The objectives of this project are to develop and test a new method for delivering a Fe3+ coagulant and disinfectant for treating flowback and produced water (FPW) at a 25 gallons per minute pilot scale. The goal is to treat the water so that it can be reused for fracking and water-flooding at an overall cost savings of at least 50% compared to commercialized processes. The proposed technology consists of: 1) an electrochemical cell for producing acid, base and disinfectant; 2) scrap iron filings as an inexpensive source of iron coagulating agent; and 3) dissolved air flotation for flocculate removal. The process eliminates the electrode fouling issues associated with electrocoagulation and reduces the cost for providing the Fe3+ coagulant by a factor of ~3 over chemical coagulation, and by a factor of ~10 over traditional electrocoagulation.
University of Arizona – Tucson, AZ 85721
WaterTectonics, Everett, WA 98203
FPW contains suspended and colloidal solids, dissolved organic compounds (e.g., naphthenic acids, BTEX), H2S, microorganisms, salt ions (mostly Na+, Cl-, SO42-), and potentially scale forming cations (e.g., Fe2+, Ba2+, Ca2+, Mg2+ Sr2+). The properties of FPW vary by region of the country and time for a given well. In most cases, the total dissolved solids (TDS) concentration is greater than that of sea water (35,000 mg/L) and can be as high as 300,000 mg/L. Treatment for FPW in fracking and secondary oil recovery requires removal of 1) solids; 2) H2S; 3) dispersed oil; 4) Fe2+; and sometimes 5) partial removal other scale forming cations (e.g., Ba2+, Ca2+). Disinfection prior to storage is also desirable to reduce the need for organic disinfectants (e.g., glutaraldehyde) during reuse. A recent publication reviewed 16 commercialized FPW treatment technologies; all but one employed some form of coagulation treatment. Coagulation and flocculation processes remove water contaminants via formation of high surface area, high porosity flocs that adsorb cations, microorganisms, and hydrophobic organics; and entrain particles and dispersed oil. For solid particle removal, coagulants promote electrical double-layer compression and charge neutralization, thereby encouraging particle aggregation. The coagulated flocs and aggregated particles can be removed from solution via settling and/or DAF. Ferric chloride (FeCl3) and alum (Al2(SO4)3•nH2O) are the most common chemical coagulants used in water treatment. Electrocoagulation is more commonly used than chemical coagulation in FPW treatment, in which a small voltage is applied to a metal sheet or plate in an electrochemical cell.
The treatment system will remove suspended solids, dispersed oil, H2S, microorganisms and scale forming cations from FPW. Technology developed through this research will improve the performance and significantly lower the costs of coagulation processes that have been proven to be effective at treating FPW for reuse.
The University of Arizona and WaterTectonics have initiated the design of the automated water treatment system which is the thrust of Task 2. This work includes the design of an electrochemical cell by the PI and securing the materials for the cell from ElectroCell North America, Inc.