Colour and turbidity removal with reusable magnetic particles—II. coagulation with magnetic polymer composites

Composite particles containing magnetic iron oxides in an insoluble polymeric matrix were used to enhance the coagulation of a turbid, coloured river water. Uncharged magnetic particles increased the turbidity removal at a given alum dose, or alternatively achieved a desired level of turbidity removal at a lower alum dose. Rates of floc formation and settling were approximately double those obtained with alum alone. Grafting linear polymers to the magnetic particles increased their effectiveness. The uncharged particles could be reused after simply washing with water. Magnetic particles with grafted chains of cationic polymers, when used in conjunction with alum, gave excellent removal of colour and turbidity and rapid settling, but required brine for regeneration. These materials were also effective in coagulating algae. When used in high doses without alum, the cationic magnetic particles initially gave good turbidity and colour removal from river water, but could not be completely regenerated     

Colour and turbidity removal with reusable magnetic particles—III immobilized metal hydroxide gels

A novel, reusable, magnetic coagulant-adsorbent was prepared and used for removing colour and turbidity from surface water. The adsorbent was made by deposition of ferric hydroxide gel onto fine magnetite. The surface charge of such a composite particle is pH dependent, and the amphoteric properties of the ferric hydroxide gel coating can be exploited in the clarification process. At pH < 6, the surface is positively charged and adsorption of negatively charged particles occurs. Conversely, the adsorbed impurities can be released by increasing the pH to above pH 10. The reactivated particles can then be reused. The particles have high sedimentation rates and are easy to handle magnetically.The magnetic gel was successfully employed to treat a number of waters. It was especially effective in treating a highly coloured reservoir water. It was possible to reuse the gel after regeneration for many cycles with a gradual deterioration in performance.     

Colour and turbidity removal with reusable magnetite particles—V: Process development

A process design has been developed for a continuous process to clarify turbid and coloured waters with alkali treated magnetite. Critical parts of the process have been investigated in small bench scale equipment, and criteria determined for the proper selection of equipment. A continuous pilot plant which appears to be both technically and economically feasible has been specified from the process design, and will be the subject of further investigations.     

Colour and turbidity removal with reusable magnetite particles—VI: Pilot plant operation

A novel process which utilizes fine magnetite particles for the removal of colour and turbidity from water has been tested in a 60 1 min⁻¹ pilot plant on water from an unconfined aquifer in Perth, Western Australia. The performance of the pilot plant closely matched jar test results. The process design was optimized to achieve a high quality product water on a raw feed which was difficult to treat in the conventional alum coagulation and filtration plant. A comparison of the conventional and magnetite treatment systems is made, which shows that the magnetite process is viable as an alternative water treatment technique.     

Colour and turbidity removal with reusable magnetite particles—IV: Alkali activated magnetite—A new solid. Reusable coagulant-adsorbent

Alkali treated magnetite (Fe₃O₄) is shown to be an excellent solid coagulant-adsorbent which is regenerable and reusable. It is effective for the removal of colour and turbidity from water. Alkali treated magnetite can be used alone or in conjunction with another primary inorganic coagulant or organic flocculant. Because of the accelerated kinetics of coagulation and particularly of sedimentation, this new technique is 3–6 times faster than the conventional coagulation-flocculation-sedimentation process. It also appears that filtration of the product water may not be necessary. Regeneration of the spent magnetite is achieved by contacting the used magnetite with 0.1 M sodium hydroxide. The development of the process on the laboratory scale using a jar test technique is discussed.     

Colour and turbidity removal with reusable magnetite particles—VII: A colloid chemistry study of the effect of inorganic ions on the efficiency of clarification

The removal of colour and turbidity from natural waters by the addition of magnetite is an interfacial process. Furthermore the components of this system are either of colloidal dimensions or of a surface active nature and thus this method of water clarification is very much in the realm of surface and colloid chemistry. Electrokinetic techniques have been used to examine the influence of a number of inorganic species, commonly encountered in the practical situation, on the surface properties of magnetite and consequently on the efficiency of the process.     

