Reed bed dewatering of agricultural sludges and slurries

In trials at Rugeley, UK, reed beds were used for dewatering agricultural sludges and slurries. Three beds, each of 3.5 m2, were employed, two planted with Phragmites australis, the third left unplanted as control. The sludge contained partly oxidised solids from a Biological Aerated Filter (BAF) treating weak pig slurry. It was supplemented with untreated settled pig slurry. Following reed establishment planted Bed A was fed at a constant similar rate to the unplanted Control Bed C. The second planted Bed B was fed at higher rates alternating with rest periods. On this bed the aeration pipes were blocked off. The trials were run for 16 months, which included two summer periods. The results showed that the planted Bed A had definitely better dewatering ability than the unplanted one fed at a similar rate. During the summer months Bed B could be fed at over twice the rate used for the constant input beds. The percolate from the control bed was more highly oxidised than from the planted beds, probably due to a longer holdup time in the absence of reeds. On Bed B the reed quality deteriorated during the second year, after use of untreated slurry as feed.