Showing papers in "Journal of Chemical Technology & Biotechnology in 2003"

Process intensification of biodiesel production using a continuous oscillatory flow reactor

Abstract: Oscillatory flow reactors (OFRs) are a novel type of continuous reactor, consisting of tubes containing equally spaced orifice plate baffles. An oscillatory motion is superimposed upon the net flow of the process fluid, creating flow patterns conducive to efficient heat and mass transfer, whilst maintaining plug flow. Unlike conventional plug flow reactors, where a minimum Reynolds number must be maintained, the degree of mixing is independent of the net flow, allowing long residence times to be achieved in a reactor of greatly reduced length-to-diameter ratio. Many long residence time processes are currently performed in batch, as conventional designs of plug flow reactor prove to be impractical due to their high length-to-diameter ratios, which lead to problems such as high capital cost, large 'footprint', high pumping costs and, also control is difficult. The OFR allows these processes to be converted to continuous, thereby intensifying the process. The transesterification of various natural oils to form 'biodiesel' is a 'long' reaction, usually performed in batch. Conversion to continuous processing should improve the economics of the process, as the improved mixing should generate a better product (rendering the downstream separation processes easier), at lower residence time (reduction in reactor volume). These improvements can decrease the price of 'biodiesel', making it a more realistic competitor to 'petrodiesel'. This paper shows that it is feasible to perform this reaction in an OFR at a lower residence time. The reaction was performed in a pilot-scale plant, using rapeseed oil and methanol as the feedstocks, and NaOH as the catalyst. # 2003 Society of Chemical Industry

Particle-scale modelling of gas-solid flow in fluidisation †

Abstract: Various approaches have been proposed to model the gas-solid two-phase flow at different time and length scales, including the so-called two-fluid model (TFM), direct numerical simulation (DNS) and combined continuum and discrete model (CCDM). This paper briefly discusses the key features of these models and their relative merit with special reference to modelling gas fluidisation. Focus is then given to CCDM in which the motion of individual particles is obtained by solving Newton's second law of motion and fluid flow by the Navier-Stokes equation based on the concept of local average. The applicability of CCDM is highlighted by its successful simulation of complicated phenomena associated with the transition between fluid-like and solid-like behaviour in raceway formation and bed expansion. At the same time, the usefulness of the resulting particle-scale information is demonstrated in elucidating the fundamentals governing the gas-solid flow. Finally, areas for future development are discussed. # 2003 Society of Chemical Industry

Process integration technology review: background and applications in the chemical process industry

Abstract: Process integration is a holistic approach to process design and operation which emphasizes the unity of the process. Process integration design tools have been developed over the past two decades to achieve process improvement, productivity enhancement, conservation in mass and energy resources, and reductions in the operating and capital costs of chemical processes. The primary applications of these integrated tools have focused on resource conservation, pollution prevention and energy management. Specifically, the past two decades have seen the development and/or application of process integration design tools for heat exchange networks (HENs), wastewater reduction and water conservation networks, mass exchange networks (MENs), heat- and energy-induced separation networks (HISENs and EISENs), waste interception networks (WINs) and heat- and energy-induced waste minimization networks (HIWAMINs and EIWAMINs), to name a few. This paper provides an overview of some of these developments and outlines major driving forces and hurdles. The fundamental aspects of this approach along with their incorporation in an overall design methodology will be discussed. The paper also highlights several recent applications of process integration to industrial processes.  2003 Society of Chemical Industry

Kinetics, degradation pathway and reaction mechanism of advanced oxidation of 4‐nitrophenol in water by a UV/H2O2 process

Abstract: Photooxidation of 4-nitrophenol (4-NP) in water by the UV/H2O2 advanced oxidation process was carried out in order to investigate the kinetics and pathway of 4-NP degradation. The experimental results showed that the photodegradation of 4-NP accorded well with pseudo-first order kinetics. The effects of different parameters, such as H2O2 dosage, pH value and various anion scavengers on the degradation of 4-NP have been investigated in detail. It was found that acidic conditions are more favorable to the degradation of 4-NP but many anions, such as HCO3 − ,N O3 − and Cl − , slow down the photooxidation rate of 4-NP. Hydroquinone, 1,2,4-trihdroxybenzene, 4-nitropyrogallol, and 4-nitrocatechol were tentatively identified as the intermediates of 4-NP degradation by GC/MS after samples were derivatized by N,O- bis(trimethylsilyl)-trifluoroacetamide (BSTFA). A degradation pathway was proposed to account for the observed intermediates produced during 4-NP degradation by the UV/H2O2 process.  2003 Society of Chemical Industry

