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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 Norway Water Pollution Control Facility

Executive Summary


Lagoons and ponds refer to basins constructed in, or on the ground surface, using earthen dikes to retain wastewater within which natural stabilization processes occur with the necessary oxygen coming from atmospheric diffusion, photosynthetic and/or mechanical sources. In Maine, most of the lagoons and ponds are partial mix aerated lagoons and facultative stabilization ponds. Some of these facilities have experienced problems meeting biochemical oxygen demand (BOD5) and total suspended solids (TSS) permit requirements. More recently, it has been recognized that nitrification occurs in these systems and that the effects of nitrification may be measured in the BOD5 test.

Maine Task Force

In 1994, a Maine Department of Environmental Protection (DEP) staff committee was formed to evaluate the performance of lagoons and ponds. The DEP staff presented its findings and recommendations at a public workshop on October 24, 1995. During that workshop, several issues were identified and workshop participants agreed that a task force should be established to resolve the issues.

A task force made up of DEP staff, consulting engineers and lagoon treatment plant operators held its first meeting on December 13, 1995. The task force identified problems (BOD5, TSS and pH) at some of the lagoons and ponds and agreed that it would work to produce written, experience-based guidelines, recommendations and collaborative procedures for the licensing, design, and operation of these systems. The task force further agreed that the guidelines, recommendations and procedures would promote cost-effective, environmentally-sound and flexible industry practices which recognize the interrelationship of everyone concerned. After nearly 18 months of work, the task force prepared this manual. The following is a summary of the task force's findings and recommendations.

Findings : Lagoons and ponds have unique design and operation requirements in comparison to high rate treatment systems.

Lagoons and ponds are thought of as simple systems that trade size (land area) for mechanical complexity, energy use and operation and maintenance intensity. The larger treatment volume in the ponds results in physical and biochemical inertia that tends to keep them on course. This is beneficial when treatment is good, but makes operation difficult when problems occur. The performance of lagoons and ponds is highly dependent on their initial design and proper operation as well as the characteristics of the microorganisms in the system. Lagoons and ponds are affected by seasonal changes, e.g., spring benthic demand, summer algal blooms, autumn algal die-off and winter cold temperatures. These concerns are unique to lagoons and ponds and need special design and operational considerations.

Recommendations: Operator training and technical assistance for lagoon operators should be developed and provided for operators in Maine. A network of lagoon operators should be established to promote the exchange of operator experience and new control strategies. Operators should develop specific operational plans for their facilities that account for all of the seasonal changes (i.e., spring turnover, algae and nitrification in the summer, and winter cold). Design engineers should design for these seasonal variations and, in particular, recognize that partial nitrification and denitrification do occur in lagoons and may result in higher BOD5 and that algal growth can be significant and may result in high effluent TSS.

Finding : Overall, most of the lagoons and ponds in Maine are meeting secondary treatment permit requirements for BOD5 and TSS.

The task force found that most of the lagoons and ponds in Maine' can meet secondary treatment requirements of 30 mg/L monthly average BOD5 and TSS. The data from plant performance indicates that half of the POTWs achieved a BOD5 effluent quality of less than 25 mg/L and a TSS of less than 22 mg/L 95 percent of the time on a monthly average basis. The task force found that some lagoons and ponds do not meet secondary treatment, but do meet "equivalent to secondary treatment" (45 mg/L monthly average) for effluent BOD5 and TSS due largely to varying climatic and seasonal conditions. In the late winter and early spring, BOD5 problems occur primarily because of reduced biological treatment activity due to the colder temperatures. In the warmer months, algae cause increases in effluent TSS and also increases the apparent effluent total BOD5.

Recommendation: Adjust BOD5 and TSS permit limits on a case-by-case basis for facilities with problems due to cold weather and algae.

The Task force recommends that effluent BOD5 and TSS concentrations could range up to a maximum of 45 mg/L as a 30-day average when:

  • a) the facility cannot consistently achieve secondary treatment defined as a 30-day average of 30 mg/L 95 percent of the time based on at least three years of monthly average data,

    b) the facility provided information and data to demonstrate that the problem is uncontrollable while using a properly designed and operated lagoon or pond as the principal biological treatment process, and

  • c) there are no extenuating circumstances such as overloading or industrial wastes.

The task force recommends that a facility not be allowed to obtain effluent limitations that are any less stringent than the level of effluent quality that the facility is capable of achieving within the range of 30 - 45 mg/L. That level should be defined based on the 30-day average achieved 95 percent of the time over the last three years for the seasonal period of non-compliance.

Finding: BOD5 is misleading as a performance indicator for some facilities.

The 5-day biochemical oxygen demand (BOD5) test is currently used to determine the operating efficiency of lagoons and ponds and the quality of their effluent. The task force found that BOD5 is a misleading parameter for measuring the treatment performance of some aerated lagoons.

