Two-stage mesophilic anaerobic digestion from waste activated sludge enhanced by low-temperature thermal hydrolysis

Abstract

Two-stage mesophilic anaerobic digestion of waste activated sludge was conducted to enhance methane production by low-temperature thermal hydrolysis. Two steady stages were evaluated: the first acidogenic stage was operated at sludge retention times of 2 d, and the second methanogenic stage was controlled at hydraulic retention times of 8 d. Thermal hydrolysis results showed that more chemical oxygen demand, proteins and carbohydrates were released from sludge as temperature increased from 50 to 120°C. Protein-like substances were major components from three-dimensional (3D) excitation–emission matrix analysis, and their fluorescence intensities were matched with temperatures. Sludge extracellular structure was disintegrated from scanning electron microscope analysis when the temperature was beyond 80°C. The volatile fatty acids (VFAs) and methane production had positive relation to the soluble organic matters after low-temperature hydrolysis. About 100°C was the suitable temperature for sludge digestion, and corresponding VFAs and biogas productions were 1,672 mg/L and 123 mL/gVSS, respectively.

Keywords:

• Waste activated sludge
• Mesophilic anaerobic digestion
• Thermal hydrolysis
• Methane production

Acknowledgement

This work was financially supported by the National High Technology Research and Development Program of China (863 Program) (No. 2012AA063503).

Notes

Presented at the 7th International Conference on Challenges in Environmental Science and Engineering (CESE 2014) 12–16 October 2014, Johor Bahru, Malaysia