the value of humanure as a carbon source within the soil

Hi Eric,

Recently I wrote a report for Feasta (the Foundation for the Economics of Sustainability) about closing the loop on agricultural nutrients. There are many benefits. In short we in Ireland (and elsewhere in the world) produce nitrogenous fertilisers using large quantities of natural gas, grow food with these nitrates, harvest and eat the food, deposit the nutrients in the toilet and then flush them down to sewage treatment systems where more energy goes into stripping them to the atmosphere again - or flushing them direct to our groundwater and surface waters. Meanwhile in agriculture, the chronic use of nitrogenous fertilisers has gradually stripped away the soil organic matter content to the point where soils hold less moisture, and consequently less capacity to soak up slurries spread on them, which make their way to watercourses. The recent problem of flooding in Ireland is in part due to this lost moisture holding capacity of soil organic matter.

Agriculture and sewage effluents account for almost 90% of all suspected cases of slight and moderate pollution in Ireland, and c.80% of serious pollution. If we could reroute nutrients and biomass from toilets back to our fields, after composting the humanure to stabilise it in the soil, then we could dramatically reduce this huge source of pollution here - both agricultural and sewage related.

My question to you is about the value of humanure as a carbon source within the soil. I've looked at the figures, and I've estimated that about 44,400 T Carbon/yr could be fixed in Irish soils if all humanure were to be captured and composted. Do you have any figures on humanure in your book and do you estimate the value of capturing human nutrients and biomass as a carbon building tool?

Here's the link to my report if you're interested: http://www.feasta.org/2016/01/12/draft-report-promoting-closed-loop-agricultural-practices-for-biodiversity-enhancement/

Many thanks, Féidhlim Harty

I've asked questions similar to this, because I worry about urine acting essentially the same way that a nitrogen fertilizer does. Things I've read suggest that human feces will compost on it's own, as it's nitrogen/carbon ratio is sufficiently balanced, but that bad things happen when you add urine to the mix. It seems that from what I've read, using humanure responsibly to improve farmland will require large quantities of high carbon "brown" material to balance the urine, the way traditional farmers use lots of bedding to capture the animal nitrogen in barns. In other words, how do you get humanure to be a source of carbon?
J.

how do you get humanure to be a source of carbon?

By building up the Soil Organic Matter with the composted humanure, the resulting humus will sequester more carbon than soils fertilized with processed nitrogen. It will certainly be adding to the carbon layers of the soil, rather than being flushed into water and probably lost to the ocean in a polluting way.

Sorry Roberto - I don't quite understand. Do you mean that the presence of humus in the soil encourages more carbon to be sequestered, or that the humus itself is the carbon that is being sequestered or both? It seems that from what I read, urine needs to be composted with something high in carbon in order to develop into humus. Should we only consider calling it "humanure" after it's been through the composting process - before that it's urine and feces? If that's the case, then my question made no sense - I should have asked, "How do you get human excrement to be a source of carbon?" and the answer would be, it's not. You compost it by mixing it with high carbon materials such as sawdust or dead leaves, until it turns into humanure, and then give it time to turn into humus. That leads to the question, if we're going to try to do this on a grand scale, what will the source of carbon be? In our area, sawdust/woodchips/bark from logging related industries would be a potential source. On the prairies, straw would probably be available. But if you're trying to compost all the human raw material from a large city, that's a lot of nitrogen that needs balancing!

I certainly agree that the way most of our human excretion is landing in the ocean is ridiculous. Farmers during the Edo period in Japan used to pay city dwellers for the right to dig out their latrines and cart the results back to their farms. There are better ways, but those don't make the chemical companies rich!

Hi Jay, in answer to your question about where to get the carbon, faecal material contains c.48% carbon (dry weight). Thus the carbon content per person is c.10kgC/p/yr. Based on a population of 4,635,400 in the Republic of Ireland (where I live) the total potential production is therefore c.44,400 T Carbon/yr, assuming full capture of all faecal material for composting.

