GB1586949A - Two-stage biological treatment of effluent - Google Patents

Description

(54) TWO-STAGE BIOLOGICAL TREATMENT OF EFFLUENT (71) We, BAYER AKTIENGESELL SCHAFT, a body corporate organised under the Laws of Germany of 509 Leverkusen, Germany, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particular-.

ly described in and by the following statement: This invention relates to a two-stage biological treatment of effluent and, in particular, to a process for the biological treatment of effluent which, in addition to readily biodegradable substances. contains substantially non-biodegradable substances.

Reduction of the biochemical oxygen demand (BODs) is not normally a significant problem in a biological treatment plant using the activated sludge process. In many cases, BOD- elimination rates of more than 90% are obtained. By contrast. substantially non-biodegradable substances are only partially eliminated, for example by adsorption on the activated-sludge flake. The COD (chemical oxygen demand) elimination rates in the activated sludge process generally amount to only between 5() and 80%, depending upon the type of effluent to be treated.

The residual COD in the discharge of an activated sludge treatment plant can be at least partly eliminated by adsorption on active carbon. This process involves high running costs attributable to the thermal reactivation of the active carbon.

We have sought further to reduce the COD-content in the discharge of a biological treatment plant.

Accordingly. the present invention provides a process for the biological treatment of effluent which. in addition to readily biodegradable substances. contains substantially non-biodegradable substances. wherein at least part of the readily biodegradable material is degraded in an aerobic stage, wherein the resulting aerobically treated effluent is subjected to a semi-aerobic or anaerobic treatment on an inert supporting material, and wherein readily biodegradable effluent having a BODS - content of at least 25 mg/l is introduced during this semiaerobic or anaerobic treatment.

We have surprisingly found that the COD-content in the discharge of an aerobic biological treatment plant can be further reduced by adding a second stage operated under semi-aerobic or anaerobic conditions.

In this second stage, an inert supporting material, for example, pumice stone, slag, activated aluminium oxide or macroporous adsorber resins, preferably active carbon, is used for the microorganisms. In the second stage, the organic ingredients which are substantially non-degradable under aerobic conditions are only degraded in the presence of readily biodegradable compounds.

In one embodiment of the process according to the present invention, therefore, a component stream of the untreated effluent is branched off before the aerobic treatment and directly added to the effluent to be treated semi-aerobically or anaerobically which result from the aerobic treatment stage. The component stream should amount to between 5 and 50goo by volume and preferably to between 10 and 30% by volume, based on the aerobically pretreated effluent present in the semi-aerobic or anaerobic second treatment stage.

In another embodiment of the process according to the invention. a concentrated effluent from a source other than that from which the effluent to be aerobically treated emanates may also be added to the already aerobically treated effluent intended for the semi-aerobic or anaerobic second treatment. Similarly. soluble waste products which predominantly contain readily biodegradable substances. such as communal sewage. for example. may be added to the effluent intended for the semi-aerobic or anaerobic treatment which still contains the aerobically substantially non-degradable compounds.

According to the present invention, it is essential for the effluent added in the semi-aerobic or anaerobic treatment stage (which effluent did not go through the first stage) to have a BOD5-content of at least 25 mg/l and preferably of at least 50 mug/1.

The temperature in the semi-aerobic or anaerobic treatment stage is generally in the range from 10 C to 600C while the pH-value is generally in the range from 5 to 10 and preferably in the range from 6 to 9.

Suitable inert supporting materials for the microorganisms of the semi-aerobic or anaerobic effluent treatment stage are porous stones (0.5 to 3.0 mm in diameter), slag, activated aluminium oxide (grain size 0.05 to 3.0 mm) or macroporous adsorber resins for example, styrene-divinyl benzene and acrylic acid-divinyl benzene resins or active carbon, preferably in granulated form. Granulated active carbon is preferably used in the process according to the invention.

