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PubMed2006

Surface chemical studies on selective separation of pyrite and galena in the presence of bacterial cells and metabolic products of Paenibacillus polymyxa.

Selective separation of pyrite and galena from mixture of the two minerals was achieved through interaction with cells and metabolic products from a culture of Paenibacillus polymyxa. Adsorption of cells and metabolic products onto minerals and electrokinetic studies of minerals after interaction with cells and metabolic products were carried out to examine the resulting surface modification on the mineral surfaces. Flocculation and flotation techniques were successfully applied in the selective separation of minerals after bacterial interaction. The effect of varying conditions for production of extracellular polysaccharides and protein provided an insight into the possible mechanism involved in microbially induced flocculation and flotation of pyrite and galena.

Bacillus↗

PubMed2006

Preliminary evaluation of the electrochemical and chemical coagulation processes in the post-treatment of effluent from an upflow anaerobic sludge blanket (UASB) reactor.

The main objective of this paper was to perform a preliminary comparative study between chemical and electrochemical coagulation processes, both followed by flocculation and sedimentation of an effluent from an upflow anaerobic sludge blanket (UASB) reactor treating simulated wastewater from an unbleached Kraft pulp mill. The electrochemical treatment removed up to 67% (with aluminum electrodes) and 82% (with stainless-steel electrodes) of the remaining chemical oxygen demand (COD) and 84% (stainless steel) and 98% (aluminum) of the color in the wastewater. These efficiencies were achieved with an energy consumption ranging from 14 to 20 Wh l(-1). The coagulation-flocculation treatment with ferric chloride and aluminum sulfate removed up to 87% and 90% of COD and 94% and 98% of color, respectively. The addition of a high molecular weight cationic polymer enhanced both COD and color removal efficiencies. The two post-treatment processes proved to be technically feasible; however the economical feasibility could not be assessed since the experiments were performed with small reactors that could distort scale factors.

Anaerobiosis↗

PubMed2004

Advanced sludge treatment affects extracellular polymeric substances to improve activated sludge dewatering.

The management of wastewater sludge, now often referred to as biosolids, accounts for a major portion of the cost of the wastewater treatment process and represents significant technical challenges. In many wastewater treatment facilities, the bottleneck of the sludge handling system is the dewatering operation. Advanced sludge treatment (AST) processes have been developed in order to improve sludge dewatering and to facilitate handling and ultimate disposal. The authors have extensively reported lab-scale, semi-pilot and pilot investigations on either thermal and thermochemical processes, or chemical oxidation using hydrogen peroxide. To understand the action of these advanced sludge technologies, the essential role played by extracellular polymeric substances (EPS) needs to be understood. EPS form a highly hydrated biofilm matrix, in which the micro-organisms are embedded. Hence they are of considerable importance in the removal of pollutants from wastewater, in bioflocculation, in settling and in dewatering of activated sludge. The present paper reviews the characteristics of EPS and the influence of thermochemical and oxidation mechanisms on degradation and flocculation of EPS. Experimental investigations on waste activated sludge are conducted by the authors to evaluate the various literature findings. From the experiments, it is concluded that AST methods enhance cake dewaterability in two ways: (i) they degrade EPS proteins and polysaccharides reducing the EPS water retention properties; and (ii) they promote flocculation which reduces the amount of fine flocs.

Flocculation↗

PubMed2004

Structure of conditioned sludge flocs.

Free settling tests, small-angle light scattering, microtome-slicing techniques, and confocal laser scanning microscopy were performed to examine how the cationic flocculation or freezing and thawing affected the floc structure. The floc size, internal pore size, mass fractal dimensions determined from free-settling test or small angle light scattering test, aeral porosity, boundary fractal dimension and Sierpinski carpet fractal dimension of pore boundary from 2D slices, and the volume porosity, compactness, and the pores' box-counting fractal dimension from 3D reconstructed image, were estimated and compared. Cationic flocculation would produce large flocs with internal pores of shape resembling a long "tube" with rough surface. Freezing and thawing would produce flocs with internal pores with lower aspect ratio and a smoother boundary.

