Produced water (PW) is the largest waste byproduct generated in oil and gas industry. PW is a complex mixture of dissolved/suspended organic and inorganic compounds which globally, is more than three times than oil production from wells and this ratio is increasing over time. Stringent regulations are being placed on deep well disposal of PW, and there is increasing incentive to examine beneficial uses of the water. Pretreatment is likely to be required using membranes which inherently suffer from fouling, where the membrane flux decreases due to accumulation of unwanted particles or solution on their surface which lead to higher energy required to overcome mass transfer resistance. Before implementing membranes in PW treatment, it is critical to understand the fouling mechanism and pathways to mitigate the performance loss.<br/>The Hermia model was used to characterize the fouling mechanism with various blocking models including: complete and intermediate pore blocking which cause reduction in the active surface area of the membrane, pore constriction which reduces pore membrane radii and cake filtration where membrane resistance is increased due to the forming layers of particles on the membrane surface. In this study, flux measurements were carried out under constant transmembrane pressure (TMP) in a dead-end ultrafiltration cell. The rate and intensity of fouling were experimentally investigated and modeled for three polyethersulfone (PES) ultrafiltration membranes (MWCO of 10, 100, and 500 kDa). Moreover, the effect of TMP and pre-filtration were assessed on the fouling behavior for those membranes when treating PW.<br/>According to flux decline analysis of the experimental data, blocking mechanisms were observed for 10 and 100 kDa membranes followed by cake formation, while the rapid particle accumulation on 500 kDa membranes led to cake formation almost immediately. In very low TMP experiments, the smaller driving force also led to immediate cake formation at a very early stage of filtration. Complete pore blocking mode was not observed in any of the experiments. We hypothesize that this is due to the interactions between the particles in PW, which lets foulants to deposit on other particles rather than occupy free membrane surface.

Evaluation of fouling mechanisms on ultrafiltration membranes for produced water pretreatment

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