Dewatering sludge originating in water treatment works in reed bed systems

The dewatering process of the liquid water works sludge was examined in a trial with a series of six trial beds, each 20 m2. These were monitored from April 2008 to June 2010. It is possible to get the vegetation to grow in ferric sludge (approximately 300,000 mg Fe/kg dry solid, pH 7,7). It has not been necessary to use fertilizer. The influence of the loading programs (15-50 kg dry solid/m2/year) was tested with 1-5 days of loading and 35-55 days of rest. It is possible to drain and treat ferric sludge. Generally the dewatering profile is a peak with a maximum over 0.015-0.025 L/s/m2. The times for dewatering of 6-12 m3 are approximately 15 h and over 90% of the load is dewatered in that period. The dry solid (0.16-0.20%) in the sludge has been concentrated approximately 200 times. The dewatering phase results in ferric sludge with 30-40% dry solid which cracks up very quickly. The volume reduction is over 99%. The trend shows that the main volume of reject water has a turbidity level below 5 NTU even in the loading periods.