Dewatering of waterworks sludge in reed beds system
Nielsen, S.1, and Cooper, D.J.2, 1Orbicon A/S, Denmark, 2ARM Ltd, UK
(free)
Sludge drying reed beds have been used for dewatering and mineralisation of sludge since the late 80’s, but there is no experience with treatment of water works sludge in reed beds system.
Historically the sludge wastes have been pumped to the sludge lagoons at Hanningfield Reservoir. However, these are now nearing the end of their serviceable life and a new sludge handling process is required. The proposed use of reed bed systems not only reduces the capital and operating cost, but also provides the site with an environmental friendly operation area. Therefore in 6 trials bed of 20 m2 each have been monitored (2008 – 2009) to examine the dewatering processes of the liquid sludge produced from the water treatment process, which includes treatment with Iron Sulphate to help dirt particles to coagulate.
METHODS
Long-term sludge reduction takes place in reed-planted basins, partly due to dewatering (draining, evapotranspiration) and partly due to mineralization of the organic solids in the sludge. The dewatering phase results in the dry solids content of the sludge remaining on the basin surface as sludge residue, whereas the majority of its water content continues to flow vertically through the sludge residue. The water content is further reduced through evapotranspiration.
In addition to dewatering, the organic solids in the sludge are mineralized, thereby minimising the sludge volume. Oxygen diffusion via filter aeration and through the cracked sludge surface and oxygen diffusion from the roots into the sludge residue enable aerobic micro-organisms to exist close to the roots and in the sludge residue. The overall reduction of the sludge volume occurs without the use of chemicals. The process involves only a very low level of energy consumption for pumping the sludge and reject water. What loading (dry solid/m2/year) can the trial system treat (20 – 40 kg dry solid/m2/year) before changing to another trial bed and how many days rest are necessary for drainage and drying?