'Greening' the chemical industry: Research and development priorities for biobased industrial products

Abstract: The chemical industry developed over the past century using petroleum as its primary feedstock. A variety of economic, political and social forces are now leading the chemical industry to use or consider renewable plant-based feedstocks in addition to or instead of petroleum. The next century may see a gradual transition away from petroleum as the primary feedstock for chemicals, materials and liquid fuels. If this transition is to occur, and if the chemical industry is to become more sustainable, a considerable amount of research must be done. This paper summarizes the research and development priorities for a more sustainable, or ‘green’, chemical industry based on renewable plant resources and relies heavily on a recent report of the National Research Council (NRC) of the United States. Copyright © 2003 Society of Chemical Industry

Internal heat integration – the key to an energy-conserving distillation column

Abstract: This paper illustrates the thermal energy conservation potential of the so-called heat integrated distillation column (HIDiC), which combines advantages of direct vapour recompression and diabatic operation at half of the normal column height. In a typical close boiling mixture separation, compared with a column utilising the usual vapour recompression scheme, HIDiC halved the consumption of exergy at approximately the same capital cost, indicating a strikingly short pay-off time. The complexities of integrating the heat transfer equipment in the stripping section with proven gas/liquid contacting devices, which may work adversely to practical implementation of HIDiC concept, are also addressed.

The removal of reactive azo dyes by natural and modified zeolites

Abstract: The adsorption mechanism of three reactive dyes by zeolite has been examined with the aim of identifying the ability of zeolite to remove textile dyes from aqueous solutions. Towards this aim, a series of batch adsorption experiments was carried out, along with determination of the electrokinetic properties of both natural and modified zeolites. The adsorbent in this study is a clinoptilolite from the Gordes region of Turkey. The reactive dyes CI Reactive Black 5, Red 239 and Yellow 176 are typical azo dyes extensively used in textile dyeing. Adsorption tests were carried out as a function of mixing time, solids concentration, dye concentration and pH. The adsorption results indicate that the natural zeolite has a limited adsorption capacity for reactive dyes but is substantially improved upon modifying its surfaces with quaternary amines. An electrostatic adsorption mechanism involving the formation of a bilayer of amine molecules on the clinoptilolite surface onto which anionic dye molecules adsorb, depending on their polarities, is proposed. The results are also supported by electrokinetic measurements. The adsorption data were fitted to the Langmuir isotherm and it was found that the modified sepiolite yields adsorption capacities (qe) of 111, 89 and 61 mg g−1 for Red, Yellow and Black, respectively. These results are comparable to a popular adsorbent, activated carbon. Copyright © 2003 Society of Chemical Industry

Hydrogen production from sucrose using an anaerobic sequencing batch reactor process

Abstract: Studies on hydrogen production in an anaerobic sequencing batch reactor (AnSBR) indicated that the anaerobic acidogenic conversion of sucrose could produce hydrogen. The hydrogen production of acclimated sewage sludge depended on hydraulic retention time (HRT) and reaction period/settling period (R/S) ratio. A short equivalent HRT, even up to 4 h, gave good hydrogen productivity and high hydrogen production rate (HPR) values. For each equivalent HRT, R/S ratio control also increased the hydrogen productivity and HPR. Reactor operation at an intimate control of HRT and R/S ratio was preferable for hydrogen production. At HRT 8 h, R/S ratio 5.6 and an organic loading rate of 0.23 mol-sucrose dm−3 day−1, each mole of sucrose in the mesophilic hydrogenic reactor yielded 2.6 mole of hydrogen; each gram of biomass produced 0.069 mole of hydrogen per day. Copyright © 2003 Society of Chemical Industry

Modelling aspects of the biotechnological valorization of raw glycerol: production of citric acid by Yarrowia lipolytica and 1,3‐propanediol by Clostridium butyricum

