A modern well-functioning dry toilet is odourless and pleasant to use. A well-functioning dry toilet requires that certain basic rules have been observed when building, installing and selecting appliances.
Urine and seep liquid separated from dry toilets is very rich in nutrients and - to varying extent - in excrement-borne load. Therefore, the liquids should not be conducted from the toilet directly into the ground where they contaminate the soil and can be transferred to bodies of water, ground water or wells.
To the largest extent possible, the liquids created in the toilets should be utilized and their valuable nutrients returned to natural circulation.
Urine from a healthy person is relatively sterile and does not contain a large number of pathogens. In many cases you can utilize the collected urine in your own garden.
In a domestic garden the urine can be spread as fertilizer using a watering can either as such or diluted. The dilution eliminates the risk of excess fertilization but increases the work input, evaporation of nitrogen and total amount of fertilization required. The dilution ratios commonly applied are 3:1 or 10:1. If you spill a lot of urine on the leaves of the plants, you should rinse it off with clean water. The recommended spreading distance is 10 cm from the plant"s base.
In permanent residences the separated urine is usually collected in a closed tank of several cubic metres. Whether the size of the tank is sufficient, mostly depends on the number of dwellers. In weekend houses can be used collecting tanks smaller in size.
One person produces about 1-1,5 litres of liquid daily. Urine is very rich in nutrients and the major nutrient load of wastewater from a water toilet derives from urine. Urine is mostly a nitrogen fertilizer. It must be spread on the plants, while the soil is still unfrozen, well before the autumn so as to avoid disturbing the preparation of perennial plants for winter.
The data in the following calculation are based on the publication 1/2000 of Työtehoseura, Human Manure as Fertilizer by Anja Weckman:
According to a study made in Sweden, the average amount of urine/water produced was 1,3 litres/person/day, which makes about 480 litres per year. This amount contains about 1,6 kg of nitrogen. This means, for a family of five people the amount of urine produced will be about 2400 litres and the amount of nitrogen will be about 8 kg.
Urine is excellent for watering the lawn. If the mulch is left on the lawn, not much fertilizer will need to be added, just about 1 kg/are. If the cutting waste is collected up, the required amount of nitrogen in the fertilizer is at maximum 2 kg/are. Slightly more urine can be spread on a vegetable plot than on the lawn.
It is likely, that at least 10 % of the nitrogen in the urine will evaporate during spreading, which means the lawn area required for spreading for a family of five people should be about 720 m2.
We recommend that the seep liquid separated from the bottom of the tank be collected into a seep liquid canister for controlled utilization later on for disposal. Seep liquid originates from excrement and therefore is rich in nutrients.
Hygienic issues must be taken into account while handling seep liquid. Use protective gloves while handling seep liquid and wash your hands afterwards. Keeping the seep liquid in a separate canister for half a year improves its hygienic qualities.
Seep liquid rich in nutrients is, because of its nutrient balance, perfectly suitable for the fertilization of plants. It can be used for ornamental plants, flowers, trees, bushes and grass in the yard and garden. Using seep liquid for the plants in the vegetable plot, which are eaten as such, is not recommended.
A suitable dilution ratio for seep liquid, when it is used as fertilizer, is about 1/3-1/5. If watering with fertilizer is to be repeated regularly, the liquid should be diluted more.
Seep liquid, rich in nutrients, can be utilized as compoststarter liquid. The nitrogen of seep liquid intensifies the activity of the garden compost in particular, which is rich in nutrients but poor in carbon. Use seep liquid in a new compost just after its creation. Adding seep liquid to relatively mature compost is not beneficial.
You can also recycle seep liquid back to the toilet compost gradually.