Stabilization Pond
The stabilization pond is basically a large pond of low depth where bacteria stabilize
the wastewater introduced to this pond under warm weather conditions. Stabilization
pond is of two types: aerobic and anaerobic based on biological activity. Normally,
refinery biological wastewater treatment involves the aerobic type pond or the
oxidation pond (International Petroleum Industry Environmental Conservation
Association 2010; Shahryar 2017).
The oxidation ponds have excessive weed growth and normally have a depth of
about 1.2 m. Oxygen is supplied to the surface of pond by natural aeration and by the
photosynthesis reaction of algae (Chlamydomonas, Chlorella). The organic matters
are aerobically degraded by the algae, bacteria, fungi, etc., in presence of sunlight.
The efficiency of oxidation ponds is influenced by some factors like temperature,
presence of turbidity and emulsions in the pond. The microbial activity in the pond
slows down with temperature and when ice forms over the surface of pond due to
shortage of oxygen and sunlight, the activity drops abruptly. The emulsion and
turbidity in the pond also diminishes the light transmission and during such situation,
the photosynthetic action of bacteria is inhibited. However, the oxidation ponds
require a sufficiently large space. The advantages of this system are low maintenance
cost. A report of the Environmental Protection Agency states that the removal
efficiency of oxidation pond is 40–95% for biochemical oxygen demand, 65–85%
for chemical oxygen demand, 80–90% for suspended solids and 50–90% for oil
(International Petroleum Industry Environmental Conservation Association 2010;
Shahryar 2017; Alireza 2014).
Aerated lagoons are artificial aerobic stabilization ponds, where oxygen is supplied usually by mechanical devices like pump, diffuser, and bacteria consume the
organic matter, suspended solids in warm weather. It requires less area for wastewater treatment but requires high maintenance of mechanical equipment. According
to the Environmental Protection Agency, the removal efficiency of lagoons is
75–95% for biochemical oxygen demand, 60–85% chemical oxygen demand,
60–95% for suspended solids, 70–90% for 90–99% for phenol and 95–100% for
sulphides. But the efficiency of lagoons also diminishes in cold weather similar to
oxidation ponds, because in absence of sunlight, the bacterial growth reduces,
generating bad odour. By incorporating the clarifier, sludge-return pumps and
additional aeration equipment aerated lagoons can be stepped up to an activated
sludge system (International Petroleum Industry Environmental Conservation Association 2010; Central Pollution Control Board, India 2018; Shahryar 2017; Alireza
2014; Mareddy 2017; Patwardhan 2008).
Attached Growth Process
In the attached growth process, microorganisms are immobilized on inert polymeric
materials. The microorganisms digest the oily wastes with the help of oxygen for
growth of excess biomass, producing carbon dioxide. When a huge amount of
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M. Samanta and D. Mitra
The stabilization pond is basically a large pond of low depth where bacteria stabilize
the wastewater introduced to this pond under warm weather conditions. Stabilization
pond is of two types: aerobic and anaerobic based on biological activity. Normally,
refinery biological wastewater treatment involves the aerobic type pond or the
oxidation pond (International Petroleum Industry Environmental Conservation
Association 2010; Shahryar 2017).
The oxidation ponds have excessive weed growth and normally have a depth of
about 1.2 m. Oxygen is supplied to the surface of pond by natural aeration and by the
photosynthesis reaction of algae (Chlamydomonas, Chlorella). The organic matters
are aerobically degraded by the algae, bacteria, fungi, etc., in presence of sunlight.
The efficiency of oxidation ponds is influenced by some factors like temperature,
presence of turbidity and emulsions in the pond. The microbial activity in the pond
slows down with temperature and when ice forms over the surface of pond due to
shortage of oxygen and sunlight, the activity drops abruptly. The emulsion and
turbidity in the pond also diminishes the light transmission and during such situation,
the photosynthetic action of bacteria is inhibited. However, the oxidation ponds
require a sufficiently large space. The advantages of this system are low maintenance
cost. A report of the Environmental Protection Agency states that the removal
efficiency of oxidation pond is 40–95% for biochemical oxygen demand, 65–85%
for chemical oxygen demand, 80–90% for suspended solids and 50–90% for oil
(International Petroleum Industry Environmental Conservation Association 2010;
Shahryar 2017; Alireza 2014).
Aerated lagoons are artificial aerobic stabilization ponds, where oxygen is supplied usually by mechanical devices like pump, diffuser, and bacteria consume the
organic matter, suspended solids in warm weather. It requires less area for wastewater treatment but requires high maintenance of mechanical equipment. According
to the Environmental Protection Agency, the removal efficiency of lagoons is
75–95% for biochemical oxygen demand, 60–85% chemical oxygen demand,
60–95% for suspended solids, 70–90% for 90–99% for phenol and 95–100% for
sulphides. But the efficiency of lagoons also diminishes in cold weather similar to
oxidation ponds, because in absence of sunlight, the bacterial growth reduces,
generating bad odour. By incorporating the clarifier, sludge-return pumps and
additional aeration equipment aerated lagoons can be stepped up to an activated
sludge system (International Petroleum Industry Environmental Conservation Association 2010; Central Pollution Control Board, India 2018; Shahryar 2017; Alireza
2014; Mareddy 2017; Patwardhan 2008).
Attached Growth Process
In the attached growth process, microorganisms are immobilized on inert polymeric
materials. The microorganisms digest the oily wastes with the help of oxygen for
growth of excess biomass, producing carbon dioxide. When a huge amount of
256
M. Samanta and D. Mitra