Biological Oxygen Demand

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WTW BOD Measurements and Respiration

Biochemical Oxygen Demand
In “dilution BOD” the oxygen content of a sample is measured with a dissolved oxygen sensor before and after an incubation period of 5 days. The difference between the measurements is the BOD5 value; this is the official EPA method.
In “BOD self-checks” with the respirometer, the reduction in oxygen causes a definite pressure difference that can be measured by a pressure sensor. This practical method is very easy to perform.
Both methods are very different, but the measurements correlate directly to the discharge seen at municipal wastewater treatment facilities. Both methods require the samples to be kept at 20 °C for 5 days. WTW offers a wide range of temperature controlled incubators.

As environmental consciousness increases, microbiological degradability tests have become increasingly important, from soil surveys from waste sites to environmental impact surveys to characterize new chemical substances. The necessary respiration measurements for anaerobic or aerobic degradation can be easily performed using the high performance OxiTop®-C systems. WTW offers a wide range of application specific packages complete with the appropriate sample vessels.

BOD Self-check Measurement

Respiration/Biogas Determination with OxiTop® and OxiTop® Control

OxiTop® IS 6, IS 12


  • High-precision
  • 5-day automatic storage of measured values
  • Portable
  • Extendable

Complete packages for 6 or 12 simultaneous measurements
Measurement using OxiTop® is based on pressure measurement in a closed system: microorganisms in the sample consume the oxygen and form CO2; the CO2 is absorbed by NaOH, creating a vacuum that can be measured as a mg/l BOD value. The sample volume used regulates the amount of oxygen available for a complete BOD. Measurement ranges of up to 4,000 mg/l can be measured using different volumes. The OxiTop® heads (green and yellow for inflow/outflow differentiation) have an AutoTemp function: if the sample temperature is too cold, the start of measurement is automatically delayed by at least 1 hour until a constant temperature has been reached. Apart from the automatic storage of 5 measured values (1 value per day), further measured values can be read at all times during or after the period of 5 days, which permits the tracking of check values or measurements over longer periods.

Measurement range 0 ... 40 digit
corresponding to
0 ... 40 / 80 / 200 / 400 / 800 / 2000 / 4000 mg/l BOD

BOD Self-check Measurement – for a larger number of samples


  • Controller-driven
  • Simultaneous measurement of up to 100 samples
  • Statistical evaluation
  • Automatic sample ID

Complete package for 6 or 12 simultaneous measurements OxiTop® Control system uses software-controlled functions and infrared interface to communicate with the powerful OC 100 controller. This connection enables the simultaneous, group start, management, storage and tracking of 100 measuring heads, and tracks results on a large graphic display. Data can be transferred to the PC for evaluation and documentation via the AK-540/B cable (order no. 902 842) and the communication program Achat OC (order no. 208 990). The OC 110 controller, in combination with the OxiTop® Control S6 / S12, is ideal when other applications in addition to BOD are required.

Controller OC 100/OC 110



  • Simultaneous sample management with option of grouping up to 100 OxiTop®-C measuring heads.
  • Data call-up of one parallel sample with statistical evaluation and as individual data.
  • Automatic calculation and graphical display of BOD value.
  • Data transfer even through glass doors.
  • Protocol and documentation of data via Achat OC communication program in combination with a PC
  • GLP and AQS with inspection intervals for calibration with the OxiTop® PM calibration tablets

Data sets per measurement 180 … 360 (depending on duration)
Measurement period 0.5 h … 99 days

OxiTop®- C Measuring Head


  • The OxiTop®-C measuring heads have an AutoTemp function; if the sample temperature is too cold, the start of measurement is automatically delayed, by up to 4 hours, until a constant temperature can be reached. This mode can be deactivated for BOD standard.
  • The measuring heads can store up to 360 data sets. Data are automatically stored in the corresponding interval according to the interval period set (0.5 h to 99 days).
  • The built-in pressure sensor can register differences in pressure ranging from 500 to 1,350 hPa.

Instead of the usual display and keys, the OxiTop®-C measuring head has an infrared interface with which it communicates with Controller OC 100 or OC 110. By pointing the controller at an OxiTop®-C measuring head the sample can be identified and the measurement is started. Data can be called up or deleted and sampling progress can be displayed. 
Each sample is automatically assigned a unique ID number; eliminating manual sample identification even for multiple samples. In addition, statistical evaluations can be easily performed for multiple samples.