Bacteria↗

PubMed2005

Membrane bioreactor operation at short solids retention times: performance and biomass characteristics.

This study investigated the performance and biomass characteristics of a membrane bioreactor (MBR) and a completely mixed activated sludge (CMAS) system operated at short solids retention times (SRT) ranging from 0.25 to 5 d and hydraulic retention times of 3 and 6 h. The lab-scale reactors were fed with synthetic wastewater to ensure consistency in feed composition. Results show the MBR was capable of achieving excellent quality effluent regardless of the extremely short SRT. The MBR removal efficiencies ranged from approximately 97.3-98.4% (TCOD) in the MBR, compared to 77.5-93.8% (TCOD) and 94.1-97.0% (SCOD) in the CMAS. Nitrification completely ceased when SRT was < 2.5 d. The MBR biomass was composed of small, weak and uniform-sized flocs with large mass of short filamentous organisms and mainly dispersed microorganisms at SRT of 5 and 0.25 d, respectively. In contrast, the CMAS sludge was composed of large flocs with filamentous organisms as a backbone at SRT > 2.5 d. The CMAS flocs were smaller and weaker at shorter SRT. The MBR sludge contained a much higher fraction of non-flocculating microorganisms. This fraction increased significantly with decreasing SRT. It was found that the concentrations of protein and carbohydrates in the exocellular polymeric substances for both the MBR and the CMAS decreased with increasing F/M ratio or decreasing SRT. The combination of increasing amounts of non-flocculating microorganisms and a reduction of EPS at shorter SRT in both reactors contributed to deteriorating sludge settling properties. A significant presence of dispersed biomass and small flocs in MBR contributed to better reactor performance probably due to less mass transfer resistance.

Biomass↗

PubMed2005

Strength of natural soil flocs.

To obtain the strength of flocs against breakup is crucial for controlling flocculation in water treatment and predicting transport of colloidal particles in aqueous environments. Recently, the author reported a method to obtain floc strength from a simple experiment of floc breakup subjected to a laminar converging flow. In this study, this method was applied to natural soil flocs. The flocs were formed by coagulation with 0.5 M NaCl (pH 5.4-5.5, pH 6.6) solutions, 0.1M CaCl2 (pH 6.4-6.9) solutions, or acidified distilled water with dilute HCl (pH 5.6). Obtained floc strengths were 0.3, 0.7 and 4 nN for Na-, Ca-, and H-coagulated flocs, respectively. Also, floc strength did not change with floc size. These values of floc strengths were 1-3 orders smaller than those of flocs formed with polymer flocculants and/or precipitated ferric or aluminum coagulants.

Aluminum Compounds↗

PubMed2005

Removal of cosmetic ingredients and pharmaceuticals in sewage primary treatment.

Two physico-chemical processes, coagulation-flocculation and flotation, have been assessed for enhancing the removal of some selected pharmaceutical and personal care products (PPCPs) present in sewage. Eight compounds, representative of three main groups of PPCPs according to their physico-chemical properties, have been selected: lipophilic compounds (the synthetic musks Galaxolide and Tonalide), neutral compounds (the tranquillizer Diazepam and the antiepileptic Carbamazepine) and acidic compounds (the anti-inflammatories Ibuprofen, Naproxen and Diclofenac). During the coagulation-flocculation assays, the main parameters considered were the selection of the additives, their doses and the temperature of operation (12 or 25 degrees C). Musks-which are highly lipophilic and Diclofenac-with significant sorption affinity-were removed around 50-70% at both temperatures independently of the dose and type of coagulant used. However, the rest of the compounds, which are more hydrophilic, were affected to a lesser degree (with maximum reductions below 25%). The exceptions to this behavior were Carbamazepine and Ibuprofen, which were not removed under any condition tested. During the flotation assays, the parameters studied were the initial content of fat in wastewaters and temperature. Again, musks were removed to a greater degree (35-60%), followed by Diazepam (40-50%) and Diclofenac (20-45%) and, to a lesser extent, Carbamazepine (20-35%), Ibuprofen (10-25%) and Naproxen (10-30%). The best results were always obtained at 25 degrees C, although in some cases the operation at 12 degrees C gave similar results. The removal of musks and neutral compounds was higher in wastewaters with a high fat content (around 150 mgl(-1)).

