DISCUSSION

Mr G. AINSWORTH

The most significant advance in water pollution control has been non-technical. Less reliance is placed on the traditional sludge drying bed and on fickle agricultural demand so that at last sludge treatment and disposal facilities are provided concurrently with other stages of treatment when new works are built.

Since the Paper was written, performance data have become available on belt press filters.43,44 These units consist of a woven filter belt on to which the conditioned sludge is fed, to be dewatered by a parallel compression belt which bears upon it. Primary sludge and mixed raw sludges dewater better than digested or activated sludges. Good conditioning is essential. Filter cakes of up to 25% solids can be obtained, but filtrates may contain up to 1% solids.