INTRODUCTION

This chapter considers briefly a number of processes, most of which have been developed to comply with the prescriptive water-quality standards that have come into force over the past 20 years. Several of the processes notably ozonation and GAC adsorption are still being developed. One thing that the processes considered have in common is that it would be possible to write entire books on them, and this chapter only gives a broad overview of the processes and introduces some of the key concepts. The processes considered are:

• adsorption using activated carbon initially used in the 1970s to treat for taste and odour but adopted on a large scale in the 1980s in particular for pesticide treatment;

• ozonation used for many years in continental Europe for disinfection but developed in the 1980s for treatment of organic chemicals, notably pesticides, and for disinfection in treatment works where chlorination would lead to failures of the THMs standards;

• nitrate removal to meet the nitrate standard;

• air stripping to remove volatile organic chemicals;

• chemical dosing to reduce the corrosiveness of water in distribution systems, particularly with respect to lead;

• water softening the odd man out in that it has been used for many years and is now little used for new plants;

• arsenic removal; and

• chemical dosing for lead treatment.