GB2112768A

GB2112768A - Microbiological waste water purification

Info

Publication number: GB2112768A
Application number: GB08234216A
Authority: GB
Inventors: Toshio Kikuchi; Yasunobu Hirama; Takao Hashimoto; Isao Takemura
Original assignee: Ajinomoto Co Inc
Current assignee: Ajinomoto Co Inc
Priority date: 1981-12-04
Filing date: 1982-12-01
Publication date: 1983-07-27
Also published as: JPS5898189A; GB2112768B; MY8600046A

Abstract

A method for the aerobic purification of waste water whereby the waste water and aerobic microorganisms are introduced into the first zone or compartment of an aeration tank comprising three such zones (1,2,3) connected in series, and that the aeration in the middle zone or compartment (2) is carried out to a greater extent than in the first zone or compartment (1), and that the aeration in the last zone or compartment (3) is carried out to a lesser extent than in the first zone or compartment (1). <IMAGE>

Description

SPECIFICATION Microbiological waste water purification This invention relates to improvements in the purification of waste water such as industrial waste water or sewage, by decomposing the organic matter contained in such waste water by the use of aerobic microorganisms.

Waste water purification by the use of aerobic microorganisms has been developed in various ways and embodied, for example, in the so-called activated sludge treatment. An aeration tank in which vigorous aeration is carried out to facilitate the microbiological oxidative decomposition of organic matter is needed for the activated sludge treatment. A conventional aeration tank usually has no partitions in it, and the aeration in it is uniform throughout.

In view of the fact that the microbiological oxidative decomposition of organic matter takes place by (1 ) the adsorption of organic matter on the microorganisms, (2) the assimilation of organic matter by the microorganisms, and (3) the regeneration of the microorganisms, we have studied the relationship between the removal rate (i.e. decomposition rate) of organic matter and the extent of aeration in the various zones of the aeration tank.As a result, we have found that, for example, the capacity for waste water purification may be remarkably increased if the extent of aeration in the middle zone (i.e. the zone where the assimilation of organic matter by the microorganism takes place) is increased while the extent of aeration in the last zone (i.e. the zone where the regeneration of the microorganisms take place) is decreased, and that an increased capacity may be attained by a somewhat reduced overall extent of aeration.

Thus according to the present invention, there is provided a method for the microbiological purification of waste water, which comprises introducing the waste water into an aeration tank, decomposing the organic matter contained in the waste water by the use of aerobic microorganisms, and draining the treated waste water from the tank; wherein the aeration tank comprising three zones or compartments connected to one another in series, wherein the waste water and aerobic microorganisms are introduced into the first zone or compartment, wherein the aeration in the middle zone or compartment is carried out to a greater extent than in the first zone or compartment, and wherein the aeration in the last zone or compartment is carried out to a lesser extent than in the first zone or compartment.

In accordance with this invention, the adsorption of organic matter, the oxidative decomposition of organic matter, and the regeneration or refreshment of the microorganisms are carried out in the different zones or compartments, i.e. the microbiological functions of decomposing organic matter are carried out in different places. According to this invention, the ability or properties of the microorganism are strengthened or improved.

Preferably, the aerobic microorganisms are ones which have been freshly separated from sewage or from the last zone of the tank.

An apparatus for use in this invention comprises an aeration tank, preferably having means for separating the microorganisms.

The tank must have three zones or compartments. The zones or compartments may be formed by providing the aeration tank with two partitions. Instead, for example, three separate aeration tanks (or unit tanks) may be connected with one another in an appropriate way to form an aeration tank for use in this invention. In the latter case, the three separate tanks form three zones or compartments.

When the three compartments are formed by using two partitions, each partition extends from the base of the tank to enable the waste water to overflow them. Alternatively, one of the two partitions may have an opening near the base of the tank through which the waste water flows instead of overflowing. When an aeration tank is formed by the use of three unit tanks, two neighbouring unit tanks may be connected with a pipe at their upper part. Alternatively, one pair of two neighbouring unit tanks may be connected at their upper part and the other pair at their lower part. Furthermore, all of the zones or compartments of the unit tanks need not be at the same level. For example, they may be arranged in staircase form, allowing the waste water to overflow.

The volume ratio of the three zones or compartments is preferably about 25-30% (first zone); about 40-55% (middle zone) :about 20-30% (last zone).

Each zone or compartment may be subdivided.

Various known means for pre-treatment or after-treatment may be connected to the tank, if desired.

The first zone or compartment of the three zones or compartments is equipped with an inlet for introducing waste water, and preferably with a means for receiving microorganisms recycled from the last zone or compartment.

