ENVIRONMENTAL IMPACT OF SEWAGE SLUDGE ASH ASSESSED THROUGH LEACHING

As part of a wider feasibility study on the possible reuse potential of Croatian sewage sludge ash, ash has been produced by laboratory incineration of sewage sludge from two Croatian wastewater treatment plants. The Croatian sewage sludge ash was tested for soluble heavy metals according to EN 12457 and the results were considered in the context of EU landfill Waste Acceptance Criteria. With sewage sludge ash alone, the main soluble elements/ions of concern were (in decreasing order): Mo, SO4, Cr and Cl. When obtained ash was incorporated into cement mortars at cement replacement rates of 20%, EN 12457 leaching of the crushed mortars demonstrated compliance with the strictest limits for inert landfill Waste Acceptance Criteria and well within other limits specified for use in road bases. However, much of the reduction in leaching levels can be attributed to the dilution effect of sand used in mortars. In the cases of Se, Cr, F and Cl, results imply that the cement used in the mortars actually represents a more significant source of soluble Se, Cr, F and Cl than the produced ash. Regardless, the overall results reveal that leaching of heavy metals and other ions were not a significant concern that would prevent the potential reuse of Croatian sewage sludge ash in cement mortars or concretes should Croatian wastewater treatment plants opt for sewage sludge incineration as an alternative sludge disposal and management option.