Wostman EcoDry separating porcelain pedestal

Urine-diverting and non-diverting toilets

Discussion about urine separation has always been hot and almost emotional among people interested in dry toilets. Some strongly argue in favor of strict separation of urine, while others are more hesitant for example about unusual toilet seats. For many new dry toilet users, the topic is entirely unheard-of. Truly objective information may be difficult to filter from biased marketing letters. The issue emerges from the fact that there are so many different dry toilet models required to fit all the different varying use-cases (compare for example the toilet needs of a private household or public glamping site). Therefore, it is pivotal to consider your own toilet needs and reflect which dry toilet model would work the best for my use-case. The solution your neighbor suggests, may not necessarily work the best for you.

The purpose of this blog post is to take part in discussion of urine-diverting and non-diverting toilets and provide as objective information as possible about both of these dry toilet techniques. We list the pros and cos of both. Also, we try to educate our audience about urine-diversion in general, but first, let us clarify what are non-diverting toilets.

What are non-diverting toilets?

Non-diverting toilets are toilets that do not separate liquid waste (mostly urine) from the solid waste (excreta, toilet paper etc.) at any point. Instead, all the waste goes into same container or piping where they stay mixed. Probably the simplest execution of a non-diverting toilet is the old outhouse with a bucket under the wooden toilet seat. The execution is simple and cheap, but also in most cases horribly smelly, due to rotting toilet waste. In many countries, raw toilet waste is not allowed to be let in the environment without proper treatment first. That is why, fewer and fewer outhouses with regular buckets only are seen – luckily.

Onko sinullakin laiton vessa
An example of a non-diverting toilet is the old outhouse with a regular bucket below toilet seat. The toilet smells bad because the waste is too wet to compost and is rotting.

Is there any use for non-diverting toilets? Frankly, there is and quite a lot if we broaden our perspective of possible toilet solutions. For example, there are a number of tiny bucket toilets (a.k.a. chamber pots) serving highly temporary toilet needs e.g. in camping and on boats. If we take even wider perspective, flush toilets may also be categorized to belong in the group of non-diverting toilets. All the toilet waste goes into the same piping where it mixes with flush water. In this blog post, we will nevertheless limit the scope of discission to only consider dry toilets.

One can easily have a nice non-diverting dry toilet by for example using a lot of dry material that can absorb the liquid waste – especially if the use is only temporary and/or the dry toilet is used as a secondary toilet. However, even in this case, raw toilet waste must eventually be treated properly (e.g. composted).

In sum

+ In many cases, simple non-diverting toilets are cheap / DIY models.

+ In small and temporary use-cases they work well.

– The user has to know how to avoid problems of odor

– Proper mechanism for safe treatment of raw toilet must be on place anyway (usually in case of dry toilets it is composting).

– Bucket toilets and chamber pots do not fit for many users and/or continuous use.

What are urine diverting toilets?

As the name suggests, urine diverting toilets divert urine from the rest of the toilet waste. There are several ways how the separation can be done, but generally we can identify two kinds of urine diverting toilets:

1) toilets that divert urine directly in the toilet seat (or squat slab) before it gets mixed with solids.

2) toilets that divert urine only after mixed with feces and other solid waste.

Let us focus on the former first. Toilets that divert urine directly in toilet seat always have two-bowl structure, one for urine, one for solid waste. This means that the user should urinate to the urine bowl in front part of the toilet seat and do the rest of the needs in the back. The great advantage of this technique is that the toilet stays odorless in almost all conditions, because the excreta is not mixed with any extra liquid that could cause it to rotten. Thus, no dry material is needed except for covering tracks. The urine coming out of the toilet will be sterile because it has not been mixed with feces. When diluted with water, the urine can safely be reused for example in garden as growth booster for plants and flowers. However, you should avoid urine from getting into water areas because there it eutrophicates the water.

The downside of urine diverting toilets that separate straight in the seat is the heavy liquid load they often produce. For example, in family of five people, a 20-liter urine canister will fill up just in few days after which someone has to go empty it. Moreover, for many new dry toilet users, the two-bowl design may feel uncomfortable, because they are not used to urinate and excrete in different sections of the toilet seat. Finally, the urine diverting toilets that divert straight in the seat are usually a little more technical in terms of moving parts and hence more vulnerable to malfunctions.

