Grey and black water is the term for all household wastewater. Black water carries the faecal matter and the urine, while grey water refers to the rest of household wastewater. All wastewater except yellow water (urine) will be treated in decentralised sewerage devices.

From the user, the wastewater will be directed into a septic tank. This tank has to have at least 3 chambers to guarantee proper sedimentation. Once the water reaches the third chamber of the septic tank, it should be nearly sediment free and will then be directed onto phyto clarification plants (PCP). Researches on pre-separation of faecal matter through rotting screens in the septic tanks are in process at the moment under: http://www.ioev.de "Ökologische Kreislaufwirtschaft an der Valley View University in Accra (Ghana)". The idea is to reduce the amount of septic tank sludge and at the same time to be able to incorporate at a much earlier stage the faecal matter through co-composting into the nutrient cycle. Further information on this research project can be obtained from Dipl.Ing. Nicola Jokisch at the chair of Fundamentals of Ecological Planning and Building at the Bauhaus-University Weimar, Germany.

Source: Bahlo, K. Naturnahe Abwasserreinigung, Ökobuch, Staufen, 1992

These plants are also called constructed wetlands and can be designed in different forms. The form I choose for Sitio Joaninha has a vertical flow-through and is technically more reliable than the ones who have a horizontal flow-through, but they require a preliminary pump shaft, because the PCP has to be fed intermittently. In central and northern Europe a surface area of > 2,5 m2/P of PCP is required, but in tropical countries one estimates, that the required surface area, due to the higher bio-activity can be reduced by 50%. I designed the PCPs with 2 m2/P. Minimum size of a vertical flow-through PCP is 10 m2 and its depth should be > 0,8 m.

The amount of wastewater should be the same as the amount of used drinking water. This is so, because due to a sufficient drinking water supply, I do not recommend the individual use of rainwater for toilet flushing and washing machine use at the moment. This means, calculating with 80 l/d/p of drinking water, the hydro strain on the wetland would be 40 mm/m2/d. The limit for hydro strain on vertical flow-through PCPs is 60 mm/m2/d.

How does a vertical flow-through phyto clarification plant work?

The pump shaft has to be dimensioned in a way, that it can hold 50% of the daily accruing wastewater. The wastewater will be pumped from here in at least four feeding intervals per day onto the PCP. On the surface of the PCP the water will be distributed evenly. If smell disturbance accrue the distribution pipes can also be put under a layer of gravel. PCPs are basically with helophyte overgrown sand filter.

Source: Bahlo, K., Naturnahe Abwasserreinigung, Ökobuch, Staufen, 1992

Once the water did pass the plant root layer, it has to pass through layers of sand with different coarseness. Here the used aggregate will build up the prime pore system, which determines the final hydro strain capacity. The roots of the plants and channels dug by animals create a secondary pore system, which helps the extension of microscopic live at deeper levels of the filter and thus rises the clearing capacity of the PCP. At the bottom of the PCP is a layer of gravel, which contains the usually with coco mats involved drain pipes.

The drained water flows of into a control shaft and from there into the orchards. In case the water is not totally absorbed by the ground a downstream trench will retain and percolate the access water.

PCPs do not only clean the wastewater but are also an important element for the creation of microhabitats for animals and insects. Furthermore do the helophytes evaporate about 30% of the water and are thus playing an important role in the creation of the microclimate. They also, choosing a good combination of plants, can visually enrich the area.

When building PCPs, one has to observe, that no rainwater at any time can enter the PCP from outside.

The following shows a selection of plants, appropriate to be used in PCPs.

     Iris pseudacorus

     Acorus calamus

     Sparganium erectum

     Schoenoplectus lacustris

     Juncus effusus

     Typha angustifolia

Source: http://www.mpiz-koeln.mpg.de/~stueber/thome/Alphabetical_list.html