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    Urine Diversion Application

    Urine diversion divides the composting toilet community. Some advocate for it, others advocate against it. So, is it actually beneficial, and what is its application?

    Contrary to popular belief, urine is not actually harmful to compost. Not only does it enrich compost with nitrogen, but it also hydrates it. Additionally, when the urine is absorbed into the compost pile and processed via compost maturation, it becomes a controlled substance that can go into the environment without runoff. This is better for the environment and for soil regeneration.

    Too much urine, however, can be problematic. It can saturate the pile and overload it with ammonia. It can also hinder compost in cold climates by decreasing its ability to retain heat. Therefore, urine diversion is beneficial in some scenarios.

    At a Glance

    Urine diversion is not automatically better or worse. Its usefulness depends on the application.

    • Urine Diversion to Soak Away (UD-S) is generally suited to residential applications where urine can be discharged to a soak-away.
    • Urine Diversion to Container (UD-C) is generally suited to mobile toilets and emergency or back-up applications where urine is manually emptied.
    • Urine can be beneficial to compost in the right amount, but too much can overload the system, especially in cold climates or regular high-urination scenarios.

    How Urine Diversion Works

    There are two types of urine-diverting composting toilets: urine diversion to soak-away, suitable for residential application, and urine diversion to a container, suitable for mobile composting toilets and emergency or back-up toilets.

    Below are the applications of both types of systems.

    Note that although compost does need hydration to stay healthy, weekly cleaning of the toilet should generally be sufficient to introduce enough water to the compost pile of a urine-diverting compost toilet. However, in hot climates, above 20°C average temperature, the compost pile of urine-diverting toilets will dry out and will need rehydration.


    Main Application Types

    Urine Diversion to Soak Away (UD-S)

    Best suited to residential-type applications where urine can be discharged to a soak-away, and where the aim is to protect compost balance under particular use or climate conditions.

    Urine Diversion to Container (UD-C)

    Best suited to mobile, RV, back-up, and emergency toilet applications where urine is stored separately and disposed of manually.


    Urine Diversion to Soak Away (UD-S)

    Composting toilets with urine diversion to soak-away are mainly applicable to two scenarios: fluctuating high urination and cold climates. Such systems see solids composted in their own composting chamber, while urine is diverted to a substrate soak-away.

    See the product as an example:

    Fluctuating High Urination Scenario

    Regular parties and group gatherings

    If you are prone to throwing parties or hosting large numbers of visitors regularly, urine diversion may be a good idea. Group gatherings tend to see a lot of drinking and, as a result, a lot of peeing.

    When such a large amount of peeing is taking place regularly, urine can saturate the compost and become a problem. It can overload the system with ammonia, offsetting the composting balance and causing foul odour. Urine diversion is a great way to prevent this from happening. It will help keep the compost healthy and prevent smells.

    Note that fluctuating high urination is different to intermittent high urination. Fluctuating high urination applies to regular scenarios of high urination only. Intermittent high urination applies to the odd occasion of group gatherings and can usually be managed by an all-in-one composting toilet with the temporary addition of highly absorbent bulking agent and compost black, an ammonia absorbing agent.

    Cold Climate Scenario

    Below 13°C average temperature

    Urine diversion is beneficial in colder climates in which the composting toilet is installed outside, or inside a non-acclimatised building, below 13°C average temperature.

    Reducing the moisture content of organics makes them less susceptible to thermal sink, heat loss and heat gain. A dryer compost is a more insulated compost, capable of better heat retention.

    If your toilet is inside an acclimatised building, urine diversion is not essential. If, however, the toilet is in a cold environment and the chambers are in a location without solar gain or other forms of passive heating, urine diversion is beneficial and will help to avoid the loss of bio-activity caused by low temperature.

    Note that composting will take place down to 3°C, but its efficiency is greatly reduced below 13°C. Read How to Maximise Passive Heating to learn about keeping your compost warm and operational in cold climates.


    Urine Diversion to Container (UD-C)

    Urine diversion to container systems is great for mobile toileting in RVs and as back-up or emergency toilets. Such systems see urine collected in its own separate container, rather than having it plumbed into a sub-strata soak-away.

    This means that you will need to dispose of urine manually, which requires having an appropriate way to do so available to you. Urine can be poured down existing public or private toilets or disposed of at dump stations. For more info, see How to Dispose of Urine from a Urine Diversion to Container System.

    See the product as an example:

    Mobile Toilet Scenario

    Love hitting the road, but unsure of which toilet to install in your RV? Composting toilets that divert urine to a container are a strong solution to mobile toileting.

    Such systems separate solids and liquids into separate chambers, providing a decent berthing cycle and convenience in terms of waste disposal. Having the urine in a separate container means it can be easily disposed of in public toilets or dump stations you encounter on the road.

    It also means the solids chamber fills up slower, giving you more time on the road before it needs to be emptied.

    Emergency / Back-up Toilet Scenario

    If you live in an emergency-prone area and would like to ensure your family is able to toilet should disaster strike, or if you are simply looking for an additional toilet to accommodate more people, then urine diversion to a container is a great option.

    Provided, however, that you have the appropriate means of urine disposal available to you. Generally, this means the existence of another toilet on-site, connected to sewerage or a septic tank.

    For more info, see How to Dispose of Urine from a Urine Diversion to Container System.

    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.