Modelling approach to an ultrafiltration process for the removal of dissolved and colloidal substances from treated wastewater for reuse in recycled paper manufacturing

In this work, ultrafiltration (UF) is used to remove dissolved and colloidal substances (DCS) from a secondary clarifier effluent from a wastewater treatment plant (WWTP) in a papermaking factory. The approach has been to examine and model the decline in permeate flux resulting from membrane fouling. Effluent from a WWTP at a papermaking factory, previously filtered, was used as feed. UF experiments were carried out in a laboratory-scale plant using a 10 kDa polyethersulfone (PES) UF membrane in a flat sheet module with an active area of 154.8 cm2. The transmembrane pressure (TMP) (1-3 bar) and crossflow rate (1.5-4.5 L/min) were varied during the experiments, at constant temperature (22 ± 0.5 °C). Experimental results from UF tests were expressed in terms of permeate flux (Jp) as a function of time to check modified Hermia's models adapted to crossflow filtration. The parameters of these models were theoretically estimated. The predicted results were compared with experimental data with a high goodness of fit. The results showed that the phenomenon controlling fouling, under most of the conditions tested, was intermediate blocking (R2 > 0.96). Measurements of particle size distribution and zeta potential near the isoelectric point, showed a substantial reduction in colloidal compounds. Additionally, given that COD was removed down to 110 mg/L, it could be said that UF is suitable for producing water that can be reused in different papermaking processes.