BOD Analysis

What is Biochemical Oxygen Demand (BOD)?

Biochemical Oxygen Demand (BOD) is defined as the amount of dissolved oxygen that must be present in water in order for microorganisms to decompose the organic matter in the water, used as a measure of the degree of pollution. The decay of organic matter in water is measured as biochemical oxygen demand. Biological oxygen demand is essentially a measure of the amount of oxygen required to remove waste organic matter from water in the process of decomposition by aerobic bacteria.

There are a few methods approved for determining biological oxygen demand, although one of them is used overwhelmingly by the analytical community. It is known as Standard Methods 5210B. This method analyzes the difference in dissolved oxygen from a sample for five days. A known volume of sample has its initial DO content recorded and after a five-day incubation period at 20°C, the sample is removed from the incubator and the final DO content is taken. Generally, the BOD5 is perceived as the BOD for controlling wastewater treatment plants (WWTP). However, there are nitrification inhibitors added to the BOD5 to suppress the nitrogen degradation. Obviously, the nitrification is an important part of the biological degration of organics and thus is very important for the control of wasteawater treatment plants. Consequently, the BOD5 is poorly suited for the control of wastewater treatment plants.

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SOURCES OF BOD

Leaves and woody debris; dead plants and animals; animal manure; effluents from pulp and paper mills, wastewater treatment plants, feedlots, and food-processing plants; failing septic systems; and urban storm water runoff.

WHAT IS TOXICITY?

Toxicity is described as the direct harmful effect of a substance on organisms. These effects can already occur at low concentrations of toxic substances and are dependent on the incubation period and the dosage. Some test methods that are available on the market can detect toxicity, but they do not however identify exactly which toxins are present. By using fish, daphnia, mollusks, algae or luminous bacteria, they simply test whether a water sample has a toxic effect.

The goal of toxicity testing is to develop data that can ensure appropriate protection of public health from the adverse effects of exposures to environmental agents.

NITRIFICATION RESPIRATION INHIBITION TEST

The bacteria (nitrifiers) used live on oxygen from the conversion of ammonia to nitrate. Our NitriTox™ and ToxAlarm™ measures this oxygen consumption. Toxic substances in the sample contents can inhibit the respiration of the bacteria leading to a lowering of the oxygen consumption. Thereby the nitrifiers’ oxygen consumption enables to draw conclusions about the toxicity of a sample. Our analyzer test takes 5-15 minutes and is characterized by its self-regenerating, integrated bacteria culture. Hence, no purchase or external breeding is necessary.

THE DIFFERENCE TO COMMON METHODS

The LAR Process Analysers AG’s measurement method uses a bacteria culture which constantly and independently produces biomass in a fermenter. This fermenter is separated from the measuring cell. For each measurement a fresh amout of bacteria is used. This guarantees that there is always enough bacteria for new measurements and the risk of the fermenter being contaminated is removed. For this reason, there is no purchase or external breeding of organisms necessary.

being contaminated is removed. For this reason, there is no purchase or external breeding of organisms necessary.

	*Algae*	*Bioluminescence*	*Daphnia*	*Fish Test*	*Nitrifiers*
Supply	Purchase / breed	Purchase / breed	Purchase / breed	Purchase / breed	Self-regenerating
Duration	72 h	50 min	24 or 48 h	48 h	5 min
Sensitivity	very high	middling	very high	high	very high
Continuous monitoring after accident	yes	yes	no	no	yes

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COMMON TOXICITY MEASUREMENT METHODS

ALGAE

Often the unicellular green algae are used to indicate toxicity. This method measures the inhibition of cell division caused by toxic substances. At high toxic concentrations, algae can die. Hence, new algae have to be stored and kept in stock to ensure further toxicity measurements after a toxic effect. The algae test takes 72 hours, and the supply of the test organisms must be secured by purchase or breed.

BIOLUMINESCENCE

Bioluminescence is the production and emission of light by a living organism. Specific detectors measure the emitted light and draw conclusions on toxicity. Toxic substances cause a reduction of the emitted light. Commonly, this standard method uses Vibrio fischeri as test organisms. These bacteria glow under optimal growth conditions (bioluminescence). The bioluminescence is reduced by toxic substances in the sample and may lead to death of the organisms. The bioluminescence test takes 50 minutes. The used test organisms must be purchased or bred.

DAPHNIA

Daphnia are crustaceans between 0.2 to 5 mm in length. Commonly, these small animals called water fleas and are often used for the determination of toxicity. However, for toxicity measurements, they must not be older than 24 hours. The used Daphnia Magna are very sensitive to heavy metals but less to other substances. Toxic substances cause the death of the organisms, following which the number of surviving organisms are counted. The daphnia test takes 24 or 48 hours, and the organisms must be bred.

FISH TEST

The fish test – also known as golden orfe test – describes an animal experiment, which aims to determine at what dilution of wastewater all animals survive 48 hours. The result is the smallest integer value of the dilution of the wastewater (GF value). As with the common test methods, the toxic substances cause the death of the organisms. At the end of the test the number of surviving fish are counted. In Germany the fish test has been replaced since 2005 by the fish egg test. The fish test takes 48 hours. The used test organisms must be purchased or bred.

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