Breathable membrane technology for drying wastewater treatment plant sludge
Date
2017
Authors
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Publisher
University of Delaware
Abstract
Drying of wastewater treatment plant sludge enclosed in hydrophobic breathable membrane was investigated for the potential application of breathable membrane for dewatering sludge. Loss of moisture from the membrane-enclosed sludge was studied using a cylindrical drying module that was composed of two chambers separated by a breathable membrane sheet. The top compartment contained the sludge while the sweeping air was supplied to the bottom compartment. Mass loss from the sludge was examined under two sludge heating strategies: direct heating of drying module in an oven and heating sweeping air. Sludge temperatures and flow rate of sweeping air were varied under both conditions to determine the optimum operation conditions for sludge drying. Drying test with the oven heating of drying module showed that vapor flux through the membrane increased from 0.13 to 2.4 g/cm2/hr as the oven temperature increased from 80 to 120 OC. Similarly, increasing the sweeping air temperature from 25 to 100 0C increased vapor flux from 0.05 to 0.19 g/cm2/hr. Increasing flow rate of sweeping air also increased vapor flux, but changing sludge thickness did not affect the sludge drying rate. As expected, direct heating of sludge in the oven resulted in higher vapor flux than drying with heated sweeping air. This difference may be attributed to greater temperature gradient across the membrane between the feed and permeate side. However, heating of sweeping air may be more efficient way of raising the sludge temperature at the membrane interface while achieving comparable drying rates. Furthermore, drying tests suggest that effective drying of from membrane-enclosed sludge depends on whether or not sludge is in contact with the membrane. COMSOL simulation program was used to predict vapor flux through breathable membrane using the same experimental conditions. The simulation model was calibrated with the experimentally derived model parameters. Computer simulation results closely matched the experimental results from various sweeping air temperatures, sweeping air flow rates, and sludge thickness. This model was used to estimate a full-scale dimension of membrane-based drying system for a typical sludge dewatering plant.
Description
Keywords
Applied sciences, Breathable, Drying, Membrane, Plant, Sludge, Technology, Treatment, Wastewater