nitrification in the distribution system · nitrification •nitrate and nitrite are currently not...
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Nitrification in the distribution System
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Take Home Messages
• Nitrification is a naturally occurring biochemical process
• Nitrification causes water quality problems and can occur in any distribution system
• The increased use of monochloramination has increased the likelihood of nitrification episodes
• Distribution system monitoring can help to anticipate the onset of nitrification
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Nitrification
• Prepared from literature provided by AWWA with assistance from Economic and Engineering Services, Inc.
• http://www.epa.gov/ogwdw/tcr/pdf/nitrification.pdf
Additional information about the chemistry and parameters for analysis for Nitrification can be found below
• http://water.epa.gov/lawsregs/rulesregs/sdwa/tcr/upload/nitrification.pdf
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Nitrification – What is it?
A microbial process by which reduced nitrogen compounds (ammonia) are sequentially oxidized to nitrite and then to nitrate
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Nitrification
• Nitrate and Nitrite are currently not monitored regularly in the distribution system
• Action levels for Nitrite in distribution system are often listed at ~ 0.05 mg/L to ~ 0.15 mg/L
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Method 10271
Primarily, two types of bacteria cause nitrification
• Nitrosomonas
• Nitrobacter
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Nitrification
• Note the production of excess Hydrogen Ion (H+) in the preceding reactions
• This is the reason pH changes
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NH3 NO2 NO3
Hydrogen Ion
Impacts of nitrification-chemical
• Increase in nitrite and nitrate levels
• Reduced alkalinity, pH, DO, and chloramine residual
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Impacts of nitrification-biological
(bacteria)
• Ammonia oxidizing bacteria increase
• Nitrite oxidizing bacteria increase
• HPC increase ( general indicator of bioactivity )
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Decrease in pH and
Alkalinity
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Change in pH and alkalinity-
• Affects the Langelier calculation
• Can lead to corrosion (lead and copper rule)
• Optimum for nitrifying bacteria is
pH 7.0 – 8.0
• Affects chloramine decomposition
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Nitrification indicators
• Loss of chloramine residual
• Decrease in DO
• Drop in pH and alkalinity
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Nitrification indicators
• Increase in water temperature
• Increase in HPC populations
• Nitrite/nitrate levels increase
• Nitrifying bacteria counts increase 13
Ammonia
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Free ammonia
• Almost completely eliminated when proper ratio of chlorine to ammonia is used to form chloramine (5:1)
• Important for treatment and “boosting”
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Ammonia
• Excess can sometimes be found in finished water due to treatment errors
• Also occurs naturally in some ground and surface waters
–(normal levels are usually very low unless influenced by agriculture, for example)
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Nitrification – Ammonia
Ammonia is released by many complex reactions within the distribution system
Two species :
• ionized (NH4+) aka ammonium
• un-ionized (NH3) aka ammonia
–Species depends on pH and temperature at time of sample collection
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Ammonia
• Can be released by:
–Chloramine decay (autodecomposition)
–Corrosion products at pipe surfaces (catalysis)
–Oxidation of nitrite by chloramine
–Oxidation of organic matter
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Nitrogen,Free Ammonia and Chloramine (Mono) –
Method # 10200
• Patented method
• Works well in most samples
• A sequential method used to determine both analytes
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Method 10200
Method 10200
• First measure the monochloramine
• Next convert remaining free ammonia to monochloramine by adding hypochlorite
• Then determine the increase in monochloramine and calculate free ammonia
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Nitrification Monitoring
• Total chlorine
• Monochloramine
• pH
• Alkalinity
• Nitrite/Nitrate
• DO
• HPC
• DBP’s
• Nitrifying bacteria
• Free ammonia
• Temperature
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Distribution Monitoring
• It is nearly impossible to measure every parameter
• Use indicators to monitor your system
• Collect data to establish baseline
• Look for deviations in “normal” readings
• More data increases chances of correct interpretation
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Grab Sample
• Good way to start
• Characterize your system
• Begin to accumulate data, select monitoring sites
• “Better than nothing”
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Trending – Data Accumulation
• Collecting baseline data is a crucial aspect of monitoring in the distribution system
• Need to collect enough reliable data to determine:
–Normal variation
–When a deviation has occurred
–When the problem has been corrected
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What Tests?
• A baseline must be established of standard tests values
–pH, free ammonia, disinfection residual, temperature, turbidity, conductivity, chlorine, alkalinity, …
–Nitrite and Nitrate25
Look for Patterns
• No single analysis can give the complete picture
• Try to reduce errors in sampling and analysis to improve data quality
• Compare trends to baseline:
–learn to distinguish between seasonal, known variables
–true excursions or other anomalies
–when data has returned to baseline26
Nitrification in the distribution System
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