Performance and cost modeling of ultrafiltration
Models describing permeate flux, rejection, and cost are coupled to evaluate the performance and cost of ultrafiltration as a function of raw-water quality. The model for permeate flux extends a previous model for colloidal fouling based on shear-induced diffusivity to include Brownian diffusion. Contaminant removal is modeled as mechanical sieving and molecular diameter is regressed against weight to describe removal of natural organic matter (NOM). Time-dependent permeate flux is considered in estimating operating times required to achieve a specified recovery. Costs are calculated as a function of particle-size distribution in the raw water. Particles with diameters on the order of 10-1 μm display minimum diffusivities, which leads to maximum system costs with respect to particle size. Fine materials (<0.5 μm), with high cake resistance, demonstrate pressure-independent permeate flux for conditions typical of hollow fiber ultrafiltration. In some cases, a minimum in system costs as a function of recovery is observed due to a trade-off between operating time and time-averaged permeate flux. Simulations for four scenarios of variable particle and NOM concentrations suggest that irrespective of adsorptive fouling, permeate flux may be limited by reversible accumulations of NOM on ultrafiltration membranes.
Journal of Environmental Engineering
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