Dissertations submitted in compliance with the requirements for the Master's Degree in technology: Biotechnology, Technikon Natal, 2001. / Hexavalent chromium [Cr(VI)] or chromate, is a toxic, water-soluble contaminant present in many soils and industrial eflluents. As a result of contaminated discharges from industrial applications, and inappropriate wastedisposal practices, significant amounts of chromate have found their way into the environment. This poses a health risk to man as well as animals and plants due to the carcinogenicity, mutagenicity, and teratogenicity of chromate. In man, acute, high level exposures to Cr(VI) can result in ulceration of the skin, eyes, and mucous membranes. Exposure of plants to Cr(VI) can result in reduced biomass production, and in extreme cases, death. Upon reduction ofCr(VI) to trivalent chromium [Cr(III], the toxic effects are significantly decreased because of a decrease in the solubility and bioavailability of Cr(III). Traditionally, Cr(VI) has been recovered from aqueous systems using processes exploiting the differential solubility properties described above. The use of chromate reducing bacteria represents a potential mechanism for the development of an efficacious, cost effective alternative to traditional chemical/physical processes for Cr(VI) recovery from the environment. Therefore, the aim of this research was to isolate and identify chromate reducing bacteria from soil, and characterise the chromate reductase enzyme in order to determine the potential of bacteria to detoxify chromate by reduction. Bacteria from soils and wastewater were examined for chromate reducing potential and identified on the basis of biochemical tests and API 20E. Organisms were isolated by the spread plate technique. Species of Pseudomonas maltophilia, Bacillus subtilis, Acinetobacter calcoaceticus, and Cellumonas cellasea were capable of catalyzing the reduction ofCr(VI) to Cr(IlI) in batch experiments. Reduction capability as high as 99% by the isolates was detected from an initial Cr(VI) concentration of 150 mg.L' in batch cultures. Chromate reduction was determined by means of the diphenylcarbazide method and total chromium was measured by atomic absorption spectroscopy. Pseudomonas maltophilia was observed to be the most suited organism for the efficient detoxification ofCr(VI) due to its wide temperature and pH requirements, low substrate utilization, and tolerance to heavy metal ions of'Cu', Cd2+,Zn2+,and Ni2+which commonly appear in industrial eflluents along with Cr(VI). Reduction rate in a batch reactor for this organism was calculated to be 1.75 mg.g+h'. Comparison of the rates of chromate reduction by Cr(VI) grown cells and cells grown without chromate indicated that the chromate reductase activity is constitutive. Reductase activity was detected by means of the lysozyme-EDTA method in aerobically grown cells, with highest specific activity in the cytoplasmic fraction of the cell. The Cr(VI)-reductase was found to be NAD(p)H-dependent and yielded an activity of 3.24 ml.I.mg' of protein in the cytoplasmic fraction. Once optimization of the parameters in the batch reactor was achieved, cells of Ps. maltophilia was immobilized into polyacrylamide gel and packed in a column. Mass balance studies indicated that ca 147 mg.L' chromate passing through the column undergoes reduction with an initial Cr(VI) concentration of 150 mg.L' resulting in a Cr(VI) reduction efficiency of98%. An amount of 0.11 mg.L' remained in the cells, 0.11 mg.L' in the cell wash water, and 1.65 mg.L' was unaccounted for in the mass balance. Chromate reduction rate in the continuous-upflow reactor system was calculated to be 5.34 mg.g'l.h', which was 3-fold higher than that calculated for the batch reactor. Chromium-contaminated industrial eflluent obtained from Sheffield, Natal, and Saayman Danks Electroplaters was pumped into the continuous-upflow reactor containing immobilized cells of Ps. maltophilia to determine the industrial applicability of the reactor to treat chromate-containing effluents. Complete Cr(VI) reduction / M

M. Tech. Engineering: Chemical / Researches the usability and efficiency of the synthesized PPy/Al2O3 nanocomposite as adsorbent in Cr(VI) remediation from contaminated wastewaters.The specific objectives of the study are:to synthesise and characterize the PPy/Al2O3 nanocomposite ; to characterize the prepared nanocomposite using several sophisticated instruments such as, SEM, BET, XRD, et cetera ; to carryout batch adsorption equilibrium and kinetics studies for evaluating the performance of the nanosorbent and to gain insight into the underlying adsorption mechanisms.; to apply adsorption equilibrium and kinetic models.; to assess the breakthrough performance of the PPy/Al2O3 nanocomposite for Cr(VI) adsorption by varying operating parameters, in fixed bed column mode and to apply existing mathematical models to predict the performance of fixed bed adsorption systems and to obtain column design parameters.

M.Tech. Engineering: Chemical. / Aims at demonstrating the application of semi-continuous and continuous magnetic adsorption separation (MAS) techniques to extract Cr (VI) ions from wastewater streams using PPy-Fe3O4 nanocomposite. Specifically, the research aims to achieve the following objectives: to design, synthesize and characterize new generation PPy-Fe3O4 nanocomposite with varied magnetite composition for hexavalent chromium removal ; to generate batch adsorption kinetic data in a continuously stirred tank reactor (CSTR) and apply existing kinetic models to aid in water treatment system design.; to design and construct magnetic adsorption separation (MAS) device that can operate in a semi-continuous and continuous mode and explore their performances and to optimize the systems' performance.

