User Tools

Site Tools


toilet:composting

Composting toilet

Composting toilets are waterless (dry) toilets designed for use in applications without a plumbed sewage system. They operate on two principles:

  1. dessication of solid waste in an absorbant media to eliminate odor and mess.
  2. separation of liquid and solid waste to avoid messing up the first step

The media would compost over time, but composting toilets are emptied regularly, even if infrequently. This means the media is actually not composting to any significant degree in the toilet. Some have argued a better term for this system is “dessicating toilet” but the name is not in widespread use.

While composting toilets are often vented by a fan, this is to remove moisture from the toilet rather than to control waste odors (which are negligible).

use

In general an RV-appropriate composting toilet is designed for use by 1-2 people. In this use the solids compartment is used for about 2 person-months. The liquids tank fills in a few person-days.

Normal 1-ply toilet paper is safe for the solids compartment though overuse can reduced capacity and over-dry the compost medium.

liquids

Commercial composting toilets are a sit-to-pee design for both sexes. The urine diverson systems are designed to work when sitting and keeping urine out of the solids compost is critical to the operation of the toilet.

Calcium deposits (if any) on the diverter can be removed with Lime-a-way.1)

solids

Commercial composting toilets generally keep the solids container closed by a door when not in active use. There are two approaches:

  1. “straight drop” - the cover is removed before use and deposits are made directly into the solids compartment
  2. platform - there is a trapdoor mechanism that opens when the deposit is completed (as when flushing a plumbed toilet). A coffee filter can be placed over the trapdoor as a liner to reduce mess.

Some RVers keep a spray bottle of water handy to rinse down traces of liquids or solids that remain in the bowl.

media

images-na.ssl-images-amazon.com_images_i_51umntihb5l._ac_us160_.jpg

  • coconut coir (shredded and compressed husk) - recommended by Nature's Head.2)
  • sphagnum or peat moss - recommended by C-Head3), Airhead4), and Nature's Head.5)
  • sawdust - recommended by C-Head6)
  • ground cob

models

There are several commercial models suitable for RV use. One can also make a simple DIY model.

Nature's Head

images-na.ssl-images-amazon.com_images_i_41k7tv5c0kl._ac_us160_.jpg Features:

  • made in the USA
  • stainless fittings
  • 5 year warranty
  • 2.2gal liquid tank with visible level
  • relocatable compost crank
  • relocatable vent outlet

C-Head

Features:

  • relatively low cost (about $300 less due to simpler components)
  • straight drop system.7)
  • a template for making a cardboard mockup
  • uses normal 1gal milk jugs for liquid tank

Note: The C-Head's use of an inexpensive, cut-down 5gal bucket for the solids reduces costs but has some side effects the prospective buyer should consider:

  1. solids compartment needs to be emptied about 2x as often as other commercial models (every 2 person-weeks).
  2. auger-style agitator does not mix in toilet paper in very well; it tends to float on top.

Airhead

butterfly not included Features:

  • designed to mimic domestic toilets
  • 5 year warranty
  • can remove liquids tank without opening solids compartment

DIY bucket system

images-na.ssl-images-amazon.com_images_i_417jm1vilrl._ac_us160_.jpg A simple composting toilet can be made with a bucket, seat, liner and absorbent media. It is very cheap but has significant shortcomings compared to the commercial models:

  • no liquid diversion - one must arrange a separate system for urine; it cannot go into the bucket. Female RVers may want to look into clever and collapsible "go girl" funnels which allow them to pee standing up (and into a bottle). Because it can be difficult to control urine flow while pooping it may be best to pee before pooping.
  • no agitation - deposits are simply covered.
  • will probably not qualify as self-contained if a Ranger is checking that.

operation

Before inital use a layer of media goes in the bottom of the bucket; this makes cleanup easier if the liner breaks. Then a kitchen trash bag or other liner is placed in the bucket and a layer of media8) is added.

After pooping in the bucket the deposit is covered with another layer of media.

To clean out the bucket: remove any lid, tie off the bag or liner, and remove from the bucket. Toss in a dumpster as one would baby diapers or dog droppings. Install a new liner and bottom layer of media.

bucket

The bucket is an ordinary 5-gallon bucket, as one might find at a home improvement store, food prep area, or the side of the road in a ditch. :-)

For those with less space, there are reports that some 3.5 or 4 gallon buckets have the same top dimensions as the larger 5 gallon units.9) This might be important if you are planning to use a commercial seat/lid.

seat/lid

One can use a normal lid over the bucket when not in use, but this precludes the attachment of a commercial lid (below). The rim is quite narrow and can be uncomfortable to sit on directly. Because of this, some use a length of pool noodle split down the middle and pushed down on the rim. It has to be removed again to replace the lid.

The most common commercial seat/lid the Luggable Loo. It snaps onto the top rim like a bucket lid would.

The Privy 500 is a urine-diverting seat designed for tiny house installations. It might be adaptable to a bucket system, running the liquid into a nearby milk jug or similar. The shipping box has a cut-out template printed right on it.

There are separators/diverters sold on eBay.

comparison

Feature Nature's Head C-Head Airhead DIY
Approximate cost~$950 ~$600 ~$1000 ~$20
liquid separationyes yes yes no
liquids capacity2.2gal10) 1gal11) 2gal12) n/a
solid depositstrapdoor straight drop trapdoor straight drop
can add toilet paper yes not recommended13),14) yes yes
must open solids compartment to empty liquids yes yes no n/a
warranty 5 years15) 30 days16) 5 years17) n/a
toilet/composting.txt · Last modified: 2017/12/31 06:35 by frater_secessus