Anaerobic, Aerobic, and Aerated Lagoons

All sewage lagoons rely on some kind of bacteria to break down waste. While some of these bacteria are harmful to our health, they’re still valuable in their ability to reduce the nutrient levels of wastewater so it doesn’t cause toxic conditions that can infiltrate soil and water life. Different bacteria flourish if a sewage lagoon has plenty of oxygen mixed into the water rather than the anaerobic conditions of a still and deep pond. Planning the decomposition and primary treatment of a steady supply of sewage often requires the use of more than one of the three main types of lagoons.

How Anaerobic Digestion Works

Anaerobic lagoons are primarily used for processing animal waste and not human sewage. This is because manure ponds provide a more uniform mixture of sewage for steady and slow breakdown throughout the layers of the water and sludge. Sewage from businesses and homes usually contains a mix of food particles, soap residues, and even bits of non-biodegradable trash that respond best to a straining and aerobic treatment system. Anaerobic means without oxygen, so the treatment of this water requires deeper ponds with less surface area than other lagoons. Covers are also common in anaerobic designs to minimize air contact with the water. You’ll find these ponds have the slowest retention times and can take months to process manure to discharge parameters, but they are also completely passive and require no pumps and little maintenance other than sludge removal.

The Power of Aerobic Processing

Aerobic sewage lagoons are naturally aerated in some way. This can be created by a drop from the inlet pipe in a very small residential lagoon, but most larger ponds achieve it by keeping the total depth as shallow as possible. This introduces air into the water as wind blows across the surface and creates waves. Naturally aerobic ponds process water faster than anaerobic lagoons and are less likely to release unpleasant odors or dangerous gases. However, they require a much larger area and may take up more space than is practical for large operations like commercial facilities or livestock farms. Seepage amounts are also increased due to the surface area on the bottom of the pond unless a reliable liner is installed. If aerobic treatment is required but natural methods require too much space and time, powered aeration is the only choice.

Aeration Equipment

Adding aerators and pumps to a sewage lagoon may increase its costs and maintenance requirements, but it’s often the only option to safely and pleasantly treat waste in a crowded environment. Neighbors around the lagoon or treatment plant don’t want to smell the methane and other gases produced by the bacteria breaking down waste. Ensuring a steady supply of oxygen reaches the water, keeps the balance of bacteria on the aerobic side for odor control and thorough breakdown of dangerous compounds. However, the energy costs grow substantially for larger ponds. These methods are generally limited to small sewage lagoons and treatment ponds located in neighborhoods or for polishing steps at a large treatment plant.

Using Multiple Ponds of Various Types

Many designs call for combining multiple ponds into one complete system, to clean sewage as much as possible before it’s reused or discharged. Settling is often accomplished in an initial anaerobic pond, or chamber, before the water runs into aerated evaporation ponds for further refinement. Saving powered aeration methods for the last stage of polishing allows you to shrink the size of equipment you’ll need since you’ll have a smaller volume of water left at a late stage of treatment.

All of these various sewage treatment lagoons share a common need for a reliable, leak-proof liner. If the sewage becomes more concentrated over time due to constant water through seepage into the soil, it may turn more hazardous, rather than less, through the course of treatment. Choose an RPE geomembrane from BTL Liners to ensure your lagoons operate as designed, whether they’re anaerobic, naturally aerobic, or aerated.


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