Curious about biochar and its benefits? Learn what biochar is, how to use it effectively, and why choosing top-quality biochar makes a difference. We also explain what super compost is, how to make it at home, and how Soilfixer SF60 works as a powerful super soil improver. Whether you want healthier plants, richer soil, or more sustainable gardening methods, this guide covers everything you need to know.

Biochar for water and gas filtration

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)

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Making a fantastic raised bed, container compost mix

Making a fantastic raised bed, container compost mix

This blog was updated in March 2023 to reflect latest information on the new SF40 biochar multi-purpose compost.

SoilFixer has been supplying Biochar and SF60 (Biochar Super Compost) for many years. Our biochar-humus-rich compost is added to your topsoil to improve soil health and plant growth – it’s the closest means yet for you to make your own Terra Preta!

Many customers grow plants and vegetables in raised beds, containers, planters, and hanging baskets using “all-purpose compost” rather than soil.  (We are not fans of using the term compost to describe a soil-less growing media (mix) – especially when very few of the growing media mixes use any green waste compost. Most are formulations of peat/coir/wood fibre! see our compost definitions).

Our goal is to find a better-performing raised bed mix that is also environmentally friendly – not just peat-free, but actually carbon negative (i.e. it locks carbon into the mix for hundreds of years). With a bit of annual care, our mixes should not need replacing each year.

Below we cover our journey to date.

Raised bed and container mix challenges

Container mixes present special challenges – they lose water and dry out faster than soil and the roots have a limited space to grow.  If you add lots of material that holds water (e.g. clay or humus), the mix can become ‘airless’ which restricts the root even more leading to stress, and disease problems like damping off (stem rot). It is not easy – ask any of the big growing media companies who have spent millions working on peat-compost alternatives.

We have been using our knowledge of compost, biochar, soil, and colloidal humus to create a fantastic raised bed container mix. We have looked at two routes: adding SF60 to the soil, and creating a wholly new mix from biochar and compost (now called SF40).

We tested the two options last year:

  • Raised bed one: two parts finely sieved PAS100 green waste compost, 1 part SF60, to give a 10cm layer on clayey soil base
  • Raised bed two, two parts PAS100 and 1 part biochar, 10cm layer on clayey soil base.

The differance is SF40 is a mixture, SF60 is made by co-composting biochar with green waste, then sieving the final compost-biochar mix.

SoilFixer raised bed mix benefits

Both work extremely well – giving 100% increase in plant growth. There are differences in water retention and growth in different plants towards the end of the season.

  • Enhanced growth results
  • Strong water retention and resistance to drying out
  • Good re-wetting ability
  • Viable cost for the “biochar raised bed mixes”
  • Re-usable year on year (with some minor care)
  • 100% peat-free
  • Climate positive – unlike other raised bed mixes, biochar-based will lock carbon for +100 years

What next?

  • SF40 is our preferred option for supplying a growing media – in part because it is much easier to make and control
  • We need to test SF40 at a much larger scale… ongoing
  • We believe SF60 will be the default for soil improvement
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Improve soil health ahead of the growing season

Improve soil health ahead of the growing season

The first step to improving your garden soil is to identifying which soil type you have. In the UK there are six types, clay, chalk, loams, peat, sandy and silt, each comes with its own positive and negative characteristics and you can adapt and enhance it to ensure you have fertile soil all year round. See the RHS’s soil guide to check which variety you have.

If you are a keen gardener or you grow your own vegetables and fruit you will probably dig the soil over or cultivate it fairly regularly, if this is the case you need to provide a combination of nutrients that will enhance it.

To get started, remove the weeds and as much of their roots as possible to prevent them growing back and begin to dig the ground over, digging will loosen the soil and also expose some of the larvae from garden pests such as slugs and snails, leave these for the birds to deal with. If you are following a no-dig routine, details can be found here.

There is a lot of advice around adding ‘organic matter’ to the soil to help improve it, the term itself is fairly ambiguous and many of us assume that it means add compost when the two actually differ significantly.

The next stage is to add a nutrient-rich soil improver, the SoilFixer SF60 Super Compost is ideal for use in domestic gardens and allotments and contains high levels of colloidal humus and biochar the combination of these two ingredients acts as a sponge for water and essential nutrients which contribute to improved plant health and resilience against extreme weather conditions such as drought and frost, the biochar acts as a host to a series of microbes which transfer nutrients from the ‘sponge’ the nutrients right down to the plants’ roots.

We call SF60 a ‘Super Compost’ because not only is it packed with valuable ingredients, it also offers numerous additional benefits, it can be used to improve garden soil, its results are long-lasting as the biochar remains in the soil for over 100 years, plus both biochar and colloidal humus sequester carbon which means using them in the garden helps to offset greenhouse gases.

If you don’t have an area that can be dug over but you have established beds and borders you can still use SF60 and get all of the benefits, simply fork it in as a top dressing around existing plants and shrubs and leave it to its hard work.

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