What Is BOD?
BOD analysis measures the amount of dissolved oxygen consumed as micro-organisms break down organic matter in water. The specimen is incubated in sealed bottles in the dark at constant temperature; the difference between the initial and final oxygen values is calculated as BOD.
Purpose of BOD
The purpose is to determine wastewater's biodegradable pollution load and generate design and operating data for biological treatment plants.
Which Products Is BOD Applied To?
- Domestic and industrial wastewater
- Treatment plant inlet and outlet waters
- Surface waters
- Food and beverage sector wastewater
- Discharge monitoring specimens
In Which Sectors Is BOD Used?
Standards Related to BOD
- TS EN 1899-1 (BOD — dilution and seeding with allylthiourea addition)
- TS EN 1899-2 (BOD — for undiluted samples)
- TS EN ISO 5815-1/-2 (biochemical oxygen demand)
- TS EN ISO 5667-3 (preservation of samples)
BOD Conditions
- Incubation
- At the temperature defined in the standard, in the dark, for the defined number of days
- Seeding
- Seed is added to specimens without sufficient micro-organisms
- Nitrification
- Nitrification is suppressed with allylthiourea; otherwise the result is elevated
- Dilution
- Suitable dilutions are prepared so oxygen is not exhausted
Equipment for BOD
- BOD incubator (temperature-controlled, dark)
- Dissolved oxygen meter or BOD measurement system
- BOD bottles
- Dilution water preparation equipment
Sample Requirements for BOD
- Sampling is the largest component of total uncertainty in environmental analysis. The specimen container, preservation (acidification, cooling, storage in the dark), fill method and time to reach the laboratory are all defined in the standard; if any one is not met, the result loses its validity. Sampling must be carried out by authorised personnel per a written plan.
- The specimen must be delivered cooled and without delay
- Must be reported if it contains a disinfectant or toxic substance — it kills the micro-organisms
- The specimen must be well homogenised and no air bubbles left
Duration of BOD
The incubation period is an integral part of the method and cannot be shortened; the result can only be given once this period is complete. This makes BOD one of the longest routine parameters among environmental analyses.
BOD Procedure
- 1Dilutions are prepared per the specimen's expected BOD range.
- 2Seed and a nitrification inhibitor are added if required.
- 3Bottles are filled leaving no air bubbles.
- 4Initial dissolved oxygen values are measured.
- 5Bottles are incubated in the dark at the defined temperature.
- 6Oxygen is measured again at the end of the period and BOD is calculated.
BOD Acceptance Criteria
The acceptance criterion is the BOD limit value in discharge legislation per the facility's sector, or the value defined in the discharge permit. 91/271/EEC also requires a minimum treatment efficiency for urban treatment plants.
Evaluation of Results
If a toxic substance or disinfectant is present, the micro-organisms cannot function and BOD comes out below the true value; this is a common error in treated but chlorinated specimens. If nitrification is not suppressed, nitrogen oxidation also consumes oxygen and the result shows the organic load as higher than it is.
BOD Report
- Specimen identification, sampling point and date
- Standard and dilution ratios applied
- Seeding and nitrification inhibition information
- Initial and final oxygen values
- BOD result (mg O2/L) and measurement uncertainty
- Limit value compared against
Accreditation
EUROLAB holds internationally recognised accreditation obtained from accreditation bodies party to the IAF and ILAC multilateral recognition arrangements, under ISO/IEC 17025 for laboratory testing, ISO/IEC 17020 for inspection and surveillance, and ISO/IEC 17021-1 and ISO/IEC 17065 for system and product certification. This chain ensures the reports and certificates issued are accepted worldwide.
Whether this test can be offered within accredited scope depends on your product and the standard applied; since accreditation is method-based, the scope is confirmed in writing at the quotation stage.
Scope and authorisationsRelated Regulations
- 91/271/EEC Urban Waste Water Treatment Directive
- 2000/60/EC Water Framework Directive
- (EU) 2010/75 Industrial Emissions Directive
Environmental Analysis — What Does This Testing Field Cover?
