Limitation of the environmental impact of ashes from combustion of sewage sludge by the synthesis of zeolites

Abstract

The combustion of municipal sewage sludge allows for the recovery of renewable energy. However, it simultaneously causes the formation of ash which is not neutral for the environment. The study presents the research on the possibility of using sewage sludge ash as a raw material for the synthesis of zeolites. The synthesis of zeolites was performed with the use of an indirect fusion method and a direct hydrothermal method. The research on sewage sludge ash after zeolitization included the identification of crystalized phases, the observation of changes of ash particles surface and the measurement of cation exchange capacity (CEC). The research results proved that optimal conditions for the formation of zeolite Y were the synthesis with the indirect fusion method at the sewage sludge ash to hydroxy sodalite ratio of 1:1.8, the activation temperature of 60°C and the crystallization temperature of 90°C. Hydroxy sodalite was found in samples from both methods of zeolitization. However, in the case of direct hydrothermal method, particles of hydroxy sodalite structure were less numerous indicating a small conversion of sewage sludge ash to crystalline zeolite. CEC values comparable to commercial zeolites resulted from zeolitization with the indirect fusion method.