DESC:FIELD OF INVENTION
The present invention relates to a device for determination of chemical oxygen demand of an effluent. The invention also relates to a method for determination of chemical oxygen demand of an effluent.
BACKGROUND
Chemical Oxygen Demand (COD) measurements usually involve treatment of the effluent with an oxidant and subsequent (quantitative) analysis of the oxidant to determine the quantity of reacted oxidant. This two-step determination of COD is cumbersome since it is characterized by performing treatment (digestion) and analysis separately requiring transfer of the treated effluent to a container used for analysis. Also, practically it is difficult to perform the treatment (digestion) in such a container because the container is not usually configured to perform the treatment. In a typical example of using a spectrometric analysis for the determination of the oxidant, it is nearly impossible to perform such digestive treatment in sample container (cuvette) because cuvettes used for spectrometry do not usually withstand the temperature of digestion. To overcome this limitation, cylindrical cuvettes with circular cross section may be used. Multiple optical analyses, involving multiple samples as well as the standard sample, necessitates use of such multiple cuvettes for optical analysis. Individual cylindrical cuvettes are characterized by varying thickness at the point of incidence of the optical beam, used for measurement, and at the point of exit of the cuvette surface. This significantly alters the convergence of the optical beam in the instrument, thus altering drastically its size and shape where it falls on the photosensitive surface in the photodetector. This in turn affects the accuracy and precision of quantitative analysis. Further, in the usual spectrophotometers, the analysis system is not adapted to have provision for heating. High temperatures significantly reduce the time required for determination of COD that involves treatment with an oxidant and analysis of the reacted oxidant/products of the treatment. Furthermore, in the conventional COD analysis systems, the accuracy of determination of reacted oxidant is impacted by the presence of chemical interferences such as chlorine in the effluent. There is, therefore, a long standing need to have a system for determination of COD that overcomes all such problems in conventional COD systems so as to enable measurement and operation in a less cumbersome and more accurate manner.
SUMMARY OF INVENTION
Accordingly, the present invention provides a device for determination of chemical oxygen demand, the device comprising:

a) a sample treatment unit

b) a syringe drive unit and

c) an optical measurement unit

In one embodiment, the invention also provides a device for determination of chemical oxygen demand, the device comprising:
a) a sample treatment unit

b) a syringe drive unit and

c) an optical measurement unit

wherein the sample treatment unit is in liquid communication with the optical measurement unit.

In one embodiment, the invention also provides a device for determination of chemical oxygen demand, the device comprising:
a) a sample treatment unit

b) a syringe drive unit and

c) an optical measurement unit

wherein the optical measurement unit is coupled to the syringe drive unit.

In one embodiment, the invention also provides a device for determination of chemical oxygen demand, the device comprising:
a) a sample treatment unit

b) a syringe drive unit and

c) an optical measurement unit
wherein the sample in the sample treatment unit is adapted to be heated up to 2000C and is adapted to
be treated with an oxidant

In one embodiment, the invention also provides a device for determination of chemical oxygen demand, the device comprising:
a) a sample treatment unit

b) a syringe drive unit and

c) an optical measurement unit
wherein the sample treatment unit is adapted to be treated with an oxidant at a temperature of up to 2000C.
In one embodiment, the invention also provides a device for determination of chemical oxygen demand, the device comprising:
a) a sample treatment unit

