Hydroxide Flocs Research Articles

Color and suspended solid removal with a novel coagulation technology

A novel coagulation technology using atomized molten slag with ferrous sulfate has been developed to treat a turbid and colored water or wastewater. The atomized molten slag is produced by atomizing the molten slag from the steel-making process. The atomized molten slag has magnetic iron oxide in its constituent molecules so that it is magnetized. In this novel coagulation technology, the atomized molten slag acts as nuclei for coagulation process and weighting agent for the resultant floc. In this study, this new coagulation technology was compared with metal hydroxide flocs such as FeCl3 and PAC in treating textile wastewater. A batch settling test was conducted to investigate the settling characteristic of sludge formed with the atomized molten slag. The settling velocity of sludge formed with the atomized molten slag is almost ten times greater than that of sludge formed with FeCl3 or PAC. The coagulation using the atomized molten slag showed a higher removal rate of color, suspended solid, TOC, COD, TKN and T-P. The atomized molten slag is capable of adsorbing organic substance, ammonia and phosphate. This characteristic leads to higher removal rate than FeCl3 or PAC. The gel permeation chromatography of the wastewater treated using the atomized molten slag illustrated that this novel coagulation technology is more efficient in removing the particles with low molecular weight. The removal rates of color, suspended solid, COD, TOC, ammonia and phosphorous increase with increasing amount of atomized molten slag addition. Even though the atomized molten slag was overdosed, restabilization of particles was not encountered.

A study of coagulation mechanisms of polyferric sulfate reacting with humic acid using a fluorescence-quenching method

A fluorescence-quenching method is developed to assess the effect of pH on the coagulation mechanism of humic acids (HA) reacting with metal ions. A polyferric sulfate (PFS) synthesized in our laboratory is adopted as the coagulant to simplify the hydrolysis process and increase the experimental precision. The following results are discovered. When the concentration of PFS increases from 2 to 10 mg/L, the effective pH range of HA removal changes from 4.0–5.0 to 4.0–7.5. At increased coagulation pH, the ferric ions may still react with HA but unable to neutralize the surface charge completely. The residual concentrations of HA measured by fluorescence spectrophotometer are lower than those by TOC, as a consequence of the fluorescence-quenching effect. This demonstrates that the coagulation of HA by PFS at low pH is mainly due to charge-neutralization. The adsorption of the HA on the pre-formed iron hydroxide flocs is accompanied by the dissociation of Fe ions from the floc structure until the equilibrium has been reached, which is evidenced by the presence of the Fe-HA complexes in the solution during adsorption experiment. This is quite different from the characteristics of flocs formed by PFS associated with HA in the coagulation. Within the pH range investigated, the complex-formation and the hydrolysis are the two competitive reactions happened between the hydroxide ions in solution and the functional groups of HA. Therefore, the removal of HA is not caused by adsorbing onto the iron hydroxide resulted from PFS hydrolysis, but through the complex-formation between the PFS and the HA.

Enhanced pre-coat engineering (EPCE) for micro- and ultrafiltration: the solution for fouling?

The feasibility of ultra- and microfiltration depends strongly on the achieved net flux. Direct treatment of surface water frequently results in low net fluxes and high cleaning frequencies. Experiments have been conducted at constant flux on surface water with an ultrafiltration pilot plant with direct filtration, in-line coagulation and pre-coating (EPCE) with ferric hydroxide flocs. The aim was to control and reduce the rate of fouling. With the use of a pre-coat at the beginning of the filtration cycle a stable ultrafiltration process was obtained. This is contrary to the use of in-line coagulation and direct filtration which resulted, due to a very high fouling potential of the feed water, in high fouling rates at low fluxes. The result of this exploratory research is an important step towards a higher feasibility of micro- and ultrafiltration.

