their reactivity and then introduced to the oxidation reactor. After oxidation, the
effluents from this reactor are sent to another vessel to maintain the pH. Sometimes,
the efficiency of this treatment process can be enhanced by using ultra-violet rays as
catalyst. When the refinery wastewater contains high level of toxic materials like
aromatic fractions, then secondary biological treatment is unsuitable; however,
chemical oxidation can degrade these wastes (International Petroleum Industry
Environmental Conservation Association 2010; Shahryar 2017; Alireza 2014).
Disinfection
During disinfection, chlorine solution (bleaching) is injected into the disinfectant
tank to destroy the microorganisms including bacteria, viruses and protozoa, like
Salmonella, Shigella and Vibrio cholera. Disinfection is also sometimes referred to
as chlorination. Chlorine is the most widely used disinfectant, because it controls
odour, activated bulk sludge, foaming, removes grease, ammonia and destroys
cyanides, phenols. In some refineries, ozone or ultra-violet rays are also used for
disinfection to enhance the efficiency.
Nowadays, chlorination is frequently used for wastewater treatment before
discharging water to river, streams, local aquatic bodies and ocean. The amount of
chlorine solution depends on the quality, quantity and pH of wastewater, contact
time and effluent temperature. However, the dosage of chlorine used usually ranges
from 5 to 15 mg/L. The chlorine-containing chamber is maze shaped, equipped with
baffles to avoid short-circuiting. In the reaction chamber, the contact time usually is
about 30 min, but for advanced wastewater treatment, the contact time may be as
long as 120 min in order to use the treated water for irrigation (International
Petroleum Industry Environmental Conservation Association 2010; Shahryar
2017; Mareddy 2017).
Sand Filtration
After secondary wastewater treatment, typically 25–80 mg/L of total suspended
solids, 5–25 mg/L of organic suspended solids in colloidal form are present in the
effluent ,depending on the working condition of the clarifier. But some refinery
effluents are required to meet low levels of suspended solids (15 mg/L). Hence, the
solids of effluents from clarifier should be filtered by sand filter. For better removal
of large suspended particles, dual filter is used (described earlier in Section Induced
Air Floatation). Filtration can reduce colloidal and suspended solids level to around
3–20 mg/L (International Petroleum Industry Environmental Conservation Association 2010; Shahryar 2017; Mareddy 2017).
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effluents from this reactor are sent to another vessel to maintain the pH. Sometimes,
the efficiency of this treatment process can be enhanced by using ultra-violet rays as
catalyst. When the refinery wastewater contains high level of toxic materials like
aromatic fractions, then secondary biological treatment is unsuitable; however,
chemical oxidation can degrade these wastes (International Petroleum Industry
Environmental Conservation Association 2010; Shahryar 2017; Alireza 2014).
Disinfection
During disinfection, chlorine solution (bleaching) is injected into the disinfectant
tank to destroy the microorganisms including bacteria, viruses and protozoa, like
Salmonella, Shigella and Vibrio cholera. Disinfection is also sometimes referred to
as chlorination. Chlorine is the most widely used disinfectant, because it controls
odour, activated bulk sludge, foaming, removes grease, ammonia and destroys
cyanides, phenols. In some refineries, ozone or ultra-violet rays are also used for
disinfection to enhance the efficiency.
Nowadays, chlorination is frequently used for wastewater treatment before
discharging water to river, streams, local aquatic bodies and ocean. The amount of
chlorine solution depends on the quality, quantity and pH of wastewater, contact
time and effluent temperature. However, the dosage of chlorine used usually ranges
from 5 to 15 mg/L. The chlorine-containing chamber is maze shaped, equipped with
baffles to avoid short-circuiting. In the reaction chamber, the contact time usually is
about 30 min, but for advanced wastewater treatment, the contact time may be as
long as 120 min in order to use the treated water for irrigation (International
Petroleum Industry Environmental Conservation Association 2010; Shahryar
2017; Mareddy 2017).
Sand Filtration
After secondary wastewater treatment, typically 25–80 mg/L of total suspended
solids, 5–25 mg/L of organic suspended solids in colloidal form are present in the
effluent ,depending on the working condition of the clarifier. But some refinery
effluents are required to meet low levels of suspended solids (15 mg/L). Hence, the
solids of effluents from clarifier should be filtered by sand filter. For better removal
of large suspended particles, dual filter is used (described earlier in Section Induced
Air Floatation). Filtration can reduce colloidal and suspended solids level to around
3–20 mg/L (International Petroleum Industry Environmental Conservation Association 2010; Shahryar 2017; Mareddy 2017).
260
M. Samanta and D. Mitra