D. Tech. Chemical Engineering / Aims of this research project was to add value to largely wasted South African sawdust by development of low-cost AC of high efficiency for removal of toxic Cr (VI), phenol and glutaraldehyde from dilute aqueous media. The main objectives of the research project were: a) To develop low-cost AC based on South African P. patula sawdust using economical physical superheated steam activation.Characterization of carbon samples for selection of optimum preparation conditions for development of low-cost AC of effective microporosity mesoporosity and surface functionality for enhanced adsorption capacity of Cr (VI) and/or phenol and/or glutaraldehyde from dilute aqueous solution. Acid-amine surface groups modification of optimally developed AC for further enhancement of adsorption capacity for mixed polarized glutaraldehyde molecules from aqueous solution. b) To evaluate the aqueous phase batch adsorption properties of developed AC for Cr (VI) and phenol and, of acid-amine modified developed AC for glutaraldehyde. Determination of optimum pH for adsorption; accurate adsorption isotherm modelling for determination of maximum adsorption capacity, comparison of maximum adsorption capacities for Cr (VI) and phenol of developed AC with commercial AC and literature ACs, and attempt to establish average micropore size for enhanced capacity for Cr (VI) and phenol from dilute aqueous solution.Kinetics reaction and diffusion modelling for determination of adsorption rate constants and diffusion parameters; and determination of adsorption thermodynamic parameters.Evaluation of equilibrium selectivity of developed AC for Cr (VI) and/or phenol in binary aqueous solutions. c) To evaluate aqueous phase fixed-bed adsorption characteristics of developed AC for single Cr (VI) and mixed solution using Rapid Small Scale column Tests (RSSCTs). Generation of breakthrough curves at optimum adsorption conditions for evaluation of column performance indicators at different process conditions, bed regeneration-reusability potential, and dynamic adsorption selectivity of developed AC for Cr (VI) from solution of base metals. Determination of column diffusion parameters; accurate mass transfer and empirical modelling of breakthrough data; determination of applicable RSSCT scaling equation; and optimization of breakthrough data for accurate RSSCT scale-up.

The presence of heavy metal ions in waste streams is one of the most pervasive environmental issues of present times. A rotating biological contactor (RBC) was used to investigate the potential capacity of microbial biofilms in remediation of the metal ion species from a mixed metal contaminated effluent solution containing Cr+3 , Pb+2 and Cu+2 , each at a concentration of 200 mg r1 • In the first part of this study the effectiveness of various support materials for the development of microbial biofilms capable of removing heavy metals from a synthetic effluent was investigated. EDX analysis showed that none of the support matrices investigated, viz. gravel, polyester batting and sand, adsorbed metal ions on their surfaces; hence, metal adsorption was due purely to microbial activities. The biofilms attached more firmly and uniformly to polyester batting than to gravel and sand. The characteristics of polyester batting which made it a superior support matrix were its surface roughness and porous hydrophilic nature, which provided a larger surface area for the adhesion of microorganisms and attraction of nutrients during the biofilm development process. The selective accumulation of metal ion specIes by various microbial populations grown as biofilm using polyester batting as support matrix in separate compartments of a single-stage RBC bioreactor was examined. Lead ions were readily accumulated by almost all the microbial biofilms tested. Fungus-dominated biofilms selectively accumulated chromium ions whereas biofilms comprising mainly bacteria more readily accumulated copper ions from the mixed metal contaminated effluent solution. However, where interactions between the bacterial and fungal components were encouraged the mechanical stability of the biofilms was enhanced so that large amounts of all three metal ion species were removed by this biofilm. The combined effect of a series of bench-scale columns containing liquid humic acid and a three stage RBC bioreactor on the removal of metal ion species from a mixed metal contaminated effluent was investigated. After seven days of treatment the combined system had removed approximately 99% of the Cr+3, 98% of the Pb+2 and 90% of the Cu+2 ions from the mixed metal contaminated synthetic effluent. Complexation of the metal ions with humic acid was the predominant factor accounting for approximately 68-86% Cr+3 , 70-86% Pb+2 and 53-73% Cu+2 removal levels within the columns. A large proportion of the remaining Cr+3 and Pb+2, but not of the Cu+2, was removed in compartment 1 of the RBC. This suggested that the presence of the former two metals in solution might have reduced the removal of the Cu+2 ions from the system. The removal of substantially large amounts of the competing ions chromium and lead during the initial stages of the treatment process meant that copper was successfully taken up in the second and third RBC compartments. Hence, the economy of the treatment process was improved as larger quantities of the metal ions were removed in a shorter period of time than was possible when using the individual treatments (humic acid-metal complexation and biofilm adsorption) separately. More than 75%,92% and 86% of the adsorbed Cr+3 , Pb+2 and Cu+2 ions, respectively, were recovered from the three RBC bioreactor compartments following repeated washing of the biofilms with 0.1 M HCI. This relatively easy desorption suggested that the metal ions were simply adsorbed onto the surfaces of the biofilm cells rather than being taken into the cytoplasm of the cells. / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.