Dewatering aerobic pig slurry in reed-planted drying bed

The reed-planted drying bed is a phosphorus separation and concentration process which has been tested with aerobic slurry. Two prototypes of 6.6 m2 received 76 835 liters of aerobic slurry which came from an activated sludge-treatment.One of the filtering tank was covered with a plexiglas hothouse. Thoughout one year, 200 kg DM/m2 was distributed with weekly supply of 1.4 kg DM/m2 in winter and 8.4 kg DM/m2 in summer. During the whole distribution period, namely 19 months, losses in percolation flow exceded 80 % for dry matter, 90 % for KN, P2O5, SS, BOD5, COD and 99 % for copper and zinc. At the end of this period, sludges height were 131 cm (average in the two tanks) and they have an average concentration of 15.3 % DM – 0.51 % KN – 1.17 % P2O5 and 0.25 % K2O. The dryness reaches 17.0 % after 5.5 months of dewatering in situ, then 26.4 % after 2.5 additional months dewatering on a covered platform.Covering the drying bed had neither effect on purification performances nor on by-products compositions. The building cost of 2 units of 200 m2 which can filter 1800 m3 of aerobic slurry and retain 4320 kg P2O5 was estimated under 50 000 euros.