Integrating Wastewater Reuse with Seawater Desalination

Freshwater shortages are forcing industrial customers to rethink water supply options. Industrial facilities located near oceans or saline aquifers around the world are relying more on desalination technology to provide freshwater.  Industrial facilities are also facing stricter discharge regulations that can favor development of nonconventional water resources, such as wastewater effluent and produced water.  Therefore, innovations in technologies that improve wastewater treatment to meet restrictive discharge limits and requirements for reuse, may ultimately lower costs and allow for production expansion without the need to secure more freshwater or increase wastewater treatment capacity. 

Seawater desalination and wastewater reuse are now common in coastal regions that experience freshwater shortages. This paper reviews a recent application of desalination and industrial wastewater reuse by reverse osmosis (RO), and describes the methodology used in designing an integrated freshwater production plant and wastewater reuse unit at a large grass root industrial facility in the Middle East.  The characteristics of the treated wastewater and reuse requirements and their impact on the overall system are discussed in detail.  However, production of potable water by RO is not considered in this paper.

Although the energy costs associated with desalination remain a concern, improvements from advances in system design, energy recovery and operating knowledge have resulted in lower overall costs.  The cost for implementing desalination technologies is site specific.  For a large desalination plant with a capacity over 100,000 cubic meters per day (m³/day), which is typical for a city or a large industrial application, the cost per cubic meter is inversely proportional to the production capacity.  The economic considerations discussed in this paper compare the cost of increasing seawater desalination capacity by RO technology to installing and operating a membrane bioreactor (MBR) based wastewater reuse treatment system capable of producing plant utility water.  Included in the cost comparison are a wastewater treatment process designed only for ocean discharge and an upgraded system designed for feed to a post-treatment effluent reuse system, such as an RO, that utilizes a Membrane Biological Reactor (MBR) unit as the biological treatment step.