Abstract: Raw glycerol, produced in significant quantities during several industrial processes, could be further considered as a potential substrate for microbial conversions. In the present report, modelling approaches are used in order to quantify the kinetic behavior of microorganisms capable of producing growth- and non growth-associated metabolites when cultivated on raw glycerol. Citric acid production by Yarrowia lipolytica strain ACA-DC 50109 was successfully simulated by Monod-, Verhlust- and Williams-type models, while the optimized parameter values were found to be similar to those experimentally measured. It has been demonstrated that the production of citric acid from raw glycerol, in terms of specific production rate and conversion yield, was similar or even better as compared with that obtained during cultivation of yeasts or molds on various conventional (eg sugar-based) media. The production of 1,3-propanediol by Clostridium butyricum strain F2b from raw glycerol was successfully simulated by a Contois-type model. It was found that the maximum theoretical 1,3-propanediol productivity was comparable with the highest one achieved during growth of various bacterial strains on pure glycerol in batch and continuous cultures. Raw glycerol could be used as an alternative substrate for citric acid and 1,3-propanediol production, and possibly for other microbial products. Copyright © 2003 Society of Chemical Industry

Large‐scale sonochemical reactors for process intensification: design and experimental validation

Abstract: Acoustic cavitation results in substantial enhancement in the rates of various chemical reactions but the existing knowledge about the application of reactors based on acoustic cavitation is limited to very small capacities (of the order of few millilitres). In the present work, an overview of the application of acoustic cavitation for the intensification of chemical reactions has been presented briefly, discussing the causes for the observed enhancement and highlighting some of the typical examples. A novel reactor has been developed operating at a capacity of 7 dm 3 and tested with two reactions, ie liberation of iodine from aqueous potassium iodide and degradation of formic acid. The energy efficiency of the reactor has been calculated and compared with the conventional sonochemical reactors. The effect of frequency of irradiation on the percentage conversion of the reactants has been studied. Due to quite low conversions in the case of formic acid degradation, further intensification was attempted using aeration, addition of hydrogen peroxide, and the presence of solid particles (TiO 2 ). Compared with conventional reactors the novel reactor gives excellent results and it can be said that the future of using acoustic cavitation for process intensification lies in the development of large-scale multiple frequency multiple transducer reactors.

Capacity of activated carbon derived from pistachio shells by H3PO4 in the removal of dyes and phenolics

Abstract: Two activated carbons were obtained from pistachio shells by impregnation with H3PO4 under standard conditions of acid concentration (50 wt%) and heat treatment at 773 K for 2 h. The soaking time was 24 and 72 h for the two samples before thermal pyrolysis. Analysis of the N2/77 K adsorption isotherms proved that both were highly adsorbing carbons with considerable microporosity, and that the prolonged contact with activant enhanced total porosity (surface area and pore volume) and increased the amount of mesoporosity. Adsorption isotherms of probe molecules, viz methylene blue (MB), rhodamine B (RB), phenol (P) and p-nitrophenol (PNP), were determined at room temperature, from aqueous solutions. Both the Langmuir and Freundlich model adsorption equations show satisfactory fit to experimental data. Both carbons exhibit similar adsorption parameters irrespective of their porosity characteristics. The sequence of uptake per unit weight was: PNP > MB > RB > P. Low affinity towards phenol may be associated with its competition with water molecules which are more favourably attracted to the acid surface which has a high oxygen functionality. Preferred adsorption in the order PNP > MB > RB is proposed to be a function of carbon porosity, related to the increased molecular dimensions of the solutes. Adsorption from a binary mixture of equal concentrations of MB and RB showed reduced uptake for both sorbates in comparison to the single component experiments. RB removal surpasses that of MB in the binary test and may be attributed to lower water solubility and higher molecular dimensions. Copyright © 2003 Society of Chemical Industry

Kinetic analysis of the sorption of copper(II) ions on chitosan

Abstract: The removal of copper ions from aqueous effluents by chitosan was studied in equilibrium and agitated batch contacting systems. The sorption capacities of chitosan for copper ions are 1.26 and 1.12 mmol g−1 at pH 3.5 and 4.5, respectively. The equilibrium experimental data were best correlated by the Langmuir equation. The kinetics of sorption were studied at an initial solution pH of 4.5 and a chitosan particle size of 355–500 µm. The kinetics were analyzed using four models: the pseudo-first-order, pseudo-second-order, modified second-order and Elovich equations. The rate parameters for the four models were determined and the Elovich equation provided the best correlation of the experimental kinetic data. Copyright © 2003 Society of Chemical Industry

