A covered lagoon stands out as an excellent choice among lagoon types for several reasons. Similar to other lagoons, this variant constitutes a sizable, earthen basic designed for wastewater treatment. Covered lagoons leverage the absence of oxygen to decompose raw sewage into other compounds, which can be extracted as effluent. The lagoon is shielded by roust material, like high-density polyethylene (HDPE), to contain gases and odours.
Ensuring a minimal oxygen presence covered lagoons generally boast a greater depth, ranging from 8 to 15 feet. Their operation typically extends over a more extended period compared to other lagoons, involving a gradual breakdown of organic compounds. The treatment duration spans approximately 20 to 150 days. Operating without heating, these lagoons require a cool environment without freezing or optimal efficiency. Just like any other lagoon, the treatment process stops when the water freezes.
Working of a Covered Lagoon
In a covered anaerobic lagoon (CAL), an intricate microbial process tackles raw wastewater, diving it into layers without dissolved oxygen. The lower layer transforms into methane and carbon dioxide. The stable anaerobic conditions in the lagoon combat volatile organic compounds, with a top layer containing scum and grease. Microbially, the process involves acid formation and methane production, converting organic compounds into acids. The production of methane is influenced by certain external factors, with temperature being the most significant one.
Selecting the right climate and lagoon type is crucial for optimal microbial processes. The best temperature for a covered lagoon is between 77 ℉ and 104 ℉, and the pH levels should be between 6.6 and 7.6. Extreme temperatures or low pH can disrupt the process. Once treated, the water becomes effluent for various uses, including other treatment systems or recycled water for irrigation.
Pros and Cons of Covered Anaerobic Lagoon (CAL)
Anaerobic covered lagoons come with a mix of advantages and disadvantages. Depending on your circumstances, location, and climate, it’s crucial to weigh the benefits against the downsides.
Pros of Covered Anaerobic Lagoon (CAL)
- Added Value: The methane biogas produced can be converted into electricity, serving as a power source for buildings. Excess electricity can even be sold for profit.
- Odour Control: The cover acts as a barrier, containing unpleasant odors within the lagoon and preventing them from spreading into the surroundings.
- Cost-effectiveness: Opting for a covered lagoon is a smart and cost-saving move. It operates efficiently without requiring additional energy inputs.
Cons of Covered Anaerobic Lagoon (CAL)
- Space Requirements: Building a covered lagoon demands a significant amount of land, often challenging in residential areas. Regulatory hurdles, including land and EPA regulations, can further complicate the construction process.
- Time: Treatment in covered lagoons often requires more time compared to other alternative methods. It relies on natural microbial processes, making it a gradual procedure.
- Cleaning challenges: The influent in anaerobic lagoons separates into layers, with the bottom layer accumulating and requiring periodic cleaning which requires professional services. Excessive buildup can lead to performance issues and odors.
- Climate dependency: The lagoon’s efficiency is heavily influenced by climate and temperature. Mismatched conditions can disrupt the biological processes occurring beneath the surface.
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