Bulk Properties

BOD5

Biochemical Oxygen Demand (BOD) is an empirical test that measures the relative oxygen requirements of waters. It is an index of the biochemical degradation of organic material and the oxygen used to oxidise inorganic material such as sulphides and ferrous iron present in the sample.

The test measures molecular oxygen consumption (depletion) over an incubated time period. AST's BOD5 method incubates samples at 20°C for a period of 5 days.  Dissolved Oxygen (DO) is measured before and after incubation, and the BOD5 is computed from the difference. This method is based on APHA method 5210 B (16.1).

The BOD5 test is applicable to most types of water samples including waste waters, sewage effluents and trade wastes. The “Oxitop" or respirometric (continuous oxygen uptake) method is less robust then the BOD5 method and hence the BOD5 method is the preferred BOD method offered by AST. BOD is measured as mg O2/L.

 

COD

Chemical Oxygen Demand (COD) is used as an estimate of the amount of organic matter in wastewater. COD is often used as a measurement of pollutants in wastewater and natural waters.  It is related to BOD and Total Organic Carbon.  The quantity of oxidant consumed is expressed as its oxygen equivalence as mg O2/L. The test is suitable for water and waste water. Saline samples (with chloride >2000 mg/L) are not suitable for this method due to interference.

 

Oil and Grease

“Oil and Grease" is any group of substances that are soluble in a solvent extraction and are non-volatile at 85ºC.  The major components are usually fatty matter from animal and vegetable sources and hydrocarbons from petroleum sources. Other components can be present, depending on the industrial source of the effluent. Oil and Grease substances can have an influence on biological processes including those occurring in wastewater treatment plants and thus may require monitoring.

At AST the Oil and Grease analysis takes place by extracting the dissolved or emulsified sample using hexane. The hexane is evaporated from the extracted sample compounds and the remaining mass of material (defined as Oil and Grease) is measured gravimetrically. The method is based on US EPA Method 1664 and APHA Method 5520 B and is measured in mg/L.


Chlorophyll a

All green plants contain chlorophyll a, which constitutes approximately 1 to 2% of the dry weight of planktonic algae.  Photosynthetic pigment measurements are used extensively to estimate phytoplankton biomass.

Chlorophyll a is sometimes linked to nutrient levels and is sometimes measured as part of environmental monitoring programs.

Light and heat will degrade chlorophyll. Keep water samples and filters protected from light and keep chilled and as much as practicable.

Chlorophyll a is measured as mg/m3 (water samples) or mg (filter).

AST also offers the Tasmanian River Condition Index (TRCI) methodology.


Organic Carbon

Carbon is one of the most abundant elements on earth and occurs as many different chemical forms. The following diagram gives a general break down of how the different forms of carbon are described from an analytical laboratory perspective:


The methodology offered by AST for organic carbon in water is Nonpurgable Organic Carbon (NPOC) and dissolved (filtered) NPOC (dNPOC). Bicarbonate, carbonate and carbon dioxide are offered by the Alkalinity method. Suspended organic carbon can be estimated from Volatile suspended solids (VSS).

It may be desirable to monitor NPOC as a check for natural background levels, or for checking for organic contaminants in otherwise clean waters.

AST's NPOC method separates inorganic carbon and purgable organic carbon from the sample by addition of acid and subsequent purging of the formed CO2.   The sample then undergoes wet chemical oxidation with heated persulfate. The formed CO2 is then measured directly by infrared detector. AST's method is NATA accredited to measure NPOC and dNPOC in drinking (potable), surface, ground, effluent, trade waste and saline waters. NPOC is measured as mg/L.

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