The task force identified a fundamental misunderstanding regarding the relationship between effluent BOD5 and treatment performance. Treatment performance relates to how well the system removes the influent BOD5, whereas effluent quality is measured by the BOD5 in the effluent. For some lagoons and ponds, effluent quality does not reflect treatment performance. In fact, very little of the BOD5 in the effluent of a lagoon or pond is residual influent. Some of the effluent BOD5 (in the summer) is caused by algae. In addition, the effluent BOD5 is often inflated by nitrification in the BOD5 test during the warmer months.

The task force also found that the use of BOD5 may lead to unintended, undesirable outcomes. The BOD5 test measures the oxygen utilized in a 5-day period for the biochemical degradation of organic material (carbonaceous biochemical oxygen demand, CBOD5) and the oxidation of reduced forms of nitrogen, such as ammonia and nitrite (nitrogenous oxygen demand). Significant nitrogenous oxygen demand can be exerted when sufficient numbers of nitrifying bacteria and ammonia (or nitrite) are present in the test sample. In other words, BOD5 test results of the effluents from lagoons and ponds exhibiting partial nitrification may have higher values than other systems with either no nitrification or complete nitrification3 even when overall treatment for BOD5 is satisfactory or better than facilities that are not nitrifying.

Recommendation: Substitute CBOD5 for BOD5 in some cases.

In order to reduce their BOD5 values to meet compliance requirements, some operators try to suppress nitrification when they are not required to meet ammonia limits. This practice usually results in increased effluent toxicity and oxygen demand on the receiving waters. Therefore, to eliminate this situation and because the BOD5 test is not reflective of effluent quality under nitrifying conditions, the task force is recommending that a monthly average CBOD5 limit Of 25 mg/L be substituted for the current 30 mg/L monthly average BOD5 on a case-by-case basis when:

  • a) parallel CBOD5 and BOD5 data (at the BOD5 permit test frequency for a time period of April through November) have been provided and show a problem with BOD5 compliance due to nitrification in the BOD5 test results and that the CBOD5 is not directly correlated with the BOD5 test results, and

  • b) baseline influent and effluent ammonia, nitrite and nitrate data (same frequency and duration as the parallel CBOD5 and BOD5 data) have been provided.

Prior to relicensing facilities that have CBOD5 limits, the licensee and DEP should develop a procedure to determine whether nitrification is still occurring. This procedure should include submittal of information and data as outlined in conditions a) and b) above for the year prior to relicensing.

Finding: The literature and available knowledge about the management and control of sludge accumulation and algal growth in lagoons and ponds is limited.

Recommendation: Organizations that are interested in the operation of lagoons and ponds should continue to support the research of the management and control of sludge accumulation and algal growth in lagoons and ponds.

Finding: The current DEP 49 Form is designed for activated sludge systems.

Recommendation: The DEP should revise the 49 Form for parameters typically used at lagoon facilities and allow facilities to tailor it specifically for each individual lagoon system as needed.

Finding: The existing DEP data management system is inadequate, cumbersome, and inefficient.

Recommendation: Provide a computer system at lagoon facilities to store historical treatment reporting data and a means to transport data over a telephone line. The DEP should develop a computerized data management system to receive and store the data sent electronically.

Finding: Most of the lagoons in Maine are meeting secondary treatment permit requirements and are generally similar.

However, there is a wide variety of flexibility and amenities, i.e., the size and type of facilities, building space and layout, provided from one facility to another.

The newer facilities have benefited from the earlier lagoon designs, operational experience, and the advancement in technology. Those lagoon facilities with greater flexibility, such as, additional storage capabilities or long detention times, structures to vary the water level within lagoons, the latest equipment systems, i.e., grit removal, screening, instrumentation, and flow proportional discharge capabilities were found to produce high effluent quality along with being cost effective. Also, the operators task of meeting secondary permit requirements was made easier.

Recommendation: Adequate funding should be available to provide a consistent level of wastewater treatment and for the completion of the facilities.



A common misconception is that effluent BOD5 is residual influent BOD5- influent BOD5 is made up of two fractions -a  particulate fraction and a soluble fraction. In waste stabilization ponds, most of the particulate fraction is removed within hours by physical entrapment and adsorption. Removal of the soluble fraction takes a few days. Even at 10* C, the predicted effluent soluble BOD5 is less than 10 mg/L. Most of the particulate BOD5 in the effluent of waste stabilization ponds results from algae. Each milligram per liter of algae in the effluent exerts approximately 0.5 mg/L of BOD53As a rule-of-thumb, whenever the BOD5 values are greater than two-thirds of the corresponding TSS values (during the warmer months), the BOD5 values have been inflated by nitrification. Whenever the BOD5 values exceed those of the TSS, nitrification is significant.

aerated lagoons


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