In sum

+ A lot of nutritious sterile urine that can be used as eco-fertilizer or growth booster for plants.

+ Problems of odor are very rare, when used according to instructions.

+ Only small amount of solid waste to compost

+ No need for dry material, except for covering tracks

– Storing urine may turn out to be arduous, especially during winter when there is no place to reuse the urine

– The amount of urine may be substantial

– Getting used to the two-bowl structure may take time and confuse guests. Men must always sit to use the toilet.

– Avoiding the urine bowl and hose from getting blocked

What are post-diverting toilets?

The other option is to separate the urine after it is mixed with feces and rest of the solid toilet waste. We will call these toilets post-diverting toilets. They drop all the waste into single toilet container where a part of the urine will get absorbed to the solid waste while the rest will just flow out from the bottom of the container. This outflowing urine is sometimes called leachate, seep or excess liquid. Most of the modern composting toilets, like the Green Toilet, Kekkilä and Biolan, are in fact post-diverting toilets – although the way in which the urine is separated inside the toilet container may differ from one model to another.

Post-diversion as a notion is still very new even for professionals, even if the technique has been on the market for many decades already. This may be because the post-diverting toilets have traditionally been grouped to belong to the category of non-diverting toilets, although they in fact separate the urine from solid waste. We argue post-diverting toilets should not be considered as non-diverting toilets, because they do separate the urine. The question is more about when and how do they actually separate the urine from solids.

Probably the greatest advantage of all post-diverting toilets is the low amount of urine that needs to be taken care of, as most of it will get absorbed into the compost mass and evaporate through ventilation. This advantage is really important especially for larger families and public use-cases. Consider for example that whereas a urine diverting toilet that separates straight in the seat can produce 10 liters of urine per day, a post-diverting toilet may produce few deciliters of excess liquid. The difference is in the amount of liquid produced is very different between the two techniques. Moreover, post-diverting toilet do not require abnormal toilet seat structure, so people are more comfortable in using them, in particular, if the toilet is in business or public use.

As you might guess, post-diverting toilets have the challenges of their own. Unlike pure urine diverting toilets, post-diverting toilets are more vulnerable to problems of odor. The most common cause of this problem is lack of dry material used. The compost mass inside the toilet container is too wet and therefore produces bad smell. In addition, the leachate coming out from the toilet is hazardous for health as well as for the environment if not treated properly. Luckily, there are several ways to deal with the excess liquid:

  • Pour the leachate to ornamental plants (plants that are not eaten), far from water areas. We recommend switching the place where the leachate is poured to avoid stressful peaks for the environment.
  • Storing the leachate in a sealed canister for 6-12 months after which all hazardous bacteria should be dead, and it is safer to be used in garden.
  • Utilize special filters like the GeoTrap to filter the hazardous nutrients from the excess liquid.

In sum

+ Post-diverting toilets are easy to use by anyone

+ They are very robust (no moving parts)

+ The composting process starts already while in use

– Must use dry material

– Must manage the excess liquid properly

– Misuse may cause problems of odor

To separate or not? If, how?

Separating and non-separating toiletsAs mentioned, the discussion of urine separation will probably never end as there simply is no single patent solution that would work for everyone. In our experience, there are geological differences between countries to what people are used to. For example, in Sweden, urine diverting toilets that divert straight in seat are the most common solution, whereas in Finland post-diverting dry toilets are mainstream. In addition, there are legal aspects that may affect the discussion of which technique is the best. For instance, in UK, there is an exception law that allows small about of leachate to be poured straight to ground without any treatment. In Finland, the same is prohibited.

Here at Pikkuvihreä, we slightly prefer post-diversion, but also emphasize that there are many things weighting on the scale simultaneously and everything should be balanced case-by-case: environment, users, maintenance process, climate, local legislation etc. Finally, we wish to point out that urine separation is only one of the many important technical aspects related to dry toilets. Proper ventilation and maintenance process are for example equally important.

We highly recommend contacting us for more information and help. We are true experts in this field with almost 30-years of experience.

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