BOD System Oxi700 with 6 sensor heads 115V/230V

Highlights Direct Sample Selection Automatic Storage of all values Easy to use Accurate and direct display of BOD values in mg/L Automatic start after temperature equalization Mercury-free Inductive stirring system with automatic re-centering of stirring rods Biochemical Oxygen Demand (BOD) is an expression for the quantity of oxygen required for biological degradation of organic matter in a waste water sample. BOD measurement is used as a basis for the detection of biologically degradable organic matter in water.The difference between BOD and chemical oxygen demand (COD) is that COD additionally registers biologically non-degradable organic matter.

Manometric respirometers relate oxygen uptake to the change in pressure caused by oxygen consumption while maintaining a constant volume. The integral pressure sensors, make it unnecessary to use mercury for pressure measurements.

How it Works

Respirometric methods provide direct measurements of the oxygen consumed by microorganisms from an air or oxygen-enriched environment in a closed vessel under conditions of constant temperature and agitation.Carbon dioxide produced metabolically by the bacteria is chemically bound by the potassium hydroxide solution contained in the seal cup in the bottle. The result is a pressure drop in the system, which is directly proportional to the BOD value and is measured by the Orbeco-Hellige BOD sensor. The BOD level is then displayed directly in mg/l.

Measuring ranges and sample volumes

The BOD level of a sample depends on the quantity of organic matter present, which can vary considerably. The Orbeco- Hellige Oxi700 is calibrated for the various sample volumes and the corresponding measuring ranges listed in the table below. The overall measuring range of the system is 0 – 4000 mg/l. For all measuring ranges, BOD is shown directly in mg/l.

Temperature equalization

Temperature equalization is essential prior to biological testing, as temperature has a major effect on biological activity. BOD measurements, for example, are always performed in a thermostatically controlled cabinet at a temperature of 20°C.

Day	Display/Sensor
1. Day	150 mg/L
2. Day	220 mg/L
3. Day	240 mg/L
4. Day	250 mg/L
5. Day	260 mg/L

Evaluation of measurements

If the measuring period is set at 24 hours, the Orbeco-Hellige Oxi700 BOD measuring system records a measurement once every hour. With a measuring period of 48 hours, the unit measures and stores a BOD value once every 2 hours. If the measuring period is between 3 and 28 days, one value is measured and stored each day.

Current values and stored values may be called up at any time. The table/graph below illustrates an example of BOD5 evaluation. The development of BOD over a period of 5 days is easily seen.

Automatic start function

Variations in sample temperature prior to testing result in pressure variations within the measuring system during the temperature equalisation period in the thermostatically controlled cabinet (if BOD measurement is to take place at 20°C, for example). Such variations would normally cause errors during manometric measurement.

In order to prevent such errors, the Orbeco-Hellige Oxi700 BOD meter is equipped with an automatic start feature: measurement does not commence until the temperature in the samples is the same as that in the thermostatically controlled cabinet. This rules out the possibility of temperature (and hence pressure) fluctuations that are not related to the manometric measurement.

The complete OxiDirect measuring system

In addition to the BOD unit for measurement and storage of BOD levels, the Orbeco-Hellige Oxi700 BOD measuring system includes sample bottles, measuring sensors, non-wearing inductive stirring system, overflow measuring flasks for monitoring of sample volumes, nitrification inhibitor and potassium hydroxide as an absorbent.

*No standard is available to check the accuracy of respirometric oxygen uptake measurement. Tests with a glucose-glutamic acid solution having a known theoretical BOD have shown that the variation is approximately 5% in the range of 50…100 mg/l BOD, and 3% for higher range. Minimum Response or sensitivity of respirometric systems is about 0.05 … 1 mg/l.

The Orbeco-Hellige microprocessorcontrolled inductive stirring system is non-wearing and maintenance-free. At regular intervals, the magnetic stirring rods are accelerated and slowed down again, taking them up to maximum speed and back down again. This ensures the centralization of the stirring rods. Stirring rods that move away from the centr of the bottle are re-centered quickly and reliably. The inductive actuation system guarantees maintenance-free operation.