Whereas the use of recycled municipal wastewater has been practiced for a number of years, the use of recycled wastewater in the petroleum industry has been limited. Nonetheless, tightening effluent regulations and diminishing freshwater supplies have generated interest in the treatment of refinery wastewaters for reuse. Historically, refinery wastewater has been treated to various degrees of effluent quality by means of oil/water separation and biological secondary treatment. This level of treatment was not able to produce a treated effluent that is suitable for reuse in the refinery process. Recent developments in membrane technology have enabled refineries to implement treatment strategies that allow process wastewater to be treated and reused. Applications of the reuse within the refinery include cooling tower make-up and boiler feed water.
An added benefit of membrane technology is the flexibility of how it can be implemented into greenfield sites or retrofitted into existing plants. Membrane bioreactors eliminate the need for a secondary clarification step and ensure a minimal footprint. Tertiary filtration is an excellent polishing step for existing plants that need further treatment or the reliability that membranes are able to guarantee. Regardless of which configuration is chosen, the end result is a high quality effluent that is suitable for re-use, including feed to reverse osmosis.
Case studies of full-scale systems operating with reinforced immersed hollow fiber membrane technology are included to provide an example of applications where refineries have employed this technology to achieve their treatment objectives and reuse goals.
The use of recycled municipal wastewater, specifically Title-22 quality water, has been practiced for several years in many areas of the United States with varying degrees of success. With tightening effluent regulations and diminishing freshwater supplies as well as advances in membrane technology, reuse is now being practiced reliably in applications previously not considered economically or technically feasible. There has also been a trend in recent years to restrict or eliminate access to publicly owned treatment works (POTW) for any type of oily wastewater or refinery discharge. In the past, the reuse of oily or refinery wastewater has been restricted due to perceived limitations of both the technology and the cost of treatment. However, thanks to continued developments in membrane based wastewater treatment technology, the cost associated with designing and constructing reuse facilities in plant upgrades or expansions can be the same or lower than the cost associated with a new fresh water treatment system.
Historically refinery wastewater flows have been treated in a number of process steps generally consisting of oil/water separation, biological treatment and perhaps tertiary filtration/absorption. Biological treatment has included a vast range of treatment technologies, including activated sludge (conventional, contact stabilization and extended aeration) as well as some limited applications of sequencing batch reactors. This treatment configuration was successful when high quality reuse water was not required or when effluent regulations permitted direct discharge to the environment. However, it suffered from an inability to provide a consistent final effluent quality especially during wastewater flow or load changes common in an operating refinery. Consistent high quality reuse water is critical, especially when followed by additional downstream polishing to reduce total dissolved solids (TDS). The type and quality of wastewater generated from oil production facilities or a refinery depends on a