Evaluation of municipal compost/limestone/iron mixtures as filling material for permeable reactive barriers for in‐situ acid mine drainage treatment

Abstract: The aim of the present study was to assess the potential of municipal compost as a carbon source for sulfate-reducing bacteria for acid mine drainage bioremediation for use in permeable reactive barriers at high flow rates (>0.1 m d−1). Two different mixtures of municipal compost, limestone and zero-valent iron were assessed in two column experiments. The effluent solution was systematically analysed throughout the experiments. At the end of the experiments precipitates from both columns were withdrawn for scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffractometry examination and solid digestion and sequential extraction were carried out. Results showed that the effluent was free of metals and acidity. It seems that metal removal was not due to biogenic sulfide generation but to pH increase, ie metal (oxy)hydroxides precipitation. These precipitates can sorb other metals onto the surface. Sorption to organic matter could also contribute to metal removal. When zero-valent iron was present, cementation of copper also occurred. It can be concluded that municipal compost was a poor carbon source to support continuous bacterial activity under high flow rates. Copyright © 2003 Society of Chemical Industry

Identification and modelling of aerobic hydrolysis – application of optimal experimental design

Abstract: Hydrolysis mechanism plays a dominant role in the delicate balance of electron donor/electron acceptor ratios in BNR (biological nutrient removal) and EBPR (enhanced biological phosphorus removal) systems as an important carbon source. In this study, the surface-saturation-type hydrolysis kinetics was investigated based on respirometric measurements, within the context of the theoretical and the practical identifiability of mathematical models. The identifiable parameters of a selected model were derived from respirograms. In addition, the information from the experiments was evaluated on the basis of Optimal Experimental Design (OED) methodology for different initial conditions of the batch respirometric experiment.

Ozone oxidation in a rotating packed bed

Abstract: The feasibility of applying a novel rotating packed bed to the ozone oxidation process is investigated. Ozone oxidation experiments were conducted to examine how various operating variables affect the decolorization of dyes in aqueous solutions system. Rotor speeds ranged from 380 to 1748 rpm, providing 10∼202 equivalent gravitational force. Experimental results indicate that the centrifugal force positively affects the decolorization efficiency. Furthermore, it is shown that owing to its low ozone mass transfer resistance, a rotating packed bed can be used to increase the efficiency of the ozone oxidation process. The results further demonstrate that the decolorization efficiency increases with either an decreasing initial dye concentration or liquid flow rate.

Electrolytic removal of hexavalent chromium from aqueous solutions

Abstract: The removal of hexavalent chromium from a synthetic solution and from an industrial sample by electrolysis using stainless steel plate and titanium mesh cathodes is studied. It is found that the process proceeds in two steps: (1) electroreduction of hexavalent chromium to trivalent chromium in highly acidic medium and (2) electrochemical precipitation of trivalent chromium in an alkaline medium. A comparative study of electroreduction, electrochemical reduction and chemical reduction of hexavalent chromium is carried out and the electroreduction process is shown to be a clean technique. It is concluded that, in the absence of addition of any chemical as reducing agent, the Cr(III) solution formed on the reduction of Cr(VI) can be recycled in other industrial processes. Copyright © 2003 Society of Chemical Industry

Biotechnological production of lactic acid integrated with potato wastewater treatment by Rhizopus arrhizus

Abstract: This paper describes a feasibility study of a for lactic acid production integrated with are treatment of wastewater from an industrial starch plant. Rhizopus oryzae two strains, Rhizopus arrhizus and Rhizopus oligosporus were tested with respect to their capability to carry out simultaneous saccharification and fermentation to lactic acid using potato wastewater. Rhizopus arrhizus DAR 36017 was identified as a suitable strain that demonstrated a high capacity for starch saccharification and lactic acid synthesis. The optimal conditions, in terms of pH, temperature and starch concentration, for lactic acid production were determined. The selected fungal strain grew well in a pH range from 3.0 to 7.0. The addition of CaCO(3)10 g dm(-3) maintained the pH at 5.0-6.0 and significantly enhanced lactic acid production. Kinetic study revealed that almost complete starch saccharification and a lactic acid yield of 450g kg(-1) could be achieved in 20 h and 28 h cultivation, respectively. The maximum lactic acid production 21 g dm(-3) and mycelial biomass (1.7 g dm(-3)) were obtained at 30degreesC. Besides the multiple bioproducts, total removal of suspended solids and 90% reduction of COD were achieved in a single no-aseptic operation. (C) 2003 Society of Chemical Industry.