In comparison, the total volume of sewage sludge produced per person per year is similar, at c.19kg/p/yr (dry solids content). The carbon content of sludge varies from c.5.2-46.7%, dropping with each successive stage of treatment. The average within the range of figures given by Le Blanc et al. ( 2008 ) is 27%, yielding an extrapolated carbon content of sludge of c.23,600 T Carbon/yr inclusive of both septic tank and municipal sewage sludges.

Thus the potential carbon content of humanure (direct faecal composting) is c.1.9 times higher than that of sewage sludge (depending on the degree of effluent treatment giving rise to the sludge).

When urine is used as part of the composting process, along with straw (Jenkins' Humanure Handbook), you end up with a nutrient rich compost that is high in carbon and excellent for the soil. The urine is an essential component of the ingredient list, since it breaks down the fibrous straw into a stable humic material in the finished compost.

So in the Irish context at least, humanure could be a valuable source of soil organic matter - albeit a minority compost ingredient compared with the volumes of animal manures that we have here given the importance of dairying and agriculture in general.

Hi Feidlim,

That's exactly my concern - the logistics. Our current infrastructure does not allow for the separation of urine and feces. There are some committed humanure composting people with urine diverting toilets, but they are still fringe to my knowledge. The quickest change to our infrastructure would involve collecting urine and feces together, and as you mentioned, Jenkins adds straw to add the necessary additional carbon to the system to balance the nitrogen rich urine. O.U.R. Eco-village on Vancouver Island uses shredded wood waste from the lumber industry in a simple two batch outhouse system (year 1 in use, year 2 sits to compost, shovel out and repeat). I have no idea how many hoops the Eco-village people had to jump through to get their system approved, but they're some of the best hoop-jumpers I've ever met! They seriously rock at getting local laws changed to permit - and hopefully eventually insist on - more ecologically responsible building and waste management systems.

I believe the best Canada has done in this regards is some medium-sized towns with access to cheap land have educated the public of what *not* to put down their toilets and have built artificial wetlands to completely recycle the nutrient load. Local and migrating wetland birds are thrilled with the results, but it's still not capturing the humanure for farm use.

I completely agree that the system needs to change. The first step is proposing realistic changes to new buildings (separation of grey and black water would be a huge step in the right direction). Australians managed much of that under the pressure of a major drought some time ago. The next step is installing systems that are effective at digesting the black water effluent which some farms are hopefully already doing with animal waste, so I'm hoping there's a model out there that is considered truly safe and effective already invented. The third step would be pushing into retrofitting existing buildings. I'm still concerned with coming up with enough balancing carbon on a large scale without causing other problems (like driving the price up so farmers start using less bedding so there is more surface run-off of contaminants from their farms into local waterways). Joel Salatin has a policy that if he removes straw from a section of farmland, he makes sure the equivalent finished manure goes back on that section. So farms contributing straw to balance human urine, need to be guaranteed to get the equivalent back in end product.

Maybe I'm wrong above - maybe the first major step is convincing the system this needs to happen. You've convinced yourself. Can you convince your neighbor? Can you convince your street? Sometimes big changes happen from a small ripple spreading out.

Hi Jay,

Sorry Roberto - I don't quite understand. Do you mean that the presence of humus in the soil encourages more carbon to be sequestered, or that the humus itself is the carbon that is being sequestered or both? It seems that from what I read, urine needs to be composted with something high in carbon in order to develop into humus. Should we only consider calling it "humanure" after it's been through the composting process - before that it's urine and feces?

I think that neither of us were being super clear at first. Thanks for clarifying both what you were thinking and your perceptions of mine. When I think humanure, I do not think of urine, I think of manure human style, so therein lies the primary divergence in our perspectives. Yes I mean that humus itself is sequestered carbon; the living processes (wastes) as well as the dead bodies of microbes/fungi/and plant roots in a healthy soil food web lock carbon into the soil structure. The darker mineral topsoil that one sees as a result of humus buildup is because of the carbon sequestering, from my understanding.

