Persulfate in Remediation of Soil and Groundwater Contaminated by Organic Compounds

The use of persulfate for the abatement of a wide variety of organic pollutants in soil and groundwater has proved to be an efficient technology in the last 10 years, mainly for in situ application. Persulfate shows higher stability in soil and groundwater than hydrogen peroxide, has moderate cost and benign by-products. Moreover, it can be applied to a wide range of pH and show less affinity for natural organic matter than does the permanganate ion. Persulfate can be activated in different ways to generate free radicals able to react with organic pollutants at higher rates than the persulfate anion. Heat, iron and base are the main activators used, although dual oxidant systems hydrogen peroxide–persulfate has been also investigated. The radical species formed in persulfate activation can be sulfate, hydroxyl or superoxide, depending mainly on pH and the activator used. These radicals can attack the organic matter in an oxidative mechanism, as sulfate and hydroxyl radicals do, or in a reductive pathway, as does the superoxide radical. Therefore, by choosing the proper activator and conditions, activated persulfate system can be used to eliminate a wide range of organic contaminants. Moreover, the stability of the activators in the subsurface is critical to assess the feasibility for an in situ application and must be taken into account to choose the optimal method for each particular case.