Removal of aqueous phenolic compounds from a model system by oxidative polymerization with turnip (Brassica napus L var purple top white globe) peroxidase

Abstract: Turnip roots, which are readily available in Mexico, are a good source of peroxidase, and because of their kinetic and biochemical properties have a high potential as an economic alternative to horseradish peroxidase (HRP). The efficiency of using turnip peroxidase (TP) to remove several different phenolic compounds as water-insoluble polymers from synthetic wastewater was investigated. The phenol derivatives studied included phenol, 2-chlorophenol, 3-chlorophenol, o-cresol, m-cresol, 2,4-dichlorophenol and bisphenol-A. The effect of pH, substrate concentration, amount of enzyme activity, reaction time and added polyethylene glycol (PEG) was investigated in order to optimize reaction conditions. A removal efficiency ≥85% was achieved for 0.5 mmol dm−3 phenol derivatives at pH values between 4 and 8, after a contact time of 3 h at 25 °C with 1.28 U dm−3 of TP and 0.8 mmol dm−3 H2O2. Addition of PEG (100–200 mg dm−3) significantly reduced the reaction time required (to 10 min) to obtain >95% removal efficiency and up to 230% increase in remaining TP activity. A relatively low enzyme activity (0.228 U dm−3) was required to remove >95% of three phenolic solutions in the presence of 100–200 mg dm−3 PEG. TP showed efficient and fast removal of aromatic compounds from synthetic wastewaters in the presence of hydrogen peroxide and PEG. These results demonstrate that TP has good potential for the treatment of phenolic-contaminated solutions. © 2002 Society of Chemical Industry

De‐hairing activity of extracellular proteases produced by keratinolytic bacteria

Abstract: The depilatory activity of keratinolytic bacteria was investigated. Three keratinolytic bacteria isolated from feather waste were tested for their ability to grow in mineral medium containing bovine hair as sole carbon, nitrogen and energy source. The strains kr2, kr6 and kr10 grew well on bovine hair, producing proteolytic activity as judged by assay with azokeratin as substrate. The proteolytic enzymes from all three strains showed similar pH and temperature optima. Strain kr2 showed mainly serine-type protease activity, whereas kr6 and kr10 enzymes showed metalloprotease characteristics. The culture supernatants were used as crude enzyme preparations for depilatory studies on bovine pelts. All three strains were efficacious in promoting de-hairing. Microscopic analysis revealed that the epidermis was completely removed and the absence of hair in follicles was observed. Proteases of keratinolytic bacteria were efficient in promoting depilation of bovine pelts. Enzymatic de-hairing represents a suitable alternative to the conventional tannery process, with the benefit of avoiding environmental pollution. Copyright © 2003 Society of Chemical Industry

Optimization of extraction of bulk enzymes from spent mushroom compost

Abstract: The profiling of ligninase, hemicellulase and cellulase of Pleurotus sajor-caju after inoculation of spawn in bags containing sawdust was done at monthly intervals for a period of 6 months. Xylanase (EC 3.2.1.8) was produced throughout the 6 months studied with the productivity range from 5.60 to 7.51 U g−1. Cellulase (EC 3.2.1.4) and β-glucosidase (EC 3.2.1.21) productivities were highest at 4 months, producing 3.31 U g−1 and 121.13 U g−1 respectively. Laccase (EC 1.10.3.2) productivity was highest at 2 months with a value of 7.59 U g−1. Lignin peroxidase (EC 1.11.1.14) productivity was highest at 5 months with a value of 206.20 U g−1. Total soluble proteins were highest at 4 months with a value of 0.139 mg cm−3. The profiling of lignin peroxidase in 5-month-old spent mushroom compost was monitored over a period of 10 months. It was observed that lignin peroxidase was produced throughout the period but productivity was variable. The average lignin peroxidase productivity ranged from 30 to 110 U g−1. The activities of the enzymes extracted in tap water at pH 8.4 were comparable to that extracted in 50 mmol sodium citrate buffer at pH 4.8 and distilled water at pH 5.2 at 4 °C using an incubator shaker at 200 rpm for 18 h. The optimum extraction time was 1 h using an incubator shaker at 4 °C. When an incubator shaker was used, there was no significant difference in the recovery of xylanase, cellulase and laccase at different pH values at 4 °C and 28 °C. No significant difference was observed in the recovery of β-glucosidase using an incubator shaker at different pH values at 4 °C although the enzyme recovery was slightly higher at pH 8.12, with a value of 29.27 U g−1. The optimum extraction of β-glucosidase was at pH 4 at room temperature using an incubator shaker. For the lignin peroxidase enzyme, the optimum pH for extraction was 6 at 4 °C and pH 7 at room temperature using an incubator shaker at 200 rpm for 1 h. Homogenization for 8 min at 8000 rpm using tap water at pH 4 had an advantage over the use of the incubator shaker for the extraction as high titers of enzymes were recovered. Copyright © 2003 Society of Chemical Industry

