On the advantages of using prehydrolysed aluminium coagulants

The advantages of applying polyaluminium chlorides (i.e. prehydrolysed aluminium coagulants differing in basicity) are specified. Experiments were carried out on riverine water samples (from the Odra and its tributary, the Olawa) which varied in temperature and pollution level. Polyaluminium chlorides yielded a greater destabilisation of colloids and their efficiency in the removal of water pollutants was higher compared with conventional aluminium sulphate coagulant. They were also of greater utility than aluminium sulphate because of a lower residual aluminium concentration and a smaller increase in water corrosivity. The increase in the basicity of the prehydrolysed coagulants exerted a favourable influence on their efficiency and allowed reduction of their doses.