General Catalogue

BiochemicalOxygen Demand (BOD)BOD – biochemical oxygen demand – is anexpression for the quantity of oxygen required forbiological degradation of organic matter in awaste water sample. BOD measurement is thereforeused as a basis for the detection of biologicallydegradable organic matter in water. Thedifference between BOD and chemical oxygendemand (COD) is that COD additionally registersbiologically non-degradable organic matter.BOD measurement is therefore an importantmeasurement of the effects of domestic andindustrial waste water on sewage plants andoutflow points.Manometric, respirometricBOD measurement using theLovibond ® OxiDirectThe Lovibond ® sensor system OxiDirect is a 6sample system that allows precise measurementsof BOD based on the manometric principle.Manometric respirometers relate oxygen uptaketo the change in pressure caused by oxygen consumptionwhile maintaining a constant volume.Thanks to the modern integral pressure sensors, itis no longer necessary to use mercury for pressuremeasurements.Measuring ranges and samplevolumesThe BOD level of a sample depends on the quantityof organic matter present, which can vary considerably.The Lovibond ® BOD measuring systemOxiDirect is therefore calibrated for the varioussample volumes and the corresponding measuringranges listed in the table below. The overall measuringrange of the system is 0 – 4000 mg/l.For all measuring ranges, BOD is shown directly in mg/l.Range mg / l BOD0 – 40 4280 – 80 3600 – 200 2440 – 400 1570 – 800 940 – 2000 560 – 4000 21.7Sample Volume mlO 2CO 2Sample bottlePressure sensorSeal cupGas phaseWaste waterOxiDirect PrincipleRespirometric methods provide direct measurementsof the oxygen consumed by microorganismsfrom an air or oxygen-enriched environment in aclosed vessel under conditions of constant temperatureand agitation. Carbon dioxide producedmetabolically by the bacteria is chemically boundby the potassium hydroxide solution contained inthe seal cup in the bottle.The result is a pressure drop in the system, whichis directly proportional to the BOD value and ismeasured by the Lovibond ® BOD sensor. The BODlevel is then displayed directly in mg/l.The BOD values are stored in the sensor memoryand can be called up on the large-format displayat any time without the need for time-consumingconversion using factors. This means that test seriesthat end on a Sunday can be evaluated duringthe following week without any problem.The measurement period is user-selectable between1 and 28 days to suit the application. Whileshort measurement periods are useful for scientificapplications, standard BOD measurements typicallyextend over a period of 5 days – and manometricdetermination of OECD, for example, generallytakes place over a period of 28 days.BOD-MeasurementGeneral Catalogue November 2010105