Measuring principle Manometric with pressure sensor
Measurement of BODn
Pressure range 500 - 1350 hPa
Accuracy ±1% of value ±1 hPa
Resolution 1 hPa (corresponds to 0.7% of BODn measuring range)


Dilution BOD

According to DIN EN 1899-1 and DIN EN 1899-2; official EPA method


BOD determined reliably…

… with the innovative inoLab® Multi 9310 IDS


inoLab? Multi 9310P IDS

IDS Sauerstoff-Elektroden

  • Optimum measuring quality
  • Digital sensor recognition
  • Intelligent sensor rating

FDO® 925 – Flexible and powerful

  • fast responding optical D.O. sensor
  • no own-consumption of oxygen
  • matching stirrer can be mounted easily
  • universal use

The new inoLab® Multi 9310 IDS is ideal meter for digital measurements of optical D.O. in the laboratory. The IDS technology enables in the easiest way ideal measurements and efficient documentation. The optical D.O. sensor FDO® 925 allows precise BOD measurements.

Measuring channel 1 (universal)
Display LCD graphic, backlit
Data storage Manual: 500 data sets/Automatic: 5000 data sets
Logger Manual/time-controlled
Interface Mini USB
Printer (optional) Thermo printer, width 58 mm
Power supply Universal power supply 100 to 240 V, 50/60 Hz, 4 x 1,5 V AA or 4 x 1.2 V NiMH rechargeable battery

BOD documented precisely ...

… with the inoLab® Oxi 7310


inoLab? Oxi 7310P

WTW StirrOx?

StirrOx® G Self-stirring dissolved oxygen sensor – simultaneous stirring and measurement

  • Single-handed operation for series measurements
  • Constant flow for high reproducibility
  • Immediately ready for measuring – no polarization period required
  • Extremely low self-consumption of oxygen – only 0.008 μg h-1 (mg/l)-1
  • Zero-current free – no zero point calibration necessary
  • Calibration and storage vessel OxiCal®-ST included
  • Membrane life of up to 6 months
  • Temperature compensation with 2 built-in sensors
  • Membrane leakage monitoring – damaged membranes are indicated

The new inoLab® Oxi 7310 is the perfect laboratory meter for measuring BOD with theproven, galvanic D.O. sensors. With automatic GLP compliant documentation/AQA supports the traceability not only throughout the environmental laboratory. On demand also available with integrated printer.

  All values ±1 digit
Concentration 0.00 … 20.00 mg/l ±0.5 % Mw.
0 … 90 mg/L ±0,5 %
Saturation 0.0 … 200.0 % ±0.5 % v. Mw.
0 … 600 % ±0.5 % v Mw.
Partial pressure 0 … 200.0 hPa, 0 to 1250 hPa
Temperature -5.0 … 105.0 °C ±0.1 °C


Depletion/Respiration with OxiTop® Control OC 110

OxiTop® Control B6/B6M – Determination of Soil Respiration

Laboratory method for determining the microbial soil respiration according to DIN ISO 16072.


  • Simple and precise
  • Cost-efficient
  • Optimum measuring vessels for subsequent quantitative determination of CO2

Soil respiration measurements are used for forecasting, surveying and checking remediation work, for biodegradability measurements of substances (pesticides, fungicides, fertilizers, etc.) and for carrying out toxicity tests. Thanks to specially designed, test-proven vessels, these measurements are made accurate and simple with the OxiTop® Control System. A cost effective alternative compared to conventional methods. Soil respiration measurements can be carried out in 2 different vessel types. For actively respiring soils with strong CO2 development, the MG 1.0 measuring vessel is recommended: its large opening (approx. 100 mm / 3.9 in dia.) easily fits large-volume CO2 absorber vessels for later quantitative CO2 determination.

OxiTop® Control A6/A12 and OxiTop® Control S6/S12 – Determination of Biodegradability

Laboratory procedures for determination of biodegradability according to DIN EN 29 408 / ISO 9408 / OECD 301 F


The determination of the biodegradability should be checked before new chemicals are used for the first time, not only for environmental reasons but to minimize disposal charges. The sample and a blank are stirred at a constant temperature for 28 days in closed bottles. The CO2 produced is removed by means of an absorber, the resulting negative pressure is a measure of the biodegradability. The OxiTop®-C continuous value recording guarantees proper documentation. The measuring bottles and adapters can be autoclaved at 121 °C (249.8 °F).

