Landfarming of Polycyclic Aromatic Hydrocarbons and Mineral Oil Contaminated Sediments

Joop Harmsen, Alterra Wageningen UR, The Netherlands

The large amounts of dredged sediments require an efficient treatment procedure to reduce contaminant levels at low costs and with reasonable spatial demands. Landfarming offers a good solution for sediments contaminated with Polycyclic Aromatic Hydrocarbons (PAHs) and mineral oil. Sediments become aerobic during landfarming, which enables aerobic organisms to biodegrade the contaminants. Two main principles and types of landfarming are distinguished:

• Intensive landfarming, in which processes are optimised using active management activities to reduce contaminants to residual concentrations as quickly as possible,
• Passive landfarming, consisting of minimal management activities that are used when rapid bioremediation is not necessary, but residual concentrations of contaminants must be reduced.

PAHs and mineral oil are strongly ad- or absorbed by the organic matter in the sediment. Biodegradation of these contaminants in landfarmed sediment is shown to be a slow process. Limiting conditions that are discussed and mathematical described include:

• Desorption and diffusion of the contaminant within soil aggregates to a place with active micro-organisms,
• Presence of active micro-organisms,
• Aeration of the dredged sediment.

Landfarming of dredged sediment has been applied from 1990 onwards on the landfarm Kreekraksluizen in the Netherlands. From these long-term experiments it was possible to recognise fast, slow and very slowly degradable fractions of PAHs, degradable in respectively respectively, 1 year, about 7 years, and 30-60 years. Risks are reduced more rapidly and small effects in bio-assays were still measurable after 7 years of treatment. No measurable risks were present after 10 years of treatment.