Urine is best used in the following ways:
1.)Watered down to ten parts water to one part urine, and applied directly to the soil where nitrogen is desired, but only when the soil organic matter needs the water (thus eliminating nitrogen pollution issues).
2.)Apply to new compost piles, straight or watered down.
3.)nitrogen inoculate bio-char or hugulkultur
4.)break down carbon rich sites like drilled out stumps.

I agree that the large scale application of humanure requires different thinking/processes and probably the inclusion of blackwater systems, which is very different than that which I am proposing above, but these methods are what I would do with the homestead scale permie thang, with urine separation, and feces being vermi-composted.

But if you're trying to compost all the human raw material from a large city, that's a lot of nitrogen that needs balancing!

Most large cities have a massive amount of woody debris that is accumulated that would be a great place to begin. It would be best to source separate, but even if the effluent was forced through this chipped woody material as a sponge and then maybe having any excess liquids fed through cattail and bullrush beds to draw moisture up through transpiration while oxygenating it with their aerobic bacterial colonies on the roots.

in regards to Cattail and Bullrushes from this link: "any herbaceous plants, such as cattails and bulrushes, have spongy, air-filled stem and root tissues, called aerenchyma, which helps to facilitate the transport of oxygen to underwater tissues."

Once the system is in place, the prolific growth of these wetland plants can be added to the carbon source. Willows, poplars and birches, or other water loving trees from other climates, planted around the edges of these treatment areas would also grow rapidly and could be chopped for coppice for chipping and adding to the carbon source.

I imagine large treatment ponds that instead of being open areas of water, are more like a serpentine flow around chipped woody chinampa fingers extending from the sides. The chinampas would be large enough to grow water loving shrub and tree species on, and to drive trucks on for servicing the replenishment of woody wastes and manage the trimming of the cattails and coppice of woody perennials. The water channels would be shallow and full of cattails, bullrushes, or other similar reeds, and be flowing to increase oxygenation. A solar powered pump (at the end of the system to bring water to the next pond if it's necessary because of lack of elevation for further gravity flow), could deliver the liquids to the next pond via a vortex drain to further oxygenate the liquids.

Thank you Roberto for your detailed reply. I feel we are both understanding the issues now. I wonder if for cities, the woody debris could be in large tanks in such a way that there would actually be useful high-carbon fertilizer captured for farm use. That would require moving people to a low to no water toilet system, but not require them to separate urine and feces, which I suspect would be difficult to achieve when you consider all the different sizes and shapes humans come in and the problems I've read about with urine separating toilets.

I love your description of a woody-chinampa-fingered sewage treatment system. It would require some energy to chip and shred the woody material and to move that material to the areas that need it, but it would make so much more sense than most of the chemically run systems in current use which also require energy inputs. I actually need something like that at the exit of our winter creek to capture the nitrogen that I'm sure comes off our field in the winter rains (from our ducks - they think the whole field is their toilette). I've already been picturing some sort of artificial wetland for the purpose, but you've given me some excellent ideas.

Thanks again

I wonder if for cities, the woody debris could be in large tanks in such a way that there would actually be useful high-carbon fertilizer captured for farm use.

Or a pond could be put out of service after a time and be drained and then used for the purpose of farming, or it's contents removed and exported for farming.

It would require some energy to chip and shred the woody material and to move that material to the areas that need it

In my little Ecotopian pipe dream, a bioreactor at the Swamp would be creating methane to fuel the chipper, and hauling trucks.

I've been brainstorming this sort of thing for my own greywater system for a while. My humanure system will be mostly separated--meaning that there will be enough absorptive material added to the bottom of the manure containers and with each addition of waste, that the system can handle the odd error addition of urine. There will be a drain going to a biochar pit.

