Comparison and Optimization of Pyrolysis Bio-Oil Composition from Sewage Sludge and Spirulina Microalgae

The abundant presence of spirulina microalgae and sewage sludge led to the researchers pay attention to recycling and economical conversion into valuable materials. This study investigated the simultaneous pyrolysis composition of two materials, spirulina microalgae and sewage sludge, and also the factors affecting the production of bio-oil from them. The effect of temperature, the weight ratio of spirulina to SS, and the heating rate were investigated. Optimal conditions for pyrolysis were obtained at 519.3 °C, a weight ratio of 0.73, and a heating rate of 17.9 °C/min and bio-oil production yield also was obtained at 69.35%. The heat value of bio-oil was obtained at 25.52 MJ/kg and its energy efficiency was 66.3%. The results showed that with increase in the temperature, the number of aromatic substances that enhance the heat value increased. Also, by directing the reaction to optimal conditions, the oxygenated and nitrogenous compounds detected in the bio-oil were reduced. The highest bio-oil yield was obtained at 69.09% and 450 °C, a weight ratio of (spirulina /SS) 0.5 and a heating rate of 20 °C/min. The simultaneous combination of spirulina and SS increases the number of aromatic substances and decreases oxygenated and nitrogenous group spirulina in bio-oils.