The treatment of sludge, which is produced from raw water treatment, has been considered as an ecologically sensitive problem in terms of energy and pollution. In this context, this study presents many series of solar drying tests that were carried on three samples of sludge obtained from several drinking water treatment plants in Marrakech-Safi regions, Morocco. The main aim is to develop further management processes of these wastes such as upgrading or storage. A partially solar indirect convective dryer operating in forced convection was used to run experiment tests. The temperature of air has ranged from 50 to 90°C and the relative humidity from 24% to 46%. The drying airflow was kept at about 0.0833 m3/s. An estimation of the mass diffusion coefficient and the activation energy during vacuum drying besides the characteristic convective drying curve were established. In addition, six semi-theoretical and/or empirical and statistical models were used to predict experimental data. It was found that the temperature was the most important factor during the drying process. Furthermore, the obtained results of mass diffusion coefficient and activation energy were found consistent with those already existing in the literature. The mathematical model called “Midilli–Kucuk” was found to be the most appropriate to describe the drying curves of the three samples. The total energy consumption was also studied. It showed a downward tendency with the increase in temperature. The efficiency of drying energy ranged from 4.89% to 7.5%. Although it was found to be low, it can be improved by increasing the load.

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.

The significant production of sewage sludge by wastewater treatment plants on a global scale and the lack of correspondence between housing development and the expansion of sanitation infrastructure indicate a genuine concern regarding environmental preservation. This study addresses the crucial...

Phosphate extraction process produces large amounts of waste sludge, that is disposed of in the environment. Phosphate sludge (PS) is characterized by high moisture content (70–80%) which is a major handicap for any further disposal. To overcome this issue, the drying of this waste could be an appropriate solution to minimize its volume. The present work is focused on the convective drying behavior of PS and its mathematical modeling to optimize the drying processes. Drying experiments were conducted using thicknesses of 1, 2 and 4 cm. Drying air temperature and velocity ranged respectively in 50–70°C and 1–2 m/s. The findings showed that improving drying air temperature and velocity, and decreasing sample thickness enhance considerably the drying rate. Furthermore, the drying curves showed the presence of two main drying periods corresponding to constant drying rate and falling drying rate periods. Moreover, a model considering heat and mass transfer equations for each phase in wet sludge was used to fit the experimental results. Based on the analytical solutions and according to the statistical criteria R² and RMSE ranged from 0.9957–0.9996 and 0.0157–0.0276, respectively, it was concluded that the model describes the drying behavior of washing PS in all tested convective drying conditions.

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.