Flocs in Shear and Strain Flows

Preflocculated ferric hydroxide flocs were subjected to either a simple shear flow or a two-dimensional straining flow, and their motion was optically observed. Digital image analysis was applied to extract information on orientation and deformation from the digitized frames. It was found that the simple shear flow led to a rotation of the flocs whose motion can be understood from the behavior of a solid ellipsoid. In the extensional flow, no continuous rotation occurred and flocs were broken apart along the axis of straining. The rupture forces estimated from an ellipsoid model were found to be in the range of 0.1 N/m2.

Break-up of flocs in contraction and swirling flows

The break-up of ferric hydroxide flocs was observed by optical methods in a contraction and a swirling flow. The corresponding flow fields were produced by pumping water through two pipes of different diameter, which were either kept stationary or rotated around the axis of symmetry. Digital image analysis was applied to obtain data on the orientation and deformation of the flocs. It was found that flocs were broken apart by both flow fields before they passed the orifice. Based on a simplified model the rupture forces were estimated to be on the order of 0.1 N m −2.

Characterization of Aluminum Flocs in Distribution Drinking Water Using Differential Interference Contrast (DIC), Transmission and Scanning Electron Microscopy (TEM & SEM) and Energy Dispersive X-Ray Analysis (EDXA)

Conventional water treatment plants that use alum (aluminum sulfate) as a coagulant have been dealing with the issue of residual alum carry over from the treatment plant into the distribution system. The basic product formed whe alum is added to water is aluminum hydroxide floc. This floc grows in size and density as it captures suspended particulates and then is settled out. Smaller floc aggregates that pass through the settling process are in the most part removed by sand filtration. However due to the amphoteric characteristics and solubility properties of aluminum alon with it’s many different compounds, carry over of aluminum compounds through the filter is a phenomena that is a great concern to the water industry. These residual aluminum compounds produce small hydroxide floes that coat the inner surfaces of distribution pipes causing head loss or increased energy requirements for water pumping.In addition phosphate compounds (poly and ortho blends) have recently been added to the distribution system to reduce the leaching and corrosion of lead and copper from pipes.

Size distribution of aluminum hydroxide flocs in dilute aluminum(III) Solutions

Electronic particle counting and sizing technique was used in this study to characterize the particle size distribution of Al(OH)3(s) precipitates that are produced from AlCl3, Al2(SO4)3 and two preformed polymeric aluminum salts (polyaluminum chloride and polyaluminum sulfate) solutions. Results indicate that polyaluminum chloride solutions tend to form a large number of small particles with a relative dense structure. On the other hand, alum and polyaluminum sulfate form large particles with a loose structure and which dominate the particle volume distribution. The repulsive electrostatic barrier between primary particles is suggested to be the main factor affecting the particle growth for different Al salt solutions.

Adsorption of Natural Organic Matter on Preformed Aluminum Hydroxide Flocs

Natural organic matter (NOM) was extracted from a raw water source (Forge Pond, Granby, Mass.) and fractionated into eight groups: fulvic acid, humic acid, hydrophilic acid, weak hydrophobic acids, hydrophilic neutrals, hydrophobic neutrals, hydrophilic bases, and hydrophobic bases. The extent of adsorption of these fractions on preformed aluminum hydroxide flocs was determined. Also, the adsorption affinities of various fractions were correlated to selected NOM properties, i.e., organic charge, molecular weight, and specific ultraviolet absorbance. The nature of the reactions leading to adsorption was discussed, along with the induced dissolution of aluminum from the floc surface and its resulting association with NOM in particulate or colloidal forms.

Determination of the capture radii of magnetite bearing hydroxide flocs in magnetic filtration

Magnetic filtration may be applied in water technology for the separation of flocs which are formed in a flocculation tank together with magnetite as an additive. The capture radius is an important mathematical quantity to calculate the performance of such filters in advance. Thus, the capture radii of magnetite bearing copper hydroxide flocs were measured with a direct visual evaluation of the floc trajectories in the neighborhood of a single magnetized wire. For this purpose, an experimental setup was assembled, which allowed the observation and the measurement of the trajectories. With the image processing system used, it was possible to observe flocs larger than 30 /spl mu/m and the flow velocity was limited to a maximum value of 20 mm/s. Capture radii were calculated by the established single-wire theory under the assumption of potential and creeping flow conditions. It has been proved that further information on the solids content of the flocs, which strongly influences the floc susceptibility, was necessary to obtain an agreement between the experimental data and the theoretical predictions. By introducing a flee size dependent solids content into the single-wire theory, measured by means of sedimentation analysis, an accurate description of the observed capture radii was possible.

