Chloramine: An Effective Biocide for Produced Waters Andrew K. Boal, Ph.D. and Charles Mowery Presented at SPE Produced Water Handling & Management Symposium on May 21, 2015
Microbial Population Control in Produced Waters Bacteria populations in produced waters can cause a number of issues Souring of an in-production well Microbial induced corrosion Biofilm formation To prevent these problems, an effective biocide program must be used when treating produced waters
Biocides Used in the Treatment of Produced Water Oxidizing Biocides Hypochlorite, Chlorine Dioxide Oxidizing biocides can chemically react with other components of produced waters Nonoxidizing Biocides Glutaraldehyde, Quaternary Ammonium Compounds Some nonoxidizing biocides can interfere with other water treatment chemicals
Biocide Selection Criteria NaOCl ClO 2 Many factors are involved in biocide selection Efficacy Cost Safety Ease of use Bacteria have also been shown to adapt to the produced water environment Bacteria living in produced water can become more resistant to glutaraldehyde and more susceptible to hypochlorite
Perceived Limitations of Hypochlorite-Based Biocides Several common constituents of produced water readily react with chlorine Not all of these reactions are parasitic and some can form useful biocides Specifically, the reaction between ammonia and hypochlorite produces chloramines, a common biocide used in potable water disinfection applications Oxidant Demanding Substance Reaction Rate with Free Chlorine Oxidation Product Microbiologically active? Hydrogen Sulfide 1 10 8-1 10 9 SO 4 2- NO Ammonia 5 10 5 Chloramines/N 2 YES/NO Iron 1.7 10 4 Iron Oxide NO Bromide 5.3 10 3 HOBr/BrO - YES
Chloramines Chloramines are biocides containing at least one nitrogen-chlorine bond Most common chloramines are produced through the reaction of chlorine with ammonia Ammonia-based chloramines are used in a number of disinfection applications, including potable water Treatment of produced water containing ammonia can result in the in situ production of chloramines
Ammonia-Chloramine Formation Chemistry ClO - + NH 4 + NH 2 Cl + H 2 O Monochloramine ClO - + NH 2 Cl NHCl 2 + HO - Dichloramine ClO - + NHCl 2 NCl 3 + HO - Trichloramine Monochloramine is the most stable ammonia chloramine and is generally the desired product when using chloramines as a disinfectant Dichloramine and trichloramine are both effective biocides, but can cause the production of unpleasant chlorine odors When an excess amount of chlorine is added to the water, ammonia nitrogen is converted into nitrogen gas (with some nitrate and nitrite) through breakpoint chlorination
Residual (mg/l) In Situ Generation of Chloramines in Produced Water Overall breakpoint is where a FAC residual is observed, indicating all of the oxidant demand of the water has been satisfied Breakpoint graphs are used to determine how water behaves towards chlorination 35 30 25 20 15 10 5 0 FAC Residual TC Residual 0 5 10 FAC Dose:Initial Ammonia Concentration Ratio Breakpoint graphs are generated by dosing water with chlorine and measuring residuals Free Available Chlorine (FAC): hypochlorite and hypochlorous acid Total Chlorine (TC): FAC as well as chloramine species
Residual (mg/l) In Situ Generation of Chloramines in Produced Water 35 30 25 20 15 10 5 0 TC Residual MCA Residual 0 5 10 FAC Dose:Initial Ammonia Concentration Ratio Presence of different chloramine species is determined in part by the chlorine dose relative to initial ammonia content When the FAC dose relative to ammonia is 5 or lower, almost all of the chloramine present is monochloramine (MCA) At higher FAC doses, dichloramine and trichloramine appear until enough chlorine is added to convert the initial ammonia into nitrogen gas
Residual (mg/l) ORP (mv) In Situ Generation of Chloramines in Produced Water 35 30 25 20 15 10 5 0 900 800 700 600 500 400 TC Residual 300 ORP (mv) 200 100 0 0 5 10 FAC Dose:Initial Ammonia Concentration Ratio Oxidation/Reduction Potential (ORP) is often used to control oxidizing biocide addition to produced waters When chloramines are present as a result of reactions between ammonia and hypochlorite, ORP is typically in the range of 400-500 mv Once breakpoint is achieved and free chlorine is the oxidant in the water, ORP jumps quickly to the 800-900 mv range
Efficacy Demonstration in the Disinfection of Produced Water Chloramines are effective disinfectants but less active than free chlorine Testing is required to demonstrate that chloramines produced through in situ chemistry are effective biocides for produced water Demonstration that in situ produced chloramines are effective produced water biocides has been demonstrated in the lab and in the field
Study Design Laboratory Analysis Testing was primarily conducted on produced waters from a recycling facility in the Fayetteville Shale Untreated water samples collected and shipped to the lab for compositional analysis and breakpoint evaluation Additional microbiology evaluation carried out on waters from Arkansas, Colorado, and California Field Testing Field testing was accomplished using an oxidizing biocide produced with an onsite generation system to treat produced water on location Treated water samples were quenched with sodium thiosulfate before shipping to the lab for analysis