Adsorption of viruses on magnetic particles—II. Degradation of MS2 bacteriophage by adsorption to magnetite

Washed samples of finely-divided magnetite are found, after alkali treatment, to adsorb MS2 bacteriophage very efficiently, from suspension in 100 mg 1⁻¹ NaCl at pH 6.Suspended material, such as clay, components of sewage effluent and ions interfere with virus adsorption, but this interference can be largely overcome by the addition of suitable polyelectrolyte in low concentration.     

Photodecomposition du bioxyde de chlore et des ions chlorite par irradiation U.V. en milieu aqueux—partie I. Sous-produits de reactionPhotodecomposition of chlorine dioxide and chlorite by U.V.-Irradiation—Part I. Photo-products

Literature data about the photochemistry of oxychlorine compounds in aqueous solutions (flash photolysis, pulse radiolysis, solar radiation) indicate that the products (ClO, Cl, O, O⁻,…) generated from the primary photochemical reactions of decomposition of chlorine dioxide and hypochlorite can then initiate complex reactions which lead to the formation of many secondary products (Cl₂O₂, Cl₂O₁, ClO⁻,…) and of chlorate, chloride and molecular oxygen as end-products (Table 1). The aim of this work was to study the photodecomposition of aqueous solutions of chlorine dioxide and chlorite in u.v. reactors equipped with low pressure mercury vapour lamps in order to show the effects of pH and of the initial concentrations on the nature of photoproducts and on the rate of photodecomposition of ClO₂ and ClO₂⁻. This paper presents the data obtained for the identification of photoproducts. The kinetics of photodecomposition will be presented in another paper (Part II).     

Speciation of aluminium in forest soil extracts by size exclusion chromatography with UV and ICP-AES detection and cation exchange fast protein liquid chromatography with ETAAS detection

Aluminium speciation was studied in forest soil extracts by size exclusion chromatography (SE) with UV and inductively coupled plasma-atomic emission spectrometric (ICP-AES) detection and cation exchange fast protein liquid chromatography (FPLC) with ETAAS detection. Size exclusion chromatography was performed on a Superdex HR75 10/30 column. Isocratic clution with 0.15 mol dm(-3) NaCl in TRIS-HCl buffer (pH = 5.5) was applied over 100 min at a flow rate of 0.35 cm(3) min(-1). The chromatographic run was followed at 278 nm and separated Al species also determined 'off line' in 0.875 cm3 fractions by ICP-AES. The analytical procedure enabled speciation of high molecular weight Al complexes. Cation exchange FPLC was performed on a Mono S HR 5/5 column. Aqueous 8 mol dm(-3) NH4NO3 linear gradient elution was applied over 10 min at a flow rate of 1 cm3 min(-1). Separated Al species were collected in 0.5 cm3 fractions and Al determined 'off line' by ETAAS. The analytical procedure enabled speciation of some positively charged monomeric Al species. Negatively charged species were eluted with the solvent front. The combination of the two analytical techniques was successfully employed in speciation of Al in forest soil extracts. Water was used as an extracting solution. It was found experimentally that 80-95% of Al in aqueous extracts of forest soils exists in monomeric Al forms. Water soluble Al (30-40%) is bound to high molecular weight complexes with humic substances. The remaining monomeric Al in the low molecular weight fraction exists as AIF2+, Al-oxalate and Al-citrate species.     

