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
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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 6


Effluent ammonia exerts an oxygen demand on the receiving body of water. Furthermore, ammonia in water exists in two forms – the ammonium ion (NH4+) and unionized ammonia (NH3). At a high pH, most of the ammonia in solution is in the unionized form, whereas at a low pH the ammonia is mostly in the ionic form. Since the unionized form is toxic to the aquatic organisms in the receiving body of water and since both the ionized and unionized forms exert an oxygen demand, effluent limits now often include a maximum limit on the total ammonia. This technical note considers the fundamentals of nitrification and the removal of ammonia in aerated lagoons.

     Nitrification is defined as the oxidation of ammonia to nitrate. The oxidation occurs in two steps – the oxidation of ammonia to nitrite by the bacterium Nitrosomonas followed by the oxidation of nitrite to nitrate by the bacterium Nitrobactor. The stoichiometric equations for nitrification are


Being chemosynthetic autotrophs, nitrifying bacteria derive their energy from ammonia and nitrite and their carbon from carbon dioxide.

Below a pH of 8.5, almost all of the ammonia in solution will exist as the ammonium ion. The conversion of ammonium to nitrite results in the formation of hydrogen ions (Eq. 1). If the pH of the wastewater is less than 8.3, which is typical for domestic wastewaters, the hydrogen ions produced are neutralized by bicarbonate ions in the wastewater.

This reaction results in the decrease in bicarbonate alkalinity as well as an increase in the carbon dioxide concentration, both occurrences of which lowers the pH. If the wastewater has a relatively low alkalinity, the change in pH can be dramatic. In turn, the low pH can significantly reduce the rate of nitrification. Below a pH of 7.2, the rate falls precipitously, approaching zero at a pH of 6. Based on Eqs. 1 and 3, approximately 7.2 mg of bicarbonate alkalinity (as CaCO3) are required to neutralize the hydrogen ions produced by the oxidation of 1 mg of ammonium nitrogen to nitrite. Thus, wastewaters with low alkalinity require the addition of alkalinity to support uninhibited nitrification. In addition to pH, nitrification is very sensitive to temperature, the dissolved oxygen concentration, and toxic materials. The literature on nitrification is extensive. Papers by Sharma and Ahlert (1977) and Barns and Bliss (1983) offer excellent reviews of factors influencing nitrification.


     During warm weather months, some nitrification generally occurs in most aerated lagoons treating domestic wastewaters. However, such nitrification is usually unpredictable and cannot be depended upon to meet effluent limits. The reason is that the organisms responsible for nitrification are slow growers and more sensitive to environmental factors than are those that remove BOD5. Figure 1 illustrates the impact that temperature has on nitrification. The curves, which was prepared by using the kinetics used by Downing et al. (1964), Downing and Knowles (1966), and Parker (1975), predicts the hydraulic retention time (HTR) required in an aerated lagoon to achieve an effluent ammonia nitrogen concentration of 2 mg/L if all the biomass is maintained in suspension, if sufficient alkalinity is present to meet the requirement for nitrification, if the dissolve oxygen is maintained at 2 mg/L, if there are no toxic materials present, and if the influent conditions do not vary. Obviously, these limitations are not met on a consistent basis in the real world; hence even longer retention times would typically be required. Since cold weather temperatures in lagoons in the Southeast may drop to as low as 8 to 10°C, an HRT of at least 6 to 7 days would be required for year-round nitrification. Considering the fact that the completely-suspended biomass conditions require aeration power of about 6 W/m3 of basin volume (30 hp/106 gal), such retention times are excessive from the stand point of power usage. Power for solids suspension would be about three times that required to meet the oxygen demand. Therefore, for aerated lagoons to be considered as viable processes for nitrification, the lagoon process must be modified so that the solids age can be uncoupled from the HRT. This can be accomplished either through sedimentation in clarifiers with solids recycle or through the retention of solids by use of sequencing batch reactor (SBR) technology. An example of the latter will be discussed in a later technical note. However, there are available add-on processes that can be used to nitrify effluents of aerated lagoons. These include the intermittent sand filter, a process for which long term performance records are available that demonstrate its success as a nitrifier and polisher with respect to TSS and CBOD5.