Adsorption↗

PubMed2006

Characterization of tributyltin in shipyard waters and removal through laboratory and full-scale treatment.

Characterization and treatment studies were conducted in an effort to evaluate treatment options capable of removing tributyltin (TBT) in shipyard waters from above 1,000,000 ng/L to effluent concentrations below 50 ng/L. Laboratory studies and operation of a full-scale treatment plant were used to examine treatment options for TBT removal and included physicochemical treatment processes of coagulation-clarification, filtration, and granular activated carbon (GAC) adsorption. Significant variability was observed in TBT-containing shipyard waters (generated from different ships) in terms of their particulate solids, conductivity, and TBT and dissolved organic carbon concentrations. Laboratory tests with aluminum sulfate and ferric sulfate showed that on average 90% of TBT in shipyard waters could be removed by coagulation-flocculation-clarification under optimum conditions. No statistically significant difference was found in TBT removal capabilities between the two metal salts when compared at equivalent metal doses and coagulation pH. Much lower removals were observed for the coagulation-flocculation-clarification portion of the full-scale plant while the complete full-scale treatment plant averaged 99.8% TBT removal over a period of 3 years. While relatively high % removals were achieved, the total treatment process did not consistently remove TBT to levels that would meet the regulatory requirements proposed (50 ng/L) at the time the study was conducted. Based on the results from limited efforts to characterize the dissolved and particulate TBT fractions in the full-scale treatment plant effluent, particulate TBT was observed to be the dominant component of the effluent TBT from the full-scale plant and may be associated with polymer carry through.

Adsorption↗

PubMed2006

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 offers 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.

Alkalies↗

PubMed2006

Agglomeration of struvite crystals.

Struvite crystallisation is widely studied as a way to remove phosphorus from wastewater effluents and simultaneously generates a valuable product for the fertiliser industry. However, to date, some crystallisation processes experimented at either pilot/or full scale face problems linked to the formation of fines. This paper presents results on the investigation of struvite agglomerative properties and the possible application of coagulants and/or flocculants to remove fines. Coagulants investigated were hydrolysing metals salts (Al(3+) and Fe(3+)), calcium compounds and a cationic polymer, polydiallyldimethylammoniumchloride (polyDADMAC). The effects of a natural flocculant (alginate) have also been tested. Results demonstrated that destabilisation of struvite particles by chemical addition was feasible and identified polyDADMAC as a good option for the agglomeration of struvite particles. However, optimisation of its dosage under typical pH conditions for struvite formation showed floc formation to be very pH sensitive.

Alginates↗

PubMed2007

High temporal resolution in situ measurement of the effective particle size characteristics of fluvial suspended sediment.

This paper reports the use of a LISST-100 device to monitor the effective particle size characteristics of suspended sediment in situ, and at a quasi-continuous temporal resolution. The study site was located on the River Exe at Thorverton, Devon, UK. This device has not previously been utilized in studies of fluvial suspended sediment at the storm event scale, and existing studies of suspended sediment dynamics have not involved such a high temporal resolution for extended periods. An evaluation of the field performance of the instrument is presented, with respect to innovative data collection and analysis techniques. It was found that trends in the effective particle size distribution (EPSD) and degree of flocculation of suspended sediment at the study site were highly complex, and showed significant short-term variability that has not previously been documented in the fluvial environment. The collection of detailed records of EPSD facilitated interpretation of the dynamic evolution of the size characteristics of suspended sediment, in relation to its likely source and delivery and flocculation mechanisms. The influence of measurement frequency is considered in terms of its implications for future studies of the particle size of fluvial suspended sediment employing in situ data acquisition.

Environmental Monitoring↗

PubMed2001

Anaerobic treatment of fibreboard manufacturing wastewaters in a pilot scale hybrid usbf reactor.

