Why should people in rural municipalities be concerned about the sludge levels in their sewage lagoons?
Many towns have simply outgrown the capacity of their current sewage lagoon. Unfortunately, excessively high levels of sludge make it difficult for outdoor lagoons to function correctly. Strict new guidelines for releasing lagoon effluent to the natural environment have put a heavy burden on public works managers. Communities with recent population booms or with older lagoons have been seeing sludge levels rise faster than expected. This is a problem as higher sludge levels make it difficult for lagoon effluent to meet the specification required to be released into local tributaries. When this happens, the only remaining solution for the public works manager is to remove the sludge, which is a costly process.
An outdoor sewage lagoon typically consists of two or more ponds called effluent ponds or cells. The function of the primary lagoon is to allow bacteria and algae to work together to breakdown raw sewage in a sequestered area, away from natural waterways. Solids in the sewage water will either be consumed by both anaerobic and aerobic bacteria or separate and settle to the bottom of the pond. The remaining water is transferred to a secondary cell where it is given time to mix with more bacteria and settle out more solids. If there are only two effluent ponds, the second pond will be treated until it meets all the required specifications for release into the natural environment. After test results determine the effluent in the final finishing cell meets Manitoba provincial specifications, the water can be released directly to the outside environment. Recently, the Province of Manitoba updated the water quality guidelines for sewage lagoon effluent. The new guidelines are much stricter and come with hefty fines if breached.
What Can Be Done To Reduce The Sludge Levels in a Sewage Lagoon?
- Dredging and Sludge Removal. Extremely difficult and expensive. Ferric chloride or aluminum sulfate are often added to lagoon ponds to bind with phosphorus suspended in the water. This makes the sludge removal even more expensive for the municipality as it would all have to be transferred by truck to a suitable landfill site capable of receiving heavy metals.
- Aeration. The main advantage of a properly aerated lagoon system is reducing the need for frequent sludge removal. Since a large portion of the municipal wastewater consists of biodegradable organic carbon matter, much of the settled sludge in the lagoon can be quickly decomposed by active aerobic, or oxygen using bacteria. If sufficient oxygen is not present in the ponds, the sludge layer will accumulate faster than it can be biodegraded. When this occurs, the sludge materials may build up to a point where they must be removed faster and more frequently than necessary.
- Bacteria Treatments. Application of sludge friendly bacteria & enzymes is beneficial because it helps decompose the organic carbon matter substantially. It is reported a public works manager could remove 1000 Tones of sludge/acre in a single season by merely adding aggressive bacteria treatments to the cells.
Recommendations for operating your outdoor sewage lagoon:
- Closely monitor the levels of the sludge in your lagoon (2x per year).
- Reduce the amount of sludge by installing a combination of coarse and fine bubble aeration in your primary lagoon and fine bubble aeration in your secondary cells.
- Treat your lagoon aggressively with sludge friendly bacteria & enzymes. *This recommendation is exceptionally inexpensive when comparing to the costs of dredging or paying fines.
Benefits from adding the combination of aeration, bacteria, and enzymes to your primary and secondary lagoon ponds:
- Increase your lagoon capacity by dramatically reducing the sludge levels in your lagoon ponds. Up to 6-8 inches in the primary and even more in the secondary over 6 months.
- Save thousands by avoiding the expense of dredging and trucking hundreds of loads of sludge out of your lagoon.
- Reduce odor! Especially in your primary or facultative pond where the most anaerobic decomposition is taking place.
- Aeration and the addition of bacteria and enzymes will not damage the lagoon liners or other infrastructure, and they are environmentally safe!