In the context of the present invention, the expression "semi-aerobic effluent treatment" has the following meaning: After leaving the reactor filled with inert supporting material. the effluent has an oxygen content of 0 to 2 mg 02/1. The microorganisms- which participate in the biodegradation process may be either aerobic or anaerobic.

In the context of the invention, the expression anaerobic effluent treatment" has the following meaning: On leaving the reactor filled with an inert supporting material the effluent contains no 02 The biodegradation process involves: optional and obligatory anaerobic microorganisms with fermentation metabolism and/or nitrate breathers, and/or sulphate breathers.

In one particular embodiment of the process according to the invention. it is possible to use the supporting material for the semi-aerobic or anaerobic effluent treatment in the form of a fluidised bed.

The supporting material is preferably arranged in column form. the effluent being introduced at the foot of the column and the rate of flow of the effluent added in this stage being permanentlv or periodically regulated so that the filter bed with the effluent approaching from below expands by 5 to 5()% of its volume. In one variant of this process. the expansion of the fixed bed approached from below can be obtained by recirculating the effluent.

The residence time of the effluent in the semi-aerobic or anaerobic stage may amount to between 10 minutes and 10 hours and preferably amounts to between 1 and 5 hours. The COD charge per unit volume in the semi-aerobic or anaerobic stage is adjusted to values of from 0.1 to 5 kg of COD/m3 per day and preferably to between 0.5 and 2 kg of COD/m3 per day.

In another embodiment of the process according to the invention, chemically bound oxygen which can react with the microorganisms, for example oxygen in the form of hydrogen peroxide, nitrate and sulphate, may be added to and mixed with the aerobically pretreated effluent either before it enters or during its treatment in the semi-aerobic or anaerobic stage. This addition is made in a quantity such that the chemically bound oxygen makes up 20% to 200% and preferably 40% to 170% of the COD-content of the effluent to be semiaerobically or anaerobically treated.

One embodiment of the process according to the present invention is further illustrated with reference to the accompanying schematic flow chart.

Effluent which contains readily biodegradable and substantially nonbiodegradable substances flows through effluent input 1 into a preliminary clarification tank 2 where the sediment formed is separated off. Preclarified sludge is removed from the circuit through conduit 3.

The effluent leaving the preliminary clarification tank 2 is then introduced into an activated-sludge tank 6 where the aerobic treatment is carried out. A component stream 4 is branched off to by-pass the activated sludge tank 6 and is directly introduced into a semi-aerobic or anaerobic stage 11. After the aerobic treatment in the activated sludge tank 6, the aerobically treated effluent is introduced together with the activated sludge into a final clarification tank 7 from which aerobically formed excess sludge is removed through conduit 8 and recycle sludge returned through conduit 5 to the aerobic section. After the activated sludge has been separated off, the aerobically pretreated effluent is introduced through conduits 9 (discharge from the first stage) and 10 (input for second stage) into the second semi-aerobic or anaerobic biological stage. being mixed before-hand with the effluent of component stream 4. The aerobically treated effluent delivered from 7 through 9 mainly contains only substantially non-biodegradable substances. Excess sludge is removed from the second stage through conduit 12 and the purified effluent is run off through exit means 13. In one variant of this embodiment effluent may be recirculated as indicated by the chain line 14.

The process according to the invention is illustrated by the following Examples.

Example I An effluent from a textile dyeing plant which, in addition to dye, contained a non-ionic surfactant, sodium sulphate and acetic acid, was adjusted to pH 7 and treated in a laboratory activated sludge plant with an aeration time of 4 hours. No change in colour occurred.

After a test duration of 5 weeks, the following active carbon column had produced a decolouration level of 55. In a plant operated in parallel, in which 20% of the input of aerobians together with nitrate and sulphate breathers (active carbon column with obligatory and optional anaerobic bacteria) were directly delivered to the second stage, the decolouration level had reached 99% after the same period.

