Composite filtration plant - for water purification or sewage sludge treatment

摘要

The filter beds are in the form of two concentric troughs separated by vertical divider walls and each of a perforated plastic sheet, above the concrete sloping floor, on which a coarse grained layer followed by a fine grained layer of esp. pretreated gravel/chippings is laid, the chemical used for the pretreatment neutralises the water or binds acids, alkalis or phosphorus. The water or sewage is fed to the beds from a travelling gantry on a rotary bridge which also carries scarifiers/smoothing blades and spray nozzles for flushing and cleaning. The purified water or liquid sewage effluent is drained through perforated plastic tubing in the bases of the beds. Fertilizing additives may be laid on top of the filter bed some being skimmed off each time the dried sludge is taken from teh top of the filter beds by the gantry.