Greywater system

November 3, 2020
Module is suitable for
Urine diverting dry toilets (UDDT). The dimensions of a sewage system without faeces using urine diver-ting dry toilets are about 10 times smaller than a "wet toilet" system. This has considerable economic and ecological advantages. When a local treatment system needs to be considered, this type of toilet is an obvious choice. The most important advantage, however, is that because of the small dimensions, it becomes fairly easy to internally recycle the output of the water treatment system, and you are there-fore (in principle) exonerated from any legal requirements concerning sewage. However, in order to prove that you have no leakage in the ground, it is necessary to construct a system that operates in a closed environment. This can be done by putting a pond liner under the whole system, and use the surplus water within this closed environment.


This system is designed for 200 liters of urine and hand washing water per day. This capacity is enough for about 50 guests per day. One load of 200 liters wastewater diluted with rainwater, is flushed in about 2 to 3 hours through a 12-meter long gravity-fed helophyte filter. In the end, it is pumped back to the beginning. This loop is repeated throughout the day. At the end of the day, the filtered water is stored for irrigating the greenhouse where bamboo and young trees are grown. The compost from the toilets is also produced in this space and applied after at least one year of maturation to the non-consumable vegetation system, and use the surplus water within this closed environment.

The treatment has 5 stages:

  1. Pre-treatment. This is a 1m2/ 50cm high container filled with wood chips in which the wastewater arrives. This takes out the biggest particles.
  2. Grease trap. This trap has three compartments (3 barrels) through which the wastewater runs up and down in order to stimulate settlement.
  3. Mixing and oxygenation. These are three barrels. The first one receiving the wastewater from the grease trap, the second from the filter, in which the new wastewater is mixed, and the last barrel in which extra rainwater is mixed. All three barrels are oxygenated by a solar air pump.
  4. Helophyte filter. This 12 meter long filter contains gravel and sand and is vegetated with reeds. The main purpose is to transform ammonia into nitrates and to reduce the nutrient level to a level acceptable for irrigation. A bell siphon empties the barrel in one flush, and gives a volume of 200 liters to the filter, resulting in a "flood and drain" type growing system.
  5. Bamboo filter. At the end of the day, the water is pumped to an irrigation tank and is used to irrigate fast-growing plants, mainly bamboo and willow producing biomass, but also a nursery for young trees.
Urine diverting dry toilets (UDDT) integrated system. Illustration by Alessandro Rosa


Most of the material for this unit can be made of scrap or be bought second hand. In order to prove it is a closed environment though, it is advisable to buy a new pond liner and tank connectors. - a large box in the ground, at least 2 m3- the barrels are from a pickle factory- the IBC’s are bought second hand - two bilge pumps


  1. In a 5x12 meter greenhouse, a pond liner buried in the ground, 1,5 meter deep at its deepest point.
  2. In the middle, there is a buried box containing the grease trap and collection point of the helophyte filter.
  3. The hole for the pond liner is dug out 1,5 meter, creating three terraces, in order for the soil to hold irrigation water. The pond liner is protected by a sandwich of fabric. In order to prevent dead zones, the first layer in filling up the hole consists of a coarse, draining, material like rough sand with gravel.
  4. In the middle, in the deepest point, the box for the grease trap is constructed.
  5. The filter is laid out, ending in the middle, at the deepest point. In this case, the filter has an inclination of 1 meter, over 12 meters length, following the three terraces down. Then the original dug out soil can be put back in.
  6. A pump for pumping up the urine to the helophyte filter.
  7. A pump for redirecting the water from the end of the filter to the beginning of the filter for its second or third loop. Because the last two barrels are interconnected, the two pumps also function as each other's back-up pump in case of malfunction.


Wood chips and grease trap barrels should be emptied out every 6 months in the composting unit.

Kitchen filter

The main difference between the kitchen filter and the Urine filter is the last part of the process; At the end of the day, the water is pumped to an irrigation tank and is used to irrigate instead of bamboo and willow, tomatoes and other edibles plants in the vegetable garden.The use of IBCs for the Helophite filter is another possibility, best for projects with a duration lower than 6 years.

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