Example 2 Effluent from the chemical industry was treated in a semi-industrial activated sludge plant with an aeration time of It hours. The analytical data of the input to the first stage was as follows: COD = 1810 mg/l BOD5 = 837 mg/l.

The aerobic treatment produced an effluent with COD = 643 mg/l BOD5 = 67 mg/l.

One part by volume of the discharge from the first stage was mixed with one part by volume of mechanically preclarified communal effluent. The communal effluent had the following analvtical data: COD = 257 mg/I BOD5 = 151 mail.

The mixture of both effluents was delivered to an anaerobically operating active carbon filter. This treatment produced a second-stage effluent with COD = l(i6 mu/l BOlD5 = 7 mail.

The contact time of the effluent with the active carbon, based on the free crosssection, amounted to 4 hours.

By contrast, an activated sludge plant operated in parallel with the second anaerobic stage (aeration time 6 hours) produced an effluent of only the following quality: COD = 339 mgil BOD5 = 16 mull.

WHAT WE CLAIM IS: l. A PROCESS fi)r the biological treatment of effluent which, in addition to readily biodegradable substances, contains substantially non-biodegradable substances, wherein at least part of the readily biodegradable material is degraded in an aerobic stage.

wherein the resulting aerobically treated effluent is subjected to a semi-aerobic or anaerobic treatment on an inert supporting material, and wherein readily biodegradable effluent having a BOD5 - content of at least 25 mg/l is introduced during this semiaerobic or anaerobic treatment.

2. A process as claimed in claim 1, wherein a component stream of the effluent is separated before the aerobic treatment stage and directly introduced into and mixed with the effluent intended for the semiaerobic or an aerobic treatment which results from the aerobic treatment stage.

3. A process as claimed in claim 2, wherein the component stream amounts to between 5% and 50% by volume based on the aerobically pretreated effluent present in the semi-aerobic or anaerobic treatment stage.

4. A process as claimed in claim 3, wherein the component stream amounts to between 10% and 30coo by volume based on the aerobically pretreated effluents present in the semi-aerobic or anaerobic treatment stage.

5. A process as claimed in any of claims 1 to 4. wherein the effluent added in the semi-aerobic or anaerobic treatment stage has a BOD > -content of at least 50 mg/l.

6. A process as claimed in any of claims 1 to 5. wherein the temperature in the semi-aerobic or anaerobic stage is in the range from 10 to 60"C whilst the pH-value is in the range from 5 to 10.

7. A process as claimed in claim 6, wherein the pH-value is in the range from 6 to 9.

8. A process as claimed in any of claims l to 7. wherein the residence time of the effluent in the semi-aerobic or anaerobic stage amounts to between l() minutes and 10 hours.

9. A process as claimed in claim 8, wherein the residence time is between 1 and 5 hours.

1(). A process as claimed in any of claims l to 9, wherein the COD-charge per unit volume in the semi-aerobic or anaerobic stage is adjusted to a value of from 0. l to 5 kg of COD/m' per day.

l l . A process as claimed in claim l(J.

wherein the COD-charge per unit volume in the semi-aerobic or anaerobic stage is adjusted to a value of from ().5 to 2.0 kg of COD/m-' per day.

12. A process as claimed in anv of claims l to l l. wherein chemically bound oxygen which is capable of reacting with the

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (1)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   Example I An effluent from a textile dyeing plant which, in addition to dye, contained a non-ionic surfactant, sodium sulphate and acetic acid, was adjusted to pH 7 and treated in a laboratory activated sludge plant with an aeration time of 4 hours. No change in colour occurred.

   After a test duration of 5 weeks, the following active carbon column had produced a decolouration level of 55. In a plant operated in parallel, in which 20% of the input of aerobians together with nitrate and sulphate breathers (active carbon column with obligatory and optional anaerobic bacteria) were directly delivered to the second stage, the decolouration level had reached 99% after the same period.

