Anions in sewage effluent - Determination of Anions in Natural and Treated Waters - page 572

Chapter 9
Anions in sewage effluent
9.1 Borate
9.1.1 Spectrophotometric method
Borate has been determined [1] in amounts down to 0.02mg L −1 in sewage effluents
spectrophotometrically by reaction with phenol and carminic acid in concentrated
sulphuric acid to produce a coloured compound with an absorption maximum at 610nm.
9.2 Chloride
9.2.1 Ion selective electrodes
Hindin [2] has shown that chloride concentrations in sewage can be determined by the
ion specific electrode method as an alternative to the standard mercuric nitrate method
providing the following precautions are taken: the addition of an ionic strength adjusting
solution to overcome any effect the ionic strength of the sample or standard may have,
and the removal of sulphide ions by a cadmium ion precipitating solution.
9.2.2 Miscellaneous
Official methods issued by the Department of the Environment UK [3] describe various
methods for the determination of chloride in sewage and trade effluents and waters.
These methods are silver nitrate titration with chromate indicator (Mohr's method),
mercuric nitrate titration with diphenyl-carbazone indicator, potentiometric titration with
silver nitrate and an automated mercuric-ferric thiocyanate colorimetric method. With
one or other of these methods concentrations from 1 to 1000mg L −1 chloride may be
determined. Brief notes are given in respect of the chloride ion selective electrode, silver
coulometry and ion chromatography, the latter being relevant at very low concentrations
down to the µg L −1 level.
Miscellaneous methods for the determination of chloride are also discussed in section
14.12.6.1.