April and Kevin in Kuna Yala, the northeast coast of Panamá

Thursday, May 1, 2008

Composting Latrines

It isn’t gross, so keep reading.

Our house was just a storage room and office before we moved in, without a spot to go to the bathroom, a deficiency we had to remedy before moving in. It is just a few feet above high tide level so we figured a normal latrine (with a nine-foot deep hole) would likely hit water quickly, and since we’re only going to be there for a short time, we didn’t want to make any huge permanent changes. So we did some research, talked to some Environmental Health sector volunteers, read some of a book titled The Humanure Handbook, and decided to go with a composting toilet.

Now please know that the system that we are about to describe is tailored to our needs and does not follow exactly any of the systems that Peace Corps or The Humanure Handbook recommend. However, we did keep a healthy respect for all of the sanitary and pathogen related issues involved. We carefully used the concepts taught by those respected sources to try to make a system that was going to be safe, sanitary, and yield pathogen-free results while fitting the needs of our housing site.

First, what is compost? Compost is the process of using the soil’s normal microorganisms to eat organic materials (plant based products like leaves, coffee grounds, grass, paper, sticks, vegetable waste, manures, etc.) and turn them into rich healthy soil. Normally composting is done by putting together a pile of organic matter so that the pile has the right conditions to encourage those microorganisms to be happy, multiply rapidly, and thus to eat more organic materials. When the conditions are right the microorganisms actually produce heat from all of their liveliness and this heat can kill weed seeds and pathogens in the compost pile.

Why use human waste in a compost pile? Well, any gardener or farmer can tell you that manure is good for plants and the health of the soil. If you look at the main nutrient (nitrogen, phosphorus, and sodium or NPK) values contained in various types of manure, horse and cow are good but chicken poo has very high values. Well, human manure has values comparable to a chicken in sodium and phosphorus. Nitrogen is higher in chicken poo…but that is found in human urine. So all told our waste has real potential for being a valuable source of fertilizer. Also, humanure is abundant (each adult produces roughly ½ lb. a day) and easily available. It does need to be treated to kill any pathogens that could spread illnesses before use…but cow and horse manure should also be composted to kill weed seeds that are capable of growing after a trip through the animal.

So what did we do? We purchased a 55-gallon barrel with removable lid (very similar to our old grease collection barrels from our greasecar system back in Maryland, if you ever saw those), cut a hole, attached a seat,

ran a funnel and tube to separate the urine (as recommended in a large collection system like ours, whereas smaller 5-gallon systems like in The Humanure Handbook do not separate), got a few sacks of sawdust (both fine, from a woodshop, and large, from a chainsaw),

and went about our business. The idea is that after every deposit you cover the poo with dry organic material to balance moisture and to prevent insect interest. The organic cover material also prevents odors. I know it is hard to believe, but you could stand next to our tank and either smell nothing or a slight smell of damp sawdust on humid days. We had very few problems with odors or insects…much less than the typical pit latrine (and we now have plenty of pit latrine experience for comparing).

After a couple of months, we started asking at the store where we’d bought the barrel about getting a second, with the idea that when the first filled, we’d swap the lid/seat, cap the full one and let it sit for six months or so in the sun to compost and kill all the bad stuff.

But even after trying all over town for 3 months, we had no luck tracking down a second barrel with a lid like the first to fit our system. We finally decided we need another solution, so we did some more research, read some more in The Humanure Handbook about what it takes to make it safe, and decided to use our tank’s contents in a bocachi compost pile. Bocachi is actually a Japanese term for a fast compost process (typically resulting in usable compost in 3-4 weeks vs the 12-20 weeks of a normal compost pile) that generates some high heat almost immediately. Amongst the recipes are several that use estericol (manure), typically from cow, horse, or chicken, but we figured (based on nutrient levels) we could use ours too.

So we set about collecting the other ingredients (measuring in gallons because 5-gallon buckets are used for everything here and thus form a basic measurement unit in the field):
· already had the sawdust and estericol mixed together (we estimate a mix of 1/3 poo and 2/3 sawdust in our tank), about 40-45 gallons;
· banana tree (chopped), about 10 gallons;
· dirt (for the microorganisms), about 5-8 gallons;
· ash and charcoal (slightly larger, not fully burned to ash), about 5-10 gallons;
· yeast (to actively grow), about three-quarters of a pound;
· a molasses-type mixture made from raspadura, which is sugar-cane pucks, about 5 gallons;
· and balo leaves, balo being a tree that is commonly used for fences here in Panama because when a branch is cut off, it can be stuck an inch in the ground and it will grow. Balo is also a plant that is known for having insect repellent properties and it fixes nitrogen and its leaves are very high in nitrogen which is good for compost piles (the sacks of leaves we collected were very warm to the touch within a day). My guesstimate for collection of enough balo was that I could do it in one morning; it took two days, with April helping the second day. We collected an estimated 120 lbs. of balo leaves.

