US 3854877 A
An integrated instrument and modified technique are provided for measuring the total carbon content (TC) and total oxygen demand (TOD) concurrently on samples of aqueous solutions or dispersions. Further, a method is provided for measuring the extent of other oxidation reactions such as nitrification occurring in processes such as the bio-oxidation of wastes.
Description (OCR text may contain errors)
[451 Dec. 17, 1974 Stenger et COMBINATION TOD-TC ANALYSIS C P O 3 2 3 2 9/1970 Blum et a].
METHOD Teal et 23/253 PC Van  Inventors: Ernoe Csaky, Midland, Mich.; C.
ll 77 99 ll 23 65 500 3 O7 66 5 5 33 Hugh Thompson, Falls Church, Va. 3,567,386 3/1971 Stengernm. 23/230 PC The Dow Chemical Company, 3'607230 9/197] Midland, Mich.
Aug. 7, 1972 Appl. No.: 278,531
Wintrell  Assignee:
-Primary Examiner-J1. E. Serwin  Filed:
Attorney, Agent, or Firm-Richard W. Hummer ABSTRACT An integrated instrument and modified technique are provided for measuring thetotal carbon content (TC) and total oxygen demand (TOD) concurrently on samples of aqueous solutions or dispersions. Further, a I method is provided for measuring the extent of other 2 4 PHQUH 12 3 a3 2nC /1P B 3 3G5 m ,2, 0 3" 2 WU ..3 "m2 mwn .c nr 3 .9 S L .d I
l fm UIF mm 555  References Cited oxidation reactions such as nitrification occurring in UNITED STATES PATENTS processes such as the bio-oxidation of wastes.
3,296,435 l/l967 Teal et 23/253 PC 4 Claims, 1 Drawing Figur COMBINATION TOD-TC ANALYSIS METHOD BACKGROUND OF THE INVENTION Instruments to measure TOD and TC individually have been developed and are now commercially available. The capability provided by these measurements has made the detection of pollution much simpler and less costly. At the same time, the instruments have afforded a technical basis for the control of remedial pro SUMMARY OF THE INVENTION The foregoing objects, and other benefits as will be-.
by introducing the carbon dioxide detecting capability into an instrument, otherwise especially adapted for the measurement of total oxygen demand, a triple capability is provided for the measurement of pollution parameters. The combined capabilities of the instrument provide means for determining an index of the degree of nitrification in certain waste treatment processes.
Details as to means for providing a feed gas stream, effecting combustion within the heated zone and measuring by detecting, recording and calibrating the recording results are further elaborated by the teachings of U.S. Pat. No. 3,560,156.
Means for conditioning the effluent gases from the combustion zone by cooling them and removing condensateprior to analysis of the carbon dioxide are shown by Teal et al. in U.S. Pat. No. 3,296,435.
Apparatus for carrying out the foregoingprocess will be better understood by reference to the accompanying which comprises the steps of flowing a feed gas stream composed of an inert gas containing-a minor proportion of oxygen into a heated combustion zone at a constant rate.'Within the combustion zone, the feed gas is passed through a combustion supporting, porous-catalyst bed. The combustion zone is heated at a combus tion-supporting temperature within the-range from about 600 up to about 1200C., preferably within the range from about 800 to about l0O0C. From the heated combustion zone, the gas stream is fed into a detector train. First in this train is means for cooling the gas, which may be simply the gas conduit itself as cooled by the surrounding atmosphere, and means for separating any condensate that may be formed as a result of the intermittent introduction of combustion products. The feed gas stream is then passed through a detector for carbon dioxide. Subsequently, the gas stream is passed through a continuous, quantitative oxygen detector. I
Once the feed gas stream containing a relatively small quantity of oxygen is established through the heated combustion zone, a small amount of an aqueous dispersion containing a combustible material is injected into the combustion zone upstream from the porous catalyst bed. This sample is vaporized and any combustibles contained therein are oxidized to produce carbon dioxide. In addition, nitrogenous compounds will be oxidized to some degree.