Valorisation of waste fractions from autohydrolysis of selected lignocellulosic materials

Abstract: Non-isothermal processing of lignocellulosic materials in aqueous media (autohydrolysis reaction) under mild conditions leads to solutions containing valuable chemicals (oligosaccharides, sugars and acetic acid) and other, undesired, compounds (belonging to the extractive and acid-soluble lignin fractions) which have to be removed in further purification treatments. Liquors obtained by non-isothermal autohydrolysis of Eucalyptus globulus wood and corncobs under a variety of operational conditions were extracted with ethyl acetate in order to remove non-saccharide components, and the suitability of the fraction dissolved in the organic phase was assayed for possible utilisation as an antioxidant. The yield and antioxidant activity of ethyl acetate extracts (measured by the α,α-diphenyl-β-picrylhydrazyl (DPPH) radical scavenging capacity) showed a strong dependence on the autohydrolysis conditions. The antioxidant activity of extracts obtained under selected operational conditions compared well with synthetic antioxidants. © 2003 Society of Chemical Industry

Black liquor detoxification by laccase of Trametes versicolor pellets

Abstract: Black liquors from a soda pulping mill were treated with the white-rot fungus Trametes versicolor to detoxify and reduce colour, aromatic compounds and chemical oxygen demand (COD). The fungus was used in the form of pellets in aerated reactors (fluidized, stirred and air-pulsed reactors). Reductions in colour and aromatic compounds of 70-80% and in COD of 60% were achieved. During the different experiments, laccase activity was detected but neither lignin peroxidase (LiP) nor manganese peroxidase activities were detected, although Tv ersicoloris able to produce these enzymes. Experiments also showed a LiP activity inhibitory effect produced by lignin. From the results obtained, it can be concluded that there is a relationship between laccase production and toxicity reduction. This correlation responds to the equation Laccase production = 1.57 LN (toxicity reduction) −16.40.  2003 Society of Chemical Industry

Calcium removal from industrial wastewater by bio-catalytic CaCO3 precipitation

Abstract: High concentrations of soluble calcium in industrial wastewater present problems due to the calcification of downstream processing. The current trend towards circuit closure and increased water re-use will escalate this problem. We investigated ureolytic microbial carbonate precipitation as a novel process for removing excess calcium from industrial effluents. Two laboratory-scale reactors, both with a hydraulic retention time of 8 h, were fed with 1.8 dm3 of anaerobic effluent (about 11 mM Ca2+) from a paper recycling plant. Both reactors were inoculated with pre-cultivated calcareous sludge and the treatment reactor was additionally dosed with urea to a final concentration of 8.3 mM. Even though the anaerobic wastewater was saturated as such with respect to CaCO3, urea addition and hydrolysis was shown to be a pre-requisite for precipitation. Almost all (85-90% w/v) of the soluble calcium was precipitated as CaCO3 and removed through sedimentation in the treatment reactor. This bio-catalytic process presents an uncomplicated and efficient method for the removal of calcium from industrial wastewater.

