Browsing by Author "De Wet, Leroi Johannes"
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- ItemDevelopment and feasibility of an electrochemical-oxidation process for water disinfection(Stellenbosch : Stellenbosch University, 2018-03) De Wet, Leroi Johannes; Pillay, V. L.; Stellenbosch University. Faculty of Engineering. Dept. of Process Engineering.ENGLISH SUMMARY: Quality of water supplies for potable use has deteriorated to such a state that point-of-use water disinfection has become a necessity. Historically, chlorine has been the most widely used disinfectant, but its shortcomings have led to the development of numerous alternative technologies over the last three decades. One of the emerging, but less understood technologies, are metal ions combined with an oxidising agent. Traditionally, chlorine disinfection has been controlled by measuring free chlorine residual and pH, but oxidation reduction potential (ORP) is emerging as an alternative indicator of the efficacy of disinfection. The objectives of the research were to (i) identify the contribution, if any, of metallic ions on the disinfection ability of bromo-chloro-dimethyl-hydantoin (BCDMH), (ii) investigate the feasibility of using metallic ions with BCDMH as a disinfectant on a typical potable water supply, (iii) evaluate ORP as an indicator of disinfection efficacy for a disinfection process that combines metallic ions with BCDMH. The feasibility investigated criteria such as efficiency, ease of implementation, financial implications and environmental implications, comparing the combined technology with the individual processes. A batch experimental setup was developed that treated a feed with a combination of metal ions and an oxidising agent. The feed consisted of tap water artificially contaminated with the bacterium Pseudomonas sp. strain CT07 at a concentration of between 0.5x107 and 2.0x107 cfu/ml. The drop plate method was used to determine disinfection by the reduction of bacterial concentrations to below detection limits. Copper, silver, and zinc ions were released by an ioniser and a BCDMH stock solution was used as oxidising agent. A fixed contact time of 5-minutes was used to keep findings relevant to point-of-use water disinfection. Experimental results were analysed using logistic regression. The logit model for combined treatment had a strong correlation with a Cox-Snell R2 of 0.516 and was significant with a p-value <0.001. The interaction coefficient (β12) was significant with a p-value of 0.036. The significant interaction coefficient showed that metal ions could improve the disinfecting ability of BCDMH at a short contact time of 5-minutes. The addition of metallic ions decreased the amount of BCDMH required to attain a certain probability for successful disinfection according to the probability model. The combined disinfection process is more efficient than the individual processes, can easily be implemented, and has environmental benefits over chlorine treatment. However, the combined technology is more expensive to operate than only BCDMH treatment. The addition of metal ions through ionisation can lead to a 25.67% reduction in BCDMH used, but it comes at an operating cost 2.5 times higher than treatment without metal ions. Final ORP values had no correlation with disinfection success. The change in ORP for the BCDMH treatment showed a significant relationship with treatment success with a p-value of 0.018. The relationship showed that a ΔORP of 164.35 mV should correspond to a 90% probability for successful treatment. However, the maximum experimental ΔORP was only 117 mV. The research showed that metal ions improve the disinfection efficiency of BCDMH. The technology has several advantages, but is not financially justifiable due to the increase in cost when compared to standard BCDMH treatment. The change in ORP was more closely related to disinfection success than to a single ORP value. A full concentration-contact time (CT) investigation would broaden the understanding of the interactions between metal ions, BCDMH, and pathogens.