The carbon dioxide detector measures the amount of total carbon (TC) that was contained in the injected sample. Subsequently, within the oxygen detector, the total oxygen demand, which includes the oxygen used in forming the carbon dioxide and in oxidizing oxidizable nitrogen compounds, is measured in terms of the decrease in the amount of oxygen relative to the background oxygen content of the feed gas stream. This measurement yields what is termed herein the total oxygen demand (TOD) of the aqueous dispersion.
The difference between the measured TOD and the calculated TOD from the measured TC measurements yields an indication of the amount of oxidizable nitrogenous materials present in the sample analyzed. Thus,
drawing. The-depicted apparatus comprises a dilute oxygen feed stream supply means 2, which in this particu- -lar illustration is composed of an arrangement of an inert gas (for example, nitrogen) supply tank 3 and an oxygen supply tank 4 integrally feeding a feed gas line.
6. Nitrogen and oxygen are metered into the feed gas line 6 through pressure and flow control valves 7 and 8. Any known means for producing a carrier gas stream containing a controlled amount of oxygen may be used in place of the particular means illustrated. Line 6 feeds the mixed gas stream into a confined combustion zone defined by that portion of the combustion tube 15 within the heating zone 13 of an electric furnace 9. Within the heated combustion zone is a gas permeable, catalyst bed 16 of an oxidation supporting catalyst material. The temperature of the heating 'zone 13 is controlled by a variable power control 10 feeding through the electrical input lines 11' and 12 which are connected to the terminalsof a resistanceheating coil 14.
accomplished by suitable injection means such as the illustrated syringe 17.,Optionally', pneumaticaut'omatic injection valves may be used. The trajectory for sample injection is such that the sample will be deposited within the heating zone 13 on the upstream side of the catalyst bed 16.
Gaseous products from the heated zone 13 of the combustion conduit 15 are passed through cooling means, which in the illustration is simply conduit 19' as cooled at ambient air conditions. The gas is passed through a water trap 54 which is vented as required through valve 52 to remove condensate. From the water trap 54, the gas ispassed through conduit 33 into the carbon dioxide-sensitized, infrared analyzer 35 containing a detection cell 36. The variable voltage signal from the carbon dioxide detector is amplified by means of a low voltage amplifier 38 connected to said detector by electrical leads 63 and 64. The enhanced electrical signal is then fed through leads 61 and 62 into a continuous graphic recorder 39, which produces a curve 41 on a continuous strip of recording paper 42. The amplitude of, and the area under, the curve 41 are each a function of the carbon dioxide concentration continuously measured in the detection cell 36 of the infrared analyzer 35. The degree of amplification and After passing through the detection cell 36 the gaseous product is passed through conduit 37 into an oxygen detector 21 and from this detector exhausts into the atmosphere through vent 20. The oxygen detector 21 produces an electrical signal which is fed through electrical connections 23 to read out means 30, which is a graphic recorder 26.
The signal from the oxygen detector, which may be measured as voltage or current, is proportional to, and therefore correlative with, the oxygen content of the gaseous effluent. If desired, the recorded signal can be calibrated for direct reading of the signal as the oxygen content of the effluent gas stream.
The total oxygen demand (TOD) is defined according to the formula:
wherein Q is a function of t, which is time, and Q, is the oxygen content of the feed gas stream, or in other terms the oxygen content of the effluent gas under steady state conditions. t and are the timesot' sampleinjection and return of the oxygen content of the effluent gas to that of the feed gas stream, respectively. A graphic illustration of the value of the above equation solved for TOD is shown in the drawing by the shaded area 3l between the base line 29 representing the oxygen content of the feed gas stream and curve 27 plotted by the graphic recorder 26 between 1 and Alternatively, variations in the oxygen content of the gaseous effluent from the combustion zone, as the result of oxygen used to oxidize combustible material present in the injected aqueous dispersion, are reflected in the amplitude or displacement of the curve 27 from the recorder base line 29. In fact, the displacement of the recorded curve 27 from the base line '29 is directly proportional to the amount of oxygen used in the combustion of the sample, i.e., the total oxygen demand of the aqueous dispersion.
