I developed an open source composting / vermicomposting toilet design based on an ordinary flush toilet


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  • goeco
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Re: History of vermifilter toilet and wikipedia article

Hi Wendy,

lets explore the science of nitrogen removal in simple terms for readers. Nitrogen is "removed" in two different ways:

Firstly, nitrogen can be removed as gas. Ammonification and denitrification are processes that remove nitrogen as gases (ammonia or nitrogen gas). Most sewage treatment plants use anaerobic processes to deliberately remove the nitrogen as gas, because the treated wastewater gets discharged into watercourses where nitrogen is a pollutant, leading to algal growth and eutrophication of the watercourse. Denitrification occurs in anoxic environments. Anoxic environments are not suitable for worms and my experience is that the substrate needs to be aerobic for worms to survive. I suppose it is possible that the bottom of your digester is anoxic, thus inducing denitrification, while the top layers are aerobic for the worms. My systems are entirely aerobic because I don't want to lose the nitrogen. I see nitrogen as a key element in the nutrient cycle, an essential plant nutrient that should be conserved. In my view an onsite sewage system that denitrifies goes against the principles of permaculture. 

The other method for removing nitrogen from your wastewater stream is using carbon to generate a high carbon to nitrogen ratio in the substrate. The nitrogen will be temporarily "locked up" as organic's oxidise the carbon. However, eventually the carbon gets used up and the nitrate is released (dissolved into the water). Please keep in mind that I use exclusively organic materials as substrates for vermifiltration. Woody materials with high carbon will remove nitrogen for a while. They also need topping up regularly because the carbon is oxidised. But what needs to be understood is that the nitrogen is not actually removed. Eventually the carbon to nitrogen ratio in the lower substrate will go in nitrogen's favour and nitrate will be discharged from the reactor. As you add more carbonaceous material to the top this will remove nitrogen, but eventually that material will work its way downwards and its carbon will reduce.

Please ensure your tests are long term and that your "composting" vermifilter has been operating continuously for say five years before you start testing for nitrogen, then test for another five years. I just don't understand why you see removal as good. And I can't accept that there are no nutrients coming out of your tank. Worm juice is rich in dissolved nutrients. You surely want to grow something in your impoverished soils?

I accept that you are achieving secondary treatment in your percolation trenches, but because they are trenches you have no control over percolation into your soils and water table. Seepage is the water table. I would accept that there is no "detectable" nutrient in your discharge if you explained nutrient levels with lab test results. But I would then ask what is happening to the nutrient? What can also occur is that by limiting one key nutrient (e.g. using woodchips to intercept nitrogen), plants will not grow even though the water is rich in P and K. So I prefer primary and secondary vermifiltration using a stable organic substrate such as pine bark, that remains porous without maintenance or topping up, followed by surface dripper feeding the plants directly with nutrient-rich treated water.

Dean Satchell, M For. Sc.
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  • joeturner
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Re: History of vermifilter toilet and wikipedia article

I think that is a helpful explanation, Dean.

Although it is is possible to remove N in other ways - if there is a fast growing crop which is being harvested, for example. Or even maybe in the worms themselves.

I am not really convinced that a reported 80-90% reduction of N is really telling us very much. As well as the potential losses Dean mentions, presumably this could just be due to dilution.

As an advocate of Soil Science, I really do recommend people read up about the term "nutrient availability" (particularly N, P and K). I am sure there are good explanations on wikipedia.
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