determined to be about 1.2% and 7.4% of the amount of total solids contained in swine manure anddairy manure, respectively. Use of a metal salt together with a polymer considerably enhanced the phosphorus removal fromthe manure and would potentially reduce the cost of chemicals, as compared with the use of a polymer alone.

Effects of Surface Charge and Shear During Orthokinetic Flocculation on the Adsorption and Sedimentation of Kaolin Suspensions in Polyelectrolyte Solutions

ABSTRACT Suspensions of negatively charged kaolin clay as a model system have been flocculated by adsorbing nonionic, cationic, and anionic polyelectrolytes under shear. Test results show that the maximum rate of settling increases with charge density of the cationic polymer being used. Both cylinder test and jar test using low shear conditions tend to underestimate the polymer dose requirements for the orthokinetic flocculation process. Under prolonged shear conditions, the optimum polymer doses required for maximum turbidity removal or minimum residual turbidity coincide with those required for zero zeta-potential or plateau adsorption of polymer. An explanation of the experimental observations based on the charge density of polymers and the shear conditions is given. It is suggested that both polymer bridging and charge neutralization mechanisms may operate in the ad- sorption/flocculation process. The relative importance between them in determining the optimum polymer doses was analyzed with supplementing Theological measurements of such flocculated systems. It was pointed out why a higher charge density polymer produces a floe structure with higher sensitivity for a shear field.

Effects of polymer dosage on alum sludge dewatering characteristics and physical properties

The proper use of polymers as conditioners is a critical aspect of dewatering processes. In this study, we investigate their physical properties, i.e. size, density and fractal dimension and correlate them with their dewatering characteristics (bound water content, CST and SRF) on alum sludge with cationic polymer conditioning. Using CST measurement to determine the optimum polymer dose may lead to an over-dosing for polymer conditioned sludge. Bound water depletion and interstitial water formation significantly affect the moisture content during polymer conditioning. Moreover, the magnitude of bound water content reflects net change in moisture content, which is decreased by bound water depletion and increased by water formation. Floc size and density measurement suggest poor dewatering performance and increased bound water content are attributable to enlargements in floc size and decreases in floc density. Experimental results indicate that increases in bound water and decreases in floc density are caused by variations of both floc size and aggregation configuration type, not degree of floc compactness.