Sampling riverine sediments impacted by acid mine drainage: problems and solutions

Sampling acid mine drainage (AMD) or natural acid rock drainage (ARD)-impacted sediments is complex, requiring appropriate field sampling techniques to ensure representative samples that are both repeatable and reproducible. The important factors affecting sampling of riverine sediments are examined. These include sample site location, field observations, representative sampling, sample collection techniques, and sample preservation. A recommended sampling and processing protocol is presented for AMD- and ARD-impacted riverine sediments, which includes sediment sampling, Fe hydroxide floc sampling, chemical analysis, interstitial (pore) water collection, sediment elutriates, sediment fractionation, and physical analysis. The importance of bioassay testing is discussed, as is quality assurance and assessment approaches to define sediment quality criteria.

Predicting As removal during metal hydroxide precipitation

Data from two utility surveys led to the development of a simple model for predicting arsenate removal at full‐scale alum coagulation, ferric coagulation, and iron–manganese removal plants.A simplified isotherm is described that can predict the extent of arsenate removal at drinking water utilities practicing coagulation or iron–manganese (Fe–Mn) removal. If all possible sources of particulate iron and aluminum hydroxide present in the system are accounted for, the model predicts arsenic (As) removal to within ±13 percent (90 percent confidence) for Fe coagulation at pH 6.5–8 and alum coagulation at pH < 7.6. Analysis of full‐scale treatment data suggests that colloidal aluminum (Al) flocs with sorbed arsenate [As(V)] may pass through filters, thereby decreasing overall As removal efficiency. Thus, Al solubility and particle stability must be minimized to improve As removal. If stability and solubility of aluminum hydroxide flocs are not a problem, alum and Fe coagulants have nearly equal capacity for sorbing As(V). Survey results also demonstrate the importance of particulate As.

Monitoring effects of shearing on floc structure using small-angle light scattering

In this work, small-angle light scattering was used to investigate the formation of iron hydroxide flocs from the hydrolysation of FeCl 3 solution. The freshly formed iron hydroxide flocs had a fractal dimension of 2.25 ± 0.05, and as the hydrolysation proceeded the flocs frew and restructured to a more compact form with a fractal dimension of 2.52 ± 0.05. The effect of shearing on the structure of the flocs was also studied. At low shearing rates, increasing the shear induced only the restructuring of the flocs, but at a high shearing rate the shear induced both the breakup and restructuring of the flocs.

Municipal wastewater treatment by lime/ferrous sulfate and dissolved air flotation

In this work a chemical treatment system for municipal wastewater using copper cementation effluent and lime as coagulants in combination with dissolved air flotation, was investigated. Copper cementation effluent (CCE) containing about 45% dissolved solids (density=1.31) is a liquid waste from a leaching process, which is disposed in large ponds by several copper mines in the North of Chile. CCE contains a combination of ferrous iron, sulfate, chlorine, magnesium, sodium, residual copper and other ions. For its use as a coagulant, CCE was treated using a low cost process. Ferric hydroxide flocs precipitated after CCE addition were efficiently removed by dissolved air flotation producing a low density froth. High suspended solid removal efficiency, process flexibility, short overall residence time in addition to low cost of chemicals used and precipitation of varied proportions of contaminants, including bacteria from wastewater, are the main features of this chemical treatment system.