Biodegradation of aromatic hydrocarbons in a compost biofilter

Abstract: Two laboratory-scale biofilters filled with the same type of packing material were operated at different gas flow rates and influent concentrations of toluene and xylene in order to investigate their performance in treating waste gas streams. The columns contained a mixture of municipal compost as a base material and wood chips as a bulking agent in an 80:20 ratio; the porosity was 54%. Microbial acclimation was achieved by addition of nutrient-enriched solution along with pollutants for a week by daily mixing and natural aeration. During the start-up of the systems with inlet concentrations of 20 and 70 ppm for toluene and xylene, respectively, high biomass growth resulted in pressure drops in excess of 2000 Pam−1. Under steady state conditions, the response of each biofilter to variations in contaminant mass loading was studied by either changing the influent concentration or flow rate of the inlet waste stream. The results show that organic loading rates of up to 110 and 150 gm−3h−1 can be handled without any indication of the elimination capacity being saturated. However, maintaining the pressure drop below 1000 Pam−1 to avoid operational problems, optimal organic loading rates for toluene and xylene of 78 ± 8 and 80 ± 14 gm−3h−1 respectively are suggested for an HRT value of 60 s. Under these conditions, elimination capacities of 73 ± 4 and 73 ± 14 gm−3h−1 and removal efficiencies of 94 ± 6% and 91 ± 8% were achieved for toluene and xylene, respectively. Copyright © 2003 Society of Chemical Industry

Removal of fluoride using some lanthanum(III)‐loaded adsorbents with different functional groups and polymer matrices

Abstract: Although fluoride is beneficial for human beings in small quantities, it causes dental fluorosis when consumed in larger quantities over a period of time. In recent years, considerable work has been conducted for the purpose of developing new and low cost absorbents for adsorptive removal of fluoride, especially chelating resins loaded with metal ions. In the present study, several types of adsorbents with different functional groups loaded with lanthanum(III) were prepared to be used for fluoride removal from water. The optimum conditions for loading lanthanum(III) on the adsorbents and the effects of pH and initial fluoride concentration as well as shaking time and solid–liquid ratio on the removal of fluoride have been investigated. Based on these fundamental data, the removal of fluoride from actual hot spring water was also tested as a practical application by comparing the efficiency of different adsorbents for the removal of fluoride from hot spring water. The following conclusions were obtained. (1) The different chemical composition and chemical structure of the polymer matrix play the most important role in fluoride adsorption, (2) strongly acidic adsorbents are more effective on fluoride removal at neutral pH than weakly acidic adsorbents, (3) the order of fluoride removal in the neutral pH range of 4.5–8.0 by the different La(III)-loaded adsorbents employed in the present work is as follows: 200CT resin > POJRgel > IR124resin > SOJR gel ≥ CPAgel ≥ WK11 resin. The column experiments showed that the 200CT resin loaded with lanthanum(III) at pH 6.0 can be successfully employed for the removal of fluoride ions from actual hot spring water. Copyright © 2003 Society of Chemical Industry

Bioleaching of copper and other metals from low-grade oxidized mining ores by Aspergillus niger

Abstract: A study was initiated to determine the feasibility of using the fungus Aspergillus niger for bioleaching metals from oxide low-grade ore. Large quantities of the metals are embodied in the low-grade ores and mining residues that can be recovered. Presently available techniques (pyrometallurgical and hydrometallurgical) are expensive or may have a negative impact on the environment. An oxidized mining ore containing mainly copper (7245 mg kg−1 residue) was studied. In this study, the fungus A niger produced a variety of organic acids. Addition of small quantities of sulfuric acid enhanced the organic acids, efficiency. Various agricultural wastes were evaluated as substrates and a maximum solubilization of 68% for copper for a medium containing potato peels was achieved. In conclusion, leaching of copper from a mining ore is technically feasible using A niger. Further research must be performed to increase the rate of copper removal. Copyright © 2003 Society of Chemical Industry

Segregation of binary mixture of particles in a bladed mixer

Abstract: This paper presents a numerical study of the flow and segregation of particles over flat blades in a vertical cylindrical mixer by means of a modified discrete element method. Simulations are conducted using a binary mixture of spheres, where the blade's rotating speed, particle size, volume fraction and particle density are the variables considered. Similar flow features are found for all the cases considered: particles rise to form a heap in front of a blade and then either flow downward on the bed surface over the blade or to the base of the heap to rejoin the flow toward the blade, and there is a recirculating zone in front of the blade. However, different types of mixing behaviour can be observed. Particles with large size or light density are mainly in the top layer of the mixing bed, while small and heavy particles remain in the bottom of the mixing bed and in front of the blades. The segregation pattern resulting from size difference is not the same as that resulting from density difference. The force evolution in these two binary systems also differs, although at the initial stage large/light particles always receive a relatively larger vertical force than small/heavy particles, leading to segregation that can be maintained at the later stage. Decreasing the size or density difference promotes the mixing performance. Changing the blade speed affects the mixing kinetics but not the mixing quality.

