Composting Toilets, Information for the DIY
What are they and how do they work?
Composting toilets are often touted as eco-friendly alternatives to conventional toilets, but what are they and how do they differ from their conventional counterparts? For the typical do-it-yourselfer, this article can offer some valuable insight.
What is a Composting Toilet?
A composting toilet is essentially a toilet that is able to treat human waste through the biological process commonly known as composting. During the composting process, aerobic microorganisms break down organic matter — in this case, human waste — into a nutrient-rich compost (humus) that can be used as a soil enricher and fertilizer. Composting toilets typically use no water (or very little) to flush away the waste, and are often referred to as dry toilets.
Rather than flushing away the waste, it is collected in a receptacle and covered with a layer of sawdust, wood chips, peat moss, coconut coir, biochar or other carbon-rich material after each use. This not only covers the waste and absorbs moisture, thereby reducing potential odours in the same way that kitty litter does, it creates pockets of air that help facilitates the aerobic decomposition process and also improves the carbon-to-nitrogen ratio of the compost produced in the composting process.
Sustainable, Off-grid Solution
There are several reasons why a homeowner may choose to opt for a composting toilet rather than a conventional flush toilet linked to a septic system or municipal sewer line. Firstly, they are very sustainable, requiring less water, and reducing waste, while at the same time producing a useful rich compost (residual organic matter).
Considering that the average person generates around 36 kilograms (80 pounds) of composted humus per year and that around 20% of the world’s drinking water is used for flushing loos, water-wise composting toilets present a sustainable alternative to their conventional flush counterparts.
A composting toilet can save over 24,984 litres (6,600 gallons) of water per person per year, and the composted humus that is generated in the process can be put to beneficial use in the garden rather than adding to the wastewater stream.
The environmental benefits extend further still. By not flushing water down the toilet you also reduce the energy consumption required to treat the sewage and reduce the number of nutrients (nitrogen) flowing into our waterways and oceans. Excess nutrients fuel algal blooms, leading to oxygen depletion as the algae die off, which is the primary cause of ocean dead zones completely devoid of plant or animal life.
Composting toilets are a popular choice for remote off-grid homes that lack municipal services. Not only may these homes have a limited water supply, but they are also not connected to a municipal sewer line.
Composting toilets are also a great option for national parks, eco-tourism resorts, holiday cabins and unserviced rural areas. Installing a composting toilet can eliminate the need for a septic system, or can substantially reduce the size of the septic system needed, thus significantly reducing costs. But more on that later.
How Composting Toilets Work
Composting toilets typically depend on mesophilic bacteria — bacteria that thrive in moderate temperatures of between 20- 45°C (68-113°F) — to take care of business. The longer the waste remains in the composting chamber the more time the mesophilic bacteria have to break down the waste and eliminate pathogens.
Once the waste has decomposed, it can be moved into a secondary composting system to further reduce any pathogens that may remain. Once the waste is broken down into compost humus, depending on local regulations, it can be applied to soils as a soil enricher/crop fertilizer or buried underground.
Some composting toilets include a urine diversion system within the toilet bowl that collects and separates urine from the solid waste in order to reduce moisture content in the compost processing compartment.
Different Types of Composting Toilets
There are two types of composting toilets: central and self-contained. While both types look similar to the average flush loo on the surface, the difference lies in the manner in which human waste is processed once it enters the toilet system. Let’s look at the differences between these two types of composting toilets.
Both types of composting toilets strive towards the same end goal: recycling human waste and destroying pathogens without the use of water. Rather than being flushed away, the waste falls through a chute into a waste-collection/composting bin that lies out of sight beneath the pedestal.
Self-contained composting toilets — where the toilet and composting chamber are combined in a single unit — tend to be smaller than central composting toilets, and are more suited for use in seasonal homes and small cabins used by one or two people. They are not recommended for year-round use by three or more people.
A self-contained composting toilet needs to be well ventilated in order for the bacteria responsible for breaking down the waste to thrive and be efficient. Air circulation also helps to keep unpleasant odours from accumulating in your bathroom. For composting to be effective, the temperature in the composter needs to be maintained at a minimum of 18 degrees Celsius (65 degrees Fahrenheit). This can be achieved by the use of an electrical or solar powered fan and heater.
A central composting toilet system is a bit more elaborate and connects to a separate composting chamber, which is typically housed underneath or adjacent to the toilet pedestal. While more expensive, central composting toilets have a larger capacity, making them more suitable for year-round use.
What Happens to Residual Organic Matter?
Composting toilets operate by one of two process methods: 1) Batch composting, or 2) Continuous process composting. Composting toilets can be further divided according to how the waste is processed as follows:
- Container collection systems that collect human waste and compost this in batches in a separate composting processor;
- Batch composting systems that collect the waste in a container or bin, which is removed for processing at a separate location;
- In-situ composting toilet systems, where waste is composted within the toilet or in a compost processing bin attached to the toilet.