b) a syringe drive unit and

c) an optical measurement unit
wherein the sample in the sample treatment unit is adapted to be treated with an oxidant at a temperature up to 2000C and wherein the sample treatment unit is adapted to be treated with an acid prior to treatment with an oxidant.
In another embodiment, the invention provides a method for determination of chemical oxygen demand, the method comprising first treating an effluent sample with an acid at temperature of more than 50 degree Celsius to obtain a first treated sample, then treating the first treated sample with an oxidant at a temperature of more than 150 degree Celsius to obtain a second treated sample, drawing the second treated sample into a syringe barrel engaged with a plunger rod having a plunger rod body extending along a longitudinal axis, irradiating the second treated sample in the syringe barrel with a radiation having wavelength in the region 580 to 600 nm originating from a radiation source and allowing the radiation transmitted through the sample to be received on a radiation detector adapted to receive the transmitted radiation
BRIEF DESCRIPTION OF DRAWINGS
Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following drawings, in which
Figure 1 displays a schematic block diagram of an embodiment of the device for determination of Chemical Oxygen Demand
Figure 2 illustrates an exploded view of the optical measurement unit
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Various non-limiting and non-exhaustive embodiments of the present invention will be described in detail with reference to the drawings wherein like reference numerals refer to like parts throughout the various views unless otherwise specified
Turning now to Figure 1, effluent sample from the effluent container (11) is conveyed to a sample treatment unit(18+21) by way of the syringe drive system(23) Typically, the syringe drive unit is subjected to PLC (Programme Logic Control) for operational convenience. In the sample treatment unit (18+21), the effluent sample is treated with an oxidant conveyed to the sample treatment unit (18+21) from a container (20) for the oxidant. The oxidant is usually an hexavalent chromium salt. Typically, the oxidant is potassium dichromate. During treatment with the oxidant, organic matter in the sample is oxidized to carbon dioxide and water while the hexavalent chromium is reduced to its trivalent state. Typically, before treatment with dichromate, the effluent sample is treated with concentrated sulfuric acid. The acid converts any dissolved chlorine to hydrogen chloride gas that is removed from the treatment unit by way of an air pump.
The sample treatment unit (18+21) is also equipped with a heating unit (18) containing an heating element as well as a treatment container (21). The heating unit allows to perform treatment of the sample with the oxidant at high temperatures. Treatment of the effluent sample with the acid is usually performed at lower temperatures. Typically, the treatment with the oxidant is performed at a temperature in the range of 1500C-1800C. Advantageously, the treatment with the oxidant is performed at a temperature of around 1800C. More advantageously, the treatment with the oxidant is performed at a temperature of 1800C for at least about 20 minutes. Treatment with sulfuric acid is usually performed at a temperature of in the range of 500C to 800C.Advantageously, the treatment with the acid is performed at around 800C.
While in operation, the effluent sample from the effluent stream (10) enters an effluent container (11). Excess amount of sample will be drained off from the sample container (11) through the drain (14). Desired amount of effluent sample is drawn from sample container (11) by the syringe drive unit (23). This sample is transferred to a treatment container (21). In the treatment container (21), the effluent sample is treated with acid (typically, concentrated sulfuric acid) drawn into the treatment container (21) from the acid container (13) using the syringe drive unit (23). The treatment container (21) is equipped with a heating unit (18) containing an heating element. The sample is then treated with concentrated sulfuric acid at a desired temperature (around 700C -800C) in the treatment container (21) with continuous purging of air (15) by way of a blowing unit (17). Typically, the blowing unit is a pump.

The acid treatment results in conversion of dissolved gases in the liquid sample to volatile gaseous components. Typically the dissolved gas is chlorine and the volatile gaseous component generated by acid treatment of the liquid sample is hydrogen chloride. The volatile gaseous component is removed from the treatment unit (21+18) by way of purging of air (15) drawn by the blowing unit (17).After removal of chloride, the oxidant is drawn, by the syringe drive unit (23), from the oxidant container (20) into the treatment container (21). Typically, the oxidant is potassium dichromate. The sample is then treated with the oxidant in the treatment container (21) at a high temperature (typically around1800C) for at least about 20 minutes. After treatment with the oxidant, the treated sample is drawn, by the syringe drive unit (23), into the syringe barrel (9) by suction using the plunger rod (1) having a plunger rod body extending along a longitudinal axis.

After treatment, by concentrated sulfuric acid as well as by potassium dichromate, the treated sample is analysed by an optical measurement unit. The optical measurement unit is displayed in figure 2.
Turning now to figure 2, the optical measurement unit (22) typically comprises a plunger rod (1) having a plunger rod body extending along a longitudinal axis, a syringe barrel (9), a light source (4) and a light detector (7). The plunger rod is usually provided with a protective cylindrical sheath (2) while the LED holder (3) and photodiode holder (8) respectively holds the LED (4) and photodiode (7). Typically, the light source is an LED source while the light detector is a photodiode. The syringe barrel is typically made of glass and is adapted to be filled by suction using the plunger rod. Analysis of the sample after treatment is performed by absorption measurements using light of wavelength in the region 580 to 600 nm.
Before analyzing the treated sample, the optical measurement unit is used to perform optical analysis of the standard sample. Typically, the standard sample comprises the reagents (the acid and the oxidant) used for treatment of the effluent sample, in the sample treatment unit(18+21). Before optical analysis, the standard sample is drawn into the sample treatment unit (18+21) from the container (12) for the standard and subjected to the same kind of heating as performed on the effluent sample . The treated standard sample (containing the acid and the oxidant) from the sample treatment unit (18+21) is then drawn, by the syringe drive unit (23), into the syringe barrel (9) and analysed for trivalent chromium ions using light of wavelength in the region 580 to 600 nm
After optical analysis of a given sample, the optical measurement unit is subjected to cleaning using distilled water from the distilled water container (16) using the syringe drive unit (23). Such cleaning prepares the optical measurement unit for accurate analysis of the next sample that is drawn into the syringe barrel. Further, the sample treatment unit is subjected to cooling by a cooling unit (19). Typically, the cooling unit is an air conditioning/air cooling system or a fan.
The invention also provides a method for determination of chemical oxygen demand. The method of the present invention comprise first treating an effluent sample with an acid at temperature of more than 50 degree Celsius to obtain a first treated sample, then treating the first treated sample with an oxidant at a temperature of more than 150 degree Celsius to obtain a second treated sample, drawing the second treated sample into a syringe barrel with a plunger rod having a plunger rod body extending along a longitudinal axis, irradiating the second treated sample in the syringe barrel with a radiation having wavelength in the region 580 to 600 nm originating from a radiation source and allowing the radiation transmitted through the sample to be received on a radiation detector adapted to receive the transmitted radiation