OxiTop® Control AN6/AN12 – Biogas Determination

Determination of anaerobic degradation processes: biogas determination


Anaerobic degradation processes take place in the absence of oxygen. A septum sealed bottle nozzle fills the head space above the sample with inert gas. When anaerobic degradation has taken place, the dissolved CO2 can be driven off and then removed from the head space by means of a CO2 absorber. The resulting pressure difference is proportional to the CO2 concentration; the remaining overpressure is proportional to the methane concentration. The degradation process can be conveniently observed in the “pressure” operating mode.

OxiTop® Control AN6/AN12 and OxiTop® Control A6/A12 – Determination of the Respiration Rate

Microbiological growth and stress investigations: determination of the respiration rate (aerobic/anaerobic measurements)


The use of special measuring bottles with a septum sealed nozzle allows the interference-free addition of substrates and solutions. Pressure alterations could indicate a reduction in oxygen concentration, which could necessitate the addition of oxygen, air, or other gases. It is possible to set a “warning pressure” or a pressure limit so adjustments can be made. The momentary pressure can be stored so the adjustments are fully documented. The recording of these measured values (max. 10 values) permits long-term measurement.



OxiTop® Box – Thermostat box with forced air circulation for 20 (±0,5 °C)


  • Compact
  • Precise
  • Uniform temperature distribution

OxiTop® Box with hinged, non-corrosive, clear-view cover accommodates a maximum of either 12 OxiTop® simultaneous measurements or 20 Karlsruhe bottles. 
The chamber is equipped with a connection for an IS 6 or IS 12 stirrer. 
A special compartment is provided for 6 methylene blue samples. 
A cross ventilation fan ensures uniform temperature distribution and automatic defrosting system with condensate evaporation, plus the compressor is CFC-free.

Temperature control 20 °C ±0.5 °C
Ambient temperature Storage: -25 °C ... +50 °C
Operation: +10 °C ... +32 °C
Power consumption 200 W
Dimensions (H x W x D) 375 x 425 x 600 mm

Thermostat Cabinets


  • Versatile
  • Powerful
  • Cost-effective

To incubate samples at a constant, desired temperature during the reaction period, a thermostat cabinet is necessary. WTW offers thermostat cabinets in various sizes with a variably adjustable temperature range of 10 °C - 40 °C (50 °F - 104 °F) and a power supply of 230 V/50 Hz. Temperature accuracy lies at ±1 °C deviation from the set temperature. 
Because the samples must be stirred, the thermostat cabinets are fitted with internal power sockets. 2 – 4 shelves are available, according to the thermostat cabinet size, thus enabling simultaneous temperature control of up to 48 standard BOD samples, or 4 IS 12 or IS 6-Var stirrer platforms. 
The largest model, TS 1006-i is especially suited for special applications, as the space between the 4 shelves allows for 1.5 l vessels or flasks with side nozzles. 
The sizes TS 606/2-i aTS 606/4-i are available with transparent insulating glass doors and are especially suited for use with the OxiTop® Control system. Data can be recalled through the closed glass door, to avoid temperature fluctuations caused by opening the door.

Model   TS 606/2-i TS 606/4-i TS 1006-i
Shelves   2 4 4 widely spaced
Number of samples   2 x 12 BOD standard 4 x 12 BOD standard 4 x 12 BOD standard 
4 x 6 special vessels
Glass door   Optional Optional
Temp. control range   +10 °C … +40 °C ±1 K; adjustment interval: 1 °C +10 °C … +40 °C ±1 K; adjustment interval: 1 °C +10 °C … +40 °C ±1 K; adjustment interval: 1 °C
Ambient temperature   Operation: +10 °C ... +32 °C (Climate class SN); 
Storage: -25 °C … +65 °C
Operation: +10 °C ... +32 °C (Climate class SN); 
Storage: -25 °C … +65 °C
Operation: +10 °C ... +32 °C (Climate class SN); 
Storage: -25 °C … +65 °C
Gross contents   180 l 360 l 500 l
(H x B x D)
850 x 602 x 600 mm
734 x 513 x 433 mm
1589x602x600 mm 
1418x513x433 mm
1515 x 755 x 715 mm 
1338 x 646 x 516 mm