The treatment of fibreboard manufacturing (FBM) wastewaters was carried out in an industrial pilot plant, which consisted of a hybrid upflow sludge bed filter (USBF) anaerobic reactor and a coagulation-flocculation unit as a pre-treatment. COD removal efficiencies of 90-93% were attained in the anaerobic reactor operating at 37degrees C at organic loading rates (OLR) of 6.5-8.5 kg COD/m3 d. Flocculant sludges were used as inoculum, and granulation was observed in the USBF reactor after 120 days of operation. The overall linear upward velocity (result of liquid and gas flow) was the key factor controlling biomass retention and, therefore, a stable operation at high OLR. According to ecotoxicity values (measured by means of bioluminescence assays), the wastewaters were partially detoxified, being EC50 values for the liquid effluent 25 times lower than those corresponding to the influent. Besides, phenolic compounds removal efficiencies of 90% were attained. The hybrid reactor configuration is an interesting alternative to treat these wastewaters since it is less sensitive to biomass clogging or floatation.

Bacteria, Anaerobic↗

PubMed2002

Destabilisation of oil-water emulsions and separation by dissolved air flotation.

The roles of aluminium and ferric sulphates as destabilising agents for oil-water emulsions that have been stabilised by a non-ionic surfactant (Span 20) are investigated in terms of oil removal. The effects of coagulant dose, pH, and the duration and intensity of both slow and fast mixing are considered. Electrokinetic measurements indicate that oil droplets have a negative zeta potential that is weakly dependent on pH. The chosen coagulants are shown to be effective in reducing the zeta potential of the oil droplets, and charge reversal was observed for aluminium sulphate. Oil removals up to 99.3% at pH 8 and 99.94% at pH 7 are seen for aluminium sulphate and ferric sulphate respectively. Rapid mixing times of around 120 s and flocculation times ranging from 15 to 20 min appear to be optimal for the DAF separation. It is concluded that relatively low average mixing speeds for coagulation and flocculation are essential for efficient operation.

Air↗

PubMed2002

NMR spectroscopy for determination of cationic polymer concentrations.

Organic polyelectrolytes are utilized extensively in wastewater treatment, but their fate after use is poorly understood. Analytical methods used for polymer determination in less complex systems appear to fail in application to wastewater systems, contributing to the lack of knowledge. Thus, the development of 1H NMR spectroscopy is reported here for specifically quantitating certain cationic flocculant polymers in environmental samples. Proton observe frequencies of 250 or 400 MHz proton were used. A copolymer of acrylamide and acryloyloxyethyltrimethylammonium chloride was used, representative of cationic flocculant polymers possessing quaternary ammonium groups with terminal methyls that provide a sharp singlet at a chemical shift of approximately 3.06 ppm. A strong linear relationship was demonstrated between polymer concentration and either height or area of this peak. Recoveries were up to 96% at higher concentrations (250 mg/L), and were greater than when using viscosity or charge titration methods for polymer determination. Lesser recoveries at lower concentrations (70% at 5 mg/L) were attributed to adsorptive losses. The detection limit of this method was determined to be <0.5 mg/L. Use of the method was exemplified by analysis of anaerobically digested sludges for residual polymer following a range of dosages, showing the resulting isotherm.

Bacteria, Anaerobic↗

PubMed2002

Elution and reconcentration of polioviruses adsorbed on coal from water samples.

Viruses adsorbed on coal particles in the form of coal bed could efficiently be recovered with elution of 6% beef extract solution in Mcllvaine buffer at pH 7.1. Significant reduction in large volume of eluate could be achieved by employing modified organic flocculation technique to obtain virus concentrate. Modified organic flocculation technique involves addition of 0.02% bovine albumin in eluate. Enteroviruses were adsorbed to flocs which were formed at pH 3.5 and were recovered by centrifugation followed by solublization of flocs in a small volume of 0.15 M disodium hydrogen phosphate solution at pH 9.5. The recovery of viruses ranged from 87.9% to 97.3% with an average of 92.2%.

Adsorption↗

PubMed2001

Flocculation/flotation/ultrafiltration integrated process for the treatment of cork processing wastewaters.

