Rapid depletion of global phosphorus (P) reserves has been challenging human’s sustainability in food, water and energy in future, seeking alternative reserves thus will be attractive and meaningful in practice. The reserve P consumed due to people’s daily life is converged into municipal wastewater and then retained in sewage sludge as a sustainable material generated from sewage biological treatment; therefore, the phosphorus-abundant sewage sludge is promisingly considered alternative P reserve. This work developed a new route to efficiently make P in sewage sludge conversed to a promising phosphorus fertilizer through calcium oxide (CaO) enhanced sludge pyrolysis. It is found that CaO addition achieved the P bioavailability-oriented transformation of sewage sludge to form the hydroxylapatite (Ca5(PO4)3OH) that is desirable for plant growth. Pyrolysis temperature and sewage sludge pristine composition both influenced the conversion of sludge P to the hydroxylapatite. The increases in the pyrolysis temperature and the ash fraction of sewage sludge promoted the formation of P species with hydroxylapatite during sludge pyrolysis with CaO added. Increasing the addition of CaO was preferable to transform P in sewage sludge into the hydroxylapatite in the obtained sludge char, and the maximum content of 25 wt % hydroxylapatite over total P was attained. This enhancement in hydroxylapatite formation could be attributed to the solid-state reactions between CaO and the polyphosphate with the presence of sludge inherent minerals potential to strengthen the immobilization of P during sludge pyrolysis. In terms of the enhanced formation of hydroxylapatite, the facile route developed for synthesizing phosphorus fertilizer from sewage sludge through CaO enhanced sludge pyrolysis is promisingly sustainable and economically viable in industry as well as sewage sludge practical treatment.

Facile synthesis of promising phosphorus fertilizer from sewage sludge through calcium oxide enhanced pyrolysis

2019 Spring National Meeting

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