Environmental Engineering Reference
In-Depth Information
25.3 Treatment Technologies
Nowadays there is much focus on the reuse of water. Hence, high-level treatment of waste-
water becomes important. If possible, wastewater should be treated to drinking water
quality. In the case of industrial wastewater also, tertiary levels of treatment should be
carried out to meet the discharge standards. Biological treatment can be used, but it is time
consuming. Presently, activated sludge process (ASP) is the most commonly used method
for wastewater treatment. It is ineficient in removing recalcitrant compounds from water.
Membrane technologies such as ultrailtration, nanoiltration, or reverse osmosis give
good results but they make the system expensive and pretreatment is required to prevent
clogging. Advanced oxidation processes (AOPs) are effective in degrading the compounds.
Photocatalytic methods are widely used for water treatment since they produce highly
oxidative species like hydroxyl and superoxide radicals. In the case of wastewater treat-
ment, photocatalysis can be used as a pre- or posttreatment system in order to increase the
eficiency of the treatment.
25.3.1 Activated Sludge Process
The ASP is the most commonly used treatment process in conventional WWTPs. The organic
matter present in the wastewater gets biodegraded under aerobic conditions. This method
is very eficient in removing the suspended and dissolved solids in water. The organic mat-
ter gets degraded by the microorganisms, and the locs get settled at the bottom of the tank.
ASPs are not eficient in removing most of the emerging contaminants from water.
25.3.2 Membrane Bioreactors
In membrane bioreactors (MBRs), the organic matter gets degraded irst, after which the
particles are removed by membrane iltration. Efluent from an MBR is superior to the
efluent from an ASP. Compared with an ASP, an MBR is more eficient in removing emerg-
ing contaminants from water. In biological processes, more time is required to degrade the
pollutants. The eficiency of the system can be improved by increasing the retention time,
which makes the biological process time consuming in treating emerging contaminants.
25.3.3 Membrane Processes
Membrane processes include microiltration, ultrailtration, and nanoiltration, and re-
verse osmosis. The particles are removed by straining in these processes. Reverse osmosis
is very eficient in removing the organic and inorganic constituents in water. The main
drawback of these methods is the high cost associated with the process. The main problem
faced is membrane fouling, which reduces the membrane lux.
25.3.4 Activated Carbon Adsorption
In this method, the pollutants get adsorbed in the pores present in the activated carbon.
Granular activated carbon or powdered activated carbon can be used for this method. The
surface area is very large for these materials, which increases the adsorption eficiency.
More hydrophobic, nonpolar, and low-solubility pollutants are easily removed by this
method. Removal eficiency depends on the time of contact between polluted water and
