Bacteria Supporting Medium, Especially Useful for Pretreatment of Waste Water

This invention relates to a bacteria supporting medium, or an object on which to load bacteria, and more particularly relates to such a medium of a special shape.

Polluted water can be purified by using such natural substances as sand or pebbles or by using an artificial filter comprising charcoal, filter paper, sponge or the like. In recent times we also use bacteria for that purpose. That is, we can encourage the growth of bacteria in a treating tank or introduce them from outside into the tank in order for them to attack the organic material in the polluted water and decompose it quickly. Of the various bacteria, Thiobacillus ferrooxidans is very unique. This bacteria oxidize ferrous iron ions in the water to ferric iron ions. The bacteria are called "chemoautotrophic bacteria" in microbiology. In addition to the above function, it oxidizes sulfur to sulfuric acid. This is a geomicrobiologically important function.

On the other hand, in the modern world the waste water discharged from factories, mines, refineries, and other industrial places, as well as from households, reaches a vast quantity. So sewage treatment is a very serious social problem in most need of attention. In particular, the waste water from mines contains, among others, such metals as iron, copper, and zinc. Then, it is economically important whether the iron contained in it is mostly ferrous iron or ferric iron. Where the iron is mostly ferrous iron, slaked lime is usually used to neutralize the water to pH 7 or 8, so that the ferrous iron settles. However, where the iron is ferric iron, ph 3 or 4 is sufficient to settle the iron and, therefore, fine powder of limestone can be used to neutralize the water to that value. Then, since limestone is about a third or fourth the price of slaked lime, changing the iron to ferric iron is an expedient step for an economical treatment of polluted water where the iron contained in it is ferrous iron. As described before, bacteria called "Thiobacillus ferrooxidans" oxidize ferrous iron to ferric iron, and so it has been in use for an economical treatment of polluted water containing a large amount of ferrous iron. The bacteria are loaded on a wool-like, netlike, or scrub-brush-like bacteria-supporting medium, and a number of such media are introduced into an oxidizing tank.

The conventional supporting medium, however, has a drawback that its surface area on which to load the bacteria is relatively small. Another drawback is that the solids in waste water are apt to get into the medium and stay there. A third drawback is that relatively large spaces, into which no portions of the media project, may exist between the media and, therefore, the polluted water may not be treated sufficiently. A fourth drawback contrasts with the third one. That is, if such flow passages are not formed between the media, then on the contrary the media may come into contact with each other at their surfaces. The fourth drawback also results in insufficient treatment of the water.

Accordingly it is the object of the invention to provide a bacteria-supporting medium which is free from the foregoing drawbacks of the conventional medium.

FIG. 1 shows a portion of a bacteria-supporting medium of the invention;

FIG. 2 shows the whole of the supporting medium;

FIG. 3 is an enlarged plan view of a portion of the supporting medium;

FIG. 4 shows a portion of the medium as viewed from its inner circumference toward its outer circumference; and

FIG. 5 shows plural media in a treating tank.

As shown in FIG. 2, a bacteria-supporting medium of the invention has a spiral shape. It is made of synthetic resin. FIG. 1 shows a portion of the medium. As clearly shown in FIG. 1, the medium comprises numerous winding, or S-shaped, portions. All the S-shaped portions are continuous with each other, and are defined at their outer boundaries by a continuous winding line S. As clearly shown in FIGS. 1 and 3, the medium has a central opening K. Each S-shaped portion extends in a radial direction.

Each S-shaped portion includes an upwardly-expanding part R1 and a downwardly-expanding part R2. Each expanding part is tapered inwardly. As best shown in FIG. 4(a), one portion O of the upwardly-expanding part R1, as well as one portion O of the downwardly-expanding part R2, slightly bulges out. At the same time, as shown in FIG. 4(b), if the continuous winding line S is divided by an inner circumferential line 1c, its upper and lower segments are offset slightly.

In use, bacteria, such as Thiobacillus ferrooxidans, are loaded on the medium, and plural such media are put into a treating tank 2 (FIG. 5). Then, polluted water to be treated is supplied into the tank 2. The medium of the invention has a treating surface area more than 10 times as large as the conventional medium. So the water is treated much more effectively. In addition, it will be appreciated that the medium of the invention has such a shape as does not allow solids in the water to accumulate in quantities in the medium. Also, since the pitch of its spiral shape is relatively small, flow passages not interrupted by anything are not readily formed between the media and, therefore, the water is treated sufficiently. At the same time, for the same reason, if the media move very close to each other, flow passages sufficiently large to treat the water remain.

After treatment in the tank 2, the water can be further treated with, for example, a suitable neutralizing agent.