Abstract
In this study, treatment of a local South African oil refinery effluent using a coagulation flotation process is designed using response surface methodology (RSM). A Box-Behnken design (BBD) implementing the RSM is applied to evaluate the effects and interactions of three operating parameters, viz., pH, coagulant dosage and flotation time, on the treatment of mineral oil wastewater (MOW). Polyacrylamide (Zetag-FS/A50), which is a water-soluble compound, is applied to enhance the adsorption mechanism and intermolecular bridging to minimise the amount of oil droplets. In addition, due to the monomeric nature and the charge density of the Zetag-FS/A50, its efficiency was evaluated to serve as an alternative coagulant for the pretreatment of the MOW. The removal of chemical oxidation demand (COD), soap oil and grease (SOG), total suspended solids (TSS) and turbidity from the MOW were used as the response variables for the coagulation flotation process. This was done with a standard dissolved air flotation jar test. The results show that the actual COD, SOG, TSS and turbidity percentage removal at optimised conditions with a coagulant dosage of 50 mg/L were 82%, 83%,70% and 83% respectively, while the predicted response was 92%, 96%, 73% and 87% for COD, SOG, TSS and turbidity, respectively. The analysis of variance (ANOVA) showed that the proposed models are significant at a 95% confidence level. A quadratic model was generated for response variables COD and SOG, while TSS and turbidity produced a linear model. The models fitted well with the experimental data with correlation coefficients (actual R2) of 0.94 for COD, 0.91 for SOG, 0.81 for TSS, and 0.75 for turbidity. The outcome of the study shows that the RSM has merit to optimise and identify the most important factor to control and the Zetag-FS/A50 coagulant has the potential to adsorb the oil droplets in order to enhance the treatment efficiency of the process.
Highlights
Chemo-physical treatment of industrial mineral oil wastewater (MOW) before discharge is necessary for the conservation of freshwater supplies and the protection of the environment
The Box-Behnken design (BBD) of experiment was adapted from the response surface methodology (RSM) to optimise the relevant operating parameters in order to reduce the researcher’s experimental workload and high cost of chemical usage, and to avoid uncertainty on industrial application
As part of this study, a field study on a local South Africa wastewater treatment process was conducted and an expert consulted at a local water treatment plant reported, based on experience, that Zetag-FS/A50 has super-surfactant merits when applied in treating industrial wastewater
Summary
Chemo-physical treatment of industrial mineral oil wastewater (MOW) before discharge is necessary for the conservation of freshwater supplies and the protection of the environment. The principal focus of addition of coagulant chemicals to physical separation processes is to effectively reduce the workload for downstream treatment This has its own limitations, with high sludge production and a high cost of operational chemical procurement (Hosny et al, 2016; Kweinor Tetteh et al, 2017). As part of this study, a field study on a local South Africa wastewater treatment process was conducted and an expert consulted at a local water treatment plant reported, based on experience, that Zetag-FS/A50 has super-surfactant merits when applied in treating industrial wastewater It has some drawbacks for the environment when attention is not paid to over- or under-dosage, such as (a) re-dispersion of impurities, (b) increase in sludge formation and (c) high turbidity (Bolto and Gregory, 2007; Guan et al, 2014; Oliveira et al, 2014). To assess the accuracy of the model, the predicted value was compared with the experimental results to find the optimal operating parameter
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