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

•

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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