the gas-stripping step with the collected sludge being either returned to the head
end of the denitrification system, or wasted. An intermediate aeration step for
stabilization (about 50 minutes) between the denitrification reactor and the
stripping step may be used to guard against carryover of carbonaceous materials.
The denitrification reactor may be covered but not airtight to assure anaerobic
conditions.
Denitrification (a) The anoxic biological reduction of nitrate-nitrogen to nitrogen
gas. (b) The removal of some nitrogen from a system. (c) An anoxic process that
occurs when nitrite or nitrate ions are reduced to nitrogen gas and nitrogen
bubbles are formed as a result of this process. (d) The biochemical reduction
reaction of reducing nitrate-nitrogen to nitrogen gas in an anoxic environment.
Derived-From Wastes USEPA’s “derived-from” rule regulates any solid waste
generated from the treatment, storage, or disposal of a hazardous waste, including
any sludge, spill residue, ash, emission control dust, or leachate (but not including
precipitation run-off) is a hazardous waste under 40 CFR 261.4(c)(2)(i), with
some specified exclusions.
Desertification Land degradation in arid, semiarid, and dry subhumid areas
resulting from various factors, including climatic variations and human activities.
Further, the UNCCD (The United Nations Convention to Combat Desertification)
defines land degradation as a reduction or loss, in arid, semiarid, and dry
subhumid areas, of the biological or economic productivity and complexity of
rain-fed cropland, irrigated cropland, or range, pasture, forest, and woodlands
resulting from land uses or from a process or combination of processes, including
processes arising from human activities and habitation patterns, such as (i) soil
erosion caused by wind and/or water; (ii) deterioration of the physical, chemical,
and biological or economic properties of soil; and (iii) long-term loss of natural
vegetation. Conversion of forest to nonforest.
Detention time The time required to fill a tank at a given flow or the theoretical time
required for a given flow of wastewater to pass through a tank.
Detoxification The act of detoxifying.
Detritus The heavy, coarse mixture of grit and organic material carried by wastewater (also called grit).
Diffused-air aeration A diffused air activated sludge plant takes air, compresses it,
and then discharges the air below the water surface of the aerator through some
type of air diffusion device.
Diffuser A device used to break the air stream from the blower system into fine
bubbles in an aeration tank or reactor.
Digester A tank in which sludge is placed to allow decomposition by microorganisms. Digestion may occur under anaerobic (more common) or aerobic
conditions.
Digger bee (Ptilothrix bombiformis) They are natural bees of wild species, not
affecting humans. Adults burrow into the ground where they store a mixture of
honey and pollen to be used as larval food. Adults often are seen visiting the
flowers of hibiscus.
12 Glossary of Natural Resources and Environmental Pollution Control
443
end of the denitrification system, or wasted. An intermediate aeration step for
stabilization (about 50 minutes) between the denitrification reactor and the
stripping step may be used to guard against carryover of carbonaceous materials.
The denitrification reactor may be covered but not airtight to assure anaerobic
conditions.
Denitrification (a) The anoxic biological reduction of nitrate-nitrogen to nitrogen
gas. (b) The removal of some nitrogen from a system. (c) An anoxic process that
occurs when nitrite or nitrate ions are reduced to nitrogen gas and nitrogen
bubbles are formed as a result of this process. (d) The biochemical reduction
reaction of reducing nitrate-nitrogen to nitrogen gas in an anoxic environment.
Derived-From Wastes USEPA’s “derived-from” rule regulates any solid waste
generated from the treatment, storage, or disposal of a hazardous waste, including
any sludge, spill residue, ash, emission control dust, or leachate (but not including
precipitation run-off) is a hazardous waste under 40 CFR 261.4(c)(2)(i), with
some specified exclusions.
Desertification Land degradation in arid, semiarid, and dry subhumid areas
resulting from various factors, including climatic variations and human activities.
Further, the UNCCD (The United Nations Convention to Combat Desertification)
defines land degradation as a reduction or loss, in arid, semiarid, and dry
subhumid areas, of the biological or economic productivity and complexity of
rain-fed cropland, irrigated cropland, or range, pasture, forest, and woodlands
resulting from land uses or from a process or combination of processes, including
processes arising from human activities and habitation patterns, such as (i) soil
erosion caused by wind and/or water; (ii) deterioration of the physical, chemical,
and biological or economic properties of soil; and (iii) long-term loss of natural
vegetation. Conversion of forest to nonforest.
Detention time The time required to fill a tank at a given flow or the theoretical time
required for a given flow of wastewater to pass through a tank.
Detoxification The act of detoxifying.
Detritus The heavy, coarse mixture of grit and organic material carried by wastewater (also called grit).
Diffused-air aeration A diffused air activated sludge plant takes air, compresses it,
and then discharges the air below the water surface of the aerator through some
type of air diffusion device.
Diffuser A device used to break the air stream from the blower system into fine
bubbles in an aeration tank or reactor.
Digester A tank in which sludge is placed to allow decomposition by microorganisms. Digestion may occur under anaerobic (more common) or aerobic
conditions.
Digger bee (Ptilothrix bombiformis) They are natural bees of wild species, not
affecting humans. Adults burrow into the ground where they store a mixture of
honey and pollen to be used as larval food. Adults often are seen visiting the
flowers of hibiscus.
12 Glossary of Natural Resources and Environmental Pollution Control
443