METHOD AND DEVICE FOR BIOLOGICAL PROCESSING OF WASTE WATER

Abstract: Method of biochemical processing of waste water including the steps of submerging a rotor of contact material giving a surface for microbiological growth in waste water to more than 50% of its volume, preferably 55-85% and that, to avoid the risk of anaerobic conditions in the center part of the rotor, the supply of oxygen to waste water is increased by for example increasing the RPM of the rotor to for example 3 RPM giving per time a greater surface subjected to atmospheric oxygen.

Description: METHODANDDEVICEFORBIOLOGICALPROCESSINGOFWASTE W A TER In biological processing or treatment of waste water the organic content- therein is broken down by micro-orga¬ nisms sometimes growing on a substrate surface. Usually this micro-biological process is aerobic; that is, oxygen is used to break down the organic material. Consequently a number of designs have been invented in the past and one of the most useful is a rotating body with an enlarged surface (rotating biological contactor) , which is brought in and out of contact with air and waste water due to its rotation. In this way the micro-organisms are brought in contact with oxygen of the air as well as the waste water in the basin. When the growth of the micro-organisms have reached a certain thickness their own weight and the shear- forces in the passage through the water will tear them off from the substrate surface and these sludge floes are carried away by the streaming water, separated from the water and dewatered in a special process. .The first rotating .biological contactors were uses in the beginning of the. century in the form -of rotating discs. Much later,in the 1950-ies, the rotating disc system was improved with respect to the material used in the discs. Expanded polystyren made it possible to design light weight biological disc systems with a specific surface in the bio- disc of approximately 50 m 2/m3. Later, rotating biological ' contactors were developed in USA, using a plastic honey comb material with a specific surface of approximately 100 m 2 /m 3 . Traditionally rotating biological contactors are sub¬ merged to about 40 % in the waste water. In this way the roller bearings can be placed on the edge of the basin and kept dry. It has been proved in practice by Antonie, USA, and Stengelin, Germany, that the process is ' optimized if the ratio between the total active area of the rotating bio- logical contactor and the volume of the waste water basin OMPI Λ. WIPO - is approximately 200 m2/m3. Thus, this parameter must be taken into account when designing the total system of the process. Due to the enormous amount of waste water that has to be treated today, waste water basins as well as the corresponding rotating biological contactors (rotors) need considerable dimensions and consequently high costs. In order to make the process more efficient thus diminish¬ ing these waste water devices few solutions have proved themselves in praxis. The way perhaps most close at hand would be to increase the specific surface of the rotor material, that is rotor area per rotor volume. This is however not so easily obtained as it may sound, as the risk of clogging the rotor and also causing anaerobic problems is increased when the specific surface is in¬ creased. This problem has however rencently been solved (PCT no. SE 80/000 70). These new rotor materials have however resulted in some further problems that has not previously been experienced. As mentioned above it has been found experimentally that the relation between available substrate surface and the waste water volume 2 should be about two hundred (the surface expressed in m 3 and the volume in m ) in order to have optimum efficiency) . As a result it has not been possible to use these new materials with expected increase in efficiency or diminish¬ ing the dimensions as much as desired, with other para- meters being unchanged. The object of the invention is to provide a method with which these new materials efficiently can be used without loss of optimal conditions. This problem is according to the invention solved by giving the waste water basin a volume according to 2 the above relation, that is, the rotor surface in 3 should be 200 times the waste water volume in m , furthermore the rotor is submerged to such a extent that the water in the basin has a higher detention time and thus a higher efficiency. This means under practical OMPI IPO conditions that the rotor may have to be submerged to more than half its size, contrary to previous praxis according to which the rotor always has to bring the substrate in contact with the air as well as with the water. In fact, according to the invention the rotor may well be submerged entirely without negative effects on the micro-biological growth conditions. In this, way it is in fact possible to use rotor materials with a specific surface of up to 300 m 2 per m3 which should be compared with the previously 2 3 used materials with a specific area up to 100 m per m . In order to have sufficient oxygen dissolved in the water very simple measurements can be taken according to the invention. At small depths of the rotor shaft no steps at all are necessary since the rotation of the rotor will give a sufficient oxygen content in the water. With greater depths however, a simple way may be to increase the rotational speed of the rotor. When the rotor is totally submerged oxygen of course has to be supplied in a different way. This can be achieved for example by blowing air or oxygen into the waste water. It is also an object of the invention to provide a device with which the method according to the invention can be carried out. This device contains a basin, a bio¬ logical rotating contactor submerged to more than 50 % and with a specific surface of 110-300 m 2 per m3 volume of rotor. If materials with a very high specific surface, for example 120-250 m 2 per m3 rotor is used it may be of great advantage to arrange material towards the center of the rotor so that the specific area is less there in order to allow the water to flow more freely and provide for aerobic conditions there. Further a central part of the rotor may be left without contact material in order to allow an axial flow out of the rotor in these parts. The placing of the rotor shaft below the waste ater basin surface will of course result in new drive solut¬ ions. These may, however, according to the invention with great advantage be solved by on the shaft and in the tank OMPI arranging a big wheel which may be cogged or toothed and with which a driving smaller wheel which may be cogged or toothed can be in contact. In this way the torque load on the primary gear box from the engine can be reduced exten- sively giving on the whole a more inexpensive arrangement. It is very essential that the drive can cope with a great torque resistance as the rotor from time to time may have unsymmetric growth and thus be unbalanced. In this way it is also unnecessary to have the driving torque transmitted by the shaft on the rotor which may thus only have the effect of supporting the rotor. In order to further di¬ minish the stress on the rotor hsaft the rotor can be pro¬ vided with closed air spaces giving a lifting effect on the rotor in the water in order to balance the total weight of rotor and biological growth. If for example the rotating biological contactor ma- terial has a specific surface of 150 m 2 per m3 this means 3 that for every m of the rotor the basin should have the 3 volume, of 0,75 m in order to reach the above mentioned relation between the substrate surface and waste water volume. This means that the rotor should be submerged to 75 % of its volume or slightly passed its center line. The oxygen supply will presumably be sufficient even with normal 2 RPM but in case a tendancy towards anaerobic con- ditions is experienced this may be increased to 3 RPM, resulting in a greater surface more often being subjected to atmospheric oxygen , If in a further example the specific surface of the "} " ** ' rotating biological contactor material is 200 m per m this means that almost the entire rotor has to be submerged in the waste water basin. In this case it may be necessary to provide oxygen by other means than with the rotor itself for example by.blowing air into the basin or adding an oxidizing agent to the water. OMP Λ. WIPO

