GROUNDWATER AND LEACHATE: EX-SITU CHEMICAL/PHYSICAL TREATMENT
(Granulated) Activated Carbon (GAC)/Liquid Phase Carbon Adsorption
Typical Fixed-Bed Carbon Adsorption System
Process:
Uses:
Note:
Limitations:
Cost:
Highly variable - dependent on wastewater flow rates, type of contaminant, concentration of contaminant, mass loading, required effluent concentration, and site and timing requirements.
e.g. Costs are lower with lower concentration levels of a contaminant of a given type. Costs are also lower at higher flow rates.
- Ground water is pumped through one or more vessels containing activated carbon to which dissolved organic contaminants adsorb.
- When the concentration of contaminants in the effluent from the bed exceeds a certain level, the carbon can be regenerated in place; removed and regenerated at an off-site facility; or removed and disposed.
Uses:
- Target contaminant treatment group: hydrocarbons, SVOCs and explosives
- Often used to treat municipal, industrial, and hazardous wastes.
- Carbon used for explosives- or metals-contaminated ground water probably cannot be regenerated and should be removed and properly disposed.
- The fixed-bed configuration is the most widely used for adsorption from liquids (shown above).
Note:
- Pre-treatment is required to remove suspended solids from stream - otherwise these would accumulate in the column, causing an increase in pressure drop.
- When the pressure drop becomes too high, the accumulated solids must be removed (e.g. by backwashing) - thus get downtime.
- The carbon bed can be modified with other materials (e.g. silicone) to increase removal efficiency and extend the length of operation. It may also be safer to regenerate.
- The duration of GAC is usually short-term (unless very low contaminant concentration)
- Carbon adsorption is particularly effective for polishing water discharges from other remedial technologies - to ensure low enough concentration levels to attain regulatory compliance.
- Carbon adsorption systems can be deployed rapidly, and contaminant removal efficiencies are high.
Limitations:
- The presence of multiple contaminants can impact process performance.
- Streams with high suspended solids (> 50 mg/L) and oil and grease (> 10 mg/L) may cause fouling of the carbon - would require pre-treatment & more frequent bed regeneration..
- Costs are high if used as the primary treatment on wastestreams with high contaminant concentration levels.
- Type, pore size, and quality of the carbon, as well as the operating temperature, will impact process performance.
- Highly Water-soluble compounds and small molecules are not adsorbed well.
- All spent carbon eventually need to be properly disposed.
- Logistic and economic disadvantages arise from the need to transport and decontaminate spent carbon.
Cost:
Highly variable - dependent on wastewater flow rates, type of contaminant, concentration of contaminant, mass loading, required effluent concentration, and site and timing requirements.
e.g. Costs are lower with lower concentration levels of a contaminant of a given type. Costs are also lower at higher flow rates.