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Modified metal oxide-based adsorbent for the removal of dye from wastewater

Author: Mandiwana Lebogang Evelyn
Publication venue
Publication date: 01/01/2021
Field of study

Abstract: Water pollution by direct discharge of textile industry waste effluents, agricultural runoffs, industrial and domestic sewage to drinking water sources is becoming serious environmental problem that causes various health problems for both terrestrial and aquatic life. Among various chemical pollutants, organic dyes are one of the major constituents of industrial discharges of effluents. Adsorption technology is an excellent treatment method of the removal and remediation of organic dyes. This is due to its economically efficiency and applicability of removing dye even at low concentrations. The adsorption of dyes onto various adsorbent have been found to be promising in water re-use. This is because of their capabilities for adsorbing specific or a broad range of pollutants efficiently. However, the synthesis of some adsorbents is considered expensive. Most researchers have used various waste materials as adosrbents, and fly ash (FA) has stand out as one of the low-cost industrial wastes and highly efficient materials for water remediation due to its attractive features such as high porosity and high surface area. In this study raw fly ash was modified and used for the adsorption of rhodamine 6G and methylene blue dyes. Fly ash was treated with sodium hydroxide to produce microporous adsorbent to remove dyes from wastewater. The optimum dye was adsorbed from wastewater onto 91 mg of modified fly ash at pH 6. The grinding of fly ash particles to less than 45m was essential for increasing its surface area. Less amount of modified fly ash (91 mg) is required to adsorb up to 97% dyes after 40 minutes of sonication whereas the amount of the raw fly ash required under the same conditions is 5000 mg. The application of isotherms and kinetic models indicated that the modified fly ash has high adsorption capacity and high removal efficiency of methylene blue under optimized conditions as the pseudo-second order experimental adsorption capacity (168 mg g−1) was higher than the theoretical estimated adsorption capacity of 102 mg g−1. Similarly, the pseudo-second order experimental adsorption capacity (130 mg g−1) of Rhodamine 6G was higher than that the theoretical estimated adsorption capacity of 93.7 mg g−1. In conclusion, the use of modified fly ash is feasible and cost-effective adsorbent of dye removal from wastewater due to its high adsorption capacity. Therefore, the application of modified fly ash for dye removal is a new development that will minimize dye pollution.M.Sc. (Chemistry

Larvicidal activity of genetically engineered escherichia coli strain harbouring the insecticidal complex protein of pantoea ananatis strain MHSD5

Author: Malomane Mosibudi Thabiki
Publication venue
Publication date: 01/01/2021
Field of study

Abstract: Most crop production practices rely on the use of chemical insecticides to combat crop diseases, caused by microbes and insect pests, and increase production yields. However, the misuse of chemical insecticides has resulted in the outbreaks of insect pests as well as environmental pollution. Furthermore, the controlled insect pests develop resistance to the insecticide rendering their subsequent applications ineffective. In addition, the use of chemical insecticides for insect pest control makes it difficult to grow crops in a sustainable and environmentally sound manner. Therefore, the protection of plant crops against insect pest damage without damaging and polluting the environment is essential. Candidate alternative is the use of proteins encoded by the toxin complex (tc) genes which are insecticidal toxins that will serve as microbial based insecticides as well as deployment of transgenic crops. Toxin complex (tc) is a tripartite high molecular weight complex and is known to be insecticidal towards insect species belonging to Coleoptera, Hymenoptera and Lepidoptera orders. This group of toxins may be used as alternatives to the toxins derived from the extensively used Bacillus thuringiensis for deployment of transgenic plants as well as usage as microbial based insecticides. The present study aimed at finding relatively low-cost and environmentally friendlier options to control and manage insect pest damage and their subsequent diseases. A codon-optimised insecticidal gene (tccZ) identified in Pantoea ananatis strain MHSD5 (a bacterial endophyte previously isolated from Pellaea calomelanos) was used to transform Escherichia coli BL21 (DE3) to allow expression of the tccZ gene and to test its larvicidal activity against Tenebrio molitor larvae. Furthermore, the bacterial cell suspension of Pantoea ananatis strain MHSD5 was used to assay its larvicidal activity against T. molitor and Galleria mellonella. Herein, we report the success of cloning of tccZ gene into pET SUMO vector and ultimately the transformation into E. coli BL21(DE3). However, despite conducting a time course of expression to determine optimal conditions for expression of tccZ protein, we were unable to detect tccZ protein expression and therefore could not purify and characterize tccZ expressed protein. Escherichia coli BL21(DE3) transformed with tccZ gene exhibited larvicidal activity against insect larvae. The injectable toxicity of the E. coli cells means that the tccZ protein may have potential to be developed as a biopesticide as well being used in deployment of transgenic plants. Keywords: tccZ gene, toxin complex, Pantoea ananatis strain MHSD5, pET SUMO, E. coli BL21(DE3), bacterial endophyte, Tenebrio molitor, Galleria mellonella, insect pest control.M.Sc. (Biotechnology