Catalytic effect of metal oxides on pyrolysis of sewage sludge

The effect of metal oxides (Al2O3, CaO, Fe2O3, TiO2, and ZnO) on the pyrolysis of sewage sludge was investigated. The experiments were performed in a thermogravimetric analyzer (TGA) to check the pyrolysis behavior of raw sludge, demineralized sludge and demineralized sludge with metal oxides added, respectively. The results showed that the presence of Fe2O3 and ZnO probably inhibited the decomposition of organic matters in demineralized sludge samples to generate more solid residues, while Al2O3, CaO, and TiO2 promoted the degradation of organic matters throughout the whole pyrolysis temperature ranges. All the metal oxides studied accelerated the initial decomposition of sludge samples. Al2O3 and TiO2 might decrease the total pyrolysis time, while CaO, Fe2O3, and ZnO prolong pyrolysis time. The structure of demineralized sludge samples might be changed due to the addition of CaO, TiO2, and ZnO. Between 550 K and 750 K, the conversion of organic matters (mainly cellulose and lignin) in sludge samples was enhanced by Al2O3 and TiO2, but inhibited by CaO, Fe2O3, and ZnO. The effects of metal oxides on the weight loss rate of cellulose in demineralized sludge samples presented the following decreasing order of DE–ZnO > DE–TiO2 > DE–SS > DE–Al2O3 > DE–Fe2O3 > DE–CaO.