Resumen de Biofouling control in reverse osmosis membranes for water treatment
Reverses osmosis (RO) filtration is one of the most competitive water purification technologies. RO systems have evolved significantly in the last years to provide real and sustainable solutions to water-related problems. They offer one of the highest levels of salts and pollutants removal, more than 99%. Its application open new possibilities for advance water reuse strategies to reduce the stress on current potable water resources. The treatment of wastewater or seawater using RO, produces high quality permeate water. One of the main hurdles that hinders RO expansion in water reuse, is the loss of performance that RO elements suffer when dealing with contaminated waters. This phenomenon known as fouling, has been studied over the last years, but still little progress has been made in the field. Fouling with a biological or organic origins, remains to be one of the biggest challenges for RO elements used in industrial or wastewater treatment plants.
Due to the complexity to study these problems in large scale systems, protocols need to be developed in order to mimic full-scale plants operation on a bench scale. Fouling problems are usually occurring after several month of operations. However, for a realistic time-scale research, the process needs to be accelerated in a controlled way and as similar as possible to what would be occurring naturally. The biofouling testing experiments performed during the thesis were mostly carried out using flat cell units. The effect of different operating variables on biofouling development was studied. The effect of RO module construction was also evaluated, testing different membranes and feed spacers side-by-side, to guide the improvements on the design of fouling resistant elements. To evaluate the amount of fouling generated under different conditions, an analytical method to determine to impact of biofouling on fouled samples was developed. Specific and reliable methods for biofouling quantification are critical for studying samples obtained using natural waters, where usually different types of fouling can be found.
The results from the trials performed clearly showed that different membrane chemistries can provide significant reduction in the levels of biofouling detected after operation. However, it was found that the main contributor to biofilm development was feed spacer. Large differences in the amount of biofouling generated could be associated with feed spacer presence. Feed spacer design was then studied in detail to achieve a balanced performance in spiral wound RO modules treating waters prone to biofouling. Feed spacers with various thickness, spacing and angle were tested and some designs showed advantages in pressure drops, as well as on biologic and organic fouling accumulation.
It could be concluded that a significant benefits in fouling accumulation could be obtained by optimizing module design. The scale-up of the results would result in more sustainable operation of RO element in water reuse pilot plants. Fouling resistant elements would provide a decrease on the footprint of system by reducing energy consumption, chemical consumption and the complexity of the pretreatments.
