MOISTURE TRANSPORT OF SLUDGE THROUGH HYDROPHOBIC MEMBRANES: MATHEMATICAL MODELING AND APPLICATION

摘要

Hydrophobic membranes are used in various separation processes, including membrane distillation to desalinate water. They are made of microporous hydrophobic materials permeable only to vapor. The process relies on a vapor pressure gradient to expel water vapor. Depending on the environmental conditions, this gradient is provided by a difference in either temperature or relative humidity. Applied to sludge, the membrane will retain other constituents, including both particulate and dissolved constituents. The permeate, therefore, is contaminant-free. The objective of this research was to investigate the feasibility and efficiency of a membrane distillation process for drying and stabilization of sludge and fecal waste. This practical application to convectional on-site sanitation systems should provide significant advantages, particularly by preventing pollutant release to groundwater and thereby to potable water sources. Experimental test methods were designed to examine the membrane's capability and effectiveness to transport moisture from sludge. Digested wastewater sludge was used as a representative waste material and various PTFE microporous membranes were tested for the process. A fundamental model, the so-called stagnant film model, was developed to predict and describe the kinetics of moisture transport across the membranes, based on compared to their measurable physical properties. The model was used to predict the in situ performance of a fullscale pit latrine in terms of moisture transfer at different temperature gradients and different groundwater elevations.