A quick correction is needed for the Jenkins system description. The Jenkins system does not use straw to provide carbon for the composting process it uses sawdust, or the equivalent, at the source. Straw is used as a cover material for the outside compost itself and while it does get somewhat mixed in the volume added would normally be minimal.

Hi Jay, apologies for the long delay in answering your post. Ironically I've been working flat out designing just the type of systems that we've been discussing - so getting people interested isn't my problem at the moment!

Vis a vis the logistics - two scenarios come to mind: One is that we can gradually incorporate more and more eco-friendly technologies as clients want to have lower impacts on their receiving environment. For example in my work, many clients come to me because the local municipality demands that they meet certain environmental standards and they just want planning for their house.

Technologies such as Swedish urine diverting toilets and the Swedish Aquatron separator are both possible to incorporate into a standard sewered system without really letting the users of the toilets know that there is state of the art humanure composting going on down the line.

Also within this gradual scenario is a greater development of P removal technologies from conventional sewage treatment systems, which is happening in Europe - albeit slowly.

The other scenario is that N and P is suddenly and dramatically limited - whether by peak P (which is on the cards anyway) or by an international carbon emissions agreement putting the N-fertiliser business on a dramatically less stable business footing. Cap and Share from Ireland's Feasta (Foundation for the Economics of Sustainability) is one such programme - recently highlighted in Naomi Klein's Beautiful Solutions page (http://www.feasta.org/2016/03/30/capglobalcarbon-has-been-accepted-as-a-beautiful-solution/).

Personally I'm not too worried about a carbon source. I've been designing willow facilities in the Irish context since 2007, in collaboration with Danish company Centre for Recycling, who have been at it for about 20 years. These are zero discharge systems whereby septic tank effluent is pumped into a plastic lined willow bed of c.6m x 35m x 1.5m deep. The willow mop up all effluent and all rainfall over the course of the 12 month cycle. Willows are coppiced on a three year rotation basis.

If we take a multi-pronged approach to this issue, then some people will want a willow system (those with no legal way to discharge to ground or water for example), some will want a dry Jenkins' type system, some will want the standard town sewer (but even here there is a move towards using willows to mop up more N and P from the final discharge). With all that willow being generated there is an abundance of carbonaceous material available for balancing N.

It takes hoop-jumpers to change the laws, so I applaud the Eco-village people that you describe. One of the things I do for a living is basically about wriggling through the existing legislation to find ways to allow clients to be more eco-friendly. And trying to get that legislation changed where necessary. I'd love to make it out to Vancouver Island to visit and compare notes!

Hi Roberto,

Great to read your thoughts on closing the loop on those nutrients. The Ecotopian chinampa fingers sound excellent! Otherwise constructed wetland systems tend to basically be a sink for nutrients and biomass rather than a useful food-growing source of them. Wetlands and reed beds are fantastic as zero energy input system for getting water clean - and providing a wildlife habitat into the bargain. However they still don't recycle those nutrients per se. Except in your version where the whole project becomes a chinampa system!

If you've any fall on the land at all then you don't even need solar pumps. Hydraulic head will push water along a flat-based wetland system on its own, displacing a litre at the far end for every litre added (precipitation and evapotranspiration excepted).

From a practical perspective, the issue of water quality is important in the chinampa system. If you have grey water only, that that addresses faecal pathogens. Otherwise a Solviva brownfilter system followed by a biochar filter may get the water clean enough to use with care - and still benefit from the brownfilter compost and nutrient enriched biochar after each maintenance process.

Ok - back to work: a space age eco-toilet file awaits me

Feidlhem,
Interesting thread going here, I am so ignorant of so many things. When you mentioned the runoff going into your lined bed with coppiced Willows I had to look up coppicing. Seems this is a great sustainable business of getting rid of any toxins that may come of the waste water, plus the coppiced wood at a three year interval would make good material for weaved fencing or a Rocket Mass Heater. https://en.m.wikipedia.org/wiki/Coppicing

Makes me wonder what fruit orchards do with all their trimmed branches each season?