Removal of Arsenic from Aqueous Solution by Adsorbing Colloid Flotation

Adsorbing colloid flotation (ACF) with ferric hydroxide as the coprecipitant, anionic surfactant sodium dodecyl sulfate (SDS) as the collector, and nitrogen microbubbles has been shown to be effective in removing arsenic from low concentration of arsenic aqueous solution ([approximately]10 mg/dm[sup 3]). Experiments were conducted to assess the effects of pH, dosages of SDS and Fe(III), gas flow rate, foreign anions including NO[sub 3][sup [minus]], SO[sub 4][sup 2[minus]], and PO[sub 4][sup 3[minus]], and Al(III) addition on the efficiency of the arsenic removal by ACF. When pH is at the range of 4--5, 99.5% arsenic removal efficiency can be achieved. The optimal operating conditions are 35 ppm SDS, 80 ppm Fe(III), 40 cm[sup 3]/min gas flow rate, 500 rpm rotary speed of stirrer, and 5 min ferric hydroxide floc formation time. The analysis results indicate that foreign anions SO[sub 4][sup 2[minus]] and PO[sub 4][sup 3[minus]] have an inhibiting effect on the removal of arsenic, while AI(III) additions can compensate for the effect. An actual mine wastewater sample containing 10.4 ppm arsenic(V), 0.76 ppm chromium(VI), and 0.55 ppm lead was tested by adsorbing colloid flotation at the optimal operation conditions. The residual arsenic, chromium, and lead are 0.07, 0.06, and 0.04 ppm, respectively.more » The interaction mechanisms between Fe(OH)[sub 3]-bearing arsenic floc and SDS were analyzed and interpreted by means of [zeta]-potential, infrared spectra analysis, and molecular orbital theory. The adsorption of SDS can occur physically and chemically on Fe(OH)[sub 3] at the pH range of 4--5.« less

On the Types of Bond Developing between the Aluminium and Iron (III) Hydroxides and Organic Substances

During the coagulation-flocculation processes involved in the treatment of surface waters, dissolved organics are also incorporated into the aluminium and iron (III) hydroxide flocs. A part of the dissolved organics can thus be removed by simple solid-liquid phase separation techniques, like sedimentation, flotation, sand filtration. According to laboratory evidence, durable bonds between the coagulant, or the metal hydroxides thereof, develop only over the extremely short (a few seconds) period which elapses from the formation of the metal hydroxides to the intense aggregation of the metal hydroxide sols. The bonds between these latter and the organic substances are mainly of the hydrogen bridge type, but other secondary chemical bonds and adsorption are also involved. Owing to the chemical structure and relatively low concentration levels of the organic substances, direct valence chemical bonds between the coagulants or the metal hydroxides thereof and the organic substances develop to a slight extent only.

Preformed Ferric Hydroxide Flocs as Adsorbents of Humic Substances

The purpose of this study is to show that previously built flocs obtained by the coagulation-flocculation of kaolinite suspension with ferric chloride are a potential adsorbent of humic substances. Flocs are prepared from kaolinite (< 50 µm) and FeCl3 according to the jar-test technique:after 3 minutes of rapid mixing at pH = 5.4 ± 0.1, 30 minutes of slow mixing, humic acids are added for a contact time of 6 hours; the effects of calcium, sodium salts (chloride, sulphate) on the adsorptive capacity of preformed flocs are also studied. The results indicate that the preformed flocs are good adsorbent materials. Langmuir equation is used to determine adsorption capacities.