Membrane fouling is the major problem in the treatment by ultrafiltration (UF) of the cork processing wastewaters. This problem leads to drastic reduction on the permeate fluxes and has been associated with wastewaters phenolic/tannic colloidal matter. The present work proposes a flocculation/flotation/ultrafiltration integrated process for the treatment of these wastewaters. A flocculation study was carried out in jar-test equipment with chitosan. The zeta-potential and the particle size were monitored at different pH values and for different chitosan concentrations. The results showed an increase of the zeta-potential when chitosan is added and a significant increase of the effluent particle size with the decrease of the pH. A dissolved-air flotation study was performed with the flocculated wastewater. The parameters varied were the operating pressure and the recycle ratio. It was observed that for higher pressures and at a recycle ratio of 0.19 the polyphenols removal was higher. The UF experiments were carried out in flat-sheet cells of 13.2 cm2 of membrane surface area at transmembrane pressures of 1-3 bar. A commercial membrane (Ropur-TS60) and four cellulose acetate membranes with molecular weight cutoff (MWCO) ranging from 4.5 to 86 kDa were used. The flocculation/flotation pretreatment led to the enhancement of the UF permeate fluxes. For the membrane with higher MWCO, the permeate flux enhancement reached 130%.

Algorithms↗

PubMed2005

Adsorption onto fluidized powdered activated carbon flocs-pACF.

This work presents a new adsorption technique where the adsorbent (powdered activated carbon-PAC) is in the form of suspended flocs formed with water-soluble polymer flocculants. Thus, the adsorption of a typical dye, methylene blue (MB), was studied onto polyacrylamide flocs of PAC (PACF) in a fluidized bed reactor. The technique is based on the fact that the adsorption capacity of PAC does not decrease after flocculation because the adsorbed polymer occupies only a few surface sites, in the form of trains, loops, and tails. Moreover, the adsorption was found to proceed through a rapid mass transfer of MB to the adsorbing PAC flocs, in the same extent as onto PAC. Because of the rapid settling characteristics of the aggregates formed, the two phase separations, loaded PAC and solution, become easier. Thus, the technique offers the advantages of conducting simultaneously both adsorption and solid/liquid separation all in one single stage. Results obtained showed that high MB removal values can be attained in a fluidized bed reactor (>90%) and that PACF presents a much higher adsorption capacity (breakthrough points) than granulated activated carbon (GAC) in the same adsorbing bed. It is believed that this technique highly broadens the potential of the use of powdered activated carbon or other similar ultrafine adsorbents.

Acrylic Resins↗

PubMed2004

Colloid stability of lipid/polyelectrolyte decorated latex.

The colloid stability of supramolecular assemblies composed of the synthetic cationic lipid dioctadecyldimethylammonium bromide (DODAB) on carboxymethyl cellulose (CMC) supported on polystyrene amidine (PSA) microspheres was evaluated via turbidimetry kinetics, dynamic light scattering for particle sizing, zeta-potential analysis, and determination of DODAB adsorption on CMC-covered particles. At 0.1 g L(-1) CMC and 2 x 10(11) PSA particles/mL, CMC did not induce significant particle flocculation, and a vast majority of CMC-covered single particles were present in the dispersion so that this was the condition chosen for determining DODAB concentration (C) effects on particle size and zeta potentials. At 0.35 mM DODAB, charge neutralization, maximal size, and visible precipitation indicated extensive flocculation and minimal colloid stability for the DODAB/CMC/PSA assembly. At 0.1 g L(-1) CMC, isotherms of high affinity for DODAB adsorption on CMC-covered particles presented a plateau at a limiting adsorption of 700 x 10(17) DODAB molecules adsorbed per square meter PSA which was well above bilayer deposition on a smooth particle surface. The polyelectrolyte layer on hydrophobic particles was swelled and fluffy (ca. 11-nm hydrodynamic thickness), and maximal adsorption of DODAB lipid onto this layer produced a compressed composite cationic film with 20 mV of zeta potential and about 10-nm mean thickness. The assembly of cationic lipid/CMC layer/polymeric particle was stable only well above charge neutralization of the polyelectrolyte by the cationic lipid, at relatively large lipid concentrations (at and above 1 mM DODAB) with charge neutralization leading to extensive particle aggregation.

Adsorption↗