The present invention relates to biological purification of waste water. Biological purification of waste water has of course always existed in the nature and with the increased demands on purification of waste water attempts have been made also to utilize these effects economically. Purification was first carried out in such a way that the waste water was kept in big basins having a large surface through which bubbles of oxygen or air were optionally passed to get a bacterial degradation of the organic substances in the water. In order to achieve a more economical biological purification of the waste water more complicated devices have also been constructed to reduce the size of these basins. One example thereof is the rotating biological contactor(RBC) which means in principle that the bacterial growth or the biological degradation in the water is made to take place on the surface of contactor materials. The contactor materials are more or less submerged in a basin and are rotated to bring the microorganism into contact with the air as well as the water and the organic material therein to be degraded. However, so far no real optimization of the constructions and the function of these RBCs has been made. One reason has been that these RBCs have been found to be so substantially much more economical than has been the case before that no further possible development has been considered. The optimization attempts that of course have been made for economical reasons have been relatively hazardous and unsystematical, and therefore no unitary rules and optimization conditions of RBCs are present so far. It is therefore the object of the invention to define a process in microbiological purification making possible an optimization of the operating conditions and consequently a minimizing of the required costs. The present invention also relates to a device based on these principles to indicate the purely practical application of the principles.
In accordance with the invention two parameters are important when dimensioning RBC plants apart from the downright dimensioning of capacity. The first parameter is that the amount of water per m.sup.2 of substrate surface should lie between 1 and 10 l water/m.sup.2, preferably between 2 and 8 l/m.sup.2 of material. The second important parameter is that the specific substrate surface per rotor volume of material according to the invention should be between 150 and 400 m/.sup.2 /m.sup.3 and preferably between 200 and 350 m.sup.2 /m.sup.3. This range has also been illustrated in the appended diagram.