EXAMPLE
Treatment with oxidant and spectrophotometric analysis of the treated sample
1 ml of the effluent sample was taken into the sample vial from a sample container using the syringe drive system. The sample was treated with 1 ml of concentrated sulfuric acid at 800C with continuous purging of air and concurrent removal of hydrochloride gas. After removal of chloride, the sample was treated with potassium dichromate at a temperature of 1800C for at least about 20 minutes. After treatment with potassium dichromate, the treated sample was taken into the barrel by suction using the plunger and optical absorption of trivalent chromium ions is measured in the region of 580 to 600 nm using the optical measurement unit displayed in Figure 2.
The device of the present invention enables determination of chemical oxygen demand in a fast, efficient and accurate manner. While the conventional COD systems require hours to perform such determination, the device of the present invention allows such determination in less than 30 minutes. Moreover, the device of the present invention enables elimination of potential gaseous interferences during such determination as well as elimination of optical errors during sample analysis while performing such determination. By enabling optical analysis of the treated sample in the syringe barrel adapted to draw the treated sample using the syringe drive unit, the device of the present invention enables determination of chemical oxygen demand in a waste stream in a continuous manner with high degree of accuracy and precision. Such a device for determination of chemical oxygen demand is hitherto unknown and is a significant technical advance over the conventional devices for COD determination.
The above description is illustrative only and is not limiting. The present invention is defined by the claims that follow and their full range of equivalents
,CLAIMS:1. A device for determination of chemical oxygen demand, the device comprising:
a) a sample treatment unit

b) a syringe drive unit and

c) an optical measurement unit

2. The device as claimed in claim 1 wherein the optical measurement unit comprises a syringe barrel, a plunger rod having plunger rod body extending along a longitudinal axis, a radiation source and a radiation detector

3. The device as claimed in claim 1 wherein the sample treatment unit is in liquid communication with the optical measurement unit.
4. The device as claimed in any one of the claims 1 to 3 wherein the optical measurement unit is coupled to the syringe drive unit.
5. The device as claimed in any one of the claims 1 to 4 wherein the sample treatment unit is adapted to be heated up to 2000C
6. The device as claimed in claim 5 wherein the sample treatment unit is heated in the presence of an oxidant
7. The device as claimed in claim 6 wherein the sample treatment unit is adapted to treatment with an acid prior to heating in the presence of an oxidant
8. The device as claimed in claim 7 wherein the acid is sulfuric acid
9. The device as claimed in claim 7 or 8 wherein the sample treatment unit is fastened to a blowing unit
10. The device as claimed in claim 9 wherein the blowing unit is adapted to blow off a gaseous component generated upon treatment of an effluent sample with an acid
11. The device as claimed in claim 10 wherein the gaseous component is hydrogen chloride
12. A method for determination of chemical oxygen demand, the method comprising first treating an effluent sample with an acid at temperature of more than 50 degree Celsius to obtain a first treated sample, then treating the first treated sample with an oxidant at a temperature of more than 150 degree Celsius to obtain a second treated sample, drawing the second treated sample into a syringe barrel engaged with a plunger rod having a plunger rod body extending along a longitudinal axis, irradiating the second treated sample in the syringe barrel with a radiation having wavelength in the region 580 to 600 nm originating from a radiation source and allowing the radiation transmitted through the sample to be received on a radiation detector adapted to receive the transmitted radiation