California Institute for Energy and Environment (CIEE)

As more tertiary processes are implemented for water reclamation, membrane filtration is gaining ground their energy intensity is being investigated. A better understanding of membrane fouling is key to reducing energy requirements, which in turn lower running costs. Nanomaterials, due to their small size, have the potential to cause pore plugging of the membranes, which is very difficult to mitigate. Previous studies by others have indicated that pore plugging by biogenic nanoscale particles may account for up to 80% of flux reduction, causing irreversible fouling that necessitates costly chemical cleaning. As a first step towards evaluating the impact of manufactured nanoparticles, we investigated here the extent of biogenic nanoscale particles impact on membrane flux reduction and energy consumption using wastewater samples from three treatment plants. For each sample, a filtration series was conducted with 0.45, 0.2, 0.1, 0.08, 0.05, 0.03, and 0.01 micron membranes. At each step, filtrate was collected, COD was measured, and Zetasizer Nano analysis was performed to quantify particle size distribution and count rate (number of particles per second detected by the instrument, i.e. total amount of particles in the water). As the pore size became smaller, the count rate in the samples reduced, showing that not only the larger particles were removed, but the overall number of particles is decreased by the filtration process. During the same incremental filtration series, COD did not vary, showing that the largest contribution to COD was given by the small particles that bypass all the filtration events.