In a further embodiment of the invention, the output results from recorders 26 and 39 can be tabulated in conventional fashion and stored in a computer for re-v above patents incorporated herein by reference. It will be apparent from reading these teachings that numerous changes in equipment'can be made without detracting from the benefit of achieving both TOD and TC measurements on a given aqueous sample plus the capability of differential measurement of oxidizahle nitrogenous materials as will be described in detail below.
In various processes for treating sewage and other industrial and municipal wastes containing organic matter biological oxidation is employed to remove much of 6 such organic matter. In such processes part of the carbon from the organic matter may be converted to carbon dioxide while a further part is incorporated into the biologically active organisms such as activated sludge. Thus, the determination of the TC of the effluent from such a process as compared to the TC of the influent provides an'index of the efficiency of the process in eliminating oxidizable organic matter from the process stream. However, the TC determination provides no information on the fate of nitrogen compounds in the treated wastes. Nitrogen occurs in sewage predominantly in the reduced state, for example, in the form of ammonium, amino and amido nitrogen. .Such reduced nitrogen moieties contribute to the TOD for a process stream but not to the TC. Thus, in a preferred embodiment, the present invention provides a method for determining the degree of oxidation occurring in a process stream such as, for example,-the degree of nitrification occurring in the biooxidation of a waste stream.
In such operations, a sample from the influent stream any oxidation of nitrogen will affect only the TOD, the
computer is programmed to read out a function such as the ratio of TC to TOD. of 'the influent minus the ratio of TC to TOD of the effluent and the values of this function serve as an index of the degree of nitrification occurring in the oxidative process. For additional precision, if desired, the apparatus is calibrated with samples of known composition and/or compared with analyses of like samples by standard methods of analysis.
In the light of modern instrumentation for electronic data processing, the foregoing method can be considered as comprising generating a first signal proportional to the TC and a second signal proportional to the TOD of an influent stream of a process and combining said first and second signals to generate a third signal proportional to a ratio of said first and second signals. Similar first, second and third signals are generated from a sample of the effluent stream from said process and the third signals from the influent and effluent streams are combined to generate a signal having a value which serves as an index of the degree of oxidation occurring in said process. Conventional electronic equipment is available for storing, reproducing and combining the above signals and for producing a readout of the resultant index value either in numerical or graphical form.
What is claimed is: V
l. A processfor simultaneously measuring the total oxygen demand and total carbon of an aqueous dispersion of combustible material which comprises the steps l. flowinga feed gas stream containing a relatively small amount of oxygen at a constant rate through a confined combustion zone heated at a combustion supporting temperature within the range from about 600 to about l200C. and, within the combustion zone, flowing the feed gas stream through a combustion supporting catalyst bed,
2. flowing the effluent gas from the combustion zone into a continuous analyzer for quantitatively indicating the carbon dioxide in the gaseous product,
3. flowing the effluent gas from the combustion zone after passing through the carbon dioxide detector of step (2) above, into a continuous quantitative detector for gaseous oxygen and while continuing to flow the feed gas stream, injecting a small amount of the aqueous dispersion of a combustible material into the combustion zone upstream from.
2. A method as in claim 1 including the additional step of calibrating each of the signals obtained from the carbon dioxide detector and oxygen detector to yield a measurement of carbon and total oxidizable material contained in the aqueous dispersion.
3. A method for determining the degree of oxidation change in a process stream which comprises generating signals proportional, respectively, to a ratio of the total oxygen demand and the total carbon in the influent stream to an oxidative reaction zone and in the effluent stream from said zone and combining said signals to generate a signal the value of which is an index of the degree of oxidation occurring in said zone.
4. A method according to claim 3 wherein the process stream is sewage and the derived value is a measure of the degree of nitrification occurring in the oxidative process.