Steam activation of the charcoal is carried out at a high temperature (up to 1000 deg C) in a steam atmosphere. The activation reaction between charcoal and steam can be described as follows:
C + H2O => CO + H2
C + CO2 => 2 CO
The activation process can be controlled to achieve specific product characteristics. Steam concentrations, temperature, activation time and CO2 concentrations influence pore development, which in turn affect pore size distributions and the level of activity.
Because of its unique structure, activated carbon possesses an exceptional ability to capture water-dissolved contaminants thereby removing taste, odour, chlorine and other unwanted contaminants. The removal takes place through the adsorption process due to the surface interactions between contaminants and carbon graphitic platelet surfaces.
These contaminant-carbon surface interactions occur through Van der Waal forces and induced dipole interactions. Activated carbon graphitic platelets induce neutral organic molecules into intra-molecular dipoles. The induced dipoles cause the molecules to be attracted to each other and stick together, so they precipitate out of solution in the carbon’s nano-sized pores or adsorption spaces. This is referred to as premature condensation, facilitated by the activated carbon.
WOOD ACTIVATED CARBON IN POWDERED FORM(PAC)
Powdered, micron-sized activated carbon particles are milled from millimetre granular activated carbon and exhibit faster kinetics and a greater capacity for contaminant removal, when compared to carbons with larger particle sizes.
Powdered activated carbon can be used for sporadic contaminant episodes, such as algae blooms and industrial spills, that contaminate municipal influent waters. The powder can be added to the clarification process settling unit to remove these contaminants with activated carbon. It can also protect fixed activated granular carbon beds against sudden influent contamination.
Plants can use powder instead if they lack the infrastructure to use granular activated carbon or do not have enough granular carbon between the influent and the effluent to economically use for removal in sporadic contaminant episodes. The single-use powdered activated carbon is used as a batch process to remove contaminants to acceptable regulated maximum contamination levels (MCLs) but not necessarily to zero or non-detected contamination.
WIDELY USED GRADES OF WOOD PAC
WOOD ACTIVATED CARBON IN GRANULAR FORM(GAC)
Millimetre-sized granular activated carbon can remove contaminants to concentrations below analytical detection limits, and compared to powder, it requires only about one-fourth the amount of carbon between influent and effluent.
Granular activated carbon use is a continuous process, and it is a multiple-use product based on thermal reactivation. Thermal reactivation enables the carbon to be classified as “green chemistry.”
Where the possibility of industrial pollution is relatively high, more activated carbon must be readily available for possible emergencies. It can be kept in fixed vessels between the influent and effluent.
WIDELY USED GRADES OF WOOD BASED GAC
- Fruit juice – Decolorization and deodorization
- Soft drinks – Sugar syrup decolorization
- Sweeteners – Sucrose, glucose and fructose syrup purification
- Monosodium Glutamate (MSG) – Decolorization and stabilization
- Citric acid – Fermentation and purification
- Lactic acid – Decolorization of extracts
- Gelatin – Remove solid impurities and decolorization
- Edible oil – PAH, PCB removal and color modification
- Glycerine – Decolorization and odor removal