• Six water treatment plants in a terrarium – Phragmitis communis/austral. | Schilfrohr; Iris pseudacorus | Wasserschwertlilie; Typha latifolia | Breitblättriger Rohrkolben; Acorus calamus | Kalmus; Scirpus lacustris | Flechtbinse and Juncus effusus | Sumpfgras.
  • Soil from the forest


[water recycling with water treatment plants]

For the plant treatment system a terrarium is filled with plants whose roots are covered with sand and contains a drainage tube with holes, into which the clean water can flow. I made a hole in the front of the terrarium to take water samples.

With this construction I can test how much time the plant needs to clean the water. With the tap I regulate the drain and the time in which the water is in the terrarium. When I open the tap I take a sample and close it again to leave the remaining water in the terrarium. After a certain time I take a new sample.

Processes: Cleaning performance of a plant sewage treatment is carried out by the interaction of different processes. Water ingredients are absorbed by the plants to cover the nutrient requirements of the plants in growth. In addition, the roots of the reed get the permeability of the soil (oxygen supply), which is reduced when entering or by deposits in the plant. Most of the cleaning is done by microorganisms or bacteria that live in the soil body. Both processes purify the water „biologically“ by biochemical reactions.

In addition to other material cycles such as the phosphorus cycle or the sulphur cycle, the nitrogen cycle has an enormous importance. The main types of discharge from a sewage treatment plant are denitrification, ammonia evaporation and anaerobic ammonia oxidation.

In the purification of water a working nitrogen cycle in the sense of a biological purification stage has a prominent role, because the waste water is contaminated by nitrogen compounds. Nitrogen is an elementary component of amino acids in proteins, nucleic acids and other essential chemical substances in organisms that absorb nitrogen from the environment during their growth (nitrogen assimilation) and after their extinction they are released from the dead biomass again.

More information about the importance of a biological purification can you read on >> WIKI >>.


Measurements start in march 2018

Since few days the temperatures in Berlin in February 2018 have been at cold 7 °C, which even on the Spree leads to the formation of an ice layer. When I visited my little test swamp bed yesterday, an ice layer had formed and I thought about whether the microorganisms in the root area of the swamp plants at these temperatures still work effectively and therefore can clean grey water.

The freezing point of water is at 0 °C, which creates an ice layer from 0 °C on the swamp bed and increases in thickness with each cold day. In winter a specifically lighter layer of ice floats on the heavier 4 °C water. This creates again a stable temperature stratification (winter stagnation).

In the case of planting with swamp plants on a roof, the vegetation layer is between 5 and 10cm deep and the water level is average 10 – 20 cm for vertical plant sewage systems, which produces quite probable an ice layer and the soil has a maximum temperature of 4 °C (temperature stratification).

„The effective microorganisms are the most effective as long as they are active, i.e. at soil temperatures from 10 °c. Under 8 °c and in winter the microorganisms in a resting mode.“ (1)

„To be able to work effectively, the water temperature must not be below ten degrees.“(2)

When used water is diverted from the house to the roof, the water freezes as well, causing the flow of water to come to a stop.

I assume that due to the current temperatures, the cleaning capacity of a swamp bed is significantly reduced or, if necessary, even completely to the end and a flowing water cycle on the roof of a tiny house is not present.

Are my assumptions correct?
What are your experiences?
Are there any solutions to this problem?


(1) Seite 5; https://www.em-schweiz.ch/Content/Images/uploaded/Schweizer%20Garten.pdf
(2) https://www.ndr.de/ratgeber/garten/Den-Gartenteich-im-Herbst-pflegen,gartenteich152.html