Compost Toilets: Don’t Pass Up the Poop

Learn how to build and maintain a composting system that includes human excreta, and transform Nos. 1 and 2 into beneficial material.

| June/July 2019

IBC-tote
Sideview of IBC tote with closed lid and reinforcing wood rim.

You might think it odd that we’d start an article about compost toilets by stating that no such thing exists. But they don’t. Composting is a specific process, one that occurs under specific conditions — and those conditions don’t exist in any toilet. A compost toilet is essentially a progressive system that collects and handles human feces and urine so they can be safely composted.

The basic aspects of using a compost toilet are straightforward: 1. You go to the bathroom; 2. The deposit is collected in a vessel; and 3. That collection is then either minimally processed to a mature enough state that it can be buried, or, better yet, it’s further composted to a state that sanitizes and reduces pathogens to a safe level so it can be used as a beneficial nutrient resource.

double-bin-compost
Figure 1: Considerations for a double-bin compost-processing pile.



When we take composted or sanitized materials and reincorporate them into the environment with no negative impacts, we, in essence, don’t create waste — and compost toilets are a tool for collecting and processing materials so they don’t become waste.

In this excerpt from our new book, we will explore some of the factors that go into creating a successful composting system — from getting over that fear of feces to creating buffer zones around your piles — so your final product is a low-impact, yet high-quality, “load of crap.”

All-In Collection: Urine and Feces

With the collection of all excreta (urine and feces) comes benefits in the composting processes. Urine serves two major functions: It provides moisture needed for the biological processes to occur, and it provides the nitrogen source that enables thermophilic (high-temperature) bacterial growth, which prompts rapid carbon breakdown. Without urine, the carbon-nitrogen balance (C-to-N ratio) isn’t ideal for the support of microorganism growth. Carbon is the energy source and building block for cell tissues, and nitrogen is implicated in enzymatic processes and is a component of the nucleic acids (DNA and RNA) and amino acids (proteins) used in cell growth. An imbalance of the ideal 30-to-1 ratio of carbon to nitrogen will impair life in the compost.

compound-compost
Figure 2: Minimum clearances and suggested sizing for a compost compound (top view).

Batch commode collection systems deal with this “all-in” approach easily, because they can be serviced (dumped and processed) as much or as little as needed. Excess moisture isn’t an issue, because bulking agents are added to absorb the excess moisture, and in doing so, also provide the added carbon to balance the nitrogen. When everything is deposited into the composting pile, all ingredients are present to enable rapid natural thermophilic processes to begin.

The other types of systems — chamber batch (or “moldering”) and continuous — need robust drainage design if all fluids are collected; leachate drain systems must be added to ensure there’s no excess buildup of moisture (see “Collection System Terms,” below). If part of this design fails (breakage, blockage, or power outage), the system fails.

The Yuck Factor

Let’s face it: The yuckier something is, the less likely we are to deal with it. But if we avoid regular maintenance, we increase the risks of system failure, we increase the health risks, and we increase the yuck factor. The best systems are the ones that are maintained — and usually the simplest are the easiest to maintain. Ultimately, no matter which system you use, you’ll have to look at raw excreta at some point.

sealed-compost-bins
Figure 3: Sealed compost bin system using IBC totes.

Whichever type of compost toilet you settle on, if your desired outcome is to process your resources to the highest level for the safest reintroduction to the landscape, then the ideal final stage in every process is to batch compost the materials through a thermophilic stage. The next best is to batch process them in a mesophilic (moderate-temperature) compost processor for the required extended time frames. What that means is that at some point, to achieve a safe and sanitized compost, materials will need to be set aside, one way or another, and given some form of treatment. The most convenient place for this is a compost pile.

drainage-pipe
Drainage pipes ensure no excess moisture remains in the compost pile.



It’s in the compost pile where the most action happens. However, the compost pile usually receives the least attention and diligence in design. It’s the only component that houses any true composting activity; and, outside of using chemicals, adding heat, or allowing extensive retention times, it’s the only component where full sanitization occurs within short time frames.

Design Recommendations

When building a compost processor (or pile), design for the “Four S’s”: safety, sanitation, signage, and security. Figures 1 and 2 provide a visual reference for the following design recommendations for a two-pile system, which you could also expand to a three-pile system.

