WO1986005770A1

WO1986005770A1 - An apparatus for the purification of water, waste water in particular, by a biological oxidation method

Info

Publication number: WO1986005770A1
Application number: PCT/FI1986/000030
Authority: WO
Inventors: Vilho Dunder
Original assignee: Insinööritoimisto Lujari Oy
Priority date: 1985-04-04
Filing date: 1986-03-25
Publication date: 1986-10-09
Also published as: SU1479003A3; NO159265B; ES553679A0; EP0258228A1; SE461146B; NO159265C; NL8620108A; DE3690150T1; GB2194526A; GB2194526B; FI80070C; FI851369L; NO864856L; ES8701694A1; GR860872B; GB8723271D0; NO864856D0; ATA903786A; SE8703835L; FI851369A0

Abstract

The apparatus comprises a biorotor (2) preferably formed by a sector modules (20), within which biorotor a granular medium (11) is provided to form a substrate for the biomass, said medium simultaneously serving as a hydraulic bearing during the rotation of the rotor partly immersed in water so that it holds up the entire biorotor structure as well as the active biomass.

Description

An apparatus for the purification of water, waste water in particular, by a biological oxidation method

The invention relates to an apparatus for the purification of water, waste water in particular, by a biological oxidation method. Biological waste water treatment is based on the principle that the natural bacterial activity ispromoted by agitation and intro¬ duction of oxygen into the waste water, usually by aeration and by providing a suitable substrate for the oxidation bacteria.

A biorotor is a slowly rotating cylinder which is horizontally positioned and partly immersed in the water to be treated. As the rotor rotates slowly, a honeycomb assembly alternately sinks in the water/waste water so as to get the bacteria moist and rises up in the air wherein there is plenty of oxygen available for an efficient bacterial activity to take place in a thin film of water. This promotes the interchange of water and air into the biomass carrying out the oxidation as well as the decomposition of organic waste matter taking place under natural conditions. The internal structure of the cylinder is intended to provide the widest poss¬ ible area for the bacteria to get attached to.

In known biorotors, the biomass substrate is honeycomb-like and made of plastic or metal. The manu¬ facture of the honeycomb assembly requires expensive manufacturing methods. Because the honeycomb assembly also serves as a load-bearing structure, this restricts increasing of the area of the biomass substrate, which would require an extremely finely built honeycomb assem¬ bly. The rotor is usually mounted in bearings at the ends thereof and the rotation is carried out from one end by means of a chain or gear assembly. The rotational power required by the rotor is high and requires heavy driving machineries. As the rotor is supported from the -ends thereof, a steady central shaft has to be provided and the size of the rotor cannot be increased unlimitedly.

In addition, it is known to use air blowing into the water below the biorotor, whereby a circulating motion of the waste water mass is effected and, conse¬ quently, rotation of the rotor. In practice this process is made more efficient by air cups provided in the rotor, which air cups provide an additional turning moment for the biorotor. A disadvantage of this kind of air blow drive, however, is the high energy requirement of the air pumping.

The biggest disadvantage of existing biorotors is perhaps the accumulation of biomass in the completely static honeycomb assembly. This results in a decrease in the active area, which reduces the efficiency of purifi¬ cation, and in overloading of the supporting structures of the rotor itself as the mass to be elevated continu¬ ously increases. In practice, collapses of the honey¬ comb assemblies have occured frequently. For the elimina¬ tion of this problem, firm and expensive honeycomb struc¬ tures must be provided or a mechanical cleaning of the honeycomb structure has to be arranged or the honeycomb must be replaced at short intervals.

The biorotor according to the invention avoids the disadvantages of existing biorotors and at the same time increases the purifying efficiency. This is achieved by means of the charachteristics disclosed in the claims.

The invention is advantageous mainly in that it is simple in construction, the honeycomb assembly,' being replaced with a light granular material. This material forms a so called hydrostatic bearing which eliminates the deflection of the central shaft and enables manufac¬ ture of rotors having a greater diameter and length than previously. At the same time, a manifold substrate for the biomass per unit volume is obtained in comparison with previously known solutions. When the grains are chafed against each other, an excessive growth of the thickness of the biomass layer is prevented as well as the disadvantages caused thereby. A simple circulation of the waste water and the purified water through the rotor drum and the separation of solid substances out of the active biomass is effected by theuse of a screen- like surface material of the rotor. The rotation of the drum by means of the incoming water saves driving power.

