Aerated Lagoons are another step within some wastewater treatment processes, using both oxygen and microbial digestion to help remove toxic chemicals. Solid waste and sediment, often referred to as sludge, is either caught in traps, skimmed from the top, or allowed to settle and decompose on the bottom of the lagoon. Algae is a concern in aerated lagoons, as an increase in algae growth can lead to high levels of TSS and BOD, even within treated water. This can wipe out microorganisms necessary in order to process organic waste. Properly operating aerated lagoons minimize algae growth, and can produce effluent with significantly lowered levels of BOD and TSS, sometimes below 10 mg/L.
These lagoons can be as simple as a single-celled retention pond exposed to air via surface area and a mixer that forces contact between air and the water. The design specifics of these lagoons will depend on how well oxygen is able to be diffused throughout the water, the depth and size of the pond, and the power source or energy available in order to aerate. When it comes to more involved aerators, bubbles are the main source of oxygen and mixing/movement. The size of the bubble is directly related to its efficiency, with finer or smaller bubbles providing the highest levels of oxygen transference.
Some aerated lagoons come in consecutive ponds with divided cells. Multiple chambers formed with baffle walls increase the flow path of the water, and therefore it’s HRT. This increases contact with open air/aeration, preventing algae growth and improving conditions for microorganisms. This is critical in wastewater treatment, where toxic dissolved gasses and other waste and chemicals are removed and transformed via these microbial processes.
A dual-power, multicellular, or DPMC lagoon provides an initial reactor cell with a high level of aeration and circulation in order to maintain its TSS levels. Higher levels of suspended particles within the water will decrease the likelihood of algae growth while the initial treatment is taking place. In other words, the primary cells are kept turbid, as these conditions are harder for algae to grow in. Here, flocculation sometimes takes place, either naturally or by adding flocculants to the water. Flocculation is when materials bind together through chemical reaction, and is useful for making dissolved solids larger, and therefore easier to remove. After the reactor cell, water is then moved to a series of settling cells, with less movement, where the solids are allowed to form sludge at the bottom. Here, aeration may continue to promote the growth of helpful microorganisms, with a reduced risk of algae growth. These cells are formed via baffle curtains or walls made out of durable, waterproof material.
