Adsorption and magnetic treatment effect on fluoride-dye mixture wastewater

Ng, Sher Li (2021) Adsorption and magnetic treatment effect on fluoride-dye mixture wastewater. Final Year Project, UTAR.

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Abstract

Semiconductor industry is one of the developing industries in the world, even though it brings high revenue, the semiconductor industry generates fluoridecontaining wastewater which could potentially bring severe impacts to the environment and humans. Semiconductor wastewater is usually high in fluoride concentration, dark in colour and slightly acidic (pH 6.3). The source of fluoride content is mainly due to the hydrogen fluoride (HF) used in semiconductor micromachining processes. The wastewater fluoride concentration typically falls in the range of 100-2000 mg/L and one of the substances that contributed to the dark appearance is the dye particles. Therefore, it is necessary to conduct wastewater treatment to remove fluoride and dye particles before releasing to the river. Adsorption treatment is effective in treating wastewater; however, since activated carbon is usually a one-time-usage product, the cost of regularly purchasing activated carbon could cause heavy burden to the semiconductor companies. On top of that, the price range of coconut shell activated carbon (CSAC) has been increasing in the last few years. A method to cut down the cost and wastage of activated carbon is required. Adsorption treatment using coconut shell activated carbon, a low cost biochar adsorbent is chosen to treat the simulated semiconductor wastewater made up of fluoride and methylene blue dye (MB) mixture. The aim is to find the optimum adsorbent dosage to achieve maximum fluoride and MB removal from the mixture, under pH 6.3. By predicting the optimal dosage, the wastage of activated carbon can be avoided. Comprehensive literature review was done to collect reference studies of existing experimental data and mathematical models for fluoride and MB removal. The models are improved and used to predict the adsorption treatment of fluoride-MB mixture based on adsorbent dosage and pH parameters. Mathematical model of the fluoride-MB mixture adsorption was constructed using Response Surface Methodology (RSM). For initial concentration of fluoride (10 mg/L) and MB (100 mg/L), the optimum adsorbent dosage is found to be 9.5 g/L with the fluoride and MB removal to be 81.80 % and 95.43 % respectively. The constructed model is useful in predicting the adsorption treatment of fluoride-MB mixture under different pH condition. Besides, magnetic treatment is also explored as a potential method to improve the adsorption capacity of activated carbon. By applying magnetic treatment on the activated carbon, the adsorption capacity can be improved and in the long run, it can potentially reduce the amount of adsorbent dosage needed. A mathematical model is constructed based on existing experimental data for the relationship of magnetic field and activation agent, potassium hydroxide (KOH) ratio to the activated carbon adsorption capacity. The constructed model portrays relatively linear relationship between the parameters. All the constructed mathematical models can be further improved in the future by possibly expanding the model parameter range through experimental validation.

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