We produce large amounts of wastewater every day. All water that enters the home must go out again. And it carries with it a lot of other things that we want to get rid of. The water from the toilet is usually called blackwater. It contains urea and faeces. This water contains a lot of dry matter, many nutrients, and has a large bacterial flora. Also gray water, which comes from showering, washing, and the kitchen, contains some dry matter and plant nutrients, but has a significantly lower bacterial population.
How can one purify this? We have a tradition of mixing everything together. However, there may be advantages to keeping them separate in order to have a simpler purification process for the greywater.
The first step in the purification process is mechanical. The solid substances must be removed. Sedimentation and/or filtration takes care of this. Alternatively, chemicals can be added here so that the pollutants will coagulate – flocculate – so that they are more easily settled or filtered. But then one must handle these chemicals in the further process, and one must control the residual chemicals if the water is to be used for drinking water. After most of the solids have been removed, nitrogen and phosphorus must be removed. Both are nutrients that plants need. The water can therefore be used directly to fertilize plants. Similarly, the solids can be used as plant fertilizer, possibly after a maturation process. The water that is not used for fertilizing plants is filtered over bio-bodies. Bio-bodies are plastic bodies that have a large surface area covered by a biofilm, a bacterial layer that feeds on the nutrients in the water. When the coating reaches a certain thickness, it is removed. This can be done automatically by taking out a certain number of bodies each day and rinsing them clean. The biofilm that is rinsed off is also excellent for growing plants. It can also be "food" for microorganisms that produce bioetanol eller biodiesel.
Finally, the water is filtered and disinfected. This can be done by adding chlorine or hydrogen peroxide, or it can be exposed to UV light, which kills any remaining microorganisms. Then, the water can be consumed with a clear conscience. This is nature's own way of purifying water – well, one out of nature's own methods.