   Example 2 Effluent from the chemical industry was treated in a semi-industrial activated sludge plant with an aeration time of It hours. The analytical data of the input to the first stage was as follows: COD = 1810 mg/l BOD5 = 837 mg/l.

   The aerobic treatment produced an effluent with COD = 643 mg/l BOD5 = 67 mg/l.

   One part by volume of the discharge from the first stage was mixed with one part by volume of mechanically preclarified communal effluent. The communal effluent had the following analvtical data: COD = 257 mg/I BOD5 = 151 mail.

   The mixture of both effluents was delivered to an anaerobically operating active carbon filter. This treatment produced a second-stage effluent with COD = l(i6 mu/l BOlD5 = 7 mail.

   The contact time of the effluent with the active carbon, based on the free crosssection, amounted to 4 hours.

   By contrast, an activated sludge plant operated in parallel with the second anaerobic stage (aeration time 6 hours) produced an effluent of only the following quality: COD = 339 mgil BOD5 = 16 mull.

   WHAT WE CLAIM IS: l. A PROCESS fi)r the biological treatment of effluent which, in addition to readily biodegradable substances, contains substantially non-biodegradable substances, wherein at least part of the readily biodegradable material is degraded in an aerobic stage.

   wherein the resulting aerobically treated effluent is subjected to a semi-aerobic or anaerobic treatment on an inert supporting material, and wherein readily biodegradable effluent having a BOD5 - content of at least 25 mg/l is introduced during this semiaerobic or anaerobic treatment.

   2. A process as claimed in claim 1, wherein a component stream of the effluent is separated before the aerobic treatment stage and directly introduced into and mixed with the effluent intended for the semiaerobic or an aerobic treatment which results from the aerobic treatment stage.

   3. A process as claimed in claim 2, wherein the component stream amounts to between 5% and 50% by volume based on the aerobically pretreated effluent present in the semi-aerobic or anaerobic treatment stage.

   4. A process as claimed in claim 3, wherein the component stream amounts to between 10% and 30coo by volume based on the aerobically pretreated effluents present in the semi-aerobic or anaerobic treatment stage.

   5. A process as claimed in any of claims 1 to 4. wherein the effluent added in the semi-aerobic or anaerobic treatment stage has a BOD > -content of at least 50 mg/l.

   6. A process as claimed in any of claims 1 to 5. wherein the temperature in the semi-aerobic or anaerobic stage is in the range from 10 to 60"C whilst the pH-value is in the range from 5 to 10.

   7. A process as claimed in claim 6, wherein the pH-value is in the range from 6 to 9.

   8. A process as claimed in any of claims l to 7. wherein the residence time of the effluent in the semi-aerobic or anaerobic stage amounts to between l() minutes and 10 hours.

   9. A process as claimed in claim 8, wherein the residence time is between 1 and 5 hours.

   1(). A process as claimed in any of claims l to 9, wherein the COD-charge per unit volume in the semi-aerobic or anaerobic stage is adjusted to a value of from 0. l to 5 kg of COD/m' per day.

   l l . A process as claimed in claim l(J.

   wherein the COD-charge per unit volume in the semi-aerobic or anaerobic stage is adjusted to a value of from ().5 to 2.0 kg of COD/m-' per day.

   12. A process as claimed in anv of claims l to l l. wherein chemically bound oxygen which is capable of reacting with the

   microorganisins is mixed with the aerobically pretreated effluent either before it enters or during its treatment in the semi-aerobic or anaerobic stage.

   13. A process as claimed in claim 12, wherein hydrogen peroxide and/or a nitrate and/òr á sulphate is added to the effluent.

   14. A process as claimed in any of claims 1 to 13, wherein active carbon is used as the inert supporting material for the microdrganisms of the semi-aerobic or anaerobic treatment stage.

   15. A process as claimed in claims 1 to 14 wherein the supporting material is used in the form of a fluidised bed.

   16. A process for the biological treatment of effluent substantially as herein described with reference to the accompanying Figure and/or either of the specific Examples.