Human Waste on the garden...

…aka “Did my FIL do a Bad Thing?”

My husband’s parents moved house a few weeks ago. Being country folks, and on a pretty strict budget, they’ve grown most of their own vegies all their lives. So, one of the first things they did at their new place was to dig out space for their veggie garden.

Now, the soil at their old house, after many years’ application of compost and chicken droppings, was pretty good. This new place … not so much. They brought bags of compost with them, but given the size of veggie patch we’re dealing with, this hardly made a difference.

So, then FIL had a bright idea. The septic tank! He wanted to investigate it anyway, to see if it needed clearing out, so when he did so he dug out all the rotting toilet paper and spread it over the new garden as mulch.

They have yet to plant anything, BTW.

Anyway, we’re all fairly sure that this is probably some dire breach of sanitary regulations on septic tanks. This is not the sort of thing that tends to worry FIL. **I ** on the other hand, am worried that their veggies will be stewing in someone else’s e-coli and they could give themselves (and maybe us!) food poisoning when the first crops come through.

So… how big a deal is this? I initially suggested to them that they might want to stick with things whose edible bits are way above ground (corn for instance). Some internet research I’ve done, OTOH seems to suggest it’s OK as long as the veggies concerned are going to be well cooked (generally not a problem at the in-laws :wink: )

Anyone have the Dope?

I don’t know if it contravenes your local health regulations, but ordinary human waste can certainly be used as fertiliser; the idea isn’t without difficulties, but it isn’t impossible. I used to read articles by a chap named John Brown in a magazine called Good Woodworking - in one of these, he detailed the construction of a compost toilet - essentially, two great big pits, ideally dug into the side of a hill so that one side can be opened easily. You use one of them for a number of months, then close it over and use the other one - by the time you have to switch back, the waste in the first has composted down and can be dug out as fertiliser (not a wholly pleasant job, I’d imagine, but also probably not as bad as you might think - if it is very well-rotted, manure of any kind is actually quite pleasant to handle).
I think you had to add straw or sawdust or something each time you use the toilet, to help decomposition and structure.

Problems with using ordinary human waste from a conventional toilet system as fertiliser include:

  • Chemical contamination; anything you’ve used to clean the bowl will have been flushed into the septic tank and may not have broken down to harmless components.
  • Pathogens - there could be a range of bacterial and other pathogens in the waste that are quite human-specific - ideally, the heat from composting will kill them, but we don’t live in an ideal world.

There’s also the problem of heavy metal contamination (I suppose that should just be included under the heading of chemical contamination) - I don’t know what it is about human effluent that makes this a particular risk (that is to say, I don’t know how these heavy metals are actually getting into the mix), but it is one of the key problems with using sewage sludge as agricultural fertiliser.

Yeah, the system you describe sounds very much like commercial composting-tolets I’ve seen described, eg here .

What I’m thinking is … I presume the way the waste is stored while decomposing has a big impact on what bugs are destroyed and/or thrive in the process . A septic tank must be fairly different from an aerobic composting system (though I’m not sure in what way)

Well, I think for one thing, compost toilet systems are supposed to be fairly dry; the one I read about was really just a big hole in the ground; the liquid components of the initial waste and any liquids from the decomposition process were free to drain into the underlying soil (this would probably be bad on a large scale); a septic tank (as I understand it) is more like a big, wet fermentation/digestion process.

Just type ‘nightsoil’ into Google and you’ll get plenty of info on using human manure for fertilizer. Apparently China has been doing it for hundreds of years.

When my brother was in the US Army in S. Korea, he came down with hepatitis B. The docs explained that the Koreans have primitive sanitation in some places, and they gather human dung for fertilizer. BroNott had been eating among the locals, eating their contaminated veggies. Hep B is spread through contact with poo, so he got it. Now, if nobody with hepatitis shat in your FIL’s septic tank, this won’t be a problem. Since he just moved in, he can’t know that.