Demonstration of Dissolved Organics Removal from Produced Water

Abstract

Abstract The biological GAC-FBR process is a high rate treatment system for economically degrading dissolved organics, such as benzene, aromatic and aliphatic hydrocarbons, and organic acids at high rates and short residence times. In many instances, removal of water soluble organics, after deoiling, is sufficient for meeting surface discharge of produced waters. At other sites, a reduction in the TDS concentration will be necessary prior to meeting surface discharge requirements. Results of a field demonstration in Wyoming (up to 350 bbl/day) where a treatment train consisting of deoiling, followed by removal of water soluble organics using the GAC-FBR are presented. Because of a high concentration of organic acids present in this water, a two-stage FBR system consisting of sequential anoxic and aerobic treatment was used to treat produced water from this site. Consistent removal of organics was observed even during periods when the up-front deoiling was not operating properly. Effluent O&G of less than 5 mg/L was consistently achieved with an O&G concentration of 53 mg/L after induced gas flotation. Most organics (i.e., BTEX, acetate) were removed to near or below detection limits. Based on the results obtained, costs for organics removal (deoiling followed by the GAC-FBR for water soluble organics removal) were estimated for 4000 barrels per day of produced water. The total cost, including 10-year amortization of capital, was estimated to be $0.068 per barrel. O&M costs for a single-stage aerobic treatment system were approximately $0.02 per barrel. Introduction The fluidized bed reactor (FBR) is a high-rate, biological fixed-film treatment system that offers stable, efficient destruction of organic pollutants from dilute aqueous streams. FBR systems can be operated under conditions where control of biofilm thickness and mean cell residence times can be achieved. The Granular Activated Carbon-Fluidized Bed Reactor (GAC-FBR) system modification of the process combines the advantages of biological and physical treatment in a single, robust unit operation. The process has been successfully used at full scale for a number of applications including wastewaters from chemical plants, refiners, bulk storage terminals, and municipal wastewaters. The process can be operated as an aerobic, anoxic (denitrifying) or anaerobic system. The use of an adsorptive biomass carrier in the form of granular activated carbon (GAC) affords the process robustness during adverse environmental conditions beyond that possible with other biological fixed film systems. The adsorptive capacity of the GAC carrier particles serves as an effective organic load-leveling system; compounds are adsorbed during periods of high concentration and later desorbed and degraded as they migrate back through the biofilm. This results in the process being an ideal candidate for treating produced waters, which can be highly variable in both concentration and composition. Background Initial Testing. Prior to conducting the field demonstration, a treatability study was conducted over two, four day periods, using produced water shipped from the site and a 550 gallon per day (maximum flow rate) laboratory-pilot GAC-FBR system operated under aerobic conditions. Produced water, amended with phosphate and ammonia at stoichiometric ratios of COD:N:P of 100:5:1, was delivered to the reactor at four different flow rates and organic loading rates (OLRs). The OLRs tested during this treatability experiment ranged from 1.5 to 8.7 Kg COD/m3-d. Effluent concentrations of organic acids and BTEX were all consistently below detection limits (3 mg/L for organic acids and 1 g/L each for BTEX constituent). Applied OLR was limited by the solubility of dissolved oxygen. P. 281^