The SOLEPUR process for the treatment of pig slurry, based on the treatment effect of the soil, was developed in France to explore the notion that a simple biobarrier approach may be a potential efficient solution to the large accumulation of liquid animal wastes residues. The unit consists of (i) a managed field (3280 m2) which allows the total recovery of all the leachate water which percolates through growing ryegrass (Lolium perenne), to which the pig slurry is applied, (ii) a system of storage-pump-reactor for denitrification and (iii) a non-managed field for completing treatment. The process involves three operations: (1) overdosing the managed field with surplus slurry (about 1000 m3 pig slurry/ha.year applied from 1991 to 1994), (2) collecting and treating the nitrate-rich leachate and (3) irrigating the final treated water over other fields. This process decreased COD of pig slurry by 99.9 % and removed 99.9 % of phosphorus and approximately 80 % of nitrogen. The remaining nitrogen was oxidized in the soil into nitrate and leached out in the drainage water. The process of denitrification was selected to remove nitrate from the leachate and raw pig slurry was used as an external carbon source.

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