The reduction in concentrations of solids, BOD and particle-bound nutrients in ponds is due largely to sedimentation (see chapter 2.3 ‘Anaerobic, aerobic and facultative ponds’). Sedimentation can be problematic in ponds, as the accumulated sludge reduces the active pond volume and residence time and, consequently, treatment efficiency.
The choice of desludging option is an important consideration during the design stage. Options for desludging usually require batch removal:
- by excavator (standard or long-reach) or dragline with subsequent dewatering
- by vacuum tanker, with or without prior agitation
- by sludge agitation and pumping to a tanker, a big-gun irrigator or a drag-hose injector.
More frequent solids removal is offered by in situ sludge removal pipes and semi-continuous pumping to a dewatering bay.
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