Vatten- och energiförbrukning är ett av mänsklighetens största nuvarande och framtida problem då världens vattenkonsumtion ständigt ökar på grund av bättre levnadsstandard samt ständigt ökande population och industrialisering. Förorenat vatten orsakar sjukdomar, sänkt livstid, reducerad sanitet och försämrad hälsa. Att rena vatten på ett energi- och miljöeffektivt sätt så att det kan återanvändas är därför ett måste för en hållbar framtid. En undersökning av koaguleringsförmågan för ett antal utvalda organiska föreningar via elektrokoagulation har utförts hos företaget Axolot Solutions AB. Axolot Solutions AB är ett företag som arbetar med rening av industriella vatten med elektrokemiska metoder, framförallt elektrokoagulation. De organiska föreningar som undersökts har delats in i grupperna sockerarter (maltos, raffinos, glukos samt laktos), organiska syror (myrsyra, citronsyra, hexansyra, smörsyra, oktansyra), alkoholer (1-propanol, 2-propanol), fettsyror (lecitin) och övriga (formaldehyd, vanillin, nonylfenol, α-pinen). Även ett industriellt vatten från en barkavvattningsprocess har undersökts samt modellvatten av ämnena xylan och lignin som kan hittas i barkvatten. Reningsförmågan av processen har undersökts genom att mäta COD halter före och efter behandling med ett kontinuerligt elektrokoagulationssystem. Varje förening har undersökts vid fyra olika initial pH: 4, 6, 7,5 och 9 och dessutom såväl järnanod och aluminiumanod testats. Även olika strömstyrkor har undersökts för ett par av de organiska föreningarna. Resultaten visar ingen COD reduktion för vatten innehållande xylan, sockerarter, organiska syror och alkoholer. Tekniken visade mycket god reduktion av ämnena: lecitin (85,5%) och lignin (98,1%). En mindre reduktion skedde även för vatten innehållande nonylfenol (33,6%), α-pinen (42,1%), och barkvatten (21,5%). En reduktion av COD skedde även för vanillinvatten med initial pH 4 vid användandet av aluminiumanod, detta var dock det enda vattnet innehållande vanillin som påverkades. Det går inte att dra någon generell slutsats kring vilket initial pH och vilken anod som bör användas vid elektrokoagulation då den mest effektiva anordningen inte är densamma för de olika undersökta föreningarna. / Water- and energy consumption is one of humanities biggest current and future problems because of ever increasing global water consumption and because of better living conditions, increasing population and industrialization. Polluted water results in diseases, reduced life expectancy, sanitation and reduced overall health of those affected. Purifying water in an energy and environmentally effective way is therefore a must for a sustainable future. A study of the coagulation capabilities for a select number of organic compounds by electrocoagulation has been performed at Axolot Solutions AB. Axolot Solutions AB is a company developing electrochemical water treatment solutions, with a focus on the electrocoagulation process. The compounds that have been studied are sugars (raffinose, maltose, glucose, lactose), organic acids (formic acid, citric acid, hexanoic acid, butyric acid, octanoic acid), alcohols (1-propanol, 2-propanol), fatty acids (lecithin), others (formaldehyde, vanillin, nonylphenol, α-pinene). Industrial water coming from a debarking process was also investigated as well as two compounds that are often present in this type of water, xylan and lignin. The treatment efficiency was determined by measuring the COD values of the investigated water before and after the electrocoagulationprocess. Each compound was studied by using an iron anode and an aluminum anode at four different initial pH values: 4, 6, 7.5, 9. Different current densities were also studied for some of the investigated compounds. The results show no COD reduction for sugars, alcohols, organic acids and xylan. The process resulted in large reductions of the compounds lecithin (85.5%) and lignin (98.1%). A lesser reduction was found for the waters containing: nonylphenol (33.6%), α-pinene (42.1%) and barkwater (21.5%). A reduction of COD was also found in the water containing vanillin with an initial pH of 4 that was treated with an aluminum anode was affected. The most efficient setup for the investigated compounds varies. For that reason, no conclusion as to which initial pH and anode that should be for electrocoagulation processes in general can be drawn.