It is of essential importance that a rotor having a modular structure can be easily manufactured in dif¬ ferent sizes. The grain size of the granular material, i.e. the inert medium, can be chosen to suit the pur¬ pose in each particular case, and, if required, it can be altered in a simple way, which is not possible with previously known solutions. The biobeds used in minor water treatment units can also be replaced by a substrate of a granular material for the biomass.

The invention will be described in the following by means of one embodiment with reference to the draw¬ ing, wherein

Figure 1 is a general view of a biorotor,

Figure 2 is a cross-section of an apparatus according to the invention, and

Figure 3 illustrates a sector module of the appa¬ ratus according to the invention.

Figure 1 is a general view of a basin 1 of a water treatment plant and a biorotor 2 according to the invention which floats within said basin held up by a loose medium contained in the rotor. Water to be: purified is passed through nozzles 4 of a feeding pipe 3 to a tooth ring 5 of the biorotor, whereby the water effects the turning moment rotating the rotor. This principle is previously known from water mills but the difference lies in that here the water is simultaneously led inside the rotor through a screen-like outer jacket 6 of the 86/05770

biorotor. After the water has been passed through the biorotor, it is further passed through-a central tunnel 8 to another end 7 of the rotor, wherefrom it can be moved on for further treatment into a subsequent rotor or, if it is completely purified, removed from the process.

As illustrated in the cross-sectional view of Figure 2, the biorotor according to the invention is formed by sector modules 20 which are more closely described in Figure 3. The screen-like outer jacket 6 can be made of a perforated sheet, a wire material, or the like. It is essential that the screen-like jacket effects a prescreening and separation of e.g. fibrous particles outside of the biorotor promoting biological oxidation. In this way it is possible to recover the so called flour contained in the waste waters of paper mills, for instance. In practice this can be effected e.g. by means of resilient brush-like scrapers 19 which, in Figure 2, are positioned above a trough 12 dis¬ charging superfluous water.

As appears from Figure 2, the water fed to the circumference of the rotor through the feeding pipes 3 and the nozzles 4 trickles through the jacket 6 of the tooth . ring 5 on the loose grains 11 , wherefrom it further trickles slowly downwards. Such loose grains can consist of e.g. cork or plastic. Because the feed¬ ing height is above the water surface of the basin 1 , a turning moment rotating the rotor is created. When the loose grains sink in the water to be treated, they are completely moistened with water and when they rise up on the opposite side the superfluous water flows away from between the grains, which brings the moistened biomass on the surface of the grains into contact with air over the entire surface thereof. During each rota¬ tion of the rotor, a complete interchange of the water to be treated and the air is effectedthroughout the biomass, which ensures the best possible operational efficiency. Furthermore, the rotor mixes the water to be treated while it rotates.

Because the sectors 20 are not completely filled with the loose medium 11 , the grains move therein during the rotation of the rotor and are chafed against each other, which effects self-purification as a result of which the biomass cannot grow excessively in thickness so that the system would be blocked. As the granular material is lighter than water, a buoyancy is crea¬ ted which holds up both the granular material 11 and the entire structure of the biorotor. So the loose medium 11 serves as a hydraulic bearing of the biorotor for the whole system, thus providing an even supportion over the whole ^'length of the rotor. Consequently, the biorotor can be constructed very light and the drums can be large in diameter and of any length.

Also the structure of the central tunnel 8 appears from the Figure 2 as well as the function of the troughs 9 positioned therein. A spiral-like structure is obtained by mounting said troughs 9 in a slanting posi¬ tion with respect to the longitudinal shaft of the rotor, whereby the water trickling into the center is displaced towards the outlet end 7 of the biorotor (Figure 1). Alternatively, a continuous circulation of the water to be treated can be arranged by providing the central tunnel 8 with closed ends and by pumping water from the outlet end 7 to a subsequent stage of the process. The wall 10 of the central tunnel of the rotor can be made of a similar screen-like material as the outer jacket 6.

