AWWA MTC93057

Membrane filtration technology has been applied recently in a variety of practical applications, including water, wastewater, and industrial waste treatment. An important consideration that may limit the applicability of the membrane process is the reduction in permeation rate resulting in less recovery. This reduction is caused by the deposition or adsorption of contaminants on the walls and within the pores of the membrane. Research and practice have shown that coagulation pretreatment is essential for the proper operation of ceramic membranes. Coagulation of colloidal materials in the feed water significantly improves the permeation rate and the permeate quality, coagulation may be used in conjunction with microfiltration and ultrafiltration membranes to remove nutrients from wastewater, color from waters, viruses and other materials. Such chemical pretreatment alters the pH and ionic strength of the feed water. In this study the effects of pH and the ionic strength on the permeate flux of a tubular ceramic membrane are considered. The permeate flux through a-alumina membranes decreased with increasing pH for the three types of waters tested, however, the effect was small for feed water containing humic materials. The permeation rate was observed to be affected less by the ionic strength of the feed stream. Humic materials produced greater absolute reductions in permeate flux than silica suspensions and are thought to mask the effects of pH and ionic strength. In the case of electrolyte solution and silica suspension, the above observations cannot be explained by electroviscous retardation. They may be attributed in part to solvation or structured water effects of the membrane pores and/or silica cake. Whereas for the organic materials, in addition to solvation effects on the membrane there appears to be effects due to conformational changes of molecules, i.e. the hydrodynamic radius and hydrophobicity of the humic molecules. These results suggest that the pH of coagulation pretreatment may play an important role in increasing the permeate flux as does the complexation of potential foulants.