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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
• Hypochlorite, Chlorine Dioxide
• Oxidizing biocides can chemically react with other components of produced waters
Oxidizing Biocides
• Glutaraldehyde, Quaternary Ammonium Compounds
• Some nonoxidizing biocides can interfere with other water treatment chemicals
Nonoxidizing Biocides
Biocide Selection Criteria
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
NaOCl
ClO2
Perceived Limitations of Hypochlorite-Based Biocides
Oxidant Demanding Substance
Reaction Rate with Free Chlorine
Oxidation Product
Microbiologically active?
Hydrogen Sulfide 1•108 - 1•109 SO42- NO
Ammonia 5•105 Chloramines/N2 YES/NO
Iron 1.7•104 Iron Oxide NO
Bromide 5.3•103 HOBr/BrO- YES
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
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
Monochloramine is the most stable ammonia chloramine and is generally the desired product when using chloramines as a disinfectant
ClO- + NH4+ ↔ NH2Cl + H2O
Monochloramine
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
Dichloramine and trichloramine are both effective biocides, but can cause the production of unpleasant chlorine odors
ClO- + NH2Cl ↔ NHCl2 + HO-
Dichloramine
ClO- + NHCl2 ↔ NCl3 + HO-
Trichloramine
In Situ Generation of Chloramines in Produced Water
Breakpoint graphs are used to determine how water behaves towards chlorination
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
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Res
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FAC Dose:Initial Ammonia Concentration Ratio
FAC Residual
TC Residual
Overall “breakpoint” is where a FAC residual is
observed, indicating all of the oxidant demand
of the water has been satisfied
In Situ Generation of Chloramines in Produced Water
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FAC Dose:Initial Ammonia Concentration Ratio
TC Residual
MCA Residual
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
In Situ Generation of Chloramines in Produced Water
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
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FAC Dose:Initial Ammonia Concentration Ratio
TC Residual
ORP (mV)
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 on-site 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- → Cl2)
• Primary cathode reaction: reduced of oxygen to produce hydrogen peroxide (O2 + 2H+ + 2e- → H2O2)
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
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
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
Water Breakpoint Analysis
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Ox
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FAC Dose (mg/L)
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
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
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TC Residual (mg/L)
ORP (mV)
Water Breakpoint Analysis
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OR
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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
Raw Water
Chloramines
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
California Produced Water
Treatment Assessment
Ammonia in Raw Water 300 mg/L
MOS Dose in Raw Water 25 mg/L
TC Residual in Treated Water 2.8 mg/L
ORP of Treated Water 461 mV
SRBs in Raw Water 4,000 MPN/mL
SRBs in Treated Water 100 MPN/mL
APBs in Raw Water 7,000 MPN/mL
APBs in Treated Water 10 MPN/mL
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Re
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FAC Dose (mg/L)
FAC Residual
TC Residual
Breakpoint: ~2,000 mg/L
Colorado Produced Water
Treatment Assessment
Ammonia in Raw Water 3 mg/L
MOS Dose in Raw Water 25 mg/L
TC Residual in Treated Water 1.2 mg/L
ORP of Treated Water 435 mV
SRBs in Raw Water 40 MPN/mL
SRBs in Treated Water <1 MPN/mL
APBs in Raw Water 3,700 MPN/mL
APBs in Treated Water 10 MPN/mL 0
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FA
C/T
C R
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FAC Dose (mg/L)
FAC Residual(mg/L)
TC Residual(mg/L)
Breakpoint: ~375 mg/L
Emerging Technology
Brine + Stabilizing Agent
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
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
