Aerial view of the Warren, Maine lagoon system. Photo courtesy of Woodard and Curran.

Lagoon Systems In Maine 

Systems In Maine

An Informational Resource for
Operators of Lagoon Systems

Mars Hill Wastewater Lagoon System - Mars Hill  Maine. Photo Courtesy of Wright-Pierce Engineers.
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Wastewater Engineering




Linvil G. Rich
Alumni Professor Emeritus
Department of Environmental
 Engineering and Science

Clemson University - 
Clemson, SC 29634-0919 USA
Tel. (864) 656-5575; Fax (864) 656-0672

Technical Note Number 4


   Chlorination of secondary treatment effluents is some times impaired by an immediate chlorine demand exerted by nitrites. Such a demand is erratic and can be so large as to prevent maintaining a chlorine residual regardless of the dosage. In most instances, the condition appears to be transitory and soon disappears. However, in some instances, especially in the case of aerated lagoons with long retention times, the condition lasts long enough to result in fecal coliform violations of the effluent discharge permit. Remedial measures to remedy the problem depends primarily on the understanding of the conditions that favor nitrite production.


Cool-Water Accumulation of Nitrites

    Nitrification (oxidation of ammonia to nitrate) is a two step process.   


Under aerobic conditions, with sufficient alkalinity, and a favorable temperature, ammonia (NH3) is oxidized to nitrite (NO2-) which in turn, is oxidized to nitrate (NO3-). At temperatures above approximately 17°C, the first step, the oxidation of ammonia to nitrite, is the slowest step. Consequently, when nitrite is formed, it is rapidly oxidized to nitrate, resulting in a relatively low ambient concentration of nitrite (< 1-2 mg/L) being found in the effluent. At temperatures below 17°C, the rate of nitrite oxidation to nitrate begins to decrease until, at a temperature of from 12°-14°C, the rate of nitrite oxidation to nitrate becomes the rate controlling step in nitrification. Under such temperature conditions, significant nitrite accumulation can occur (>15 mg/L) (Randall and Buth 1984). In addition, there can be specific compounds introduced by industrial discharges that exert a differential toxicity on the organisms responsible for the two steps, thereby resulting in nitrite accumulation.

     About the only remedy that can be suggested for cold water nitrite formation is to limit the nitrification process by reducing the level of aeration. Usually, accumulations of nitrite that occurs in the spring are transitory and will disappear with warmer weather.

    Accumulations that occurs in the fall will dissipate and disappear as nitrification ceases with falling temperature.


Warm Water Accumulation of Nitrites

   Nitrite accumulation can also occur under conditions in which temperatures are above 17°C. When oxygen is limiting in parts of the aerated lagoon system, any nitrates that have been produced in other parts of the system that have been aerobic will become reduced by denitrification. Denitrification can be simplified as a two-step process.


   However, unlike in nitrification, the second step appears to be the slowest step (Dawson and Murphy 1972), particularly if the carbon is limiting growth (Freedman 1999) or if the carbon source is complex (McCarty et al. 1969). Furthermore, it has been found that the second step, nitrite reduction, is inhibited by the presence of nitrates (Kornaros et al. 1996), and is more sensitive to oxygen (Kornaros and Lyberatos 1998). Since the second step is the slowest step, nitrite can accumulate in significant concentrations.

   When the condition of excessive nitrites in the effluent of an aerated lagoon operating at a temperature >17°C persists, the best remedy is to attempt to nitrify the nitrites to nitrates by ensuring a completely aerobic environment (all aerators on all the time) along with at least an effluent alkalinity of 150 mg/L.


Impact of Ammonia Addition
on Chlorine Demand

     When chlorine is added to effluents with nitrites but with little ammonium nitrogen, the chlorine reacts as free chlorine and is removed quickly by a chemical reaction with the nitrites, thereby increasing significantly the amount of chlorine that must be used to meet the required limit of coliform concentration. Each mg/L of nitrite nitrogen reacts with 5 mg/L of chlorine. Thus, a nitrite concentration of only 10 mg/L will exert a chlorine demand of about 50 mg/L.

            It has been shown, however, that when chlorine is added to effluents with nitrites and with a high concentration of ammonium ion (>20 mg/L), the chlorine reacts preferentially with the ammonium ion forming chloramines (Phoenix 1995). This suggests that, if insufficient ammonium is already present in the effluent, the chlorine demand exerted by effluent nitrites can be minimized by adding ammonia along with chlorine in a well-mixed chlorine contact basin. Chloramines, while effective as disinfectants, will act only slowly with nitrites (Chen and Jenson 2001).


 Chen, W. L. and Jensen, J. N. (2001). “Effect of chlorine demand on the breakpoint curve: Model development, validation with nitrite, and application to municipal wastewater.” Water Environ. Res., 73(6), 721.

Dawson, P. L. and Murphy, K. L. (1972). “The temperature dependence of biological denitrification.” Proc. 24th Industrial Waste Conf., Purdue Univ., Lafayette, IN. 

Freedman, D. L. (1999). Personal communication. Clemson Univ., Clemson, SC.

Kornaros, M. et al. (1996). “Kinetics of denitrification by Pseudomonas denitrificans under growth conditions limited by carbon and/or nitrate or nitrite.” Water Envir. Res., 68(5), 934-945.

Kornaros, M. and Lyberatos, G. (1998). “Kinetic modeling of Pseudomonas denitrificans growth and denitrification under aerobic, anoxic, and transient operating conditions.” Wat. Res., 32(6), 1912-1922.

McCarty, P. L. et al. (1969). “Biological denitrification of wastewaters by the addition of organic materials. ”Water Res., 6, 71-83.

Phoenix, City of (1995). Water Services Department Task Report 2010.

Randall, C. W. and Buth, David (1984). “Nitrite buildup in activated sludge resulting from temperature effects.” J. Water Pollut. Control Fed., 56(9),1039.


Technical Note 1 Effluent BOD5 - A Misleading Parameter For the Performance of Aerated Lagoons Treating Municipal Waste
Technical Note 2 Aerated Lagoon Effluents
Technical Note 3 Control of Algae
Technical Note 4 Nitrites and Their Impact on Effluent Chlorination
Technical Note 5 Aerated Lagoons for Secondary Effluent
Technical Note 6

Nitrification in Aerated Lagoons With Intermittent Sand Filters

Technical Note 7

Mixed Liquor Recycle (MLR) Lagoon Nitrification System

Technical Note 8 Facultative Lagoons - A Different Technology
Technical Note 9 Sludge Accumulation in High Performance Aerated Lagoon Systems
Technical Note 10

Ammonia Feed Back in the Sludge of a CFID Nitirification System


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