Typically when K values that are greater than 200 are attained the process is
considered to be economically feasible [9]. In addition, the process of GAC can be
fine-tuned, that is, certain basic parameters such as pH, temperature, or choice of
carbon source can be altered to increase efficiency of the process when certain
critical contaminants such as pesticides must be removed.
Careful monitoring and testing are required to ensure that all contaminants are
removed. The carbon media must be replaced regularly. The replacement intervals
depend on:
1. Type of contaminant
2. Concentration
3. Rate of water usage
4. Type of carbon used in the system
There is potential for bacterial growth on the adsorbed organic chemicals; routine
maintenance must be performed. When POU devices are used for compliance for
small systems, programs for long-term operation, maintenance, and monitoring must
be provided by the water utility.
4.2 Powdered Activated Carbon (PAC)
Powdered activated carbon (PAC) also functions by adsorption of contaminants
from water onto a solid phase material, in this case powdered carbon. PAC differs
from GAC in that the powdered carbon is added to the water in a large tank, a period
of time is provided for adsorption of the contaminants to occur, and then the
powdered carbon is later removed in a filtration process [40]. This process also
differs from GAC in that PAC needs to be added continually to the process;
however, the process is less expensive and less technically demanding, but it is
more labor intensive. PAC is more adaptable to short-term applications rather than as
a continual use process. For contaminants such as pesticides which are mostly used
during a six-week period in late spring and summer, PAC may be a particularly
useful choice [9]. The water being treated comes into contact with much less carbon
material per unit volume treated, so the process is not as efficient as GAC.
GAC is the BAT (best available technology) for removal of all of the selected
EDCs that were discussed in the previous section. However, since other technologies
are used in the multistep process of drinking water treatment, a brief discussion is
included for those processes that enhance the performance of GAC.
4.3 Coagulation/Filtration
Coagulation/filtration processes involve the addition of chemicals like iron salts and
aluminum salts, with and without anionic, cationic, or anionic-cationic polymers that
186
N. K. Shammas et al.
considered to be economically feasible [9]. In addition, the process of GAC can be
fine-tuned, that is, certain basic parameters such as pH, temperature, or choice of
carbon source can be altered to increase efficiency of the process when certain
critical contaminants such as pesticides must be removed.
Careful monitoring and testing are required to ensure that all contaminants are
removed. The carbon media must be replaced regularly. The replacement intervals
depend on:
1. Type of contaminant
2. Concentration
3. Rate of water usage
4. Type of carbon used in the system
There is potential for bacterial growth on the adsorbed organic chemicals; routine
maintenance must be performed. When POU devices are used for compliance for
small systems, programs for long-term operation, maintenance, and monitoring must
be provided by the water utility.
4.2 Powdered Activated Carbon (PAC)
Powdered activated carbon (PAC) also functions by adsorption of contaminants
from water onto a solid phase material, in this case powdered carbon. PAC differs
from GAC in that the powdered carbon is added to the water in a large tank, a period
of time is provided for adsorption of the contaminants to occur, and then the
powdered carbon is later removed in a filtration process [40]. This process also
differs from GAC in that PAC needs to be added continually to the process;
however, the process is less expensive and less technically demanding, but it is
more labor intensive. PAC is more adaptable to short-term applications rather than as
a continual use process. For contaminants such as pesticides which are mostly used
during a six-week period in late spring and summer, PAC may be a particularly
useful choice [9]. The water being treated comes into contact with much less carbon
material per unit volume treated, so the process is not as efficient as GAC.
GAC is the BAT (best available technology) for removal of all of the selected
EDCs that were discussed in the previous section. However, since other technologies
are used in the multistep process of drinking water treatment, a brief discussion is
included for those processes that enhance the performance of GAC.
4.3 Coagulation/Filtration
Coagulation/filtration processes involve the addition of chemicals like iron salts and
aluminum salts, with and without anionic, cationic, or anionic-cationic polymers that
186
N. K. Shammas et al.