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Hydrolysis Enhancement of Swine Wastewater by Ultrasonication

Seungmin Na, Sun-Mee Kim, and Young Haeng Lee. Center for Environment Technology Research, Korea Institute of Science and Technology, 39-1 Howelgok-Dong, Sungbuk-Gu, Seoul, 130-650, South Korea

In recent decades, intensive large-scale swine production has increased rapidly in South Korea. Accordingly, the production of swine wastewater has been drastically increased and currently amounts to 150,000 ton per day in South Korea. Swine wastewater is widely known to be a high-strength wastewater with a pollutant organic load which is much higher than domestic sewage. Therefore, minimizing the impact of swine wastewater on the environment is the single most pressing challenge facing the agriculture industry in South Korea.

Anaerobic digestion has been extensively used in the treatment of swine wastewater to stabilize and convert organics to methane gas. However, slow or limited degradation due to very slowly degradable organic matters in swine wastewater complicates the management of swine wastewater and leads to a very long retention time in anaerobic digesters.

Therefore, to accelerate hydrolysis, many chemical, microbiological, mechanical, thermal pre-treatment processes have been applied. Particularly, ultrasonic process is emerging as a popular method for wastewater sludge disintegration. Ultrasonic process leads to the formation of cavities in the liquid phase. Cavitational collapse produces intense local high pressure and temperature on liquid–gas interface, turbulence and high shearing phenomena in the liquid phase

The objective of this work was to investigate the effects of ultrasonic treatment on the solubilization of swine wastewater in order to improve the potential of anaerobic digestibility. The feature of this work was to carry out the comparison of the rate and extent of ultrasonic solubilization of swine wastewater under various operational conditions.

Solubilization of the swine wastewater was achieved by ultrasonic treatment process under various operational conditions. Ultrasonic treatment was shown to have a significant effect on solubilization of the swine wastewater. Ultrasonic treatment resulted in the high degree of solubilization of particulate organics and the degree of solubilization increased with increasing supplied energy. The highest extent of an increment of SCOD concentration and SCOD/TCOD ratio at the end of operation time of 60 min was 109.7 and 117.5%, respectively, under 120 W power output and 20°C operating temperature conditions. The observed highest hydrolysis rate constant described by pseudo-first order rate constant was 2.94 h-1 under the same conditions. Based on the estimated activation energy from modeling using the Arrhenius equation, ultrasonic solubilization of the swine wastewater under higher supplied energy conditions was more dependent on the operating temperature, which was consistent with the experimentally obtained results. Investigation on the effect of gas type and gas delivery methods for ultrasonic solubilization under 60 W power output and 20°C operating temperature conditions, oxygen gas bubbling through the liquid showed the highest degree of 67% increment of soluble organics in the swine wastewater which was possibly attributed to the influent of oxygen in an increase of radicals during the sonolysis. In view of the observed successful solubilization of the swine wastewater, the hybrid anaerobic digestion reactor configurations leading to both ultrasonic hydrolysis and microbial methane gas production are under investigation for the development of an efficient anaerobic digestion system.