What is a BioChar bag?
- Dustin Ford
- 21 hours ago
- 4 min read
You’ve probably heard the term ‘Biochar’ before, but how much do you know about it? For years Biochar was renowned for many uses in gardening and horticulture. In recent years we’ve discovered that specific types of biochar can help remove harmful substances from water. This non-chemical product is now being engineered specifically to help clean eutrophic freshwater lakes and streams.
As the name implies, most biochar is made up of charred wood and ground cover. The Biochar used in cleaning lakes is almost entirely made of timber. The wood must undergo a process called pyrolysis where it is heated at extreme temperatures in a low oxygen environment. This process is a thermal decomposition of materials which allows volatile components to escape, leaving behind a very charred, carbon-rich material.
After pyrolysis the biochar is left with a very porous surface. It has so many pores that one gram of biochar can have a surface area of 400 sq meters. It just so happens that all these pores, cracks, and crevasses make the perfect environment for beneficial microbes. When placed in water these same microbes help biochar act as a filtration system.
The biochar acts as a sponge for microbes such as nitrifiers, denitrifiers, and phosphate-solubilizing bacteria. Each of these plays a crucial part in removing harmful chemicals from a lake.
These nitrifiers draw in ammonia from the lake and convert it into nitrate. This may seem counterproductive since excess nitrate is also a problem with most eutrophic lakes, but this is where the denitrifiers come in. A denitrifier takes the converted nitrate (and other nitrate already found in the water) and converts that into nitrogen gas. This gas bubbles up to the surface of the water and evaporates into the atmosphere. These two microbes work together to eject ammonia and nitrate from the lake in a harmless and environmentally friendly way.
Phosphate-solubilizing bacteria are responsible for converting insoluble forms of phosphate (forms that cannot be dissolved in water) into soluble forms that plants can absorb. This material can often stick to the biochar. More engineered biochar can hold a positive ion charge, which attracts and binds phosphate ions to it’s surface. Unlike the nitrogen gas, this phosphate and other harmful chemicals stay locked into the biochar where they have to be removed manually.
Biochar used for this purpose is often segmented into chunks and placed into porous bags. These bags are attached to piers, docks, and any other solid surface above the water. They are meant to float in the water for months and only need to be taken out during the winter. While the bags shouldn’t be in the water when the lake ices over, they can be simply left uncovered on a flat surface when it snows. You can find videos on how to install these bags to lakefront property here: The Biochar Initiative | Paw Paw Lake Fdn
Over time the biochar might need to be replaced with new char. After many months of absorbing nutrients, the char is recycled as fertilizer. This is usually done far away from the lakes they were used in to prevent redistribution. Local organizations that issue these biochar bags will collect and replace them for free.
Many lakes around Michigan have taken to using Biochar bags in recent years. Now it’s our turn. The Paw Paw Lake Foundation has organized a biochar initiative for lakeside residents. Through crowdfunding and generous donations from local residents, the PPLF can offer this service to lakefront owners completely free.
To achieve the highest possible success rate, we need all lakeside property owners to get involved. All you have to do is sign up at the following here: Biochar Registration | Paw Paw Lake Fdn
The PPLF is planning a 3-year program for using biochar bags. The goal is to cycle as much water through the timber char bags as possible. While visual results are present within the first year, more time is often advised for best results. Paw Paw Lake has nearly 907 gallons of water in it, so being efficient will take time.
Biochar bags have proven to be a non-chemical solution to eutrophic lakes. We look forward to using them in the future. Please join us as we make Paw Paw Lake cleaner for all of us.
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