Kinetics of aggregate formation in rapid mix

The growth of porous aggregates during initial mixing is investigated in a series of numerical simulations. Hydrodynamic radii of aggregates composed of i primary particles are used to calculate collision rate constants as a function of fractal dimension, D, and aggregation number, i. D is assumed to be independent of aggregate size. The rate of floc volume formation increases by several orders of magnitude as the fractal dimension decreases from 3 to 2. Neglecting aggregate porosity is estimated to introduce an error of < 10% in calculating the collision efficiency factor from particle number measurements and a coalescing-sphere model for particle aggregation. For conditions approximating those in which ferric sulfate is added to a rapid mix basin, simulations with D = 2.5 produce a volume fraction of flocs larger than 1 μm that approximates the volume fraction greater than 1 μm measured using an electronic particle counter. A fractal dimension of 2.35 produces an aggregate volume distribution that most nearly approximates the volume distribution observed in jar tests with ferric sulfate. These values of D are within the range of values reported in the literature for larger ferric hydroxide flocs. Mixing conditions in most full scale installations are likely to favor the formation of aggregates of precipitated coagulant particles that are sufficiently large for breakup and aggregate restructuring to control the size distribution of materials leaving the rapid mix basin.

The Treatment of Wastewater from Coke Oven and Chemical Recovery Plants by Means of Bioferric Process – An Innovative Technique

The treatment of wastewater from coal-derived liquor is considered to be extremely difficult because of large quantities and fluctuating concentrations of toxic chemicals. This paper describes the performance of an innovative technique, - the Bioferric process as it compared to conventional activated sludge during pilot, semiscale and full-scale tests of wastewater treatment coke oven and chemical recovery plants. Bioferric sludge uses the affinity of ferric hydroxide floc for the bacterial surface to create a dense, strong adsorptive and good settling sludge. As a result, the biomass can be operated at 7,000 to 9,000 mg/l, with SVI ranging between 50 to 90 and F/M ratios of 0.1. These levels can be realized without requiring additional oxygen. Due to the low F/M ratio, sludge production is markedly reduced. An additional benefit is iron-rich enhances sludge dewatering. The pilot study showed that the bioferric process maintained average phenol removal at 99.93% even with influent cyanide as high as 40 mg/l. Especially under accidental spills, BOD, COD and cyanide removal were still at 98%, 81.3% and 98% respectively. In contrast, phenol, BOD, COD and cyanide removal were 80.7%, 19.7%, 25.8% and 72% respectively using conventional activated sludge. Full-scale tests confirmed the conclusions of the pilot study under conditions with high fluctuations of influent flow rate and toxic contents. They showed that the bioferric process always maintains a stable operation with effluent phenol, cyanide, BOD far below the required discharge standards and all at negligible increased cost.

Coagulation of submicron colloids in water treatment by incorporation into aluminum hydroxide floc

In a series of laboratory experiments it was observed that the rate and stoichiometry of aluminum hydroxide precipitation depended on pH and Al dose, and on HCO{sub 3}{sup {minus}}, SO{sub 4}{sup 2{minus}}, and natural organic matter concentrations. Incorporation of hydrous aluminum oxide colloids into the precipitate followed either of two paths. At pH 7.5 a loose floc formed; colloid removal involved subsequent aggregation of the colloids with the floc. At pH 6.5, the precipitate coated the seed particle surface; removal involved rapid self-coagulation of the colloids. Removal was {ge} 99.9% at both pH's. At pH 5.5, colloid removals were insignificant. Results suggest that heterogeneous nucleation and growth of precipitate at pH 6.5 gives destabilized particles and smaller, compact floc. The homogeneous pathway involving precipitation and subsequent particle aggregation was less efficient. The heterogeneous pathway had a lower precipitate OH/Al ratio and a lower electrophoretic mobility.

Adsorption d'acides humiques sur flocs d'hydroxydes daluminium: Influence de la taille des flocs et du sel d'aluminium

Abstract The purpose of this study is to show that the ability of prebuilt aluminium hydroxide flocs to adsorb humic acids is function of experimental jartest conditions. The results indicate that : I/ The size of the preformed flocs is depending of the slow mixing time and of the gradient velocity mixing values. 2/ The adsorption capacity depend of the size of the floes showing that the electrostatic and ionic exchange mechanisms are mainly effective at the area of the adsorbent material. The efficiency of aluminium salts to remove humic acids are, in decrease order : WAC, aluminium sulphate, aluminium chloride, aluminium nitrate.