Equilibrium approaches to natural water systems—6. Acid-base properties of a concentrated bog-water and its complexation reactions with aluminium(III)

A filtered bog-water, concentrated by means of a freezing technique, has been studied with respect to acid-base properties and aluminium(III) complexation reactions. Sampling was performed during autumn and winter periods with a resulting acidity or alkalinity due to oxic (autumn) or anoxic (winter) conditions. The measurements were performed as potentiometric titrations in constant ionic media (0.02, 0.1 and 0.6 M NaCl) with the use of a glass electrode. The samples show buffer ranges at 3 pH 5 and pH 7.5. The first is ascribed to the presence of carboxylate groups and is characterized by fast equilibria. The second is due to phenolic OH⁻ groups and precipitation reactions with resulting sluggish equilibria. For one sampling period comprehensive measurements were undertaken to study the possible polyelectrolytic character of the organic acids. Due to the small increase in apparent carboxylate pKa-values with the degree of dissociation at low (0.02 M) as well as at high (0.6 M) ionic strength, the possible polyelectrolytic feature of the acids was neglected. Instead, a good fit to data was obtained by introducing a di-protic acid (H₂L) as a model compound. Furthermore the medium dependence of the two acidity constants could satisfactorily be fitted to the expression:

Full-size image (1K)

, where K is the constant at infinite dilution, a and b parameters of which b has been adjusted to present data. The following K values were obtained: pK₁ = 3.65 and pK₂ = 4.30. The complexation with Al(III) could be described by the formation of AlL⁺, AlL₂⁻ and the ternary species AlLH₋₁. The stability constants (log k₁ = 4.4 (winter), 4.2 (autumn); log k₂ = 4.2, 4.7; pKa (AlL⁺) = 4.2, 4.2) show no significant trend with sampling period but indicate a stability of the complexes greater than for phtalic acid but lower than for oxalic acid. Finally, the theoretical solubility of the clay mineral kaolinite in the presence of bog-water was computer modelled. The calculations show up on a 10-fold increase with respect to soluble aluminium at pH = 5.     

A comprehensive study on the biological treatabilities of phenol and methanol—I. Analysis of bacterial growth and substrate removal kinetics by a statistical method

An unbiassed statistical method was developed to evaluate kinetic parameters in the biological oxidation of wastewaters. Through the statistical analyses of the biological oxidation kinetics, it was shown that the kinetic equations satisfactorily described the bacterial growth and substrate removal kinetics where X is biomass concentration, S is substrate concentration, t is time, a is cell yield coefficient, k_d is cell decay coefficient, K_s is Michaelis-Menten constant, and k is substrate removal rate coefficient. The coefficients K_s and a changed with temperature insignificantly while k and k_d were closely related to it. The temperature independent coefficients K_s and a were estimated to be 236 mg 1⁻¹ (standard deviation, σ = 70 mg 1⁻¹) and 1.21 (σ = 0.06) respectively for phenol, and 2330 mg 1⁻¹ (σ = 1410 mg 1⁻¹) and 1.25 (σ = 0.45) respectively for methanol based on total organic carbon (TOC) and volatile suspended solids (VSS). The oxygen utilization rate can be formulated as where Rr is the oxygen utilization rate (mg 1⁻¹ O₂ time⁻¹), as′ is a coefficient designating oxygen requirement per substrate utilized, and b′ is a coefficient designating oxygen requirement per biomass for endogeneous respiration. The coefficient a′ was 1.39 for phenol and 2.23 for methanol, and b′ was 1.42 k_d for both substances based on TOC and VSS.     

The effect of temperature on the removal of non-ionic surfactants during small-scale activated-sludge sewage treatment—I. Comparison of alcohol ethoxylates with a branched-chain alkyl phenol ethoxylate

The degree of biodegradability of three non-ionic surfactants has been assessed using small-scale activated-sludge sewage treatment plants. The effect of temperature on biodegradability was studied by operation at 15°, 11° and 8°C.The two alcohol ethoxylate surfactants tested were well degraded at all three operating temperatures. The alkyl phenol ethoxylate surfactant tested was well degraded at 15°C but at lower temperatures the biodegradability was dependent on concentration. At 5 mg 1⁻¹, greater than 90 per cent removal was achieved but at 20 mg 1⁻¹ the degree of removal fluctuated between 40 and 95 per cent at 11°C and between 20 and 80 per cent at 8°C.The present results have been compared with those obtained using the same surfactants in community trials at a small sewage works employing biological filtration. Although a similar temperature effect was observed with the alkyl phenol ethoxylate, the biodegradabilities obtained in the laboratory were consistently greater than those obtained at the sewage works, perhaps because of the constant conditions of the laboratory test.     

