The solar drying of sewage sludge in greenhouses is one of the most used solutions in wastewater treatment plants (WWTPs). However, it presents challenges, particularly in terms of efficiency and drying time. In this context, the present study explores the drying performances of an innovative Combined Solar Greenhouse Dryer (CSGD) for sewage sludge. The system integrates rock bed storage (RBS), a solar air collector (SAC), and a solar greenhouse dryer (SGD). A numerical model, developed using TRNSYS software, predicts the drying kinetics of sewage sludge through hourly dynamic simulations based on the climatic conditions of Marrakesh, Morocco. Experimental validation confirmed the accuracy of the model. The results reveal that integrating the SAC with the SGD during the day and the RBS with the SGD at night significantly enhances the drying efficiency of the sewage sludge. During daylight hours, the SAC generates hot air, reaching maximum temperatures of 64 °C in January and 109 °C in July. Concurrently, the outlet air temperature of the RBS rises notably during the day, corresponding to the charging phase of the storage unit. Moreover, during the night, the RBS air temperature exceeds ambient temperatures by approximately 7–16 °C in January and 11–37 °C in July. This integration leads to a substantial reduction in drying time. The reduction in sewage sludge water content from 4 kg/kg of dry solid (20% dry solid content) to 0.24 kg/kg of dry solid (80% dry solid content) is related to a decrease in the drying time from 121 h to 79 h in cold periods and from 47 h to 27 h in warm periods. The drying process is significantly enhanced within the greenhouse, both during daylight and nocturnal periods. The CSGD system proves to be energy-efficient, offering an effective, high-performance solution for sewage sludge management, while also lowering operational costs for WWTPs. This innovative solar drying system combines a thermal storage bed and a solar collector to enhance drying efficiency, even in the absence of sunlight.

Morocco is the leading producer of phosphate and its derivatives in the world with a total production of 35 Mt. However, the extraction and the valorization of this mine generate huge quantities of phosphate washing waste clay (PHWWC) that constitute a main environmental and economic concern. To facilitate this waste clay storage and handling, it is necessary to decrease its moisture content that represents 80% of PHWWC. The present paper is devoted to studying the conductive drying of PHWWC. Drying experiments were conducted in a laboratory pilot. Afterwards, the experiment results were implemented in a one-dimensional numerical model of heat and mass transfer in a porous media to identify the drying parameters and performances. It was found that most of the water contained in PHWWC is free water that is removed with a constant drying rate. The volume reduction with a marked cracks phenomenon attained 65% without any significant effect of drying temperature and sample thickness. The effective moisture diffusivity of the PHWWC for a conductive drying process is ranged between 10⁻⁹ and 1.1 × 10⁻⁸ m²·s⁻¹. The thermal efficiency of the drying system is up to 86%. The results could be used for the purpose of design and scale-up of the industrial dryer based on laboratory-scale experiments.

This paper investigates the effects of Doum fiber as a local materials, on the mechanical strength properties of cylindrical earth samples with a diameter of 3 cm and a height of 4.5 cm. Untreated and Alkali treated Doum fiber with a NaOH concentration of 1%, 4%, 6% are introduced in local clay with a ratio of 0.5%, 1% and 1.5% by weight of the earth samples. A tensile test of the Doum fiber and a compressive strength test of the elaborated specimens is conducted. The study findings outline an improvement in the mechanical properties of the earth samples and adherence between surface fiber and soil when the fiber is treated. And a dosage of 0.5% by weight of Alkali treated Doum fiber with a NaOH concentration of 1% is sufficient to achieve higher mechanical performances. Modifying the fiber surface through NaOH treatment enhances fiber adhesion to clay and improves the mechanical behavior of the biocomposite.

This study investigates the influence of drying temperature on the conductive drying behavior of washing phosphate sludge. A mathematical model, based on Fourier's Fick diffusion law and the heat transfer equation, was developed to simulate coupled heat and mass transfer during the drying process, incorporating the shrinkage effect. The sludge samples, obtained from the Khouribga phosphate plant in Morocco, were subjected to drying at temperatures of 70°C and 95°C. The experimental setup included continuous monitoring of temperature, humidity, and mass loss throughout the process. COMSOL Multiphysics software was used to solve the nonlinear equations governing heat and mass transfer. Results indicate that increasing the drying temperature significantly accelerates the drying rate. The model successfully predicts the moisture content and temperature distribution over time, aligning well with experimental data. Statistical validation, using the determination coefficient (R²) and root mean square error (RMSE), confirms that the model accurately describes the drying behavior, with R² values of 0.9957 and 0.9967 at 70°C and 95°C, respectively. The inclusion of the shrinkage effect enhances the model's precision in describing the drying kinetics under varying conditions.

Phosphate production generates huge quantities of waste materials that pose both economic and environmental challenges. They are characterized by a high-water content, making disposal a very difficult task. To address this issue, conductive drying emerges as a viable solution to reduce the water content in the phosphate sludge to facilitate handling and specially recycling them as construction materials. This paper presents a simplified numerical model based on Fick's law, depicting heat and mass transfer in porous media to simulate the conductive drying process within the phosphate sludge. To provide more accuracy to the numerical model solution, the experimental data are integrated into the numerical model as boundary conditions, enabling the prediction of temperature profiles, thermal conductivity, and effective moisture diffusivity throughout the conductive drying process. The water evaporation capacity is found between 1.25 and 2.1 kg water/m2.h.These findings could be a tool for designing a suitable dryer for phosphate washing sludge.