Natural Source Zone Depletion (NSZD) Quantification Techniques: Innovations and Future Directions

Natural source zone depletion (NSZD) is an emerging technique for sustainable and cost-effective bioremediation of light non-aqueous phase liquid (LNAPL) in oil spill sites. Depending on regulatory objectives, NSZD has the potential to be used as either the primary or sole LNAPL management technique. To achieve this goal, NSZD rate (i.e., rate of bulk LNAPL mass depletion) should be quantified accurately and precisely. NSZD has certain characteristic features that have been used as surrogates to quantify the NSZD rates. This review highlights the most recent trends in technology development for NSZD data collection and rate estimation, with a focus on the operational and technical advantages and limitations of the associated techniques. So far, four principal techniques are developed, including concentration gradient (CG), dynamic closed chamber (DCC), CO2 trap and thermal monitoring. Discussions revolving around two techniques, CO2 trap and thermal monitoring, are expanded due to the particular attention to them in the current industry. The gaps of knowledge relevant to the NSZD monitoring techniques are identified and the issues which merit further research are outlined. It is hoped that this review can provide researchers and practitioners with sufficient information to opt the best practice for the research and application of NSZD for the management of LNAPL impacted sites.

Automated summary

Natural source zone depletion (NSZD) is a promising technique for the sustainable bioremediation of LNAPL in oil spill sites. Accurate quantification of NSZD rate is crucial for its successful application. This review examines the latest trends in NSZD data collection and rate estimation techniques, with a focus on CO2 trap and thermal monitoring. The study identifies knowledge gaps and highlights areas for further research in NSZD monitoring.