Application of ultrasound to enhance the silt drying process: An experimental study.

Scientific and reasonable treatment of dredged silt can not only protect the ecological environment but also play an essential role in the utilization of silt resources. Due to high water content, low permeability and high organic matter content of the silt, a large amount of bacteria and harmful gases are often produced during the process of silt sedimentation. Thermal drying has been taken as a technically attractive method for harmless treatment of contaminated dredged silt. In this study, ultrasound technology is introduced to shorten the time needed for silt drying. A preliminary laboratory study is carried out to assess the effectiveness of ultrasound on thermal drying. A series of thermal drying tests, with and without ultrasound, were conducted on kaolin soil specimens that were prepared by settling and self-weight consolidation. The test results show that the length of drying time can be shortened by increasing temperature and ultrasound power. The drying time plays a dominant role in the determination of the total energy consumption. This is because reduction of drying time leads to significant decrease in energy consumption for thermal drying, and the energy consumption for additional ultrasound is relatively marginal. For thermal drying at temperatures 60 and 100°C, when combined with 100 W ultrasound, the length of drying time was shortened by 44.19% and 45.16%, and the energy consumption was saved by 30.07% and 38.16%, respectively; when combined with 60 W ultrasound, the length of drying time was shortened by 4.65% and 6.45%, but the energy consumption was increased by 9.79% and 0.48%, respectively. The combination of thermal drying and 100 W ultrasound is found to be optimal in terms of drying rate and energy consumption for silt drying.

A unit-cell model for thermal regulation of degradation of organics in solid waste.

It is a well appreciated fact that temperature is one of the key factors influencing the degradation of organics. Heat exchangers are a viable option that can be used to adjust the temperature in solid waste to an extent most suitable for waste degradation. This paper focuses on an experimental and theoretical investigation of the feasibility of using a water-circulating heat exchanger for thermal regulation of waste degradation. A cylindrical bioreactor with a central pipe connected to a water circulation system is devised and instrumented. The changes in temperature and gas production were monitored during the degradation of the organic component of the waste. Test results with and without thermal regulation are analyzed and compared. In addition, an analytical model is proposed to simulate the symmetrical heat transport behavior subjected to heat exchange. Heat generation due to the degradation of organics is taken into account. There was a good correlation between the analytical model prediction and the experimental data obtained from the laboratory test and field monitoring.