Question: Stricter wastewater regulatory environments and water availability continue to drive water reuse and recycle in the chemical and petrochemical industries globally. What should companies consider when evaluating water reuse as part of the manufacturing and wastewater process?
Answer: While reusing wastewater can be an economical alternative to internal or external fresh water supplies, there are many factors that must be addressed, which can impact the reliability of the reuse system and the associated cost of wastewater reuse. Doing a proper evaluation of these factors can ensure a well operating water-reuse system, as well as a continuous and economic stream of high quality water for the facility.
There are several key factors when evaluating whether or not water reuse is an option for your facility. Understanding the true cost of fresh water and the reliability of that water supply are just as important as the water quality and quantity requirements for your specific facility. For wastewater generated and discharged from the facility, regulatory requirements must be met. Don’t overlook treated wastewater as a water source for your facility. It can be economical to provide the additional treatment required to reuse this water within your facility. Finally, match the water requirements of your facility with the available water/wastewater generated within the facility.
Reusing water from a plant’s wastewater facility may appear to be the best place to start. However, there are many other potential sources of water within a facility that provide opportunities for reuse without the potential difficulties associated with chemical plant wastewaters. Some of those waters are storm water, washdown water and condensate. There may even be specific process operations, which generate a wastewater that is relatively easy to reuse with minimal treatment. Understanding the sources and characteristics of all wastewaters generated in the facility, as well as where water is used in the facilities and the quality of the water required at each point of use, is absolutely essential to developing any wastewater recycle/reuse strategy. The higher the water quality need is, the more complicated (and expensive) the wastewater reuse system can become.
In addition, it is critical to understand fully the water/wastewater characteristics targeted for reuse to ensure proper technology fit. Even in the best operated facilities, there are still compounds and substances that may be present in the treated wastewater, which can negatively impact reuse technologies, if they are not properly selected. Some reuse technologies, like membrane-based equipment, are significantly more sensitive to the upset conditions and pollutants commonly found in chemical and petrochemical wastewater streams. Selection of the wrong reuse technology can have serious implications.
Don’t forget the waste stream. Remember that recycle and reuse of wastewater does not make the wastewater go away — it’s just concentrated. There is always some type of waste stream that must be disposed of, whether it is liquid or solid. When making the reuse decision, consider the pollutants present in the concentrated waste stream and the associated disposal costs.
Finally, determine the economic feasibility of recycle and reuse. While 100% recycle and reuse of wastewater is a desired goal, consider the costs. It may be significantly less expensive to recycle and reuse only 80% of the wastewater, while capturing the last 20% may not be practical, due to the associated cost of equipment and operations.
Thomas Schultz is a director of petroleum and chemical industry for Siemens Water Technologies Corp. (Waukesha, Wis.; www.water.siemens.com)