The invention relates to a method for the purification of wastewater, said method comprising passing waste water into a tank for a purification treat- ment. The invention relates also to an apparatus for the purification of wastewater, said apparatus comprising a tank which contains wastewater bound for a purification treatment.

In terms of the prior art, reference is made to the patent publication EP 1583719, which also discloses in more detail the design of one embodiment for an electrolytic cell useful in this invention. This prior known method and apparatus nevertheless do not apply to the purification of wastewater performed in a tank, and the wastewater to be cleaned is delivered by pumps into electrolytic or reaction cells.

The invention is primarily applied to the purification of municipal sewage waters by making use of the clarification tanks of existing sewage treatment plants. It is an object of the invention to substantially enhance the operation of existing sewage treatment plants, and particularly to improve the degree of purification.

This object is achieved in the invention by means of the method features presented in the appended claim 1. The object is also achieved with an apparatus of the invention by means of the characterizing features presented in claim 4. Preferred embodiments of the invention are presented in the dependent claims. One exemplary embodiment of the invention will now be described in more detail with reference to the accompanying drawing, which in a schematic vertical section shows an apparatus for implementing the method. The basic concept of the invention is to employ conventional purification tanks or basins intended for receiving wastewater and containing wastewater bound for treatment. Submerged in a tank 14, or placed outside the tank below the level of wastewater present in the tank, is an electrolytic cell 3 and part of a water and flock separation tower 7. Wastewater is passed from the tank 14 across the electrolytic cell 3 into the separation tower 7 by means of a hydrostatic pressure existing in the wastewater present in the tank 14. The wastewater is passed into the electrolytic cell 3 across a filter 4 submerged in the tank, the latter typically removing particles larger than 01mm. The elec- trolytic cell 3 includes one or more cell elements equipped with an iron and/or aluminum electrode 2. The one or more cell elements are selected according to the grade of wastewater bound for treatment. The use of several successive cell elements enables a better distribution of electric current over a longer distance of water flow. In demanding purification projects, it is possible to employ an iron electrode between aluminum electrodes. An inner electrode 1 is surrounded by one or more tubular iron or aluminum electrodes 2. The outer electrode 2 is connected to the plus pole of a direct current supply 11 and the inner electrode 1 to the minus pole. If several electrodes are used, it preferable to respectively employ separate and individu- ally controlled power sources in order to enable the individual current regulation for each electrode. The inner electrode can be made of stainless steel, nickel, chromium, platinum, or precious metal alloys with a major difference in electronegativity with respect to aluminum and iron. A cell element equipped with the iron and/or aluminum electrode 2 generates iron and/or aluminum hydroxide, working as a molecular sieve. This molecular sieve and soluble and particulate impurities trapped therein are enabled, by means of hydrogen released in electrolysis, to rise up into the water and flock separation tower 7 mounted on a top end of the cell 3. The mo- lecular sieve and impurities trapped therein accumulate for a flock 13 within an upper end of the separation tower 7. In the proposed embodiment, the riser pipe is provided over a section of its length with a mesh wall 8, which does not function as a sieve but, instead, as a flow guide. The separation tower 7 is surrounded by a treated water collecting pipe 16 fitted with a pipe branch 9, which is intended for the outlet of treated water and which is adjustable in terms of its elevation level. Above the pipe branch 9, flock is re- moved from the separation tower 7 by way of a pipe branch 10, e.g. onto a conveyor.

In an alternative embodiment of the invention, a standing pipe associated with the treated water outlet pipe 9 may connect directly to the separation tower 7 below the flock formation zone, in which case the mesh wall 8 and the water collecting pipe 16 are omitted.

The level adjustment of a water discharge point, i.e. the pipe branch 9, can be used for regulating the dry content of the outgoing flock 13 as the eleva- tion level of the pipe branch 9 determines the level of water in the pipe 16, the latter establishing a communicating vessel with the separation tower 7. The further down the pipe branch 9 is lowered, the drier becomes the flock 13. The moisture of the flock 13 can be maintained sufficient for its removal from the pipe 10 by self-lubrication, with no need for a separate scraper. Of course, the flock can be removed from an open top of the separation tower 7 by means of a scraper, or the outlet pipe 10 can be provided with a conveyor.

The electrolytic cell 3 and the separation tower 7 are preferably housed in a container 15, which is submerged in and anchored to the attachment with the tank 14. Inside the container 15 is a space void of wastewater, which functions as a maintenance space, and at the same time isolates the wastewater present in the tank 14 from the cell 3 and the separation tower 7. The location level of the entire apparatus in the container 15 can be made ad- justable. The location level of the apparatus must be selected in such a way that a sharp interface between the evolving flock 13 and the purified water in the separation tower 7 settles below the wastewater level of the tank 14, whereby the hydrostatic pressure of water in the tank and the buoyancy of hydrogen jointly establish necessary flows across the apparatus.

The container 15 can also be replaced with a small casing for housing the apparatus, whereby the casing, along with the apparatus therein, can be hoisted completely away from the tank for maintenance.

A plurality of purification units, consisting of the cell 3 and the separation tower 7 depicted in the figure, can be constructed in a parallel relationship, whereby a valve 12 associated with a supply pipe 6 can be used for selecting the number of currently working purification units according to the amount of incoming wastewater. The incoming wastewater is conducted e.g. by way of a overflow or a pump from the preceding tank to the next tank, in which latter the method and apparatus of the invention are used for the final purifi- cation of wastewater. When using the method and apparatus of the invention, the purification of wastewater becomes faster and the degree of purification is improved.

A particular benefit gained by the invention is that the passage of wastewa- ter across an apparatus of the invention does not require any pumps, but the flow is established by a hydrostatic pressure and by hydrogen generated as a reaction gas.

The invention is applicable, among others, to the purification of municipal wastewaters in the way of upgrading and enhancing the presently operating facilities. Of course, the invention can be applied to the purification of all types of wastewater.

The apparatus according to the invention can be installed in an existing sew- age treatment plant without suspending its operation. Aeration and sedimentation tanks can be decommissioned for a reduced surface area.