Method and system for purification of waste water

摘要

Method and system for the purification of waste water. In the method, all purification functions, including removal of nitrogen and phosphor, are performed in one and the same reactor (1), in which several alternating oxidation and reduction zones (2 - 6) are created in unclarified waste water flowing through it by supplying each zone with gas mixtures with different oxygen contents as needed for the purification function to be performed in the zone from a gas distributor (8), in such manner that oxygen-rich gas containing 30 - 50 % oxygen is supplied for oxidation while gas with a low oxygen content of 0 - 5 % is supplied for reduction. A solid support (7) for increasing the biomass together with the biomass adhering to it is exposed to alternating oxidation and reduction zones so that the waste water to be purified and the biomass are subjected to an abrupt variation of conditions, in which phosphor is alternately bound and dissolved in biomass growth and nitrogen compounds are oxidised into nitrate, to be reduced in the next zone into nitride and further into nitrogen gas. The process is controlled and regulated by optimising the oxygen content of the gas used. The solids level in the reactor is controlled and excess solid matter is removed directly from the reactor space by means of a flotation unit (21), from where the surface sludge is removed entirely without returning any portions of it into the process.