Water Treatment with Aluminum Sulfate and Tanin-Based Biocoagulant in an Oil Refinery: The Technical, Environmental, and Economic Performance

Abstract

Water extracted from natural sources often requires treatment to meet the quality standards necessary for industrial use, involving physico-chemical processes such as coagulation, flocculation, and sedimentation. Inorganic coagulants, such as aluminum sulfate, are commonly used, although they generate a sludge with residual aluminum, classified as hazardous waste. Given this, biocoagulants, such as natural tannin-based polymers, have emerged as a promising alternative. Thus, the objective of this study was to evaluate the environmental performance of water treatment and sludge disposal at an industrial water treatment plant (WTP) of an oil refinery located in Brazil using aluminum sulfate and biocoagulant. The WTP of this study is located in the state of Bahia, Brazil, and is supplied by a surface water body, the Paraguaçu River—Lago de Pedra do Cavalo—which comes from a semi-arid region, and a lake called Catu Korea. The environmental analysis was carried out using the life cycle assessment (LCA) method, using the methodological framework recommended in ISO 14044, followed by economic analysis and circular economy analysis. The inventory used in the analyses contains field data, company records, related literature, and ecoinvent database version 3.3. The impact assessment considered the ILCD 2011 Midpoint+ method package, the AWARE method, and the cumulative energy demand (CED) method in SimaPro 8.4 software. The comparative results showed the greatest impacts in the Energy Demand, Water Footprint, Eutrophication, and Land Use categories for the biocoagulant scenario, in contrast to the Human Toxicity, Acidification, Ecotoxicity, Particulate Matter, Carbon Footprint, and Abiotic Depletion categories for aluminum sulfate. The economic analysis showed that 65% of the operational costs for material and energy inputs in water treatment are due to the use of electricity, and the water pumping stage is the biggest contributor to this consumption. Even though the price of the biocoagulant was identified as eight times that of aluminum sulfate, the water treatment cost with the biocoagulant was 21% higher compared to that with aluminum sulphate. In this regard, circular economy propositions for sludge valorization are discussed for use, recycling, or proper disposal. Thus, the environmental and economic analysis in this study offers insights into eco-efficiency promotion in water treatment and sludge management.