This paper presents an eco-efficiency analysis of five scenarios for treating a petrochemical unit effluent defined sequentially to increase the water reuse rate to the limit condition of Zero Liquid Discharge perspective. The base process, consisting of reverse osmosis, an evaporator and crystallizer, displayed pretreatment alternatives the addition of antifouling agents, desupersaturation of barium ions and coprecipitation of low solubility salts to increase osmosis efficiency. The eco-efficiency analysis applied the life cycle approach to verify environmental and energy performances and determined the costs of the treatment unit installation and operation for a time horizon of 9.5 years. The pretreatment increased water recovery during osmosis from 84% to over 97%. The environmental-energetic analysis indicated a strong influence of electric energy, consumed mainly during the thermal stages of the treatment, and of the chlorine-derived compounds used in the pretreatment. Also due to pre-treatment, it was possible to reduce impacts in terms of Global Warming Potential by up to 59%, and in Primary Energy Demand by 64% for the best scenario. The economic analysis depicted a significant influence of operating costs, and the electricity consumed in the processes is responsible for the largest share of expenses. The reuse water presented a cost ranging between US$ 1.08/m3 and US$ 1.80/m3. The systems with pretreatment by coprecipitation with Ca(OH)2 and CaCO3 and monoacids to adjust the pH of the final effluent showed to be more eco-efficient than the other options under analysis.
Keywords: Eco-efficiency; Evaporative crystallization; Oil refinery; Water reuse; Zero Liquid Discharge.
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