(a) Aerobic treatment: This treatment is done with the help of aerobic microorganisms (aerobes) in the presence of air (oxygen) which break down the organic
impurities present in the waste and convert them into carbon dioxide, water, and
simpler biomass. Aerobic wastewater treatment processes include various treatments such as activated sludge process, trickling filters, lagoon-based treatments,
aerobic digestion, etc. (Source: Mittal 2011).
(b) Anaerobic treatment: This treatment is done with the help of anaerobic microorganisms in the absence of oxygen, which can break down the organic waste
matter and convert it into methane, carbon dioxide, and simple biomass (Source:
Mittal 2011).
• The various biological and natural treatments of effluents and sludge are given as
follows.
7.5.1 Activated Sludge
This process was first operated in the early 1900s with the word “activated” referring
to solids that catalyze the degradation of the waste. Although there are many types of
activated sludge process, but all have two things in common: they rely on pumping
of surplus oxygen into the reactor, and they artificially accelerate the microbial mass
in the reactor by isolating and returning back to the activated sludge tank a large
portion of microbial cells in the reactor effluents. The activated sludge runs in two
unit operations: the activated sludge bioreactor and the secondary clarifier. Since the
production of microbial cells in the activated sludge reactor are particles; they can be
separated from the water via sedimentation. This is done in the secondary clarifier.
Much of the cell mass that is settled out in the clarifier is returned to the bioreactor
via the return activated sludge (RAS) line. However, to maintain a steady-state
concentration in the bioreactor, a portion must also be wasted through a waste
activated sludge (WAS) line to compensate for the new cell mass being synthesized
in the activated sludge tank (Master and Ela 1991).
7.5.2 Trickling Filters
Trickling filters were first used in 1893. This method is highly known for the
contribution by diversity of life forms such as rotifers, annelid worms, snails, and
many insects in treatment of wastewater. Wastewater is sprayed on a circular bed
made of plastic packing or other coarse materials with the help of rotating distribution arm. The media used in trickling filter are of two types: rock media and synthetic
media (Gonzalez 1996). “First size” rocks were used as packing media and are still in
use due to low-cost operations and their filter depth being only 0.9–3 m (3–10 ft) and
for synthetic media depth goes up to 12 m (40 ft) (Benefield and Randall 1980), but
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D. Angmo et al.
impurities present in the waste and convert them into carbon dioxide, water, and
simpler biomass. Aerobic wastewater treatment processes include various treatments such as activated sludge process, trickling filters, lagoon-based treatments,
aerobic digestion, etc. (Source: Mittal 2011).
(b) Anaerobic treatment: This treatment is done with the help of anaerobic microorganisms in the absence of oxygen, which can break down the organic waste
matter and convert it into methane, carbon dioxide, and simple biomass (Source:
Mittal 2011).
• The various biological and natural treatments of effluents and sludge are given as
follows.
7.5.1 Activated Sludge
This process was first operated in the early 1900s with the word “activated” referring
to solids that catalyze the degradation of the waste. Although there are many types of
activated sludge process, but all have two things in common: they rely on pumping
of surplus oxygen into the reactor, and they artificially accelerate the microbial mass
in the reactor by isolating and returning back to the activated sludge tank a large
portion of microbial cells in the reactor effluents. The activated sludge runs in two
unit operations: the activated sludge bioreactor and the secondary clarifier. Since the
production of microbial cells in the activated sludge reactor are particles; they can be
separated from the water via sedimentation. This is done in the secondary clarifier.
Much of the cell mass that is settled out in the clarifier is returned to the bioreactor
via the return activated sludge (RAS) line. However, to maintain a steady-state
concentration in the bioreactor, a portion must also be wasted through a waste
activated sludge (WAS) line to compensate for the new cell mass being synthesized
in the activated sludge tank (Master and Ela 1991).
7.5.2 Trickling Filters
Trickling filters were first used in 1893. This method is highly known for the
contribution by diversity of life forms such as rotifers, annelid worms, snails, and
many insects in treatment of wastewater. Wastewater is sprayed on a circular bed
made of plastic packing or other coarse materials with the help of rotating distribution arm. The media used in trickling filter are of two types: rock media and synthetic
media (Gonzalez 1996). “First size” rocks were used as packing media and are still in
use due to low-cost operations and their filter depth being only 0.9–3 m (3–10 ft) and
for synthetic media depth goes up to 12 m (40 ft) (Benefield and Randall 1980), but
112
D. Angmo et al.