Should I cover my existing anaerobic lagoon? How does a Covered Anaerobic Lagoon CAL work?
Anaerobic lagoons are a popular method of wastewater treatment, but have you considered covering your lagoon? In this blog post, we'll explore the benefits and drawbacks of covering your anaerobic lagoon, and take a closer look at how a Covered Anaerobic Lagoon (CAL) works.
Image courtesy of SIX Maps
What is a CAL?
A CAL is a lagoon that has been covered with a gas-tight membrane or other impermeable material, which helps to improve treatment efficiency and capture biogas generated during the treatment process.
Image courtesy of NZ Pork
Should I cover my anaerobic lagoon?
Before we dive into the details of a CAL, let's first explore the benefits and drawbacks of covering your anaerobic lagoon.
Benefits of covering your anaerobic lagoon:
Reduced odours: covering your lagoon can help to reduce odours that may be emitted during the anaerobic digestion process. This can be especially beneficial if your site is located near residential areas or sensitive receptors.
Improved biogas capture: covering your lagoon can help to improve the capture of biogas, which can then be used as a source of renewable energy or sold back to the grid.
Reduced water loss: covering your lagoon can help to reduce water loss due to evaporation, which can be especially beneficial in areas with high temperatures or low rainfall.
Improved treatment efficiency: covering your lagoon can help to improve the treatment efficiency by maintaining a consistent temperature and pH level, which can promote the growth of beneficial bacteria.
Drawbacks of covering your anaerobic lagoon:
Increased capital cost: covering your lagoon will come with an added capital cost, which can vary depending on the type of cover used and the size of the lagoon.
Increased maintenance: covering your lagoon will require additional maintenance to ensure that the cover remains intact and does not become damaged.
Reduced access: covering your lagoon will make it more difficult to access for maintenance and inspection purposes.
So, should you cover your anaerobic lagoon?
It ultimately depends on your specific site and needs. If you're located near sensitive receptors and are experiencing odour issues, or if you're looking to improve your biogas capture, a CAL may be a good option for you. However, if you're not experiencing any issues and are concerned about the added capital cost and maintenance, it may not be the best option.
How does a Covered Anaerobic Lagoon work?
A Covered Anaerobic Lagoon (CAL) is a type of anaerobic lagoon that is covered with a flexible, gas-tight cover. The cover is designed to capture the biogas that is produced during the anaerobic digestion process, which can then be used as a source of renewable energy or sold back to the grid. Here's a closer look at how a CAL works:
Wastewater enters the CAL: the wastewater is first directed into the CAL, where it will begin the anaerobic digestion process.
Anaerobic digestion process: the wastewater will begin to undergo anaerobic digestion, which is the process of breaking down organic matter in the absence of oxygen. During this process, biogas is produced, which is a mixture of methane and carbon dioxide.
Biogas capture: the flexible cover on the CAL is designed to capture the biogas that is produced during the anaerobic digestion process. The cover is gas-tight, which means that it will prevent the biogas from escaping into the atmosphere.
Biogas storage: the captured biogas is stored in a storage tank or other suitable vessel until it is ready to be used.
Biogas utilisation: the captured biogas can be used as a source of renewable energy, either by generating electricity or by being used as a fuel source. It can also be sold back to the grid for additional revenue.
Useful operational formula for a Covered Anaerobic Lagoon (CAL)
When considering a CAL, you might wish to use the following approximate operational formula.
Biogas production (m³/day) = 0.025 x (Lagoon Volume (m³)) x (BOD Load (kg/day))
The industry benchmark for biogas production is 0.025 m³ biogas per day per m³ of lagoon volume for every kilogram of BOD load per day. This benchmark can be used to estimate the expected biogas production for a given lagoon size and BOD load.
Handy Tips for a Site with a Covered Anaerobic Lagoon or Considering Purchasing One
If you're considering purchasing a CAL or already have one in operation, here are some handy tips to keep in mind:
Regular maintenance: make sure to regularly inspect and maintain the cover on your CAL to ensure that it remains intact and does not become damaged. This will help to prevent any biogas leaks or other issues that may impact the performance of your lagoon.
Monitor biogas production: regularly monitor the biogas production from your CAL to ensure that it is meeting your expectations. If you notice a decrease in biogas production, it may be an indication of a problem that needs to be addressed.
Utilize biogas efficiently: make sure to efficiently utilize the biogas produced by your CAL by using it as a source of renewable energy or selling it back to the grid. This can help to reduce your site's energy costs and provide additional revenue.
Consider other treatment options: while a CAL can be an effective method of wastewater treatment, it may not be the best option for every site. Consider other treatment options, such as a Moving Bed Bioereactor (MBBR), sequencing batch reactor (SBR) or a membrane bioreactor (MBR), to determine which option is best suited for your site's specific needs.
Covering your anaerobic lagoon can provide a number of benefits, including reduced odors, improved biogas capture, and improved treatment efficiency.
However, it also comes with added capital cost and maintenance requirements. If you're considering a CAL for your site, make sure to consider the benefits and drawbacks carefully and take into account the operational formula and industry benchmark.
With proper maintenance and monitoring, a CAL can be an effective and efficient method of wastewater treatment for meat processing, rendering, and winery sites in Australia.