Although it may seem simple to operate a small controlled discharge lagoon, many city council government members and even the operator new to the industry, may not understand what actually takes place in the biological treatment process. There are many misconceptions floating around about how this type of treatment should be maintained. A better understanding of the regulations and proper operations of these systems is vital for everyone do to adverse effects on numerous elements.
Controlled Discharge Lagoons, otherwise known as Facultative Waste Stabilization Ponds, have design standards outlined in chapter 18 of the DNR Design Standards Manual. This chapter outlines what is needed to sufficiently treat your waste in compliance with state regulations. These standards are not only beneficial when designing a new or upgraded plant, but can also be an essential tool in determining whether you can still provide adequate treatment with any alterations in existing processes. Facultative Lagoons are designed by how much organic matter is expected to be treated. The larger the load, the larger your treatment plant must be. The load to the plant is measured in pounds of Biological Oxygen Demand (BOD5) per day. BOD5 is a technical term for how much organic matter is being introduced to the system. This rate of loading should not exceed 25 pounds per day per acre of surface acre on the lagoon.
Ponds use aerobic, facultative and anaerobic bacteria to eliminate the harmful elements in the wastewater. These different types of bacteria use each other to make the process work in a cycle. The aerobic bacteria need oxygen to thrive. This is obtained through two ways. The most effective being through photosynthesis, and the other method is referred to as reaeration. Photosynthesis is the use of sunlight energy by small green plants; in our application the plants are algae, to convert carbon dioxide gas and water into new cells. As the algae grow, it produces oxygen. The treatment is a cycle. Algae produce oxygen, which is used by bacteria to decompose waste. The bacteria in return produce carbon dioxide, which is used by the algae to produce more cells and oxygen. The two basically feed off of each other. The other method that I mentioned was reaeration, this results from turbulence on the waters surface from wind. The amount of oxygen provided to the treatment process is too inconsistent to hold much dependency on with this method. Calm weather, ice cover, and plant location are often factors that are hard to control. To much reaereation can also lead to other problems with the system like dike erosion and unwanted mixing within the cells.
The best way to monitor the treatment process in your lagoon is by regularly checking the ph and dissolved oxygen. These tests are ones that can be done onsite and will outline what is happening in the treatment process. The temperature of the water directly affects the saturation values of dissolved oxygen in fresh water. Colder water can hold more oxygen than warmer water. 32’ water can hold around 14.6 mg/l of dissolved oxygen while 88’ water can only hold around 7.5 mg/l of dissolved oxygen.
Learning these tests and what they mean are vital in reading the biological activity in your Facultative Wastewater Lagoon. A seasoned operator can read these test results and know exactly what is happening within the treatment process. It can allow quick corrective action to inappropriate elements being introduced such as large amounts of septic waste. Talk with your laboratory, primacy agency, or a knowledgeable organization on reading your plant correctly.
