Treatment of FGD plant wastewater by enhancing microfiltration fluxes. Final report, September 1, 1992--December 31, 1993

摘要

In coal-fired boilers, the wet limestone-gypsum based flue gas desulfurization (FGD) plants produce large volumes of wastewater containing dissolved salts and heavy metals. Before discharging these wastes to the environment, the heavy metals must be removed. One of the preferred methods for removal of heavy metals is by co-precipitation of hydroxides and sulfides of heavy metals, followed by coagulation and flocculation techniques. As a post-treatment of the resulting wastewater stream, crossflow microfiltration is being considered as a cost effective and environmentally acceptable method. However, membrane 'fouling' and 'concentration polarization' in such applications remain serious problems and result in flux decline of product during filtration. In this exploratory research, we investigated a novel concept: flow oscillation as a means of controlling fouling and concentration polarization. The treatment of FGD plants wastewater (simulated) by enhancing microfiltration fluxes was studied here as an example to demonstrate the oscillatory flow system in combating concentration polarization and membrane fouling in crossflow filtration. Microfiltration experiments were conducted in a tubular membrane module. From limited experimental data, it was found that flow oscillation increases the transmembrane flux when compared with the non-oscillatory flow condition. A mathematical model has been developed to evaluate the performance of a tubular membrane module under oscillatory flow condition. Results are presented for both hydrodynamics and transmembrane fluxes for such factors as amplitudes and frequencies of oscillatory flow, membrane permeability, and operating transmembrane pressure.