Mechanisms and control of fouling during ultrafiltration of high strength wastewater without pretreatment

• Elucidated transient fouling mechanisms during ultrafiltration of impaired waters.
• Determined the roles of membrane type and feed concentration on threshold flux.
• Showed membrane type had limited impact on steady state and threshold flux.

This contribution describes the application of ultrafiltration membranes for treating wastewaters with high levels of suspended particles, fats, grease and proteins. The objectives of this research were to understand the mechanisms leading to fouling of the membranes and to evaluate how the process parameters affect membrane performance. Modeling of direct flow filtration data revealed that early stage fouling was indicative of a cake formation pore blocking mechanism, which was followed by cake layer growth. Modeling of cross flow filtration data determined that the cake layer contributed the dominant resistance to flow through the membrane. The cake layer was highly compressible, with a compressibility factor of 1.1. Thus, while higher transmembrane pressure provided a larger driving force for water transport, this driving force was counteracted by a higher resistance caused by cake layer compression. Membrane type (polysulfone and regenerated cellulose) and initial pure water permeability (from 10 to 70 L m−2 h−1 bar−1) had only minor effects on the measured steady state flux and threshold flux values. This result suggests that, in terms of membrane design, increasing membrane pure water permeability alone may not necessarily enhance filtration flux. Constant flux values higher than the measured threshold fluxes yielded rapid fouling and high rates of transmembrane pressure increase. The work provides valuable insights for subsequent cleaning studies and pilot scale testing.

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