I really like the idea of above ground biofiltration for black
water, as my area has a fair number of time expired inground septic leach fields.
However, we also have a lot of rats, and I think if it was me, I would want
concrete under it to make sure the little critters didn't chew through the bottom of a tank!
Judging by how our septic tank is managed, I wonder if at some point, one might have to have at least the first tank pumped out if sediment builds up in the bottom of it.
However, I also wonder if simply cutting the tops off the grass will be
enough of a harvest to keep it growing, or whether the gravel will eventually also need maintenance? That's not unreasonable - a septic leach field has a lifespan. A quick search gave time frames of 15 to 60 years depending on how it is managed and the type of soil. That quick search clearly identified that operator management was a big part of that lifespan.
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