Executive Summary The goal behind zero liquid discharge in a petroleum refinery refers to achieving a high enough purification of wastewater through treatment of contaminants so that water disposal is completely eliminated. By minimizing freshwater usage to that which is required only for start-up, petroleum refineries could cut freshwater consumption costs and promote a safer environment by disposing of fewer contaminants into sources of water. By modeling the contaminant outlet concentrations of the various regeneration processes, more realistic, detailed, and accurate results showed an optimal total annual cost of $950,000 associated with water using processes or a freshwater consumption of 31 tons/hour. Mathematical models have been developed that optimize the way in which water streams run through a refinery. Currently, methods are being employed which model regeneration (i.e. water treatment) and water-using processes under the assumption of fixed outlet concentrations or a fixed process efficiency.
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