A manure lagoon, also known as an anaerobic lagoon, is a constructed pool filled with animal waste. This waste goes through anaerobic respiration, meaning it occurs without oxygen. This process is part of a broader strategy for handling and treating waste from diverse animal feeding operations, particularly those involving cows and pigs.
Types of Anaerobic Lagoon
1. Uncovered Anaerobic Lagoon: It lacks a top cover. This type is often chosen due to cost constraints, but it raises concerns about odours and greenhouse gases. Uncovered lagoons rely on a naturally formed crust, composed of floating fats and fine cellulosic particles, to trap the biogas produced by the waste.
However, these crusts can vary in thickness and may crack over time, allowing untreated biogas to be emitted into the air. In comparison, CALs are generally considered a superior option, efficiently capturing odours and greenhouse gases, and offering the potential to use captured biogas as a power source.
2. Covered Anaerobic Lagoon (CAL): A covered anaerobic lagoon, or CAL, lives up to its name by having a protective cover, typically made of high-density polyethylene (HDPE). This cover forms a seal with a lagoon lining, ensuring that gases and odours stay contained beneath it.
Also See: What is HDPE Plastic – Is HDPE Biodegradable?
Anaerobic Lagoon Working
An aerobic lagoon acts where animal waste undergoes anaerobic respiration, a key part of wastewater treatment. The lagoon is formed by using manure slurry washed from beneath the animal pens. Sometimes, a holding tank holds the waste before transferring it to the lagoon.
In the lagoon, the manure forms two layers: a solid sludge layer and a liquid layer. Through anaerobic respiration, volatile organic compounds transform into methane and carbon dioxide. Organic stabilisation, however, takes time due to slow sludge digestion and methane former growth. Anaerobic lagoons are commonly used as a pre-treatment step for industrial wastewater, allowing initial sedimentation of suspended solids.
Pros and Cons of Anaerobic Lagoon
Anaerobic lagoons, like anything else, come with their own set of advantages and disadvantages. Let’s look at a few of them.
Pros of Anaerobic Lagoon
- Odour Control: A covered anaerobic lagoon (CAL) provides a means to manage and control odors.
- Reduced Odor in Fertiliser: Stabilised waste results in minimal odours when the manure is used as fertiliser
- Centralised Manure Location: All manure is concentrated in one place, avoiding spreading over a large area
- Cost Effective: Anaerobic lagoons offer a cost-effective solution for waste management.
- Greenhouse Gas Capture: CALs capture greenhouse gases, contributing to environmental sustainability.
- Biogas as a power source: The ability to utilise biogas as a power source reduces the facility’s carbon footprint
- Long-Term Manure Storage: Allows for low-cost storage of manure over extended periods.
Cons of Anaerobic Lagoon
- Odour Issues without Natural Crust: Uncovered anaerobic lagoons may emit odours, especially if a natural crust doesn’t form
- Risk of Wastewater Seepage: Improper construction or leaks can lead to wastewater seepage issues.
- Environmental sensitivity: Various environmental factors, including weather conditions, can influence the effectiveness and safety of anaerobic lagoons.
- Environmental and Health Concerns: Anaerobic lagoons can harbour and release substances with potential environmental and health impacts.
- Space Requirement: Anaerobic lagoons need a relatively large area for installation
In weighing these factors, it’s crucial to consider the unique circumstances and requirements of each situation.
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