Early-stage anaerobic zone formation by organic eluate from wood in soil

When separated soil (SS) generated from the Great East Japan Earthquake, which contains woodchips and others (WC), is utilized as ground material, microorganisms decompose the organic carbon in WC, and oxygen is consumed in the process. This reaction results in forming an anaerobic zone and generating methane gas. To effectively utilize SS as ground material, it is necessary to prevent anaerobic zone formation to ensure safety. This study clarified the relationship between WC content and the concentration of leached organic carbon (TOC) and the relationship between TOC concentration in the eluate and the oxygen consumption rate were clarified. We obtained the relationship between WC content and the extent of anaerobic zone formation from the results,. The anaerobic zone is formed below the oxygen penetration depth (L_O2). L_O2 rapidly decreases as the WC weight ratio increases from 0 to 1 w%, and L_O2 is almost constant, i.e., around 1 to 2 m above 1 w% WC weight ratio. An increase in WC weight ratio does not significantly decrease L_O2 determined by the aerobic decomposition of the solution. From the above, contamination with WC should be limited to 1 w% or less to prevent the formation of an anaerobic zone. If SS has WC above 1 w%, it is required to put a ventilating layer such as crushed stone every few meters or the other countermeasures when SS is utilized as ground material.