I have a septic tank with multiple chambers, the output of which is then pushed into a field (by design). As I'm new to living rurally, I asked a whole bunch of questions to the people who came to service the tank. I'm not sure there answers make sense, and I'm still a bit confused.

Can anyone advise how it is appropriate to use the output of the septic system - I was told that its great for fruit trees, but bad for things like tomatoes, zucchini etc - even if applied only to the roots - a claim I'm a bit skeptical of. (The reason for my skepticism stems in part from reading I did relating to "The Martian", and apparently growing potatoes in human waste is viable).

I was also told that it is toxic to people (which makes sense), but would not affect my goats or sheep (which doesn't make much sense to me, but I believe is probably correct) - Does anyone know the ins-and-outs here ?

I'm contemplating laying a new line parallel to the existing one and using it to continuously feed a line of trees - Apples, Lemons, Figs, fejoas and stone fruit. Is this a good idea ?

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    As a rule we try to keep a 35 foot (10-11 meter) buffer between septic pipes and trees, since tree roots in the septic pipes can cause blockages. "night soil" (which is rather a lot nastier than treated septic effluent) is used for fertilizer in many cultures - but it has pathogenic concerns. Depending on the exact nature of your "multiple chamber septic system" the output can be essentially pure water, or several stages of less than that (though soil bacteria in the effluent field will clean that up quickly in a functioning system.)
    – Ecnerwal
    Commented Apr 17, 2016 at 23:33
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    A decade or so ago I led some students in a sustainable desogn research project on using septic waste. The vegetated submerged bed section in the EPA manual on constructed wetlands was useful. Check it out. nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=30004TBD.TXT
    – gorav
    Commented Apr 18, 2016 at 21:08

3 Answers 3


You're going to be dripping partially treated effluent onto the ground near some fruit trees. The main concern is splash back of pathogenic bacteria onto some edible fruit. Though this risk is less when the fruit is in a tree, there is still some risk especially if someone picks fruit off the ground to consume.

It's clearly more of a risk with vegetables closer to the ground such as zucchinis and tomatoes.

Contamination of food crops with E Coli, Yersinia etc appears to be more of a risk in organic grown vegetables which has had manure come into contact with the crop.

The safest way to apply human manure to edible crops is to compost it first, and then let it stand. This might be 2 years depending on whatever the local bylaws suggest.

In countries such as China where human manure was once commonly applied to the fields, the risk was reduced since vegetables were always cooked before consumption, and water was always boiled first and drunk as tea.

Since you're using a drip line, I presume that the tree roots have no way of following this back to the septic system, or invading underground lines of the system.

  • I understand the unacceptable risk of contact with the skin of the fruit, but can pathogens pass through the root into the fruit itself ?
    – davidgo
    Commented Apr 18, 2016 at 3:44
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    Not into fruit, but can certainly be taken into leafy vegetables Commented Apr 18, 2016 at 4:47
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    aem.asm.org/content/68/1/397.full Commented Apr 18, 2016 at 4:55
  • and splashback (as @Graham suggests) - cf. the various E.coli outbreaks in recent years in the US that have been traced to leafy veg such as spinach and lettuce.
    – winwaed
    Commented Apr 19, 2016 at 13:51

I had a 2 tank septic in my backyard. The second (effluent) tank once allowed the fluid to seep through the walls into the earth. But it became so slow that the system sometimes backed up to the WC. I bought a pump and regularly pumped the effluent onto my veggie garden. Really good crops and no smell and ate the vegetables.No ill health! The effluent was supposed to be safe after the process in the fist tank. Now I'd like to know about using the fluid from a one-tank septic system which I have now. This tank has been working for 35 years without any attention. The effluent is piped off into underground drainage trenches. It seems a pity not to recycle this excellent nutrient.


If you're gonna use human effluent as fertilizer, it's best to get a composting toilet rather than go thru the joys of septic system management. Recycling of human excreta is a thousands year old practice. Since the start of the industrial revolution and adoption of synthetic fertilizer, small scale attempts to recapture this ancient practice led to many failures, namely poor hygiene, public stigma and just plain bad management by greedy opportunists who thought they could turn S*** into gold by running a business with no attention to detail. YES you can use ...waste as fertilizer but avoid direct contact with plants meant to be eaten (carrots, potatoes) plants where the edibles don't touch the soil/manure (fruit trees, corn, etc) You need a system that insures a high temperature to kill pathogens. composting toilets are approved by local sanitation authorities, homemade humanure systems are rarely approved. Professional/mass composting will bake/heat compost in kiln/rotating ovens to kill germs, then the hot mess is dumped and mixed hot with existing compost where water and dry straw is added. You can pasturize compost in an oven to kill pathogens. Then mix it back with regular soil and add beneficial bacteria.

In a septic system there's two ways you can safely convert biosolid wastes 1: Get a bioreactor: Expensive, on the other hand if you're selling compost which can fetch a price of 40 dollars per cubic yard 2: Another strategy is slow composting and water it down in small increments. Solution to pollution is dilution.You can sterilize compost by microwaving it, baking it in an oven, or pouring boiling water over it. Of the three methods, the boiling treatment is the neatest and cleanest cuz it's doable outside to avoid the odor.

A toaster oven (willing to part with) is plugged up outside. You can cook 10 liters of dried waste kill pathogens.........

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