We also collected, with permission of the owner, some left-over side boards from when folks cut down teak trees and chainsawed them into boards. We used these, along with screen material, nails and wire, to build a “box” for our pile, which according to the “special fast bocachi” directions, needed to be 8-inches off the ground to get proper air circulation for heating up. Air circulation is important because the microorganisms we wish to encourage are aerobic…they use oxygen. There are also anaerobic (without oxygen) microorganisms that compost, you can tell the difference between the two because anaerobic microorganisms release an ammonia smell. Aerobic (oxygen users) microorganisms are preferred…thus most compost is turned occasionally to admit oxygen and stored in ways that allows airflow.

To further ensure proper circulation throughout the pile (which is to be 3-feet square and 4-feet tall), April drilled holes in 1” PVC tubing we had left over from construction and we placed these in the middle as we filled the box.

Finally we had everything ready and “rolled out the barrel” to begin the mixing process. We shoveled out the sawdust/poo mixture.

As you can see, it just looked like sawdust and there was no smell beyond a faint earthy sawdust-y odor. Other than the top (most recent) layer, everything we encountered was sawdust or dried hard (think a cow patty on the Great Plains). (For the most part, we did like most places with flush toilets here in Panama and bagged then burned our TP; there was a week or two when we put the TP in the tank, but we never found that layer when emptying the tank. It had totally composted and disappeared; it looked like nothing other than sawdust.)

As I shoveled in the sawdust and carefully broke up the few lumps, April added the other ingredients.

We shoveled, stirred, and added some water to get the proper consistency (the directions said to grab a handful and see if it clumped right, but I think they were working with other types of estericol. We gauged by eye, based on lots of past composting experience not clump.) It was a large pile. Too large, we wondered?

Then we began to shovel into the box, with April holding the PVC tubes upright. It fit perfectly.

The next morning, April put her hand over the top of the tubes, to see if it was heating up like promised. A definite hot breeze of air was coming out of the tubes.

They say it will be ready in about three weeks, but we’ll give it a bit longer just to be safe. Research on common human pathogens indicates that we need about a 14 days (week then turn and a week more) at our compost pile’s normal temperature to kill the bad stuff. If you have doubts about this please refer to chapter 7 of the Humanure Handbook available at: http://www.jenkinspublishing.com/downloads/PDF_all%20chapters/Chapter_7.pdf
After it is done we plan to dig a garden bed, pour it in, cover with a thick layer of dirt, plant some seeds, and a while later, hopefully enjoy the best, biggest, tomatoes ever. Other volunteers who have done composting toilets report that tomatoes love the finished compost and we love tomatoes.

If you are interested in knowing more about using human waste in compost please check out the Humanuare Handbook by Joseph Jenkins which is available online for free at: http://www.jenkinspublishing.com/humanure.html yes, you can buy one...but scroll down and you find editions available for download for free. Great book...I think you can look forward to composting toilets at the Cropper house in the States in future years. (I hope that won´t keep you from visiting!)


dcropper said...

Wow! Sounds like we may arrive just in time to see the beginnings of the new garden! And I am really looking forward to making my own contribution to the next round of compost. What? Me worry?!
Love from Mom C.

m said...

well, shit...

Linda said...

you guys always have the most interesting blog posts. I love reading them.

The Humanure system sounds much more pleasant on the nostrils than the typical latrine =)

Sandy said...

You guys are really creative and resourceful.

How are you going to "turn" your compost box? It looks large and unwieldy.

What do the islanders think of this?
Love you! Mom

Andrew Burnett said...

April and Kevin,

Came across your blog while googleing Pit Toilets Panama. I am looking for plans for a pit toilet for a school of 90 kids on the island of Bastimentos, Bocas del Toro area. Any ideas, you seem to have done some research on the subject. Anything would be helpful. Thanks, andrew@goodimpressions.us

Sandy said...

Hi. I found your blog because I was researching composting latrines. I lived in DR Congo and worked with the Peace Corps a very long time ago so I enjoyed reading your blog. Welcome back.

I have public health projects in Ghana, Kenya and Mexico and we're just about to build composting latrines in Mexico. SO I have some follow-up questions.
How did it finally workout? Were you able to use the compost for your garden? I also wondered if you needed to turn it or were the pipes enough? Did you just reuse your drum? How did you secure your funnel?

What's next for you two?

Anonymous said...

Red wigglers, Eisenia fetida, are great at digesting human manure with the advantage over low-temperature composting being that they are truly great at killing off pretty much all pathogens - viruses, bacteria and helminths. Unless you have enough manure to compost at once to get the temperatures up, worms are the way to go. YouTube has some basic worm composting videos on the site. There are some studies on the pathogen-killing abilities of worms, but I don't have the links bookmarked.