An Improved Apparatus for Biochemical Oxygen Demand


James C. Young, William Garner, and John W. Clark, Civil Engineering Department, New Mexico State University, University. Park, N. M. SECTION AA...
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of oxygen in other highly refractory materials is being investigated. ACKNOWLEDGMENT

The authors thank C. F. LIetz, under whose supervision this work was per-

formed, for his valuable advice, and G. E. Nagy for his assistance in fabricating the sample handling device. The samples of triplex-coated beads were obtained from the Oak Ridge National Laboratory through the courtesy of W. R . Laing and J. L. Cook.

LITERATURE CITED

( 1 ) Dean, R. B., Dixon, W. J., ANAL. CHEM.23, 636 (1951). (2) Smith, E., Hansel, J. ll.,Johnson, R. B., Waterbury, G. R., Ibtd., 35, 1502 (1963). performed under the auspices of

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the U. S. Atomic Energy Commission.

An Improved Apparatus for Biochemical Oxygen Demand James C. Young, William Garner, and John W. Clark, Civil Engineering Department, New Mexico State University, University Park, N. M.

HE

CLARKMETHOD for continuous

T determination of oxygen uptake of a

large inhomogenous biological sample was first developed in 1959 (1). The technique was applied to the automatic determination of biochemical oxygen demand (BOD) of polluted water. The principle was to maintain pressure in the closed sample-containing vessel by replenishing the metabolically utilized oxygen by electrolysis of dilute acid. The metabolically produced COZ was absorbed with KOH. The internal pressure of the vessel was monitored by a device which would sense a pressure decrease and actuated the power supply to the electrolysis cell. A constant current was supplied to the electrolysis cell and β€œon” time could be monitored both by an elapsed time meter and, for short term kinetics, a strip chart recorder. The technique has undergone continual revision (2, 3). Originally, a standard 2-liter resin kettle was used as the reaction vessel. The electrolysis cell and pressure switch were separate components. COz was absorbed by circulation of the internal atmosphere through absorption towers. Improvements of the apparatus are herein reported which include reduced cost, simplicity of operation, and obviation of a large head space which with varying external barometric pressure was a source of error. The apparatus is illustrated in Figure 1. The reaction vessel is a standard 1liter, narrow-mouth, reagent bottle with a flat head stopper (Corning No. 1500). The ground neck accepts a 3- 29 joint. A horizontal slot was cut through the neck about halfway down the ground section to produce an opening 1 em. in length. The COz absorbent container was fabricated from a 29/42 to 3- 24/40 bushing type reducing adapter (Corning S o . 8825). d test tube 20 mm. in diameter and 50 mm. in length was welded on the bottom of the bushing. A small glass propeller was welded onto the lower end of the test tube to increase turbulence in the liquid sample. Two opposing, 784

ANALYTICAL CHEMISTRY

SECTION A A

i-ii 29

Figure 1. Apparatus for biochemical oxygen demand

Slot

Stirring Magnrt

Onr- Lihr Rraqrnt Bottle

horizontal slots are cut into the upper end of the tube just below the ground section of the bushing to permit circulation of the make-up oxygen and the COn produced in the digestion. A vertical groove is cut part way through the outer surface of the bushing which extends along the length a distance which permits alignment with the slot in the bottle neck. The electrolysis cell was fabricated by Micro Chemical Specialties Co., Berkeley, Calif., from borosilicate glass. The drawing is to scale. The base 3-24/40 joint is indicative of dimensions, most of which were not critical for operation. I t was important that the innermost tube was a t least 5-mm. i.d. so that it did not get plugged with condensate. The hole connecting the two electrolyte compartments had to be at least 10 mm. below the electrode levels. The electrodes were made of 0.005 inch Pt foil sweat welded to No. 20 Pt wire. Graded seals were not used a t the Pt-to-glass seal. It was sufficient to reinforce the seal mechanically with a drop of epoxy resin on the outer surface.

Adaptor- C O , Absorbent Contalnw

Elrclrolyvir COll

magnetic stirring bar coated with Teflon (Du Pont). A wick of glass wool was placed in the COS absorbent container and sufficient 30Oj, KOH added to cover two thirds of the wick. The electrolysis cell was filled with 0.7N HzS04to the level of the switching electrode. The apparatus was assembled with silicone stopcock grease coating the ground surfaces. I n practice, four or five such assemblies are placed along with stirring motors in a standard BOD incubator. The vessel is vented until thermal equilibrium is reached, after which the bushing is rotated 180’ to seal. The power supply is described elsewhere ( 4 ) . LITERATURE CITED

( 1 ) Clark, J. W., New Mexico State

University, Engineering Expt. Sta. Bull. No. 11 (1959). (2) Clark, J. W., Water Sewage Works 107 (1960). ( 3 ) Clark, J. W., Zbid., 108 (1961).

(4) Young, James C., Clark, J. W.,

Garner, W., New Mexico State University, Engineering Expt. Sta. Tech. Rept. No. 20 (1964).