2.4.2 Anaerobic Lagoon
A covered anaerobic lagoon is an excavated rectangular pool lined with HDPE at the bottom to prevent infiltration and contamination of the groundwater and covered on the top to capture the biogas. The anaerobic lagoon has enough capacity to allow for settling solid particles and digestion of organic materials. Screened faecal sludge or wastewater enters the lagoon near the bottom at the shorter side of the lagoon and mixes with the active microbial population in the sludge layer. The discharge point is on the opposite side of the slightly sloped lagoon from the influent. The effluent from anaerobic lagoons is not suitable for direct discharge and would require a post-treatment. A cover captures the methane gas produced in the process for further use or is flared, which is required for climate protection.
The table presented below outlines the pros and cons of anaerobic lagoons.
| Pros | Cons |
|---|---|
| Low operating costs. Simple operation | Requires large area. Only feasible where land is available and cheap |
| Effective for rapid stabilization | Expert design and skilled labour are required |
| Low sludge production | Low reduction of pathogens and nutrients |
| Capable of withstanding organic and hydraulic shock loads | Effluent and sludge require further treatment and/or appropriate discharge |
| Capturing and utilizing biogas can lead to a reduction in greenhouse gas emissions | Treatment performance is temperature-dependent |
| Renewable energy source if captured and utilized | |
| Adopted from: (SANIMAS, 2005) | |
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