Common Treatment Technologies for Halogenated VOCs in Ground Water, Surface Water and Leachate
It may be necessary to know other subsurface information to provide remediation of VOCs in the ground water. Treatability studies to characterize the biodegradability may be needed for any biodegradation technologies. Treatability studies are usually necessary to ensure that the contaminated ground water can be treated effectively at the design flow. A subsurface geologic characterization would be needed for any isolation or stabilization technologies. Ground water models are also often needed to predict flow characteristics, changes in contaminant mixes and concentrations, and times to reach cleanup levels.
The most commonly used technologies to treat halogenated VOCs in ground water, surface water, and leachate are air stripping and carbon adsorption. These are both ex situ technologies requiring ground water extraction.
Air stripping involves the mass transfer of volatile contaminants from water to air. This process is typically conducted in a packed tower or an aeration tank. The generic packed tower air stripper includes a spray nozzle at the top of the tower to distribute contaminated water over the packing in the column, a fan to force air countercurrent to the water flow, and a sump at the bottom of the tower to collect decontaminated water. Auxiliary equipment that can be added to the basic air stripper includes a feed water heater (normally not incorporated within an operational facility because of the high cost) and an air heater to improve removal efficiencies, automated control systems with sump level switches and safety features such as differential pressure monitors, high sump level switches and explosion proof components, and discharge air treatment systems such as activated carbon units, catalytic oxidizers, or thermal oxidizers. Packed tower air strippers are installed either as permanent installations on concrete pads, or as temporary installations on skids, or on trailers.
Liquid phase carbon adsorption is a full-scale technology in which ground water is pumped through a series of vessels containing activated carbon to which dissolved 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 taken off-site for disposal. Carbon used for explosives- or metals-contaminated ground water must be removed and properly disposed of. Adsorption by activated carbon has a long history of use in treating municipal, industrial, and hazardous wastes.
Other fairly common technologies used in separating contaminants from ground water are distillation and membrane pervaporation.
Membrane pervaporation is a process that uses permeable membranes that preferentially adsorb volatile organic compounds (VOCs) from contaminated water. Contaminated water first passes through a heat exchanger, raising the water temperature. The heated water then enters the pervaporation module, containing membranes composed of a nonporous organophilic polymer, similar to silicone rubber, formed into capillary fibers. VOCs diffuse by vacuum from the membrane-water interface through the membrane wall. Treated water exits the pervaporation module, while the organic vapors travel from the module to a condenser where they return to the liquid phase. The condensed organic materials represent only a fraction of the initial wastewater volume and may be subsequently disposed of at a cost savings.