You’ll need to keep seven factors in mind when designing a compost processor. Here are the seven items, along with considerations for each:

1. Durability

  • Build the sides or walls so they won’t rot out or splay apart when filled with compost.
  • Use appropriate materials: concrete cinder blocks, cedar, and galvanized fencing material with a minimum of 12-gauge wire.
  • Packing pallets won’t be sufficient because they’ll need to be replaced too often.

2. Buffer Zone

  • A fenced-in area should surround the compost bins to limit access to the areas most likely to be potential sources of pathogens.
  • Plan for a minimum of 5 feet of clearance around the sides and back, and 6 feet at the front.
  • Incorporate more space if moldering bins or commode buckets are to be stored for processing.
  • Use signage that notifies others that human waste is being housed or composted.

3. Serviceability

  • Build easy access and room to maneuver into the design.
  • Adjustable height and a lid is required.
  • Design a movable step or standing platform to allow easy access as the compost pile increases in height.
  • Limit the pile heights to 5 feet.
  • The fenced area in front should have opening gates for easy handling of rakes, wheelbarrows, and collection container movement.
  • The composting area should be located within easy access to your home and a water source.

4. Absorptive Mat

  • This spongelike mat will absorb leached moisture in the early stages of pile development — until the compost develops the capacity to self-handle moisture.
  • The mat can be made of straw bales, wood chips, peat, or a high-humus and soil mixture that has good percolation.
  • Dig the area to a 16-inch depth below grade to accept the materials that’ll provide the initial sponge for the processor.
  • On hard ground, either plumb to a septic or sewer system, or dig a leachate absorption trench to divert excess moisture to an infiltration trench or pit system.

5. Volume and Number of Composters

  • Size your bins to accept the expected volume of materials over time, allowing enough room for human excreta, household compost (kitchen scraps), bulking agents, and covering materials.
  • Build a minimum of two, but preferably three, compost bins at 72 inches wide by 72 inches long by 60 inches high to allow composting materials to fully mature over time (1 to 2 years).

6. Dedicated Tools

  • To limit the potential spread of pathogens, dedicate tools to managing the compost, including a hose with a nozzle, a rake, and a pitchfork.
  • Clearly label all dedicated tools.
  • If you need to transport stabilized and unsanitized materials, dedicate a wheelbarrow to use only with the composting.

7. Proper Setbacks

Setbacks are specified distances that structures must be built away from a place deemed in need of protection; this could be a street, river or other water body, shore, or flood plain. You’ll need to check your local jurisdiction to learn where you can legally put your compost pile. Where we live (in Canada), we have to locate our compost piles with the following setbacks:

  • 100 feet from a source of drinking water or drinking water supply well.
  • 100 feet from fresh water, seasonal fresh water, or seawater.
  • 50 feet from a breakout (area where water openly seeps out of the ground).
  • 10 feet from a property line.

Collection System Terms

Batch systems generally collect raw materials into a receptacle, which, when full, is removed from the collation area. The contents of the full receptacle are then processed. These batch systems all have a distinct separation between the collection and aging processes.

dumping-compost
Some batch systems require large receptacles.

Commode batch systems, a type of batch system, have smallish 20-liter buckets under their pedestals. The buckets fill up regularly and are swapped out routinely. Chambered (or “moldering”) systems, another type of batch system, leave material to sit for extended periods of time. These toilets are different from the commode batch systems in that the collection receptacles are larger, and they usually involve urine diversion and leachate drainage.

Alternatively, in continuous systems, new materials collect and undergo a degree of decomposition, all within one unit.


Sealed Systems

Completely sealed systems are available commercially, but many DIY systems are acceptable too. Figures 3 and 4 show two such systems. One uses IBC totes (Intermediate Bulk Container, or “pallet container”); the other is made from corrugated roofing material.

composting-toilets
IBC tote compost bin.

Sealed systems require less cover material, and they can be heated. It’s relatively easy to drain leachate from the bin to an infiltration bed directly below the footprint of the bins; otherwise, a sealed system can be placed on impervious surfaces and drained to an appropriate leachate system. Bins can be clad to meet one’s aesthetic preferences, and they can be insulated to promote better heat retention. The downside is that removing the fully composted material is more cumbersome because of smaller access panels.





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