Factors limiting the supply and efficiency of nutrient and oxygen supplements for the in situ biotreatment of contaminated soil and groundwater

Abstract

In situ biotreatment of contaminated soil and groundwater requires the provision of optimal conditions for biodegradation in the subsurface. The supply of inorganic nutrient solutions and oxygen in the form of dilute H 2O 2 was investigated using a number of soils in order to determine limitations of injection and infiltration technologies. It was found that migration of phosphate was limited by the precipitation of insoluble salts and that this reduced soil permeability. Sodium tripolyphosphate was found to reduce partially the amount of precipitation but disrupted soil structure. The addition of inorganic nitrogen to an oil-contaminated soil was found to inhibit mineralization of glucose and phenanthrene. The use of H 2O 2 as an oxygen source at concentrations above approx. 100 mg H 2O 2 l −1 was restricted by decomposition reactions. Precipitation of oxidation products and bubble formation owing to degassing resulted in significant reductions in soil permeability. Sodium tripolyphosphate also reduced chemically-catalysed cleavage of H 2O 2 but extensive biologically-mediated breakdown still occurred. The results demonstrate that significant difficulties may be encountered when using inorganic nutrient and H 2O 2 solutions for site bioremediation but the effects are site-specific. Detailed assessments of individual sites are a necessary pre-requisite to any in situ biotreatment programme.