Dechlorination The removal of chlorine from the effluent of a treatment plant.
Deforestation Those practices or processes that result in the conversion of forested
lands for nonforest uses. Deforestation contributes to increasing carbon dioxide
concentrations for two reasons: 1) the burning or decomposition of the wood
releases carbon dioxide; and 2) trees that once removed carbon dioxide from the
atmosphere in the process of photosynthesis are no longer present.
Denitrification filter It is an attached-growth biological process filter using wood,
plastic, rock, granular activated carbon, or sand as filtration media for denitrification (conversion of nitrate to nitrogen gas) of wastewater under anoxic/anaerobic condition.
Denitrification followed by flotation clarification The process involves the reduction of nitrates and nitrites to nitrogen gas through the action of facultative
heterotrophic bacteria. In suspended-growth separate stage denitrification processes, nitrified wastewater containing primarily nitrates is passed through a
mixed anaerobic vessel containing denitrifying bacteria. Since the nitrified feedwater contains very little carbonaceous materials, a supplemental source of
carbon (such as methanol, sugar, acetic acid, ethanol, or other compounds) is
required to maintain the denitrifying biomass. This supplemental energy is
provided by feeding methanol, for instance, to the biological reactor along with
the nitrified wastewater. Mixing in the anaerobic denitrification reaction vessel
may be accomplished using low-speed paddles analogous to standard flocculation
equipment. Flotation clarification follows the denitrification step with the floated
sludge being either returned to the head end of the denitrification system or
wasted. An intermediate aeration step for stabilization (much less than
40 minutes) may be needed to guard against carryover of carbonaceous materials.
The denitrification reactor may be covered but not airtight to assure anaerobic
conditions.
Denitrification followed by membrane clarification Same as “denitrification
followed by flotation clarification” except that the flotation clarification is
replaced by a membrane filtration reactor.
Denitrification followed by sedimentation clarification The process involves the
reduction of nitrates and nitrites to nitrogen gas through the action of facultative
heterotrophic bacteria. In suspended-growth separate stage denitrification processes, nitrified wastewater containing primarily nitrates is passed through a
mixed anaerobic vessel containing denitrifying bacteria. Since the nitrified feedwater contains very little carbonaceous materials, a supplemental source of
carbon (such as methanol, sugar, acetic acid, ethanol, or other compounds) is
required to maintain the denitrifying biomass. This supplemental energy is
provided by feeding methanol, for instance, to the biological reactor along with
the nitrified wastewater. Mixing in the anaerobic denitrification reaction vessel
may be accomplished using low-speed paddles analogous to standard flocculation
equipment. Following the reactor, the denitrified effluent is aerated for a short
period (5 to 10 minutes) to strip out gaseous nitrogen formed in the previous step,
which might otherwise inhibit sludge settling. Sedimentation clarification follows
442
M.-H. S. Wang and L. K. Wang
Deforestation Those practices or processes that result in the conversion of forested
lands for nonforest uses. Deforestation contributes to increasing carbon dioxide
concentrations for two reasons: 1) the burning or decomposition of the wood
releases carbon dioxide; and 2) trees that once removed carbon dioxide from the
atmosphere in the process of photosynthesis are no longer present.
Denitrification filter It is an attached-growth biological process filter using wood,
plastic, rock, granular activated carbon, or sand as filtration media for denitrification (conversion of nitrate to nitrogen gas) of wastewater under anoxic/anaerobic condition.
Denitrification followed by flotation clarification The process involves the reduction of nitrates and nitrites to nitrogen gas through the action of facultative
heterotrophic bacteria. In suspended-growth separate stage denitrification processes, nitrified wastewater containing primarily nitrates is passed through a
mixed anaerobic vessel containing denitrifying bacteria. Since the nitrified feedwater contains very little carbonaceous materials, a supplemental source of
carbon (such as methanol, sugar, acetic acid, ethanol, or other compounds) is
required to maintain the denitrifying biomass. This supplemental energy is
provided by feeding methanol, for instance, to the biological reactor along with
the nitrified wastewater. Mixing in the anaerobic denitrification reaction vessel
may be accomplished using low-speed paddles analogous to standard flocculation
equipment. Flotation clarification follows the denitrification step with the floated
sludge being either returned to the head end of the denitrification system or
wasted. An intermediate aeration step for stabilization (much less than
40 minutes) may be needed to guard against carryover of carbonaceous materials.
The denitrification reactor may be covered but not airtight to assure anaerobic
conditions.
Denitrification followed by membrane clarification Same as “denitrification
followed by flotation clarification” except that the flotation clarification is
replaced by a membrane filtration reactor.
Denitrification followed by sedimentation clarification The process involves the
reduction of nitrates and nitrites to nitrogen gas through the action of facultative
heterotrophic bacteria. In suspended-growth separate stage denitrification processes, nitrified wastewater containing primarily nitrates is passed through a
mixed anaerobic vessel containing denitrifying bacteria. Since the nitrified feedwater contains very little carbonaceous materials, a supplemental source of
carbon (such as methanol, sugar, acetic acid, ethanol, or other compounds) is
required to maintain the denitrifying biomass. This supplemental energy is
provided by feeding methanol, for instance, to the biological reactor along with
the nitrified wastewater. Mixing in the anaerobic denitrification reaction vessel
may be accomplished using low-speed paddles analogous to standard flocculation
equipment. Following the reactor, the denitrified effluent is aerated for a short
period (5 to 10 minutes) to strip out gaseous nitrogen formed in the previous step,
which might otherwise inhibit sludge settling. Sedimentation clarification follows
442
M.-H. S. Wang and L. K. Wang