ABSTRACT
Oxygen phase transfer plays an essential role for successful application of enhanced aerobic biodegradation (e.g. biosparging, oxygen bubble walls) for dissolved organic contaminants in groundwater. The key parameter for the efficiency of this in situ technologies is the microscopic transfer coefficient a. Assuming that diffusion in the water phase is the rate limiting process, the stagnant film model yields α ≈ 3.3·10−8 m/s (Schwarzenbach et al., 1993). Recent experimental and theoretical investigations (Donaldson et al., 1997) indicate that for column experiments with a water velocity u ≅ 4m/day the transfer coefficient is by 2 orders of magnitude larger (α ≈ 10−6 m/s); hence the stagnant film model breaks down in this velocity range. In order to prove this important conclusion, we have calculated the breakthrough curve once again both in constant volume- and in constant pressure approach. Based on our calculations we reinterpret the experimental results of Donaldson et al. and obtain α ≈ 10−8 m/s. The reason for this discrepancy is that Donaldson et al. used the wrong differential equation for the residual gas phase. Therefore our main conclusion is that the stagnant film model is still valid for higher velocities (up to 4m/day) and gives the right order of magnitude for α.