Claims: CLAIMS 1. Method at biochemical or micro-biological process¬ ing of organic material in for example waste water includ¬ ing the growth of micro biological layers on a substrate surface, which by micro biological growth when it has reached a certain thickness of its own weight is torn away from the substrate surface, is carried away from the surface, c -h a r a c t e r i z e d in that the substrate surface with the layers of biological growth is in constant contact with water or is alternatively brought in contact with the water and that the available substrate surface is 2 3 110-300 m per m preferably 120-250 of the substrate body and that the substrate body or rotor body is submerged so far in the basin that the water gets a longer detention time. 2. Method according to claim 1, c h a r a c t e r ¬ i z e d in that the rotor is submerged to 50-100 % of its volume and preferably to 55-85 % of its total volume. 3. Method according to claim 1 or 2, c h a r a c ¬ t e r i z e d in that the rotational speed of the rotor is chosen higher than normal, that is for example 3 RPM. 4. Method according to any of the claims 1-3, c h a r a c t e r i z e d in that oxygen in some form is added to the water by other means than the rotor. 5. Device to carry out the method according to claim 1, c ha r a c t e r i z e d in that it includes a rotat¬ ing biological contactor submerged in a basin to such an extent that the rotor is not by-passed by the water and that optimal conditions between waste water volume and biological contact rotor surface is obtained. 6. Device according to claim 5, c h a r a c t e r¬ i z e d in that the rotor body is submerged 50-100 % of its total vol e preferably 55-85 % . 7. Device according to claim 5 or 6, c h a r a c ¬ t e r i z e d in that the waste water is supplied with additional oxygen by other means than the rotor and its movemen . OMPI 8. Device according to claim 5, 6 or 7, c h a r a c- t e r i z e d in that the rotor is given a higher RPM than normal, for example 3 RPM. 9. Device according to one or several of the claims 5-8, c h a r a c t e r i z e d in that air enclosures are contained in the rotor giving a lifting effect on this, diminishing their stress on the rotor axle. 10. Device according to one or several of the claims 5-9, c h a-r a c t e r i z e d in that the rotor is pro¬ vided with a large diameter wheel that is cogged or toothed in contact with a driving smaller wheel that may be cogged or toothed respectively. 11. Device according to one or several of the claims 5-10, c h a r a c t e r i z e d in that the rotor has a greater specific area per volume, at the outer periphery and a lower specific area in the center in order to improve internal water flow. 12. Device according to one or several of the claims 5-11 , c h a r a c t e r i z e d in that spiral wound rotor material is fastened with strips in ' order to provide pre-stressed conditions. OMPI . . WIPO

Inventors: HALLEN L
Applicants: HALLEN L, NORDISKA VATTENPROJEKT AB NOVA, NORDISKA VATTENPROJEKT AB
Application year: 1980
Main classification: C02F3
IPC codes: C02F3