Application of Membrane Bioreactor Technology for
Produced Water Treatment
Corresponding author:
Arnold Janson, M.A.Sc., P. Eng., ConocoPhillips Global Water Sustainability Center, Doha, Qatar
Email:
Contributing authors:
Ana Santos, Ph.D., ConocoPhillips Global Water Sustainability Center
Mary Katebah, B.S., ConocoPhillips Global Water Sustainability Center
Altaf Hussain, Ph.D., ConocoPhillips Global Water Sustainability Center
Joel Minier-Matar, M.S., ConocoPhillips Global Water Sustainability Center
Simon Judd, Ph.D., Cranfield University
Samer Adham, Ph.D., ConocoPhillips Global Water Sustainability Center
Abstract
Water security has been identified as one of three “priority challenges” for the State of Qatar. The gas industry can contribute to meeting this challenge by developing novel treatment methods to enable cost-effective reuse of the large quantities of produced water (PW) extracted during gas field operations. With proper treatment to remove organics and inorganics, the PW could be used as process make-up water in on-shore operations, thereby reducing the industry’s need for potable water and making more of that potable water available for more important activities.
To remove organics from wastewaters, biological treatment is generally regarded by engineers and scientists as the most cost-effective method. In the treatment of PW though, conventional biotreatment faces distinct challenges since the PW composition can dramatically affect sludge settleability, a critical parameter in the operation of these systems. Membrane bioreactors (MBR) have an inherent advantage and have been proven to be successful in the treatment of “difficult-to-treat” wastewaters because a membrane filteris used to separate the treated water from the activated sludgerather than separation being contingent on sludge settleability.
In this study, the results of various bench-scale studies on the application of MBR technology to the biotreatment of PW from Qatari gas fields are presented. These results included tests on PW from both summerand winter operations. While the summer PW contains limited organics (COD ≈1,200 mg/L), the winter PW contains kinetic hydrate inhibitor (KHI) at a level of ≈1.5%, raising the COD to ≈30,000mg/L and putting a significantly higher organics load on the biotreatment process.
The results indicated that in treating summer PW, on average, 60% of the chemical oxygen demand (COD)could be removed in an MBR. It is noted thatabout 1/3rd of this removalwas attributed to physical processes. The results also showed that the operatingconditions(hydraulic retention time, solids residence time, temperature)hadno statistically significant impact on removal over the ranges tested. Whilst trends were consistent with some previous reported studies performed on refinery wastewater, overall removals were lower than expected. However, all feedwater acetateand over 90% of the oil and grease wereremoved by the MBR. In the treatment of winter PW, the results indicated that approximately 50% of the COD & TOC associated withKHI can be removed biologically. Upon feeding of the KHI to the bioreactor, a rapid decrease in dissolved oxygen concentration was recorded indicating a rapid response by the organisms to the presence of KHI. Oxygen uptake rates of 1.6 to 2.0 mg O2/L-min were routinely obtained.