0
-
An empty cart
You have no item in your shopping cart
The various stages of sewage processing each produce a sludge in which the wastes from that stage are concentrated, although, of course, in much smaller volumes. These sludges must all be discharged, eventually to the environment, but in as safe a manner as possible.
The primary screenings are capable of decomposition and so need very careful handling. They may be compacted and sent to landfill, or macerated and added to the primary settlement solids. The mineral matter from the grit trap is relatively clean, and is sent safely to landfill. The primary and secondary settlement sludges are considerable in quantity and are relatively thin (dilute), so that the quantity to be disposed of is high. They are therefore dewatered mechanically before shipment
to landfill or use as a soil improver or incineration. Tertiary sludges will vary in composition according to the nature of the process producing them, but they will probably all need dewatering before final disposal.
A major process for the treatment of sewage sludges is their decomposition by anaerobic digestion, at temperatures somewhat above ambient, with methane as a by-product. The sludge quantity is roughly halved by this means, the residual
sludge being more easily dewatered, and a useful fuel is generated as well.
The various sludges arising from sewage treatment will be highly organic in content, and will need extensive dewatering to render them fit for their final disposal, even if this is just to be incinerated. This is a major treatment works task, involving filter presses, or horizontal belt filters, or decanter centrifuges, with filtrate or centrate recycled to the start of the works. Even if the sludge is digested first, there is still a considerable degree of dewatering required of the resultant sludge.