Each zone or compartment is equipped with an aeration means or an air distributor. The aeration means may be a known means used for a known aeration tank.

One of the features of this invention lies in the manner or aeration, i.e. the extent of aeration in the respective zones or compartments are different. In greater detail the first zone or compartment is for the adsorption of organic matter on the microorganisms and air is distributed in this zone or compartment in a smaller amount than in a conventional aeration tank. The middle zone or compartment is for the oxidative decomposition by the microorganisms or organic matter and air is distributed in this zone or compartment in 1.5 to 2 times the amount of air used in a conventional aeration tank. The last zone or compartment is for the regeneration of the microorganisms which have been used for decomposing the organic matter and air is distributed in this zone or compartment in 1/3 to 1/4 times the amount of air used in a conventional aeration tank.If the aeration is to be controlled by the amount of dissolved oxygen, aeration may be carried out to attain about 0.2 to 0.5 ppm of dissolved oxygen in the first compartment or zone, about 1 to 2 ppm in the middle compartment or zone and about 0.5 to 0.7 ppm in the last compartment or zone. In this case, the ratio of the extent of aeration distributed in the three zones or compartments is about 3(first):6(middle): 1 (last) to 4(first): 5(middle) :1 (last), and the overall extent of aeration may be reduced to about 50 to 70% of conventional aeration amounts.

The microorganisms may be separated from the treated waste water drained from the last zone or compartment. Before separation of the microorganisms, the waste water may, if desired, be subjected to an appropriate treatment such as a treatment to coagulate the microorganisms. The separation may be carried out in any conventional manner, e.g. by separation with a settling tank or by the use of a centrifugal separator. Part of the separated microorganisms are preferably recycled to the first zone or compartment for reuse. The remainder may be used, e.g. as a fertilizer, or may be subjected to incineration.

In this invention, there may be used those aerobic microorganisms which are usually used to purify various kinds of waste water. Examples of such microorganisms include yeasts such as Trichosporon cutaneum CBS 2466 and Trichosporon fermentum CBS 2529, in addition to ordinary activated sludge bacteria used to purify various kinds of waste water, or microorganisms separated from such bacteria and cultured.

The method of this invention may of course be applied to any waste water so long as it can be purified with aerobic microorganisms. For example, sewage and waste water resulting from the processing of fermentation broths of amino acids such as glutamic acid, may be treated according to this invention.

In accordance with this invention, aeration is, in view of the decomposition mechanism of organic matter by microorganisms, controlled in a manner such that efficient use is made by the microorganisms of the oxygen contained in the air used. This control can almost double the ability of the microorganisms to decompose organic matter, i.e. the capacity of a given apparatus to purify waste water. Further advantages achieved by this invention are that waste water purification may be operated stably, and that, since the efficiency of flocculation and settling of the microorganisms is increased, the microorganisms may be separated more easily.

A conventional aeration tank may, by simple modification, e.g. by providing it with partitions, be changed to an aeration tank for use in this invention. The invention may be easily carried out accordingly. This is a further advantage of this invention.

This invention has many great advantages and is, accordingly, very important from the commercial point of view.

For a better understanding of the invention, reference will now be made by way of example to the drawings which are schematic representations of aeration tanks for use in the invention.

Figure 1 shows an aeration tank divided into three compartments 1,2 and 3 by means of partitions 4 and 5.

The tank has an inlet 6 for the waste water to be purified, an inlet 7 for aerobic microorganisms recycled from the last compartment 3, and an outlet 8 for the treated waste water, the outlet 8 leading to a means for separating the microorganisms. The waste water overflows from compartment 1 to compartment 2, and then to compartment 3.

In the alternative embodiment shown in Figure 2, three separate tanks (unit tanks) 1, 2 and 3, connected by pipes 9, are used.

In the alternative embodiment shown in Figure 3, the partition 4 has an opening at its base, for allowing waste water to pass from the compartment 1 to the compartment 2, and then to compartment 3.

In the alternative embodiment shown in Figure 3, the partition 4 has an opening at its base, for allowing waste water to pass from compartment 1 to compartment 2.

In the alternative embodiment shown in Figure 4, tanks 1 and 2 are connected by a pipe 9 at their upper part, and tanks 2 and 3 are connected by a pipe 9 at their lower part.

In the alternative embodiment shown in Figure 5, the tanks 1, 2 and 3 are arranged in the form of a cascade.

The invention will now be illustrated by the following Examples.

Example 1 An aeration tank as shown in Figure 6, having the dimensions, in millimetres, given in Figure 6, was used.

