17 Scope of Conventional Versus Advanced Technologies …
385
• Anaerobic processes: In this process, fermentation of the waste in wastewater at
a specific temperature is carried out without any oxygen supply.
• Composting: This is an aerobic process in which wastewater is treated by mixing
it with sawdust or other sources of carbon.
Chemical Water Treatment (CWT) CWT involves the use of chemicals in water
for purification. Chlorine is an oxidizing agent and forms hypochlorous acid
(HOCl) with water. This HOCl is highly effective in killing the disease causing
microorganisms.
Cl 2 + H 2 O → HOCl + HCl
Hypochlorous acid
Ozone and potassium permanganate are also utilized as oxidizing agents for
purifying the wastewaters.
If the pH of wastewaters is low or high (depending upon impurities), neutralization
is done by adding acid or base to bring the water to its neutral pH of 7. The chemicals
added to wastewater prevent the bacteria from reproducing in water, thus preventing water contamination. There are several other chemical processes, like chemical
coagulation, chemical precipitation, chemical oxidation, advanced oxidation, ion
exchange and chemical neutralization, and stabilization which are also applied to
wastewater during the cleaning process.
Sludge treatment It is a type of secondary management for removal of most of the
undesired solids present in wastewaters, leaving aside, nitrogen and phosphorous
which may remain as dissolved nutrients. It is focused on dewatering of sludge from
industrial wastewater or sewage plants whereby the disposal costs are reduced and
potential health risks of disposal options are also reduced. It can be performed by
two ways.
Activated sludge treatment This is the most commonly used modern process for the
biological treatment of sewage. In this process, the sewage having organic matter with
microorganisms is aerated in an aeration tanks using a mechanical aerator. The reactor
contents are referred to as mixed liquor. Under aerobic conditions, the microorganisms metabolize the soluble and suspended organic matter. The generalized metabolic
reaction is as follows.
CONHS + O 2 + Nutrients Bacteria
−−−−−−−→
CO 2 + NH 3 + H 2 O
(Organic matter)
In conventional activated sludge treatment process, the activated sludge is first
processed in primary sedimentation tank. The system consists of a separation, settling
or sedimentation tank, and sludge removal line (Fig. 17.1). The sewage after the
primary treatment is introduced at the head of the tank where O 2 is supplied uniformly
throughout the tank.
385
• Anaerobic processes: In this process, fermentation of the waste in wastewater at
a specific temperature is carried out without any oxygen supply.
• Composting: This is an aerobic process in which wastewater is treated by mixing
it with sawdust or other sources of carbon.
Chemical Water Treatment (CWT) CWT involves the use of chemicals in water
for purification. Chlorine is an oxidizing agent and forms hypochlorous acid
(HOCl) with water. This HOCl is highly effective in killing the disease causing
microorganisms.
Cl 2 + H 2 O → HOCl + HCl
Hypochlorous acid
Ozone and potassium permanganate are also utilized as oxidizing agents for
purifying the wastewaters.
If the pH of wastewaters is low or high (depending upon impurities), neutralization
is done by adding acid or base to bring the water to its neutral pH of 7. The chemicals
added to wastewater prevent the bacteria from reproducing in water, thus preventing water contamination. There are several other chemical processes, like chemical
coagulation, chemical precipitation, chemical oxidation, advanced oxidation, ion
exchange and chemical neutralization, and stabilization which are also applied to
wastewater during the cleaning process.
Sludge treatment It is a type of secondary management for removal of most of the
undesired solids present in wastewaters, leaving aside, nitrogen and phosphorous
which may remain as dissolved nutrients. It is focused on dewatering of sludge from
industrial wastewater or sewage plants whereby the disposal costs are reduced and
potential health risks of disposal options are also reduced. It can be performed by
two ways.
Activated sludge treatment This is the most commonly used modern process for the
biological treatment of sewage. In this process, the sewage having organic matter with
microorganisms is aerated in an aeration tanks using a mechanical aerator. The reactor
contents are referred to as mixed liquor. Under aerobic conditions, the microorganisms metabolize the soluble and suspended organic matter. The generalized metabolic
reaction is as follows.
CONHS + O 2 + Nutrients Bacteria
−−−−−−−→
CO 2 + NH 3 + H 2 O
(Organic matter)
In conventional activated sludge treatment process, the activated sludge is first
processed in primary sedimentation tank. The system consists of a separation, settling
or sedimentation tank, and sludge removal line (Fig. 17.1). The sewage after the
primary treatment is introduced at the head of the tank where O 2 is supplied uniformly
throughout the tank.