Figure 1. 
Influence of temperature on 
hydraulic retention time required to achieve nitrification in a completely-suspended aerated lagoon under optimum conditions.



     The design of intermittent sand filters can be found be found elsewhere (USEPA 1983, Rich 1999). Intermittent sand filters have been used to polish effluents of both facultative and aerated lagoon systems. Their use with the dual-power, multicellular aerated lagoon discussed in Technical Note 5 has been particularly successful. These systems produce effluents low in TSS, a factor that not only reduces the frequency at which the filters have to be cleaned, but also makes possible higher loading rates and smaller filters.

     Table 1 lists the effluent characteristics of three DPMC lagoon – intermittent sand filter systems in South Carolina. The Ocean Drive and Crescent Beach plants have been in operation for about for about 13 years; the Loris plant for about 8 years. The table tabulates the mean and 90 percentile values of the TSS, BOD5, and the ammonia nitrogen in the effluents of the plant. From a regulatory standpoint, 90 percentile compliance with effluent limitations is adequate (Rott 1996). All three systems require alkalinity addition for nitrification. In the operation of the Ocean Drive and Crescent Beach plants, it has been found that if the pH of the lagoon effluent is maintained between 7.5 and 8.0, the ammonia nitrogen of filter effluent will generally be less than 0.5 mg/L. However, since the two plants are meeting their ammonia nitrogen limits of 2 and 4 mg/L, March through October, there is no incentive to achieve the lowest concentrations possible. Figures 1 and 2 illustrate 8.5 years of the monthly records at these two plants. Table 1 in Technical Note 5 shows the effluent ammonia nitrogen found in the intensive three day study of the Ocean Drive plant by EPA described in that technical note.

Table 1. 
Aerated Lagoon -
Intermittent Sand Filter System Performance
Size, mgd




Length of record, yr




TSS, mg/L      
    50 percentile




    90 percentile




BOD5, mg/L      
    50 percentile




    90 percentile




NH3-N, mg/L      
    50 percentile




    90 percentile




Figures 2 and 3 illustrate the monthly effluent records of the Ocean Drive and Crescent Beach over the 8.5 year period. Such stability combined with the minimal skills and attention required to operate the systems, makes the systems viable alternatives to the activated sludge process, especially in those areas where land costs are not excessive and cheap sand is available. A copy of a paper entitled A Cost Comparison of a Low-Tech Alternative to Activated Sludge by Mike Bowden and Bruce Henry is available upon request at or

Figure 2.
Monthly average effluent TSS, BOD5, and NH3-N 
at Ocean Drive plant, North Myrtle Beach, SC.



Figure 3.
Monthly average effluent TSS, BOD5, and NH3-N at Crescent Beach plant, North Myrtle Beach, SC.


Barnes, D. and Bliss, P. J. (1983). Biological Control of Nitrogen in Wastewater Treatment. E. and F. N. Spon, New York, NY.

Downing, A. L. et al. (1964). “Nitrification in the activated sludge process.” Journal, Institute of Sewage Purification.

Downing, A. L. and Knowles, G. (1966). “Population dynamics in biological treatment plants.” 3rd International Conference On Water Pollution Control, Munich, Germany.

Parker, D. S. (1975). Process Design Manual for Nitrogen Control. Technology Transfer Manual, U. S. Environmental Protection Agency, Washington, DC.

Rich, L. G. (1999). High Performance Aerated Lagoon Systems. American Academy of Environmental Engineers, Annapolis, MD.

Rott, G. G. (1996). “Alternative to CBOD5-based load allocations studies on low-dilution ratio streams.” J. Envir. Engrg. Div., ASCE, 77, 669-671.

Sharma, B. and Ahlert, R. C. (1977). “Nitrification and nitrogen removal.” Water Res., 11(10), 897-925.

USEPA (1983) Design Manual: Municipal Wastewater Stabilization Ponds. EPA-625/1-83-015, U. S. Environmental Protection Agency, Washington, DC.


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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