Sometimes, undesirable toxic wastes like slugs occur in wastewater of certain
petroleum industries. These unwanted periodic wastes may harm the subsequent
biological treatment process. So, these wastes are held in another tank, mixed with
other effluents and gradually released. The elimination of these slugs is called
equalization (International Petroleum Industry Environmental Conservation Association 2010).
8.4.2 Chemical Treatment Methods
The wastewater is treated by using different chemicals for quality enhancement in
chemical treatment process. The most common chemical treatment processes in
petroleum industry are chlorination, neutralization, coagulation and adsorption.
Chlorination is used for killing the pathogens and bacteria to slow down the
decomposition of wastewater. Ozone is also occasionally used as an oxidizing
disinfectant (International Petroleum Industry Environmental Conservation Association 2010; Shahryar 2017). The acid or base is used for neutralization of base or
acid of wastewater in order to adjust pH level. Another chemical treatment process is
coagulation where polyvalent metal salts (alum, ferric chloride) are used as coagulants for treatment of wastewater by removing substances through precipitation.
Some treatment processes are both physical and chemical like adsorption. In adsorption, pollutants are attached to the surface of porous solids. The most common
industrially used adsorbent is granular activated carbon which is highly porous.
Ion exchange is also sometimes applied to wastewater treatment due to its high
selectivity. The different metal salts (iron, manganese) and hardness are eliminated
by this process (Central Pollution Control Board, India 2018; Mareddy 2017;
Shahryar 2017).
8.4.3 Biological Treatment Methods
In biological treatment microorganisms, typically, bacteria are used for biological
decomposition of polluted water. In biological treatment process, huge amounts of
microorganisms are cultured and they degrade the pollutants, oil sludge and hydrocarbons to form stable products like carbon dioxide, methane, oxygen and nitrogen
gas. Mainly there are two types of biological treatment methods – aerobic and
anaerobic; these methods are differentiated by the availability of dissolved oxygen.
In aerobic method, solid-liquid organic-inorganic contaminants are destroyed
with the help of different microorganisms in presence of oxygen, resulting in the
formation of carbon dioxide. The aerobic treatment is done by the following
methods (Shahryar 2017; Patwardhan 2008; Alireza 2014).
248
M. Samanta and D. Mitra
petroleum industries. These unwanted periodic wastes may harm the subsequent
biological treatment process. So, these wastes are held in another tank, mixed with
other effluents and gradually released. The elimination of these slugs is called
equalization (International Petroleum Industry Environmental Conservation Association 2010).
8.4.2 Chemical Treatment Methods
The wastewater is treated by using different chemicals for quality enhancement in
chemical treatment process. The most common chemical treatment processes in
petroleum industry are chlorination, neutralization, coagulation and adsorption.
Chlorination is used for killing the pathogens and bacteria to slow down the
decomposition of wastewater. Ozone is also occasionally used as an oxidizing
disinfectant (International Petroleum Industry Environmental Conservation Association 2010; Shahryar 2017). The acid or base is used for neutralization of base or
acid of wastewater in order to adjust pH level. Another chemical treatment process is
coagulation where polyvalent metal salts (alum, ferric chloride) are used as coagulants for treatment of wastewater by removing substances through precipitation.
Some treatment processes are both physical and chemical like adsorption. In adsorption, pollutants are attached to the surface of porous solids. The most common
industrially used adsorbent is granular activated carbon which is highly porous.
Ion exchange is also sometimes applied to wastewater treatment due to its high
selectivity. The different metal salts (iron, manganese) and hardness are eliminated
by this process (Central Pollution Control Board, India 2018; Mareddy 2017;
Shahryar 2017).
8.4.3 Biological Treatment Methods
In biological treatment microorganisms, typically, bacteria are used for biological
decomposition of polluted water. In biological treatment process, huge amounts of
microorganisms are cultured and they degrade the pollutants, oil sludge and hydrocarbons to form stable products like carbon dioxide, methane, oxygen and nitrogen
gas. Mainly there are two types of biological treatment methods – aerobic and
anaerobic; these methods are differentiated by the availability of dissolved oxygen.
In aerobic method, solid-liquid organic-inorganic contaminants are destroyed
with the help of different microorganisms in presence of oxygen, resulting in the
formation of carbon dioxide. The aerobic treatment is done by the following
methods (Shahryar 2017; Patwardhan 2008; Alireza 2014).
248
M. Samanta and D. Mitra