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Optimisation of Dissolved Air Flotation (DAF) for Separating Industrial Mineral Oil from Water

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Optimisation of Dissolved Air Flotation (DAF) for Separating Industrial Mineral Oil from Water Optimisation of dissolved air flotation (DAF) for separating industrial mineral oil from water A dissertation submitted in fulfilment of the academic requirements for the degree of Master of Engineering Department of Chemical Engineering, Faculty of Engineering and the Built Environment, Durban University of Technology Emmanuel Kweinor Tetteh Date: January 2018 Supervisors: Prof S. Rathilal & Ms K. Robinson Preface This project was carried out under the joint support from Durban University of Technology, Department of Chemical Engineering and FFS Refiners (Pty) Ltd, under the supervision of Prof. Sudesh Rathilal and Ms Kate Robinson as respectively affiliated. The batch DAF jar test experiments were conducted at Wiggins Umgeni Water, Process Evaluation Facility (PEF) centre. The yield analysis of the soap oil and grease (SOG) was carried out at the FFS Refiners production laboratory. This project was completed over a stipulated period of 21 months, from April 2016 to January 2018. I, Emmanuel Kweinor Tetteh, hereby declare this research report titled “Optimisation of dissolved air flotation (DAF) for the separating industrial mineral oil from water” is my own investigation results under the guidance of my supervisors, and unless otherwise indicated or acknowledged. The results presented has not been submitted in part or in full to any other University or Institute for any award of degree. Furthermore, I have indicated in detail the part that is reproduced of which I am an author, and have fully listed such publications and others been acknowledged in the reference section. I also attest that this dissertation has been evaluated using “Turnitin originality check” system and based on that, the reference (Harvard-DUT system) are in accordance with good scientific practice. Dissertation ID number in Turnitin: 900098656 Date check: 03-Jan -2018 04:58PM (UTC+0200) Word count: 48107 Character count: 274027 Emmanuel Kweinor Tetteh Signature:………………… Date:…………………….. Signature of Supervisor:……………….. Date:…………………….. i Declaration I, Emmanuel Kweinor Tetteh, the undersigned candidate declare that (i) The research reported in this dissertation, except where otherwise indicated, is my original work. (ii) This dissertation has not been submitted for any degree or examination at any other university. (iii) This dissertation does not contain other persons’ data, pictures, graphs or other information, unless specifically acknowledged as being sourced from other persons. (iv) This dissertation does not contain other persons’ writing, unless specifically acknowledged as being sourced from other researchers. Where other written sources have been quoted, then: a) their words have been re-written but the general information attributed to them has been referenced; b) where their exact words have been used, their writing has been placed inside quotation marks, and referenced. (v) Where I have reproduced a publication of which I am an author, co-author or editor, I have indicated in detail which part of the publication was actually written by myself alone and have fully referenced such publications. (vi) This dissertation does not contain text, graphics or tables copied and pasted from the Internet, unless specifically acknowledged, and the source being detailed in the dissertation and in the References sections. Signature: ……………………. Date:………………… As the candidate supervisors, we do agree to the submission of this dissertation that has orally been defended. Prof. Sudesh Rathilal (Main supervisor) Ms Kate Robinson (Co-supervisor) Signature of supervisor:……………. .. Date:……………………. Copyright © 2018 Durban University of Technology All rights reserved ii Acknowledgements Firstly, I would thank God Almighty, the giver of Life (Christ Jesus) for granting me the Grace, Mercy and Inspiration to bring this project into a reality. I would like to express my deepest gratitude to my main supervisor Prof. Sudesh Rathilal, for his useful critiques, guidance and support throughout the research work. I also wish to thank my co-supervisor Ms Kate Robison (Production and Process Development Manager, FFS Refiners Pty Ltd SA), for her encouragement, assistance and directions provided when urgently needed. Special thanks to the following personalities, Ms Keshnee Naik (R&D Chemist), Mr Theolan Naidoo (Production Supervisor) and Mr Mahendra Reddy (Plant operator) all at FFS Refiners (Pty) Ltd. Likewise Dr Rachi Rajogopaul (Snr Scientist) and Mr Lidenlani Sibiya (Process Engineer) at Umgeni Water (PEF), for their constructive discussions and suggestions from their fields of expertise. I extend my thank you to all the staff and technicians for