Produced water is the largest waste product by volume in the oil industry and its treatment in onshore or offshore fields poses bigger and different challenges than what water engineers are used to encounter. Process to achieve reuse quality of this water is very expensive with many technical hurdles to overcome making the optimization of the treatment steps necessary. Electrocoagulation (EC) generates coagulants in-situ responsible for destabilizing oil droplets, suspended particles, and common pollutant in produced water. Furthermore, EC is a very efficient technology compared with traditional primary treatments used in the oil & gas industry and has several advantages such as: no hazardous chemical handling (which diminishes the risk of accident and logistic costs), high efficiency potential concerning boron removal, potential small footprint and less sludge generation. In this research, the treatment of produced water using EC was investigated in a practical manner for the oilfield to aim for a cleaner effluent for further processing and help to achieve a reuse quality. For this, an EC cell was designed using different parameters normally used in the literature to fit this scenario. After preliminary tests, the treatment time was set to 3 seconds. Response surface method (RSM) was employed to optimize the operating conditions for TOC removal on a broad quality of synthetic produced water while varying: salinity, initial oil concentration and initial pH. TOC was chosen to be the main response because of its importance in legislation and sensibility on the method. Furthermore, turbidity removal, change of pH value after EC in water with lack of buffer capacity, aluminum concentration and preliminary tests involving boron removal and influence of hydrogen carbonate were also studied. Real produced water was treated with EC to assess the optimum conditions obtained by the RSM showing the results were closely related. Finally, an estimation of volume required and operating cost for EC in the different types of produced water was made to assess how realistic it is for onshore and offshore applications.:ERKLÄRUNG DES PROMOVENDEN I ACKNOLEDGEMENT III ABSTRACT V TABLE OF CONTENT VII LIST OF FIGURES IX LIST OF TABLES X LIST OF EQUATIONS XII ABBREVIATIONS XIV 1. INTRODUCTION 1 2. PRODUCED WATER 6 2.1 Characterization of Oilfield Produced Water 6 2.2 Produced Water Management 10 2.2.1 Discharge and Regulations 10 2.2.2 Efforts on Reuse 11 2.2.3 Cost 14 3. PRODUCED WATER TREATMENT 17 3.1 Most Common Primary Treatment 17 3.1.1 Hydrocyclones 17 3.1.2 Flotation unit 18 3.2 Further Water Treatment Technologies 19 3.2.1 Membrane Process 19 3.2.1.1 Microfiltration 19 3.2.1.2 Ultrafiltration 21 3.2.1.3 Nanofiltration 23 3.2.1.4 Reverse Osmosis 24 3.2.1.5 Forward osmosis 24 3.2.2 Electrodialysis 25 3.2.3 Biological treatment 28 3.2.3.1 Aerobic and anaerobic process 28 3.2.3.2 Combining membrane and bio-reactor 29 3.2.4 Oxidative process 30 3.2.4.1 Oxidation process 30 3.2.4.2 Anodic oxidation 32 3.2.5 Thermal technology 34 3.2.5.1 Evaporation 34 3.2.5.2 Eutectic freeze crystallization 35 3.2.6 Adsorption and ion-exchange 36 3.3 Electrocoagulation 39 3.3.1 Colloidal Stability Theory 39 3.3.2 Theory of Electrocoagulation 40 3.3.3 Mechanism of Abatement of Impurities 44 3.3.4 Operational parameters and efficiency 49 4. MATERIALS AND METHODS 51 4.1 Analytical Techniques and Synthetic Solutions 51 4.1.1 Analytical Techniques 51 4.1.2 Synthetic Produced Water 51 4.2 Design of Experiment and Models 54 4.3 Experimental Protocol for EC 56 4 .4 Development of the new Electrocoagulation cell 57 4.5 Real Produced water 58 5. RESULTS AND DISCUSSION 59 5.1 Designing EC Cell Process 59 5.1.1 Computational Fluid Dynamics for EC manufacturing 59 5.2 Preliminary Experiments 61 5.2.1 TOC Removal and Residence Time Determination 61 5.2.2 Aluminum Concentration 64 5.3 Models Quality and Range of Validity 66 5.3.1 TOC Removal 66 5.3.2 Turbidity Removal 69 5.3.3 Final pH value 71 5.3.4 Ionic Strength and Interpolation for Different Salinities 73 5.3.5 Partial Conclusions 76 5.4 Evolution of the Final pH Value 78 5.5 Operation Region for Effective Treatment of Produced Water with EC 80 5.5.1 Produced Water with Low Salinity 80 Organic Compounds Removal 80 Turbidity Removal 83 5.5.2 Produced Water with Medium Salinity 84 Organic Compounds Removal 84 Turbidity Removal 86 5.5.3 Produced Water with High Salinity 87 Organic Compounds Removal 87 5.6 Influence of Hydrogen Carbonate 90 5.7 Real Produced water 91 5.8 Boron Removal 93 5.9 Estimation of the Size for EC in Full scale 94 5.10 Produced Water with Very Low Salinity and EC 95 5.11 Estimation of Operation Cost 96 6. CONCLUSION AND RECOMMENDATIONS 98 6.1 Conclusion 98 6.2 Recommendations for Future Work 101 Scale up on EC for upstream 101 Further processing and reuse 101 Online optimization for EC 101 Recommendations for any research related to upstream produced water 101 BIBLIOGRAPHY 102 APPENDIX A 117 APPENDIX B 120