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Biochar - for water and gas filtration

Tony Callaghan 16/07/2016

Biochar - for water and gas filtration

Biochar is a sustainable form of carbon used to replace fossil fuel-derived Activated Carbons used in the following water and gas filtration applications

  • Wastewater filtration
  • Filtering excess fertiliser leachate and water run-off 
  • Anaerobic gas filtration
  • Landfill gas filtration
  • Aquarium water filtration

Biochar for aquarium and water filtration

Biochar replaces activated carbon in water filtration media. Using activated carbon to clean fish aquariums is well documented – a summary of the two main methods (chemical and biofilter) is at Federation of British Aquatic Societies (fbas). 

(If you are looking for help on using biochar (or charcoal) in aquaponics and hydroponics as a growing media you may also find this article helpful.)

We believe biochar offers something very unique over activated carbon filters:

Biochar as a "biofilter"

  • The possibility to do both chemical and biological filtration in one filter
  • Using the same filter media for many years – saving a huge amount of money, reducing waste and its negative environmental impact
  • Re-using 100% of any spent biochar filter media to make a 'super compost' soil improver. Biochar inoculated in compost helps improve soil health and plant growth. The carbon is also locked (sequestered) into the soil - offsetting your carbon footprint and helping mitigate climate change.

In a well-managed aquarium, activated-carbon filters should do two things

  • Remove organic molecules by adsorption onto the pore surface. As organic molecules are removed the water is clarified. (Many organic molecules have a yellow colour tinge)
  • Act as a living space for nitrifying bacteria. The aerobic (oxygen requiring) nitrifying bacteria convert toxic ammonia (excreted by freshwater fish) into the less toxic nitrate/nitrite molecules. 

The active pore sites quickly become full – requiring the filter to be replaced. As the bacteria work and grow biofilms build up. Eventually, this ‘slimy film’ can restrict airflow and the nitrifying bacteria cease – anaerobic bacteria become dominant and smell / odour follows. The theory goes that you should wash the activated carbon pellets and keep using – which works to an extent. Here are the issues: 

Activated carbon pellets (PAC, GAC granules 2mm pellets etc) in our opinion are poor 'homes' for bacteria. Bacteria (which are 2-10 micron in size) can only live on the surface of the pellet – which is a tiny surface area. Biochar has numerous pores that bacteria can live and hide in. 

Removing ammonia from aquarium water is just one of the challenges faced. Excess food and fish poo also need to be removed. To remove wastes, your tank needs to support a population of ‘aerobic composting’ bacteria – i.e. bacteria that eat organic matter. These will live quite happily alongside nitrifying bacteria. Aerobic bacteria like nitrifying bacteria need you to maintain oxygen levels in the tank water. As soon as the oxygen level falls too low, the anaerobic digesting bacteria take over the food digestion.

Biochar (formed from wood) is a vastly superior home for aerobic and nitrifying bacteria. Correctly made wood-based biochar not only has micropores that absorb organic molecules, but it also has larger pores (called meso and macropores) that are large enough for bacteria to live in. This porous structure also supports aeration (oxygen flow) and water flow. You can host more bacteria and hence clean more water. 

The biochar advantage continues: once the micropores are filled with organic matter the filter carries on working. The aerobic composting bacteria just keep eating it! As with activated-carbon you just need to wash most (not all) of the biofilm out every 6 months. 

Replacing filters is a great recurring business for the carbon suppliers – but it is not so good for the consumer’s pocket nor is it good for the environment as most of this carbon ends up in landfill. (on larger water treatment plants it is often returned for reprocessing. Much as we would like to believe the claims that the carbon industry ‘recycle and regenerate’ spent activated carbon filter material, we can only find one successfully documented way to regenerate activated carbon and that involves re-heating to 900C to ‘vaporise’ the filtered material off. This is as costly as making new carbon - we believe most of the spent carbon filter returned is ‘burnt’ to generate energy to make new activated carbon from oil. 

In a biochar biofilter, after many years it will become fragile due to flaking off of carbon during washing. When it reaches this point, it becomes a valuable resource used to improve your compost and soil health. Here at SoilFixer, we are trying to make the large water filter solution easy as we plan to ‘rent’ the filters, wash and eventually replace using any spent biochar in our composting process.   

The SoilFixer focus is on soil improvers, but we manufacture a lot of biochar. We now sell biochar for fish pond filters via our ebay shop in 1 litre (approx. 400g) and 30 litres (approx. 10 Kgs). We make our biochar in the UK from UK wood resources - it is the best value for money fish tank charcoal available today. If you know about filtering fish tanks and want to test biochar give us a call – we think you will be amazed about how much cheaper it is to buy biochar carbon over activated carbon. We also think you will be stunned by the possibility that with a little care, you no longer have to replace your carbon filters every few months.

Biochar to remove excess fertiliser runoff 

Eutrophication (reduction in water oxygen) occurs when large algal blooms grow using high levels of phosphorus or nitrogen in the water. This is a larger example of the fish tank issue.

To remove excess nitrogen and phosphorus there are two options - chemical or biological. Biofilter can capture the excess nutrients before the bloom occurs.  The clever part - a biofilter filled with nutrients can be reused as a soil improver. 

We are very keen to set up a trial with large fish farms and those with localised water treatments (e.g. septic tanks, with runoff), or even those with nitrogen fertiliser runoff into watercourses who are seeking a closed-loop solution.

Biochar for treating drinking water 

Biochar, like all activated carbon, will filter many types of organic and inorganic impurities from water. Water in developed countries is already well purified.  The use of biochar is more likely in developing countries without sewage treatment infrastructure. This solution is taking off in developing countries where locally made biochar can be used over expensive activated carbon. Aqueous Solutions have a great overview of their website. 

Thank you for reading about the possible uses of biochar for water and gas filtration. This is one of five articles on the uses of biochar - follow the links below:

Biochar for industrial use (link)
Biochar for gardeners - some surprising uses (link)

Biochar for farming and agriculture (link)
Biochar for Gardeners - some surprising uses (link)