INTRODUCTION

All water-treatment processes produce wastes of some form and this chapter considers the liquid wastes produced by the main processes of clarification and filtration. These wastes comprise the bulk of the waste produced by water-treatment plants. Wastewater from some other processes which involve backwashing, notably GAC adsorption, will also normally be treated with these wastes. Other wastes are also briefly considered.

A 1998 survey on waterworks sludge production in the UK ^[1] gave the figures in Table 13.1 for sludge production and disposal. The survey is of interest in that it shows disposal to landfill was the predominant disposal route followed by disposal to a foul sewer. However, the works discharging to a sewer were all operated by companies or authorities responsible for both water and sewerage services, and apparently the water-treatment plants were not charged for discharging their wastes to the sewer. If the economic cost were to be charged, disposal to sewer would almost certainly reduce. This is because sewage treatment does not significantly reduce the quantity of solids that needs to be disposed of, but it does involve diluting the waterworks wastes with sewage, passing them through the sewage-treatment works, and then still having to dispose of the solids in the sewage sludge.