their kind assistance during the experiments. Thank you also goes to Mr Christy Terrence and Mr Jaafar Mohammed for their assistance together with Lovemore Bros Machinery SA, for moving the DAF pilot plant to site for the analysis. Furthermore, I will like to thank Durban University of Technology for their financial support under Research Focus Area–Water, and Prof. Raul Munoz of University of Valladolid for an impactful experience during the Erasmus K107 programme. In addition, I appreciate the efforts of all the staff and colleagues at the Department of Chemical Engineering, including Prof Paul Musonge (Deputy Dean) and Dr Yusuf Isa (Snr Lecturer /HOD) for their steady help and remarks. I say thank you to Ms Martha Chollom, Mr Edward Kwaku Armah, Mr Nkululeko Nkosi and Mr Denis Asante-Sackey for their time in proof reading the dissertation. Finally, my warmest thank you to my father in the Lord, Pastor Dr. Obed Obeng –Addae (Christ Cosmopolitan Incorporated, Kumasi Ghana), my Parents and Siblings of the Tetteh’s Family for their endless love and prayers. To all those whose names are not mentioned, I do appreciate you all for your kind effort and support. Let the rewarder of the Heaven and Earth, the Good God bless you all in Jesus mighty name. Amen! iii Dedication This dissertation is dedicated to my lovely parents Mr Felix Tetteh and Mrs Mary Amoah Tetteh, my siblings and my good friend Light Josephine Amgbo for their support and guidance. iv Abstract Industrial mineral oil wastewater from oil refineries and petrochemical processing poses a major environmental concern. Effluents from these processes is usually poor as it is heavily polluted, thus have high chemical oxygen demand (COD), soap oil and grease (SOG), turbidity, total suspended solids (TSS) amongst others. This wastewater, if discharge without treatment, causes severe pollution, oxygen depletion, and imbalanced ecosystem and human health risks. The main aim of this research was to modify, optimise and evaluate the performance of a continuous process using dissolved air flotation (DAF) pilot to treat wastewater from a local South African oil refinery wastewater treatment plant (WWTP) with the benefit of recovery of the oil from the wastewater. The study evaluated the feasibility of using different acids and coagulants. One factor at time (OFAT) approach was used on the DAF jar tester to identify the most important variables that affects the DAF treatability performance. The factors considered were; pH, flotation time, coagulant dosage, air to water ratio and air saturated pressure. The ranges considered for the factors were pH (4−6), flotation time (5−15 minutes), coagulant dosage (10−50 mg/L), air to water ratio (5–15%) and air saturated pressure (300–500 kPa). The key process operating parameters obtained from the OFAT were optimised using the Box Behnken design (BBD) adapted from response surface methodology (RSM). The BBD used had three levels, three factors and five centre points. This was employed to establish the relationship that existed between the water quality (contaminants) and the key interacting factors of the DAF jar tester, thus employing the most applicable combination of the factors on a continuous DAF pilot plant. The study was configured into two; Acid – Coagulation-DAF (pre-treatment) and Acid –DAF – Coagulation (post treatment). Three acids were investigated for their efficiency in the pre- treatment step, while four cationic inorganic coagulants and three polymeric organic coagulants were used both for the pre and post treatments. The OFAT experiments resulted in more than 75% removal efficiency of COD, SOG, TSS and turbidity. The removal efficiency was obtained at the following optimum values of pH 5, flotation time of 15 minutes at a coagulant dosage of 50 mg/L and an air to water ratio of 10% and finally, air saturated pressure was 350 kPa. On the other hand, BBD results showed 85% treatability performance at a lower coagulant dosage (30–45 mg/L), moderate air saturator v pressure (300–425 kPa), and air-water ratio (8–12%) on the batch scale. While on the continuous process, the optimum coagulant dosage was around 100–180 mg/L. From the BBD results, the interacted factors for consideration were the air saturated pressure and coagulant dosage. These factors enhanced process control. The validation of all the response quadratic models were in good standing with the analysis of variance (ANOVA). The experimental results and the predicted models results agreed at 95% confidence level, finally, the models were significant and verified. Comparative studies of the pre and post treatment showed that 1 M H3PO4 was the most effective, economical and environmentally friendly acid to be used for both processes. Two cationic inorganic (alum and ferric chloride) and two polymeric organic (Z553D-PAC and Zetag32-FS/A50) coagulants were found to be effective with
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