Environmental Engineering Reference
In-Depth Information
• Acute toxicity - this is an indicator, which shows that the constituent leads to the death
of the animal studied. The LD 50 value indicates the lethal dose, leading to death, in
50% of the individuals tested, for a specified time, e.g. 24h.
• Chronic toxicity - this is a dose, which, if ingested on a daily basis, leads to the
premature death of the tested individuals. ADI (Acute Daily Intake) indicates a
maximum dose ingested daily over a lifetime, which could be withstood by the
metabolism of an individual without any risk.
• Cytotoxicity - this indicates doses of constituents, leading to the death of a certain
percentage of cells. The tests are performed on cell cultures, but not on animals.
• Mutagenicity - this is a toxic effect, causing mutations in the tested individuals. The
risk exists regardless of the dose of the constituent.
• Carcinogenicity - similar to mutagenicity, this is a toxic effect, which after ingestion or
exposure causes the appearance of a malignant tumor.
2.2.4
Organic constituents
In general, the tests to determine the organic content of water and wastewater may be
divided into two categories. The first category measures gross concentrations of organic
matter, greater than 1 mg/l. It includes Biochemical Oxygen Demand (BOD), Chemical
Oxygen Demand (COD) and Total Organic Carbon (TOC). The second category
measures trace concentrations in the range of 10
-12
to 1 mg/l. Normally, instrumental
methods as gas chromatography and mass spectroscopy are used to determine trace
organics.
The trace organic constituents found in water are derived from the breakdown of
naturally occurring organic materials, domestic, commercial, industrial and agricultural
activities. Naturally occurring organic materials include humic materials,
microorganisms, and aliphatic and aromatic hydrocarbons. Organic materials from
humans' activities often identified as “synthetic organic compounds” (SOCs) include
constituents such as: pesticides, herbicides, degreasers, solvents, etc. A special class of
SOCs known as “volatile organic compounds” (VOCs) is of concern in water pollution
control because many of these compounds are possible or known human carcinogens.
• Biological Oxygen Demand (BOD) - by definition this is the quantity of oxygen
consumed at 20ºC andin darkness during a given period to produce the oxidation of
the biodegradable organic matter present in water by biological means. The standard
test is performed for a period of 5 days and is denominated as BOD
5.
The BOD test is
the most common test used in the field of wastewater control and treatment. If
sufficient oxygen is available, the aerobic biological decomposition of an organic
waste will continue until all of the waste is consumed.
• Chemical Oxygen Demand (COD) - this test is used to measure the oxygen equivalent
of the organicmaterial in wastewater that can be oxidized chemically using dichromate
in an acid solution. In the vast majority of cases, COD of a given sample exceeds
considerably its BOD value, because the chemical oxidation includes organic
materials, which are difficult to biodegrade or are non-biodegradable.
• Total organic carbon (TOC) - this test is performed instrumentally, and it only takes 5
to 10 minutesto complete. It measures the organic carbon incorporated in organic
materials present in a water sample, and as such represents the amount of the