Modelling arsenic(III) adsorption from water by sulfate-modified iron oxide-coated sand (SMIOCS)

Abstract: A medium developed by coating BaSO4 and Fe on quartz sand known as sulfate-modified iron oxide-coated sand (SMIOCS) was evaluated for the removal of arsenic(III) from simulated water with an ionic strength of 0.01 M NaNO3 during batch studies. The medium was characterised for BET surface area, alkali-resistance, acid-resistance and the presence of iron and barium on the coated surface. Two simplified kinetic models, ie active available site (AAS) and chemical reaction rate models, were tested to investigate the adsorption mechanisms. The values of rate constants for both the models were found to decrease with increasing As(III) concentrations in the solute. The inverse relationship of rate constants of the reaction rate model with BET surface area showed that As(III) adsorption on SMIOCS was not due to physisorption but to chemisorption. A study of the effect of solute temperature showed that the adsorption of As(III) on SMIOCS media was due to chemisorption. The results of isothermal studies conducted at different pH values showed that adsorption data satisfied both the Langmuir and the Freundlich isotherm models. The adsorption of As(III) on the medium was pH dependent and maximum removal was observed in the pH range of 7–9. © 2002 Society of Chemical Industry

Nitrite accumulation characteristics of high strength ammonia wastewater in an autotrophic nitrifying biofilm reactor

Abstract: Selective nitrification was carried out to accumulate nitrite from high strength ammonia wastewater in an autotrophic nitrifying biofilm reactor. Nitrification efficiencies and nitrite accumulation characteristics were investigated at various operating conditions such as ammonium load, oxygen supply and free ammonia concentration. The biofilm. reactor showed very stable nitrification efficiencies of more than 90% at up to 2 kg NH4-N m(-3) d(-1) and the nitrite content was maintained at around 95%. Inhibition by free ammonia on nitrite oxidizers seems to be the major factor for nitrite accumulation. Batch kinetic analyses of ammonium and nitrite oxidation showed that nitrite oxidation activity was selectively inhibited in the presence of free ammonia. However, the activity recovered quickly as the free ammonia concentration decreased below the threshold inhibition concentration. Examination of specific ammonia and nitrite oxidation activities and the most probable number indicated that the number of nitrite-oxidizing microorganisms in the nitrite-accumulating system was less than that in the normal nitrification system due to long-term free ammonia inhibition of the nitrite oxidizers. The reduced population of nitrite oxidizers in the biofilm system was also responsible for the accumulation of nitrite in the biofilm reactor. (C) 2003 Society of Chemical Industry.

Removal of suspended solids and residual oil from palm oil mill effluent

Abstract: Palm oil mill effluent (POME) was pretreated to remove suspended solids and residual oil. The processes used were flocculation, solvent extraction, adsorption and membrane separation. Flocculation was used to remove suspended solids, and solvent extraction and adsorption processes were used to remove residual oil. Membrane separation was subsequently applied to remove any residual suspended solids and oil remaining after the pretreatments. The solvent extraction and adsorption processes were operated on a batch basis whereas membrane separation was performed in continuous mode. The treatment efficiency of the processes was measured as percentage removal of suspended solids and oil respectively. The optimum values of the process parameters obtained in the flocculation process were an alum dosage of 4000 mg dm−3, mixing speed of 150 rpm for 1 h and sedimentation time of 270 min, resulting in 93% suspended solids removal. In the solvent extraction process, a 95% reduction in residual oil was obtained using n-hexane as a solvent with 20 min of mixing at 200 rpm. The ratio of solvent to POME was 6:10 and carried out at pH 9. In the batch adsorption process, an 88% reduction in residual oil was obtained at a mixing speed of 100 rpm for 1 h, pH 9 and an adsorbent dosage of 300 g dm−3. In membrane separation processes, GH and CE(GH) membranes gave 63% and 49% reductions in suspended solids and residual oil respectively at pH 9 and pressure of 1000 kPa. Copyright © 2003 Society of Chemical Industry