2003 Maine Wastewater Salary Survey as conducted by the Maine Wastewater Control Association

2003 Maine Wastewater Rate Survey conducted by the Maine Rural Water Association

 

Clinton Water District
Case Study of the Facultative Lagoon System
By Janet Abrahamson - Maine Rural Water Association


The Clinton Water District provides a secondary level of wastewater treatment by use of a facultative lagoon system. Clinton’s lagoon system was constructed in 1987. The two lagoons are operated in series and cover approximately 26 acres and are approximately five feet deep.

Clinton has used the lagoon system to treat the wastewater for their community of about 350 users for almost twenty years without the removal of sludge. The DEP has been emphasizing the need for facilities to plan for the disposal of sludge especially if systems are experiencing process difficulties that could be attributed to the nutrient cycling in the system.

There are several natural biological cycles that occur in a facultative lagoon system. When any one cycle gets out of balance, the system will start to experience process problems. Carbon from the aerated digestion of sludge, which is dissolved in the water and from atmospheric influences, will provide a carbon source that is used by the algae and other plants in the presence of sunlight to produce simple sugars and oxygen as a byproduct. The simple sugars become the organic material that makes up the algae.

When there is no sunlight present, the algae respire and use up oxygen and produce carbon dioxide. During anaerobic decomposition, anaerobic microorganisms break down the solids forming very different products. The carbon is then converted to methane gas and soluble alcohols, which is BOD and uses up oxygen, instead of carbon dioxide.

Sulfur is converted in to hydrogen sulfide gas and some insoluble iron sulfides are precipitated out. The insoluble phosphates in the solids could be solubilized and become available to the algae, which could cause an algae bloom. Phosphorus is the energy source and in the genetic makeup of all living things. The algae eventually die and become part of the sludge layer. When plant material decays, the phosphorus is released and returned to the lagoon and is available for reuse by the algae and bacteria.

Though much of the phosphorus is not available since it is in an insoluble form, changes to the water chemistry can make it available. When the anaerobic process overtakes a lagoon due to too much plant growth, algae, or duckweed, there could be odor issues as well as poor quality effluent.


Clinton agreed to participate in a study to determine if an anaerobic microorganism could be used in the lagoon system to assist in decomposing the sludge layer during cold weather. This process would prolong the life of the lagoon before the sludge would need to be removed. Additionally, it would improve the quality of the water since the microorganisms would be competing with the algae for the available nutrients in the water.

In October of 2005, the study began with the measurement of the sludge layer throughout the first lagoon. A core sampler was used along with a GPS unit to track sample locations so that the same points could be measured at the same location each time. Surprisingly, there wasn’t as much sludge as one would expect after 20 years of usage! The treatment process had reduced solids considerably.

After about a month of treatment with the archaea there was a noticeable difference in the appearance of the lagoon. There was less anaebana, a blue green algae or cyanobacteria, at the end of the first lagoon. Additionally, there was less floating sludge on the surface and dispersed algae suspended throughout the depths of the lagoon, which allowed one to see deeper into the lagoon. The second lagoon did have more duckweed than at the beginning of the trial, but that could be a coincidence or perhaps due to the presence of many more ducks migrating.

In December 2005, a second core sampling was taken. This showed a 17% reduction in the sludge throughout the first lagoon after application of the archaea for 6 weeks. The reduction in sludge was based on the additive depths of sludge for all 60 points compared to the following measurements after treatment at all 60 points.


When the study first began in October, the sludge depths at 60 sampling points spread out all around the lagoon totaled 762 inches. By February 15th the total had been reduced to 502 inches a 34% reduction. The goal is to keep adding the anaerobic microorganisms to increase sludge digestion rates until a 50% reduction is accomplished.

 

About the Author