Inorganics Removal 11 11.1 Introduction
An inorganic compound is a chemical compound not containing carbon. However, elemental carbon (diamond or graphite) as well as carbon monoxide, carbon dioxide and carbonates are typically considered inorganic, while methane, ethanol and similar simple hydrocarbons are referred to as organic compounds. Inorganic contaminants are found in all water sources and can be present as cations, anions or neutral species and their occurrence depends primarily on their aquatic chemistry. Inorganics get into water through many routes including the dissolution of naturally occurring minerals, from industrial wastes and effluents, and from distribution and plumbing systems. Table 11.1 gives an overview of the performance of a range of conventional and advanced water treatment processes for removing inorganics from water.
In this chapter we are going to focus on the main regulated inorganic contaminants including nitrate, arsenic, fluoride, iron, manganese, bromate and lead. There are a number of other metal ions that are regulated, which are not covered here but many of the physicochemical processes described in this chapter are also suitable for these.
11.2 Nitrate
Nitrate levels in many UK waters, both ground and surface waters, are increasing and recently 55% of England has been designated as being in a nitrate vulnerable zonel (NVZ). An NVZ has been identified as having nitrate polluted waters using the following specific criteria: r Surface freshwaters which contain or could contain, if preventative action is not taken, nitrate concentrations greater than 50 mg l -1 .