The section below describes the field that the BOD test belongs to; the conditions and acceptance criteria of this particular test are given in the sections above. The scope specific to your product is confirmed in writing at the quotation stage.
Environmental analysis determines the presence and concentration of pollutants in water, soil, waste, air and flue gas samples. The output of this family is usually part of a permit, a declaration or an inspection file; the result has direct legal consequences.
In this family SAMPLING is half the result, and this is the feature that most sets the field apart. A sample taken at the wrong time, in the wrong container, under the wrong preservation or from the wrong point gives an invalid result no matter how well it is analysed in the laboratory. In waste water a grab sample and a composite sample give different information; in soil, surface and depth produce different results. Sampling therefore has its own standards and its own accreditation scope.
On the water side, physico-chemical parameters (pH, conductivity, turbidity, COD, BOD, suspended solids), ions, heavy metals, organic pollutants and microbiological parameters are measured. Drinking water and waste water carry different parameter sets and different limits; the same laboratory method leads to a different decision under the two regimes.
In soil and waste, heavy metals, hydrocarbons, PAH and PCB compounds and LEACHING BEHAVIOUR are determined. The leaching test carries a logic peculiar to this field: it is not the total amount of a pollutant in soil but the fraction that can pass into water that determines the environmental risk. Waste classification and the disposal decision rest largely on this test.
On the emissions side, dust, sulphur dioxide, nitrogen oxides, carbon monoxide, oxygen, moisture and total organic carbon are monitored in flue gas. Measurement is made on site under operating conditions and must represent the plant's actual operating regime; a measurement taken at low load does not show the emissions at full capacity.
Continuous measurement systems are a separate body of work. In large plants emissions are monitored continuously and the accuracy of these systems is verified periodically by comparison with independent measurements; the quality assurance framework governs this.
Noise and vibration measurements complete the environmental impact side of the field: environmental noise mapping, workplace noise exposure and vibration exposure measurements produce evidence for both environmental and occupational health legislation.
Method groups in this field
Sampling
Separate sampling standards for water, waste water, soil, waste, flue gas and ambient air; grab, composite and continuous sampling techniques.
Water physico-chemical
pH, conductivity, turbidity, colour, suspended solids, COD, BOD, TOC, alkalinity, nitrogen and phosphorus species.
Elemental analysis
Determination of heavy metals and trace elements in water, soil and waste by ICP-OES and ICP-MS.
Organic pollutants
Volatile organic compounds, PAH, PCB and organochlorine pesticides by GC-MS; hydrocarbon oil index.
Flue gas
Measurement of dust, SO2, NOx, CO, O2, moisture and total gaseous organic carbon; quality assurance of automated measuring systems.
Leaching and waste characterisation
Leaching tests and waste classification parameters; the basis for the disposal decision.
Commonly confused in this field
- An analytical result cannot be used on its own without the sampling record; the time, point, conditions and chain of custody are part of the report.
- Total content and leachable amount give different information; in waste classification, leaching behaviour is what counts.
- Emission measurement must be made under representative operating conditions of the plant; a result taken at partial load is misleading.
- Drinking water and waste water limits are defined in different legislation; the same parameter carries a different threshold under the two regimes.
- A sample from a single point does not represent the whole area; assessment of a contaminated site requires a grid-based sampling plan.
Which decisions these results support
- Compliance with environmental permits and discharge limits
- Quality assurance of continuous emission measurement systems
- Contaminated site assessment and the remediation decision
- Waste classification and selection of the disposal method
- Workplace exposure measurements and occupational health obligations
Related Tests
Frequently Asked Questions About BOD
Why does the result take so long?
Because the incubation period is part of the method's definition: it is the time micro-organisms need to break down the organic matter and cannot be shortened. If a fast result is needed, COD or TOC are more suitable parameters.
Can BOD be measured in chlorinated effluent?
Yes, but the chlorine must be neutralised and the specimen seeded; otherwise the micro-organisms cannot function and the result comes out unrealistically low. This is stated in the report.