Effects of microwave, ultrasonic and enzymatic treatment on chemical and physical properties of waste-activated sludge

Abstract

The effects of microwave irradiation, microwave enhanced advanced oxidation process (MW/H₂O₂-AOP), ultrasonic and/or protease enzymatic treatments on chemical and physical properties of waste-activated sludge were studied. The different treatment mechanisms resulted in various degrees of biomass cell destruction and nutrient release, as evidenced by transformation of chemical constituents, particle size distribution, and scanning electron microscopic imaging. The microwave irradiation and the MW/H₂O₂-AOP resulted in higher soluble protein concentrations, but lower amino acids. High concentrations of soluble polysaccharide and deoxyribonucleic acid were also obtained in solution. The particle size distribution profile, after treatments, remained similar to that of waste-activated sludge; however, the distribution shifted toward smaller particle sizes. Ultrasonic treatment resulted in a high concentration of amino acids and overall protein disintegration/hydrolysis. Protease enzymatic treatment, after ultrasonic disintegration, further enhanced protein degradation. The particle size distribution profile for ultrasonic treatment was altered to a further nonuniform distribution. The ultrasonic plus protease treatment yielded the best results, in terms of cell wall destruction.

Keywords:

• Microwave
• hydrogen peroxide
• ultrasonic
• protease
• sludge solubilization

Acknowledgments

The authors wish to acknowledge the research funding provided by the Natural Science and Engineering Research Council of Canada.