Once the waste has been composted into the residual organic matter it needs to be disposed of appropriately. There are several options available for discharging the residual organic matter that is produced in a composting toilet system, including:
- Discharging the organic matter offsite to a sewage treatment facility (pumped out or transported in bins or other containers);
- Discharging the organic matter onsite, either on the surface or buried underground.
As there may still be some concern that pathogens could still be present, authorities may require the composted organic matter be removed to a sewage treatment facility or buried safely underground to a depth of at least 30 centimetres (12 inches). The composted humus can still serve as a soil enricher, but burying the organic matter ensures that if there are still pathogens present, they cannot contaminate leafy salad greens and other food items in your veggie garden.
Regulations Surrounding Composting Toilets
Local regulations pertaining to composting toilets can vary from area to area, so before deciding on this option, it would be advisable to check with your local authority. The general specifications and installation standards for the use of composting toilets in British Columbia, Canada are outlined below.
Composting toilet pedestals must be made from durable, non-absorbent, non-corrodible materials that are waterproof and easy to clean. They must be designed for safe use, and need to be sealed to prevent access to pests, while still allowing adequate ventilation.
Bins or containers used to collect the waste must ensure that the environment will not become contaminated during transportation of the waste for disposal, and they need to be easy to transport either by hand or by specified handling equipment.
Measures must be provided for cleaning the collection bins/containers, that also factors in a safe method of disposing of this contaminated water to a sewerage disposal system such as a septic tank with an absorption field, or to a compost pit.
If the system needs to be heated to maintain temperatures that make the composting process viable, ensure that an adequate source of heat is provided and that the system is well insulated. The composting bin must be easily accessible to monitor both temperature and moisture content during the composting process, and there must be a way to adjust the moisture content of the material in the composting system.
The venting system that serves pedestals and collection systems, or composting processors located indoors, needs to be vented at a height that exceeds the roof line in order to comply with the building standards for chimneys. The venting system needs to provide sufficient ventilation to maintain the aerobic conditions necessary for decomposition to take place, and it must be adequately sealed to control odours and to prevent air from being discharged into the interior of the building. Vent openings must be fitted with a stainless steel mesh screen to prevent insect vendors from accessing the building.
Prevent vectors such as insects and rodent pests from accessing the waste by ensuring all components are sealed, including the pedestal lid and ventilation system, and that all openings (e.g. windows, doors) in the toilet building are fitted with a stainless steel mesh screen to keep insect pests out.
In-situ Composting Processor
Materials used for an in-situ composting processor need to be durable, non-absorbent, non-corrodible and waterproof to ensure they can withstand regular cleaning. Processing bins need to be sealed to prevent odours and/or leachate from leaking out that can potentially pollute the surrounding air and /or groundwater.
Access for Monitoring and Maintenance
Provision needs to be made to safely access the system to monitor composting progress and to facilitate routine maintenance, including replacing any electrical or mechanical system components. Signage outlining correct operation and maintenance procedures for the system should be displayed nearby. Ensure that human waste within the system is inaccessible to unauthorized people.
Leachate produced during the composting process needs to be adequately managed to:
1) prevent the organic material from becoming saturated by the leachate, and..
2) to prevent environmental contamination. To prevent leachate from leaking out and potentially contaminating soil and groundwater, the base and all four sides of the composting processor need to be watertight to a level that exceeds the maximum leachate level possible. A drainage pipe must be installed to enable leachate to drain out of the processor and be discharged to a compost area, septic system/soak away or municipal sewer.
Discharge of Residual Organic Matter
The residual organic matter or hummus that is left at the end of the composting process can be discharged off-site or on-site.
Off-site Discharge: If the organic matter will be discharged off-site, this needs to be considered in the planning so that provision can be made to allow the accumulated organic matter to be removed safely and hygienically. For off-site disposal, an approved discharge facility will need to be identified before submitting for approval.
On-site Surface Discharge: Organic matter from a small residential composting system with a Daily Design Flow (DDF) of up to 2400 L/day that will be discharged on-site must comply with all the necessary environmental requirements and the discharge must be supervised by a professional.
On-site Burial: If the Daily Design Flow (DDF) is greater than 9100 L/day a solution for on-site burial needs to custom designed according to the site and project, and this needs to be filed by a professional.
A composting toilet offers an alternative, water-wise solution that is particularly suited (but not limited) to small off-grid homes, where the water supply may be erratic or non-existent. As we can see, there are several different options to choose from, both in terms of the way the compost is processed and how it is disposed of. The growing trend towards eco-friendly living, together with increasing water scarcity around the world, is likely to see an increase in the popularity of composting toilets in the future. In fact, in a water-scarce world, they may be our only option.