By varying the grain size of the granular material 11, the amount of the active biomass in a volume unit can be effectively adjusted according to the requirement in each particular case. For example, when a grain size having a diameter of about 8 mm is used, the active biomass area obtained is as large as 500 m'Vrrr and even mpre, which is more than threefold in comparison with the honeycomb structures of previously known biorotors. By decreasing the grain size the active area can be further increased. In this way it is possible to operate the biorotor even in very small water treatment instal¬ lations, if required. On the other hand, large and effi¬ cient biorotors can be constructed in high capacity plants.

Figure 3 illustrates a sector module 20 of the biorotor according to the invention. This is formed by end walls 14, corner supports 13, toothed supports 15, bottom supports 18, a jacket 6, intermediate walls 17 and a bottom wall 10. The end walls 14, the intermediate walls 17 and the bottom wall 10 can be made of a material permeable to water, such as e.g. a wire cloth, or, if desired, the intermediate walls 17 and the end walls 14 can be solid. The sector is for a major part filled with the loose medium 11; however, a free space 21 (Figure 1) must be left so that the loose grains can move and be chafed against each other. The chafing and mutual mixing of the grains can, if required, be made more effi¬ cient by means of agitator plates 16 secured inside the sectors. By detaching the end walls 14 of the sector from the corner supports 13, the entire sector can be detached for maintenance or for the replacement of the loose medium 11, for instance. Naturally, the biorotor according to the invention can be constructed also otherwise than by the use of modules. Because there is no stationary honeycomb assembly, the sector modules or the like structures can be easily constructed in diffe¬ rent sizes or in different shapes whenever this is necessary. The loose medium used as a substrate for the biomass is suitable for any cross-sectional shape of the biorotor.

The biorotor according to the invention can be used also for the purification of flue gases or other gases or for odour removal using either a biological or a chemical method. The flue gases or any other gas to be purified is passed into the central tunnel 8 of the rotor, wherefrom it is conveyed through the loose medium 11 , thereby reacting with the liquid film of the medium. In a biological method, a biological oxidation takes place in the surface film of the loose medium and a liquid, e.g. an alkaline solution upon which the rotor floats, neutralizes the pH-value so that the biological process is not choked. In a chemical method, the flue gases react chemically with the liquid contained in the surface film of the loose medium. Both methods utilize the large area obtained by means of the loose medium for the reaction to take place as well as the self- purification of. the rotor as the grains are chafed against each other.

It is obvious that the biorotor according to the invention and the loose medium contained therein can also be used for other purifying purposes of water and gas as described above.

Claims

' Claims:

1. Apparatus for the purification of water, waste water in particular, by a biological oxidation method, said apparatus comprising a biorotor (2) partly immerse- able in the water to be treated, which biorotor during its rotation alternately sinks a substrate of the bio¬ mass in the water and lifts it up in the air to promote the activity of the active biomass, c h a r a c t e ¬ r i z e d in that a granular medium (11) used as a substrate for the biomass is provided inside the bio¬ rotor (2) , said granular medium simultaneously serving as a hydraulic bearing which holds up the entire bio¬ rotor structure as well as the active biomass.

2. Apparatus according to Claim 1, c h a r a c ¬ t e r i z e d in that the biorotor (2) preferably consists of sector modules (20) , the granular medium (11) being positioned within said modules.

3. Apparatus according to Claim 1 and 2, c h a ¬ r a c t e r i z e d in that an outer jacket (6) of the biorotor (2) is made of a perforated material, such as a wire cloth or the like.

4. Apparatus according to Claims 1 to 3, c h a ¬ r a c t e r i z e d in that nozzles (4) are provided for the rotation of the biorotor (2) , through which nozzles water is passed to a rotor tooth ring (5) .

5. Apparatus according to Claims 1 to 4, c h a ¬ r a c t e r i z e d in that troughs (9) forming a screw line are provided in a central tunnel (8) of the rotor (2) for the removal of the purified water.

6. Appparatus according to Claims 1 and 2, c h a ¬ r a c t e r i z e d in that the granular medium (11) preferably consists of cork, plastic or the like.