I mentioned a few times that I have a sewage treatment facility at my home and that I do get some use out of it outside of it cleaning water. I will say a bit more about it today, since it is rather important these days.

I have a five-stage system:

1. 3-chamber anaerobic septic tank – here the water undergoes the first stage of biological cleaning where it separates solids and the slowly decompose and ofgass. The sludge that is left behind needs to be pumped out and disposed of approximately once a year.
2. Biofilter – essentially a column of plastic foam where some further biological shenanigans happen. The water that comes out can, under certain circumstances, be let out. In my case, it undergoes further cleaning because…
3. Pumping station – the septic tank and biofilter have the water surface too low below the ground, so the biofilter is permanently and completely flooded. It was not supposed to be like that, and we had to insert the pumping station during production to compensate for a mistake in the project.
4. Gravel reed bed – a 5×10 m hole, 1 m deep, lined with heavy-duty foil and filled with gravel. I actually built this first, illegally, to clean grey water only. It was a significant improvement over what we had before, which was simply to let uncleaned grey water to seep into the ground. To this day, many households here still have some semi-legal arrangements like that.
   The gravel bed is planted mostly with Phragmites australis. The reeds clean the water further, and although they are most effective during the vegetation season, they do work in winter too. In the summer, they use up nitrogen and phosphorus to grow and create biomass. In the winter, some of that biomass dies and provides carbon for bacteria that also use the nitrogen and phosphorus. At the very end of the gravel bed is a charcoal filter, where most particulate matter and remaining chemical pollution (still mostly phosphorus and nitrogen compounds) are further absorbed.
5.  Seeping pond – a shallow (~50 cm at most) pond where the water seeps into the soil around the edges. Around the pond are planted willows and my mighty walnut tree. The willows provide me with firewood and long sticks for growing beans, the walnut provides me with food and shades the pond completely most of the summer. In the pond is a big growth of duckweed, which cleans the water even further – although that is no longer strictly necessary, since water is tested before the pond, after the charcoal filter. Ammonia is a bit of a problem, but not really.

I tried to have fish in the seeping pond and they did survive the summer, but not the winter. I would need to have active aeration in the pond for that – when sudden -20°C came, the fish suffocated under the ice. But the pond is full of life even without my interventions.

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I have introduced duckweed to the water, and it does not look very appetizing (to a human), but it is actually a sign of healthy water. I never had a harmful algal bloom in my pond, which is caused by cyanobacteria. Those thrive in environments with excessive phosphorus pollution but a lack of nitrogen, and they do release nasty chemicals into the water. This water is not drinkable, and it is not clear, because there are dead leaves, etc., in it, but it is healthy.

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This year, the weather seems to be especially favorable for the duckweed; the pond is completely covered. Thus, I finally rigged a sieve with a long handle to scoop out some of it. I am composting it – it adds nitrogen and phosphorus to the compost heap and the life cycle of shit is thus completed. When taking it out, I took out some other life forms too.

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Damselfly larvae are a frequent occurrence. I do my best to toss them back as soon as I notice them. They are the main reason why I do not simply throw a pump into the pond when I need water for irrigation anymore. However, this year I got a surprise that made me really happy.

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Alpine newt (probably) –Ichthyosaura alpestris. I did post about frogs in the pond in the past, but newts are even more sensitive to chemical pollution than frogs. That is why I was happy to see one. Especially since this year is very dry and the amphibians need every help to survive they can get.

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For smaller amounts of irrigation water, I can use watering cans to scoop water out of the pond. But since I expanded my gardening this year, right when it seems we will have another climate-change-induced drought, I have to use it to irrigate my crops. And in this picture, you can see the pump under the water level in the last stage of the gravel bed, before the water goes through the charcoal filter. It is see-through for several decimeters even before that last filtering, and it is safe to water crops that are a long way away from harvesting and that are not eaten raw. Just to be on the safe side, I still do not use it to water strawberries or anything similar that could get splashed. Potatoes, tomatoes, onions, peas, beets, and bonsai benefit greatly, though.