Degradation of 2-chlorobenzoic acid in stabilised/solidified soil systems

The possibility of facilitating organic contaminant biodegradation within eight different stabilised/solidified soil systems was investigated. Two soils, a silty sand and clayey silt contaminated with 2-chlorobenzoic acid, were mixed with two different grouts; Portland cement grout and a magnesium phosphate cement grout. The effect of a soil amendment (green waste compost) was examined. Biological activity was monitored using plate counts and dehydrogenase activity. After 106 days, contamination within the silty sand soil/Portland cement mix was reduced by approximately 60% on average, and by over 95% on average with compost addition. Cement grout addition gave substantial changes in the microbial communities present, with Portland cement leading to initial decreases in microbial numbers (by up to a factor of 104) but with a corresponding increase in dehydrogenase activity (by 250% with added compost). Subsequently, microbial numbers increased and the dehydrogenase activity reduced to negligible levels. Magnesium phosphate cement addition led to a decrease in the presence of bacteria and an increase in fungi, whilst with added compost high levels of dehydrogenase activity were maintained for 106 days. It is concluded that contaminant degradation can occur in stabilised/solidified soil systems, but the role of microbes in this removal is not certain.Scientific relevanceThis paper investigates the possibility of combining biodegradation of organic contaminants with in situ stabilisation/solidification techniques, providing both short-term and long-term contaminant control for contaminated land. The latter technique is in use around the world and is becoming more commonplace in the UK; however, there are concerns about its long-term performance in retaining contamination, which the proposed amendment seeks to address.