Convective drying kinetics of faecal sludge from VIP latrines

Area of Science:

• Environmental Engineering
• Chemical Engineering
• Sustainable Sanitation

Background:

• Sustainable sanitation requires effective treatment of faecal sludge.
• Thermal drying is key for moisture removal and disinfection in faecal sludge management.
• Understanding drying kinetics is vital for designing efficient faecal sludge treatment technologies.

Purpose of the Study:

• To investigate the drying kinetics of faecal sludge from ventilated improved pit (VIP) latrines.
• To determine the influence of temperature, relative humidity, and air velocity on drying rates.
• To develop a predictive model for faecal sludge drying times.

Main Methods:

• Faecal sludge samples from VIP latrines were dried using a convective drying thermobalance.
• Drying experiments were conducted by varying temperature (40-80 °C), relative humidity (0-25%), and air velocity (0.3-1.2 mm/s).
• Samples were tested in thin layers and as pellets (8-14 mm diameter); kinetic parameters were determined and compared to existing models.

Main Results:

• Drying rates ranged from 1-40 g/min/m², with drying times between 100-300 min.
• Higher temperatures and lower pellet diameters/relative humidity increased drying kinetics.
• Temperature had the most significant impact, followed by pellet diameter, then relative humidity; air velocity had a minor effect.

Conclusions:

• A new correlative drying model was developed based on the Page model, accurately predicting drying times.
• The model can serve as an analytical tool for designing, operating, and optimizing faecal sludge drying equipment.
• Effective diffusivity increased with temperature, with an activation energy of 23 kJ/mol, typical for wastewater sludge.