What is an Anaerobic Lagoon?

Although it may not be the first topic you consider at your dinner table at night, the topic of wastewater and it's environmental impact is an important one. Ensuring that wastewater is dealt with properly and effectively is a huge task, and one that a variety of industries are required to consider every day of the year. In particular, the red meat industry (especially cows and pigs) can generate a huge amount of wastewater (that is high strength) purely through normal operations, and this has to be dealt with somewhere and somehow, ensuring the best outcome possible for the environment. Enter the anaerobic lagoon - generally a 'first step' when it comes to efficient and cost-effective wastewater treatment. But, what is it and how do they work?

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What is an Anaerobic Lagoon?

An anaerobic lagoon, otherwise known as a manure lagoon, is a man-made pool that is filled up with animal waste. This animal waste undergoes anaerobic (without oxygen) respiration as one component of a larger scheme to manage and treat waste created by various animal feeding operations, especially ones related to cows and pigs.

What are the different kinds of Anaerobic Lagoon?

Covered Anaerobic Lagoon (CAL)

A covered anaerobic lagoon, or CAL, is exactly as its name suggests - an anaerobic lagoon with a cover over the top. The cover is generally constructed of a high density polyethylene (HDPE), which joins up with the lagoon lining and forms a 'seal', ensuring gas and odours remain under the cover.

Uncovered Anaerobic Lagoon

Like a CAL, an uncovered anaerobic lagoon is as its name suggests - an anaerobic lagoon that does not have a cover on top. Uncovered anaerobic lagoons are quite common, generally due to cost restraints meaning a cover is not possible, however there are concerns regarding both odour and greenhouse gases for this option. Uncovered anaerobic lagoons rely on a naturally formed crust consisting of floating fats and fine cellulosic particles to keep inthe biogas produced by the waste. These crusts however can be quite thin (where primary treatment is of a high standard), or may be over a metre thick (where pre-treatment is cursory), and can crack or fracture in time. If this occurs, biogas is emitted into the air mostly untreated (however the crust often deodorises it to some extent). It is widely considered that CAL's are a better option than uncovered anaerobic lagoons, due to their ability to catch odours and greenhouse gases more efficiently, as well as the potential to use captured biogas as a power source.

How does an Anaerobic Lagoon work?

An anaerobic lagoon provides an environment for animal waste to undergo anaerobic respiration as a component of a larger wastewater treatment program. Manure slurry is used to create anaerobic lagoons, which is washed out from underneath animal pens and then sent into the lagoon. If necessary, there may be a 'holding tank' located either under or beside the animal pens where the waste can be held until it is moved into the lagoon.

Once the manure slurry is in the anaerobic lagoon, the manure settles into two layers: a solid or 'sludge' layer and a liquid layer. The manure then goes through anaerobic (without oxygen) respiration, where volatile organic compounds are transformed into methane and carbon dioxide. It can take a fair amount of time however for organic stabilisation to occur, due to the slow rate of sludge digestion and slow growth rate of methane formers.

Practically speaking, anaerobic lagoons are generally used as a pre-treatment arrangement for high strength industrial wastewater solutions. The reason for this is it allows for preliminary sedimentation of suspended solids as a pre-treatment process.

Pros and Cons of an Anaerobic Lagoon

Just like anything, anaerobic lagoons have both positives and negatives... and we have listed a few of them below!

Advantages of an Anaerobic Lagoon

  • A CAL allows an opportunity to control odours
  • Cost effective
  • Anaerobic lagoons ensure all manure is in one location, as opposed to spread over a larger area
  • A CAL captures greenhouse gases
  • When waste is stabilised through digestion, odour is minimised when manure is finally used as fertiliser
  • The ability to use biogas as a power source, minimising the carbon footprint of the particular facility
  • Manure can be stored for long periods of time for low cost

Disadvantages of an Anaerobic Lagoon

  • Can harbour and emit substances which can have an adverse environmental and health effect
  • Odour emissions if a natural crust does not form (especially for uncovered anaerobic lagoons)
  • A range of environmental elements can affect the safety and efficacy of anaerobic lagoons (such as the weather!)
  • Requires a relatively large area to be housed in
  • Wastewater can seep out if there is a leak or the lagoon wasn't properly created

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If you have any questions regarding anaerobic lagoons, or would like to talk to one of our knowledgeable team regarding biogas solutions for your property, give Inoplex a call on 0448 307 282 today. We offer unique options for a variety of industries across Australia, so get in contact now.

Resources:

Wikipedia (Anaerobic Lagoon): https://en.wikipedia.org/wiki/Anaerobic_lagoon

Australian Government: Clean Energy Regulator (Participating in the Emissions Reduction Fund: Using the domestic, commercial and industrial wastewater method):
https://www.environment.gov.au/climate-change/government/emissions-reduction-fund/publications/factsheet-emissions-reduction-fund-wastewater