Composting toilets promote self-sufficiency and encourage users to take responsibility for their waste. This involves a degree of maintenance and part of this process is emptying of the composting chamber. Composting toilets collect compost and once the chambers are full, compost needs to be removed to make space for more. A question we get asked often is "how often are composting toilets emptied?".
Note that "compost removal" can refer to chamber swapping/emptying in batching systems, compost emptying from self-contained systems into dedicated onsite compost bins (Secondary Treatment Systems), or matured compost from continuous systems directly emptied into a burial site.
Obviously, emptying frequency is system and usage dependent, but there are average expected time frames. Split-systems have bigger composting chambers than self-contained systems, allowing for more time in-between emptying and resulting in less maintenance. Self-contained systems are emptied more often than split systems.
Composting toilet systems are specced for a certain number of users with an expected emptying schedule that corresponds to the spec. There are full-time personage specs, and part-time personage specs. Typically, when a toilet is used part-time, its user-spec doubles from that of its full-time user-spec (e.g. 2 people full-time becomes 4 people part-time) - because the personage is doubled, the empty time frames remain the same.
Below schedules are for full-time user-spec and part-time user-spec. Obviously, true figures are dependent on use but the below schedules will give you an idea of expected time frames.
Self-contained systems (on-floor)
Self-contained on-floor systems are typically designed to be emptied bi-weekly when used full-time by the specified number of people.
Due to short retention periods in the composting chamber, most self-contained systems need to be emptied into a Secondary Treatment System (dedicated onsite compost bins) first for maturation. Once the compost has matured in the Secondary Treatment System it can then be buried. The use of a Secondary Treatment System is not necessary if you have a processor system as materials deposited into the removal tray are already matured.
Average emptying time frames:
- Full-time user-spec (e.g. 2 person) - 2 weeks
- Part-time user-spec (e.g. 4 people) - 2 weeks
*Remember that when the toilet is used part-time, it's user spec doubles - e.g. 2 people full-time becomes 4 people part-time. Because the toilet is used part-time by double the users, emptying time frames remain the same.
**Note, any system used by full time user-specs on a part-time basis can double the maintenance period.
Batching split systems (sub-floor)
Batching split systems are operated with multiple chambers used on a rotational basis. One chamber at a time is put in-service to collect waste, while the other chambers mature their contents and prepare them for burial. A batching split system will have a minimum of two chambers to service a specified number of users. More chambers can be purchased to expand the system's capacity.
On average, a batching split system in full-time use has its chambers swapped/emptied every 2-3 months when used by the specified number of people. If more chambers are used to service more people, the chambers fill up faster, swapping becomes more regular and more chambers are needed in rotation to give the compost adequate time to mature.
Batching split systems with mixing mechanisms in the chambers outperform those without mixing and allow more time in-between swapping/emptying.
Average chamber swapping/emptying time frames:
- Full-time user-spec (e.g. 3 person) - 2-3 months
- Part-time user-spec (e.g. 6 person) - 2-3 months
*Remember that when the toilet is used part-time, it's user spec doubles - e.g. 3 people full-time becomes 6 people part-time. Because the toilet is used part-time by double the users, emptying time frames remain the same.
**Note, any system used by full time user-specs on a part-time basis can double the maintenance period.
Continuous split systems (sub-floor)
Continuous split systems have one large composting chamber which is continuously composting materials. Matured compost makes its way down to the front of the chamber where it can be accessed and removed. Note that only part of the compost is removed at any one time.
Depending on the system, compost removal times can vary between 3 months to year when used full-time by the specified number of users. Continuous split systems in commercial applications can have custom maintenance schedules specified.
Average compost removal time frames:
- Full-time user-spec (e.g. 4 person) - 3 months-year
- Part-time user-spec (e.g. 8 person) - 3 months-year
*Remember that when the toilet is used part-time, it's user spec doubles - e.g. 4 people full-time becomes 8 people part-time. Because the toilet is used part-time by double the users, emptying time frames remain the same.
**Note, any system used by full time user-specs on a part-time basis can double the maintenance period.
For technical review of system capacity for your particular site use, contact us and ask for the maintenance spec and the climate spec.
Need help choosing a system? Call WCTNZ® on 0800 022 027 for free advice on system specification and setup. Advanced design consultancy services are also available.
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