Study of flowthrough couette flocculators—I. Design for uniform and tapered flocculation

Based on published hydrodynamic data for Couette apparatuses, two flocculators were designed consisting of co-axial cylinders. The annular gap between the cylinders constituted the flocculation chamber, in one case of uniform width, and in the other tapering from a narrow to a wider gap by a taper on the inner cylinder. For best hydrodynamic stability the outer cylinder only rotated, creating a velocity gradient across the annular gap. A novel feature of the apparatuses were inflow and outflow connections allowing flocculation to be studied on a flowthrough basis, which is more realistic in water treatment, rather than as a batch process. In this flowthrough condition the tapered flocculator reduced the velocity gradient in the direction of flow reducing the shear on flocs as they grew in size. Visual studies of the flow stability, using dye, of the two flocculators used both in batch and continuous flow processes, revealed the presence of currents along the cylinder boundaries, attributed to end effects. Residence time distribution tests, using lithium tracer, indicated some short circuiting varying with velocity gradient in the tapered flocculator, but independent of velocity gradient in the uniform flocculator.     

Investigating the Social Dimensions of Transport Disadvantage—I. Towards New Concepts and Methods

This article is the first of two papers that engage critically and productively with the relationship between the socio-economic transformations of cities, the differentiation of vulnerable groups within urban space and the distribution of transport services. This article undertakes a comprehensive review of the major conceptual and methodological approaches by which scholars and policy researchers have sought to address the connection between social disadvantage and access to transport. The article critically assesses the relative merits of various spatial analytical methodologies in illuminating social-transport links. The study finds that there is a need for greater sophistication in the use of analytical methods in transport research as well as an imperative for greater sensitivity to social differentiation within urban areas and relative to infrastructure and services. The article concludes by developing a method for combining spatial social and transport service data that is then deployed in the empirical case study reported in the second paper.     

The removal of colour from effluent using various adsorbents—IV. Silica: Equilibria and column studies

The rate of adsorption of Astrazone Blue, a basic dye, on Sorbsil Silica has been studied. The parameters studied include particle size, initial dye concentration, agitation and dye solution temperature. The rate controlling step is mainly intraparticle diffusion, although a small boundary layer resistance is experienced. The activation energy for the adsorption of Astrazone Blue on silica is 13.2 ± 0.6 kJ kg⁻¹. The diffusion coefficients vary from 9 × 10⁻⁹ cm² s⁻¹ at 20°C to 10 × 10⁻⁸ cm² s⁻¹ at 82°C.     

Chemical aspects of coagulation using aluminum salts—I. Hydrolytic reactions of alum and polyaluminum chloride

This is the first of a two-part series of papers investigating the chemistry of Al coagulants. This paper examines hydrolysis reactions of alum and polyaluminum chloride (PAC1). Part II of the series addresses the coagulation of fulvic acid by these coagulants.

Monomeric, polymeric and precipitated Al were identified based on a timed spectrophotometric analysis. At typical A1 doses used in water treatment, alum showed no evidence of polymer formation. PAC1 consists of preformed polymers which are stable upon dilution below pH 6 and over the time frames encountered in water treatment. Solubility studies showed that alum and PAC1 precipitate to form different solid phases. Alum precipitates are adequately described by amorphous A1(OH)₃(s) solubility. The polymeric structure of PAC1 is retained upon precipitation yielding a solid phase with different light scattering characteristics, electrophoretic mobility and solubility than alum floc. A1 hydrolysis is interpreted as a coordination reaction between A1 and OH⁻. Effects of low temperature on alum are shown to be a result of changes in OH⁻ caused, in part, by the temperature dependence of the ion product of water. Hydrolysis products in PAC1 are preformed and therefore less sensitive to in situ hydrolysis than alum. Results suggest that when using alum, some of the adverse effects of low temperatures may be mitigated by an increase in pH, thereby maintaining a constant concentration of the complexing ligand, OH⁻.     

