On site composting of sewage can be economical and can potentially require less infrastructure than septic systems. Depending on the system, the compost and/or compost tea can be applied to plants on site.
Principles of Operation
Air supplied to refuse can encourage the biological breakdown of solid carbon based fecal matter to gaseous carbon dioxide as well as the oxidation of ammonia, predominately from urine, to nitrate. The amount of water provided by a typical toilet flush toilet often exceeds the moisture needed in the composting system. Instead, low flush (vacuum flush), no flush, or foam flush toilets are used when the destination of the flushed components is a composter.
Most composters are actively supplied with air to fulfill the oxygen demand, then vented to the exterior, to reduce odor. Depending on configuration, this air demand should be considered in the HVAC design and possibly be paired with a heat exchanger. A dry air source is preferred to encourage evaporation of liquids in the unit. Trayed composters are typically located in a louvered closet near the bathroom for good air intake. In a vacuum flush system, the composter does not have to be below the toilet, but in a pit composters, an area directly below the toilet is needed. The composter typical requires an electrical connection to drive a fan for air circulation and in some cases a heater. Certain models, like the
Many composting units include a heating element that is thermostat controlled, so it will adapt when heat source is not present. 75 to 80 degree F is optimal and below below 55 F is detrimental. External heat sources (even intermittent) ones can be paired well if given the proper enclosure. This has been done with this unit using passive solar heat in the case of Sancor systems, previously so there is precedent and the manufacturer may have input
Troubleshooting Common Problems
Odor is likely due to inadequate ventilation or overloading of the system (e.g. if many visitors have used the system in a short period of time).
Flies have been reported with in some systems. Flies are primarily combated with physical barriers (e.g. screens). Indoor composting units should be placed in an isolated room, where ventilation ports are screened to keep flies from entering.