Some Useful Definitions

To understand the concept of biological treatment processes, it will be helpful to know the following definitions.

Aerobic processes are biological treatment processes that occur in the presence of oxygen. Anaerobic processes are biological treatment processes that occur in the absence of oxygen.

Anoxic denitrification is the process by which nitrate-nitrogen is converted biologically into nitrogen gas in the absence of oxygen. This process is also known as anaerobic denitrification.

Biological nutrient removal is the term applied to the removal of nitrogen and phosphorus in the biological treatment processes.

Nitrification is the biological process by which ammonia is converted first to nitrite and then to nitrate.

Denitrification is the biological process by which nitrate is converted into nitrogen gas. Substrate is the term for the organic matter or nutrients that are converted during the biological treatment or that may be limiting in the biological treatment. Suspended-growth processes are the biological treatment processes in which the microorganisms responsible for the conversion of the organic matter or other constituents in the waste water to gases and cell tissue are maintained in suspension within the liquid. Attached-growth processes are the biological treatment processes in which the microorganisms responsible for the conversion of the organic matter or other constituents in the waste water to gases and cell tissue are attached to some inert medium such as rocks, slag, or specially designed ceramic or plastic materials. Attached-growth treatment processes are also known as fixed-film processes.

BOD5 (Biological oxygen demand): The determination of the biochemical oxygen demand (BOD) is an empirical test in which standardized laboratory procedures are used to determine the relative oxygen requirements of waste water, effluents, and polluted waters during 5 days. The test measures the oxygen required for the biochemical degradation of organic material and the oxygen used to oxidize inorganic material such as sulphides and iron. It may also be used to oxidize reduced forms of nitrogen unless their oxidation is prevented by an inhibitor. The method consists of placing a sample in a full, airtight bottle and incubating the bottle under specified conditions for a specific time. Dissolved oxygen (DO) is measured initially and after the incubation. The BOD is computed from the difference between initial and final DO.

COD (chemical oxygen demand): The chemical oxygen demand (COD) is a measure of the oxygen equivalent of the organic matter content of a sample that is susceptible to oxidation by a strong chemical oxidant. For samples from a specific source COD can be related empirically to BOD, organic carbon or organic matter content. Ammonia (NH3) is a gas that is very soluble in water. Ammonia is a base. Ammonia is produced in nature when any nitrogen-containing organic material decomposes in the absence of air.

Ammonia is a colourless gas with an irritating odour. Gaseous ammonia has a vapor pressure of about 10 atmospheres at 25°C, and is readily liquefied, giving a colourless liquid that boils at minus 33°C.

Ammonium is a weak base, ammonia readily accepts protons from acids and hydronium ions, forming salts of the ammonium ion (NH4+).

Ammonium-nitrogen or ammonium-N: both terms are used to indicate that the nitrogen is calculated as 1 mole of ammonium-N equal to 14 g of ammonium-N. It convinient to calculate from one nitrogen form to another using this term. Nitrate: (N03") Is a substrate for the denitrification process. Nitrate-N: as for ammonium-N

Nitrite: (N02") In the gas phase this exists in equilibrium with the colourless dimer N204. When it dissolves in water, nitrogen dioxide disproportionates and forms nitric acid. It is a component of the nitrification process. Nitrite-N: as for ammonium-N

PART B

BIOLOGICAL UNIT PROCESSES FOR THE REMOVAL OF NITROGEN

NITRIFICATION DENITRIFICATION ATTACHED GROWTH PROCESSES TRICKLING FILTER ROTATING BIOLOGICAL CONTACTER SUBMERGED FILTERS SUSPENDED GROWTH PROCESSES ACTIVATED SLUDGE PROCESSES

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