The aeration tank (i.e. each compartment) was filled with factory waste water mainly composed of waste water resulting from the processing of amino acid fermentation broths and having a COD value of 1500 ppm.

To the mass in each compartment was then added 4000 ppm of activated sludge bacteria which had been domesticated for 7 days in the same aeration tank, using the same waste water.

Thereafter, the same factory waste water continued to be introduced into the first compartment for 30 days under the loading conditions given in Table 1, the MLSS being maintained at 4000 rpm, part of the microorganisms being recycled from the last compartment, the temperature being maintained at 280C and the pH being adjusted to 6.5. All through that period, air was introduced (or distributed) in amounts of 7.5 litres, 15 litres and 2.5 litres per minute into the first, middle and last compartments, respectively. Other operation conditions and the results are listed in Table 1.

For the purpose of comparison, the same operation was repeated except that the same aeration tank but with with no partitions was used and that air was introduced into the tank in an amount of 50 litres per minute. The results are shown in Table 1.

TABLE 1 This invention Prior art (a) Introduction of waste water (m3/day) 1.0 0.7 (b) MLSS* (g.m3) 4000 4000 (c) COD space loading (kg/m3.day) 1.5 1.0 (d) COD value after treatment (g/m3) 150 250 (e) Removal rate of COD (%) 90 83 * Mixed Liquor Suspended Solid Example 2 An aeration tank as shown in Figure 7, having the dimensions, in millimetres, given in Figure 7, was used.

The aeration tank (i.e. each compartment) was filled with factory waste water mainly composed of waste water resulting from the processing of amino acid fermentation broths and having a COD value given in Table 2. To the mass in each compartment was then added 4000 ppm of activated sludge bacteria which had been domesticated in the same factory waste water.

Thereafter, the factory waste water continued to be introduced into the first compartment for 30 days under the loading conditions given in Table 2, the MLSS being maintained at 4000 rpm, part of the microorganisms being recycled from the last compartment, the temperature being maintained at 28 C and the pH being adjusted to 6.5. All through that period, air was introduced in amounts of 45,90 and 15 Nm3 per minute into the first, middle and last compartments, respectively. Other operation conditions and the results are listed in Table 2.

For the purpose of comparison, the same operation was repeated except that the same aeration tank but with no partitions was used, and that air was introduced into the tank in an amount of 250 Nm3 per minute.

The results are shown in Table 2.

TABLE 2 This invention Prior art (a) Introduction of waste water (m3/day) 4000 2400 (b) COD value before treatment (g/m3) 1500 1500 (c) MLSS (g/m3) 4000 4000 (d) COD space loading (kg/m3.day) 1.2 0.7 (e) COD value after treatment (g/m3) 105 108 (f) Removal rate of COD (%) 93 91 As is evident from the above Tables, in accordance with embodiments of this invention, waste water may be treated or purified in as many as 1.5 to 1.7 times those amounts which may be attained by prior-art methods, even with an overall aeration of 50% to 60% of that in the prior-art methods. Further, higher COD removal rates may be attained by the method of this invention than by prior-art methods.

Claims

1. A method for the microbiological purification of waste water, which comprises introducing the waste water into an aeration tank, decomposing the organic matter contained in the waste water by the use of aerobic microorganisms, and draining the treated waste water from the tank; wherein the aeration tank comprising three zones or compartments connected to one another in series, wherein the waste water and aerobic microorganisms are introduced into the first zone or compartment, wherein the aeration in the middle zone or compartment is carried out to a greater extent than in the first zone or compartment, and wherein the aeration in the last zone or compartment is carried out to a lesser extent than in the first zone or compartment.

2. A method according to claim 1, wherein the ratio of the extent of aeration in the first zone or compartment to the extent of aeration in the middle zone or compartment to the extent of aeration in the last zone or compartment is from 3:6:1 to 4:5:1.

3. A method according to claim 1 or 2, wherein the volume of the first zone or compartment is from 25 to 30 parts by volume, the volume of the middle zone or compartment is from 40 to 55 parts by volume and the volume of the last zone or compartment is from 20 to 30 parts by volume, the total volume of the three zones or compartments being 100 parts by volume.

4. A method according to any of claims 1 to 3, wherein part of the microorganism is recycled from the last zone or compartment to the first zone or compartment.

5. A method according to any of claims 1 to 4, when carried out in an aeration tank substantially as shown in any of Figures 1 to 7 of the drawings.

6. A method according to claim 1, substantially as described in either of the foregoing Examples.