Mathematical Modeling of Thin-layer Infrared Drying of Dewatered Municipal Sewage Sludge (DWMSS)

Insight into the Enhanced Removal of Water from Coal Slime via Solar Drying Technology: Dewatering Performance, Solar Thermal Efficiency, and Economic Analysis

In this work, solar drying technology was applied for the deep dewatering of coal slime to save thermal energy and reduce the dust produced during the hot drying process of coal slime. Solar drying technology is used to dry coal slime to realize its resource utilization. The influence of solar radiation intensity and slime thickness is investigated on the drying process. The greater the solar radiation intensity (SRI) is, the faster the drying indoor air and coal slime are heated, and the faster the drying efficiency is. As the slime becomes thinner, the internal water diffusion resistance becomes smaller and the drying efficiency correspondingly becomes faster. In addition, to facilitate the application of coal slime drying in the actual project, the Page model is fitted and found to have a good fit for solar drying coal slime. Meanwhile, the optimal drying conditions are determined by analyzing the energy utilization under different conditions. It is found that the target moisture content of 10% is optimal for coal slime drying with the highest energy utilization. The laying thickness (L) of 1 cm has the highest solar thermal efficiency of 54.1%. More importantly, economic calculation and analysis are conducted in detail on solar drying. It is found that the cost of solar drying (¥38.59/ton) is lower than that of hot air drying (¥ 65.09/ton). Therefore, solar drying is a promising method for the drying of coal slime.

Supercritical carbon dioxide drying of municipal sewage sludge - Novel waste-to-energy valorization pathway

Eighty percent of the world's wastewater is discharged back into nature without reuse and further treatment and solid byproduct of wastewater is either spread on land or landfilled. The valorization of municipal sewage sludge for energy use is a major opportunity for sustainable energy applications. This includes effective dewatering and drying of the sludge in addition to producing biogas during the anaerobic digestion. Supercritical CO 2 extraction process was investigated for the purpose of drying municipal sewage sludge. Remarkably our results showed that after sCO2 processing the higher heating value (HHV) of sludge at wet basis moisture content of 52% was 14 MJ/kg and thus higher than the HHV of brown coal with similar moisture level (12 MJ/kg). Our research also shows that under specific conditions sCO2 extraction reduces the moisture content of the municipal sludge from 89% to 53% in 15 min. Although, more research is needed this dewatering process could be considerably less energy intensive than conventional thermal and other drying processes. Another benefit is extraction of micro pollutants by sCO₂ treatment and thus making the dried sludge more useable in energy applications as per regulations. Our results show an alternative and novel pathway for highly effective dewatering and drying of municipal and other types of sludge.

Encapsulation of Lactobacillus fermentum K73 by Refractance Window drying

The purpose of this work was to model the survival of the microorganism and the kinetics of drying during the encapsulation of Lactobacillus fermentum K73 by Refractance Window drying. A whey culture medium with and without addition of maltodextrin were used as encapsulation matrices. The microorganism with the encapsulation matrices was dried at three water temperatures (333, 343 and 353 K) until reaching balanced moisture. Microorganism survival and thin layer drying kinetics were studied by using mathematical models. Results showed that modified Gompertz model and Midilli model described the survival of the microorganism and the drying kinetics, respectively. The most favorable process conditions found with the mathematical modelling were a drying time of 2460 s, at a temperature of 353 K. At these conditions, a product with 9.1 Log CFU/g and a final humidity of 10% [wet basis] using the culture medium as encapsulation matrix was obtained. The result shows that Refractance Window can be applied to encapsulate the microorganism probiotic with a proper survival of the microorganism.

Thermal treatment on sewage sludge by electromagnetic induction heating: Methodology and drying characterization

Thermal drying of sewage sludge is not only an effective way to treat the waste, but also an essential step for further energy utilization. This work focused on drying property of sewage sludge by using electromagnetic induction heating. A novel drying method for sewage sludge was designed. The effects of different electromagnetic-induction media materials, working parameters and conditioning reagents on the efficiency of drying were investigated. Then, the kinetics was analyzed. The change of temperature and heat-transfer was analyzed during the drying process. Experimental results showed that sewage sludge combined with three kinds of induction medias can be efficiently dried by applying electromagnetic induction heating. Fast formation and development of cracks indicated that an increase of drying rates of sludge can be obtained. Considering the release of volatile organic compounds from sludge during drying process, estimated moisture content was used to evaluate the drying effect. A Higher working voltage leaded to a more weight reduction of sludge during a shorter drying time, but a lower voltage prolonged the drying time. It was noted that the estimated moisture rate was very close to the experimental moisture content. Sludge content, forming and induction media significantly affected the drying process. Plate and net media were fitted for thin layer and piled sludge, respectively. However, fiber media seemed to show lower drying rate due to no circuit for induction current. An addition of CaO and sawdust improved the drying process. As a result, few volatile organic compounds released from sludge. For kinetics, three periods (warm-up, constant rate and falling rate period) can be observed and the data fitted linear regression of Lewis drying model very well. The effective moisture diffusivity was influenced by the different induction media and the thickness of sludge. Infrared images showed that outside temperature was higher than central part temperature for all sludge samples. A higher evaporation rate and diffusion of moisture can be obtained from outside part of sludge due to the easy collapse of porous structure.