Means to improve the effect of in situ bioremediation of contaminated soil: an overview of novel approaches

Different aspects of bacterial degradation of organic contaminants in soil, and how to improve the efficiency and reproducibility is discussed in this review. Although bioremediation in principle includes the use of any type of organism in improving the condition of a contaminated site, most commonl y bacteria are the degraders and other organisms, such as soil animals or p lant roots, play a role in dissemination of bacteria and, indirectly, plasm ids between bacteria, and in providing nutrients and co-substrates for the bacteria active in the degradation process. There are a number of different procedures that have been tested more-or-less successfully in attempts to improve reliability, cost efficiency and speed of bioremediation. The metho ds range from minimal intervention, such as mere monitoring of intrinsic bi oremediation, through in situ introduction of nutrients and/or bacterial in ocula or improvement of physico-chemical conditions, all the way to excavat ion followed by on site or ex situ composting in its different varieties. I n the past the rule has been that more intervention (leading to higher cost s) has been more reliable, but novel ideas are continuously tried out, both as a means to come up with new truly functional applications and also as a line of studies in basic soil microbial ecology. Both approaches generate valuable information needed when predicting outcome of remediation activiti es, evaluating environmental risks, deciding on cleaning-up approaches, etc . The emphasis of this review is to discuss some of the novel methods for w hich the value has not been clearly shown, but that in our view merit conti nued studies and efforts to make them work, separately or in combination. ( C) 2000 Elsevier Science Ltd. All rights reserved.