It is well-known in the scientific literature that alkaline hydrolysis is usable for degrading of organophosphor insecticides, such as ethyl-parathion, methyl-parathion, sulfotep and malathion, to less toxic, water-soluble metabolites. The agro-chemical industry manufacturing these pesticides has for years handled spillage in the production process by irrigation with alkaline solutions. In the same way the manufactures have used alkaline hydrolysis as pre-treatment of wastewater containing organophosphates before the wastewater moves on to biological treatment.
In situ alkaline hydrolysis has never before been used for remediation of soil and groundwater contaminated with organophosphor insecticides. But during the period 2005-2008 promising results have been attained in the lab and in small scale field experiments.
The principles of soil remediation using in situ alkaline hydrolysis
- The contaminated area is encapsulated by a steel sheet pile wall
- The encapsulated area is drained leaving as little groundwater as possible
- Treatment cycle:
Infiltration of the encapsulated soil by diluted sodium hydroxide – pH in the water phase is raised to 12.
Incubation time and enhancement of contact between alkaline solution and contamination – Some incubation time is necessary though enhancement methods will catalyze the process below the ground.
Pump and treat – the alkaline solution containing the water-soluble metabolites of ethyl-parathion is pumped to the surface and treated in a biological treatment plant.
- The treatment cycle is repeated 2 to 3 times