Extending the use of dewatered alum sludge as a P-trapping material in effluent purification : study on two separate water treatment sludges

The generation of alum sludge from drinking water purification process remains inevitable when aluminium sulphate is used as primary coagulant for raw water coagulation. Sustainable managing such the sludge becomes an increasing concern in water industry. Its beneficial reuse is therefore highly desirable and has attracted considerable research efforts. In view of the novel development of alum sludge as a value-added raw material for beneficial reuse for wastewater treatment, this study examined the maximum phosphorus-adsorption capacity of two dewatered alum sludges sampled from two largest water treatment works in Dublin, Ireland. The objective lies in clarifying the change of alum sludge characteristics and its P-adsorption capacity over the location of the alum sludge produced and the raw water being treated. Experiments have demonstrated that the two alum sludges have the similar P adsorption capacity (14.3mg P/g sludge for Ballymore-Eustace sludge and 13.1 mg P/g sludge for Leixlip sludge at pH 7.0). However, the study supports that alum sludge beneficial reuse as a low cost adsorbent for P immobilization should study its P-adsorption capacity before any decision of large application is made since the raw water quality will affect the sludge characteristics and therefore influence its adsorption ability.