Soil and Groundwater Contamination Survey and Countermeasure Technologies

Category of Tchnology	Treatment	Treatment
Media	Soil Gas, Others (Off-gas from the Stripper)
Contaminants	Volatile Chlorinated Organic Compounds (TCE, PCE, etc)
	Applied (Demonstrated) Substances	Trichloroethylene
Scope	Concentration Range
	Hydrogeological Conditions	-	-
	Chemical Soil Properties
	Other Remarks
Technology Description	Classification	Decomposition
	Status	Under Development Soil and Groundwater Countermeasure Test Study (Performed 1994)
	Outline of Technology	Trichloroethylene contained in waste gas is condensed in a tank filled with activated carbon, and the trichloroethylene removed by being exposed to hot air is thermally decomposed by catalysts in an oxygenated environment. A thermal decomposition test was made with the removal concentration controlled at 7500±2500 ppmv.  The decomposing temperature was between 475°C and 525°C.  This technology is aimed at improving the efficiency in the treatment of the waste gas by absorbing and condensing trichloroethylene even if the concentrations are low.
	Required Pre- and Post-treatment	The waste gas after the decomposing process, which may contain unintentionally formed toxic substances, needs to be treated.
	Enhance Effectiveness through Combination
	Case History	A demonstrative test, made to establish the optimum operating conditions, obtained the following results:  (1) In order to increase the decomposing efficiency, it is necessary to control the temperature for the process, including the heat desorption from the activated carbon tank. (2) The post-decomposition waste gas contains undecomposed trichloroethylene and chlorobenzens. (3) 99.9% of  the trichloroethylene was decomposed when the temperature of reaction exceeds 500°C.  However, considerable concentration of trichloroethylene remains in the treated gas, because the waste gas before treatment contains more than 7000 ppmv of trichloroethylene.  (4) Because the thermal decomposition takes place in an oxygenized environment, the waste gas contains chlorobenzenes.
	Application Examples
	Limitations	It is necessary to have the whole system, including the temperature control for the desorption from the activated carbon tank and for catalysts layer, under automatic control.
	Properties of Treated Soil	-
Schematic Flow Process	Pilot Plant for Catalytic Thermal Decomposition of Trichloroethylene
Applicability	In Situ Applicability	Possible
	Ground Structures	-
	Required Excavation	None
	Groundwater Extraction	None
	Required Space
	Operational Time
	Installation Time
	Maintenance and Control Requirements
	Additional Remarks
Secondary Impacts to Environment	Secondary Treatment Required?	Off-gas Treatment
	Effects on Living Environment
	Additives	Air
	Possibility of Contaminant Spreading	A proper treatment of the waste gas will prevent contaminants from dispersing.
	Secondary By-products	Toxic substances may form because trichloroethylene is thermally decomposed in an oxygenized atmosphere.

• Understanding the Contamination Survey and Countermeasure Technology Description Sheet
• Where to make contact

Soil Environment Management Division, Water Environment Department, Environmental Management Bureau, Ministry of Environment
Tel: +81-3-5521-8319
E-mail: MOE@env.go.jp