In the Plouvorn site, a 4 years study is realized on a pilot scale pig manure treatment system using a natural soil process. The experiment is done under field conditions. The treatment is done in 3 stages: a managed field (3280 m2) from which all the leachate water that percolate through the soil can be recovered, a storage pump reactor system (160, 350 and 450 m3 capacity) where the denitrification process occur and to complete the treatment, a non-managed field. The manure treatment follows these operations: 1) over application is done to the managed field with manure, 2) the nitrate leachate is then collected and treated, 3) and the leachate that has been denitrified is irrigated over the fields. The objective of this project is to evaluated the performances of such systems for manure treatment, considering the nitrogen removal efficiency for the soil/water system used. From 1991 and 1994, and average of 980 m3 per year have been applied to the managed field for a total of 3919 m3 of raw manure per ha. The manure spreading was done in individual spreadings of 157 m3/ha from March-April through October of each year for a total nitrogen load of 756 kg total N per hectare. The leachate coming from the managed field contained high nitrates concentrations (concentrations ranging from 440 to 828 mg/L, measured during the last season) which show that the nitrification process was in the soil. The leachate was subsequently denitrified at and average rate of 0.5 to 1 kg N per day for a retention time in the reactor of 10 to 60 days. The results obtained show that this treatment process is a promising method for nitrogen removal.

No information is given on the expected life time of such soil filter and also on the other nutrients in the manure. No mention is done of the potential leaching of other nutrients as build up in the soils occurs with applications that go on. The increase in the concentration of some nutrients could also lead to toxicity levels for the growth of the vegetal cover that are meant to uptake those nutrients.