Biocide On Site Generation System On-site generation here involves the electrolysis of aqueous sodium chloride brines Electrochemical reactions occur on both the anode and cathode Primary anode reaction: chlorine production through chloride oxidation (2 Cl - - 2e - Cl 2 ) Primary cathode reaction: reduced of oxygen to produce hydrogen peroxide (O 2 + 2H + + 2e - H 2 O 2 ) Under the right conditions, electrolysis produces a Mixed Oxidant Solution (MOS) MOS has been shown to be a more powerful biocide than commercial hypochlorite
Water Composition Analysis Variable water composition Water at the Fayetteville Shale location is constantly changing with incoming water from different sources added to the ponds Ammonia Although variable in concentration, ammonia is always present and can be used to produce chloramines Component Typical Range ph 7.41 8.32 ORP -228-87 mv Total Dissolved Solids 12,000 22,685 mg/l Alkalinity 890 mg/l Hardness 650 1,056 mg/l Ammonia 58 120 mg/l Hydrogen Sulfide 0.28 54 mg/l Iron 0.38 7.7 mg/l
Oxidant Residual (mg/l) ORP (mv) Oxidant Residual (mg/l) Water Breakpoint Analysis 1400 1200 1000 800 600 400 200 0 1400 0 1000 2000 FAC Dose (mg/l) 800 FAC Residual (mg/l) TC Residual (mg/l) Breakpoint graph reveals hydrogen sulfide and ammonia demand ~100 mg/l dose required to overcome hydrogen sulfide No TC residual is seen before this ~1400 mg/l dose required to reach complete breakpoint High TC residuals seen after breakpoint indicate the presence of organic amines 1200 1000 800 600 400 ORP readings follow measured residuals: 600 400 200 0 200 0-200 0 1000 2000 FAC Dose (mg/l) TC Residual (mg/l) ORP (mv) At FAC doses less than 100 mg/l, negative ORPs are consistent with the presence of hydrogen sulfide Higher FAC doses increase the ORP with the presence of chloramines, but no distinct transition is seen after breakpoint is achieved
Oxidant Residual (mg/l) ORP (mv) Water Breakpoint Analysis 1400 1200 1000 800 600 400 200 0 800 600 400 200 0-200 0 1000 2000 FAC Dose (mg/l) TC Residual (mg/l) ORP (mv) ORP readings follow measured residuals: At FAC doses less than 100 mg/l, negative ORPs are consistent with the presence of hydrogen sulfide Higher FAC doses increase the ORP with the presence of chloramines, but no distinct transition is seen after breakpoint is achieved
Field Water Treatment Produced water treated with on-site produced MOS Treated water had a TC residual of 55 mg/l
Microbial Inactivation Chloramines Raw Water Treated Water
Ongoing Research Additional testing is being conducted on produced waters from different geographic areas Testing process: Shipment of 2-4 gallon water samples to the lab for analysis Oxidant demand and breakpoint analysis Chemical composition analysis Microbial inactivation assay In situ produced chloramines have been fond to be effective biocides in all waters tested
Residual (mg/l) California Produced Water Breakpoint: ~2,000 mg/l 600 500 Treatment Assessment Ammonia in Raw Water 300 mg/l 400 MOS Dose in Raw Water 25 mg/l 300 200 FAC Residual TC Residual TC Residual in Treated Water ORP of Treated Water SRBs in Raw Water 2.8 mg/l 461 mv 4,000 MPN/mL 100 SRBs in Treated Water 100 MPN/mL 0 0 1000 2000 3000 FAC Dose (mg/l) APBs in Raw Water APBs in Treated Water 7,000 MPN/mL 10 MPN/mL
FAC/TC Residual (mg/l) Colorado Produced Water Breakpoint: ~375 mg/l 140 Treatment Assessment 120 Ammonia in Raw Water 3 mg/l 100 MOS Dose in Raw Water 25 mg/l 80 60 40 20 0 0 200 400 600 FAC Dose (mg/l) FAC Residual (mg/l) TC Residual (mg/l) TC Residual in Treated Water ORP of Treated Water SRBs in Raw Water SRBs in Treated Water APBs in Raw Water APBs in Treated Water 1.2 mg/l 435 mv 40 MPN/mL <1 MPN/mL 3,700 MPN/mL 10 MPN/mL
Emerging Technology Stabilized Oxidant Solution (SOS) Although some chlorine added to water is used to provide chloramine biocides from in situ transformations, some chlorine is lost in unproductive reactions Brine + Stabilizing Agent This biocide loss may be preventable through the incorporation of a stabilizing agent in the electrolysis process, which provides an effective oxidizing biocide with increased stability to produced water components
Summary and Conclusions Chloramines are readily formed by treating produced water with free chlorine biocides Oxidant demand from hydrogen sulfide must be overcome before chloramines can be produced Treatment of ammonia containing produced waters will most likely result in monochloramine production Chloramines produced through in situ processes are very effective at inactivating SRB and APB bacteria in produced water Emerging technology will provide stabilized chlorine chemistry which will enable the more efficient use of biocides for disinfecting produced waters
Interested in learning how MIOX s On-Site Generation technology can improve disinfection treatment of your produced waters? www.miox.com sales@miox.com