Reusable Petrochemical Wastewater Via High-Performance Reverse Osmosis Membranes

Increased water stress and reduced availability is driving more industrial facilities to implement wastewater reuse strategies. In the United States, specifically in Texas, petrochemical plants are typically built near oil reserves. These industrial facilities, along with the surrounding areas, are repeatedly experiencing periods of drought coupled with increased demand, straining the local water reserves[1-3]. Industrial water conservation is needed to ensure ample water availability for all consumers in a region. Unfortunately, many industries operating in the United States have been hesitant to adopt modern industrial wastewater reuse strategies. Conversely, it is common for petrochemical plants in China to implement water conservation measures through recycling and reuse of wastewater. The established experience in China can be leveraged to provide low risk and robust wastewater reuse strategies.
In a typical wastewater treatment design, a myriad of waste streams, such as used process water, storm water, boiler blowdown, etc., are combined in a wastewater equalizer tank. Then, a series of pretreatment steps are taken to reduce the total organic carbon (TOC), large sediments, oils, etc. to comply with local environmental discharge regulations. Rather than discharging the treated water, the water can be further treated with ultrafiltration and reverse osmosis modules to recover and reuse upwards of 75% of that water for reuse . This can reduce the burden on the regional water supply and provide facilities a means to operate under sustainable water consumption levels. Brackish water reverse osmosis (BWRO) modules utilized in wastewater treatment tend to face harsh conditions due to exposure to fouling-prone waters and high concentrations and variations of TOC and total dissolved solids (TDS). Modules utilized in these situations must be designed to provide a stable rejection of TDS and other dissolved organic species. Furthermore, these RO membranes, regardless of the degree of fouling resistance, must be able to withstand repeated exposure to a broad pH range to facilitate effective cleaning without gradation over a typical 3-5-year lifetime.
This work showcases the performance of FilmTec„ Fortilife„ CR200, an advanced, fouling-resistant reverse osmosis membrane module, in a small-scale, two-stage reverse osmosis water reuse pilot treating wastewater from a petrochemical plant in China. The objectives of this pilot study are to demonstrate the effectiveness of this recently released solution for treating challenging waters while also showcasing the existing wastewater treatment strategies that can be leveraged across the world and across a multitude of industries.
The pilot at the focus of this study was operated continually for 230 days and controlled to a constant system flux of 18 LMH and overall recovery of 70%. The feed water quality was highly variable and ranged from 1000-2000 mg/L TDS, 4-10 mg/L TOC, 25-40 °C, and pH 4-8. Over this period, four (4) clean-in-place (CIP) cycles occurred. Throughout the pilot, the normalized permeate flow, feed-concentrate differential pressure, and permeate conductivity were monitored for both stages. Permeate samples were periodically taken to provide additional insight into the species-specific rejection.
Throughout the pilot operation, the normalized permeate flow decreased due to the high contamination levels of the feed water. The permeate flow loss was recovered after each CIP cycle, demonstrating the cleanability of the CR200 reverse osmosis module. Furthermore, the required CIP frequency was 6-8 weeks, which is a manageable timeframe for system maintenance. The feed-concentrate differential pressure remained before 0.7 bar (10.2 psi), which is roughly 50% of an industry-standard BWRO element of similar construction. This reduced differential pressure allows for a higher net-driving pressure in the second stage and improved flux balance by minimizing regions of high flux, which increase fouling potential. The permeate conductivity remained well below the 200 µS/cm threshold for reuse, as defined by the facility. Furthermore, the TOC rejection remained above 97%, despite variable feed water quality and repeated cleanings.
In summary, this pilot study demonstrates the high-performance capability of FilmTec„ Fortilife„ CR200 to provide a robust and reliable solution for treating petrochemical wastewater. Advanced reverse osmosis technology can provide fouling resistance in conjunction with manageable and increased time between necessitated cleanings without sacrificing permeate water quality or availability. Petrochemical plants in other regions of the world, who are not implementing wastewater reuse strategies, can leverage the experience gained in the petrochemical industry in China to provide sustainable water reuse solutions for all.