Optimal periodic control of activated sludge processes—I. Results for the base case with monod/decay kinetics

Regular diurnal patterns of large magnitude fluctuations in wastewater treatment plant loadings suggest that the system should be designed as a periodic rather than as a steady state process. Substantial reductions in the daily amount of effluent substrate and in effluent variability of an activated sludge process can be achieved by intentional periodic control of sludge recycle flow and waste feed distribution.     

Fish toxicity of jet fuels—I. The toxicity of the synthetic fuel JP-9 and its components

The toxicity of the jet fuel JP-9 and its components RJ-4, RJ-5 and MCH was assessed in static bioassays on the warm water fish, golden shiner (Notemigonus chrysoleucas). The 96-h LC₅₀ of emulsions was 2.0 mg 1⁻¹ for JP-9, 0.51 mg 1⁻¹ for RJ-4, 0.61 mg 1⁻¹ for RJ-5 and 72 mg 1⁻¹ for MCH. As determined by the 96-h LC₅₀ values unemulsified fuel (pools of fuel) JP-9 was 235 times less toxic, RJ-4 was 196 times less toxic, RJ-5 was 7700 times less toxic and MCH was 3.3 times less toxic than the corresponding emulsified materials.

In continuous flow bioassays with the water soluble fraction of the fuel and its components the effect on egg hatchability and fry development of flagfish (Jordanella floridae) and rainbow trout (Salmo gairdneri) was studied. The no effect of level on flagfish egg hatchability was 0.23 mg 1⁻¹ for JP-9 and 0.05 mg 1⁻¹ for RJ-5. Concentrations of 0.83 mg 1⁻¹ MCH and 0.2 mg 1⁻¹ RJ-4 did not affect egg hatchability. In rainbow trout studies 97-day LC₅₀ values for RJ-4 and RJ-5 were 0.045 mg 1⁻¹ and 0.072 mg 1⁻¹, respectively, and 23-day LC₅₀ values for JP-9 and MCH were 0.26 mg 1⁻¹ and 1.3 mg 1⁻¹, respectively.

The accumulation of fuels in fish bodies was studied and it was found that flagfish can tolerate a total body burden of 0.5 mg MCH g⁻¹ wet weight without lethality. It was also found that body burdens of 0.43 mg RJ-4 g⁻¹ and of 0.27 mg RJ-5 g⁻¹ on a wet weight basis will produce 50% mortality in rainbow trout.

Voiding of MCH from fish bodies occurs readily in fuel-free water, but RJ-4 and RJ-5 are retained in the tissues.     

Fate of cyanide and related compounds in aerobic microbial systems—I. Chemical reaction with substrate and physical removal

The chemical reaction of cyanide with substrate was investigated in sealed glass ampoules using glucose as substrate and inorganic buffers. The reaction was found to be pseudo-first order and pH dependent, with an optimum pH near 11.0. The cyanide-glucose reaction products were found to be biodegradable by both acclimated and unacclimated heterogeneous cultures in shake flask and BOD bottle systems.Adsorption onto microbial solids was investigated using sealed, stirred glass reactors containing bacteria and potassium cyanide in water buffered at pH 7.0 with inorganic buffers. Very little adsorption occurred on a starved non-flocculating pure culture of Bacillus megaterium, although up to 15% adsorption occurred in systems containing a stirred flocculent heterogeneous culture.Stripping was investigated from a starved heterogeneous culture in an aerated microfermenter at neutral pH. Hydrogen cyanide and carbon dioxide in the off-gas were trapped in sodium hydroxide solution, separated and analyzed. Stripping removed up to 80% of original cyanide, and tests using K¹⁴CN revealed that a small amount of cyanide had been metabolized.