Assessing pathogen removal efficiency of microfiltration by monitoring membrane integrity

Abstract

This study was conducted to investigate the ability of various methods of monitoring membrane integrity to respond to changes in actual membrane integrity imposed by the compromised fibers within the microfiltration unit. In addition, the pilot-scale MF unit was challenged with high concentrations of coliform, Cryptosporidium, and spore, in order to assess the pathogen removal capability of microfiltration. A correlation between the integrity tests and microbial challenge data was also made. The integrity tests investigated in this study were pressure decay and diffusive air flow tests (direct integrity tests), and turbidity and particle counting (indirect integrity tests). Both pressure decay (PDT) and diffusive air flow (DAF) tests were sensitive enough to detect one damaged fiber out of 66,000. The extent of fouling did not affect the sensitivity of the PDT and DAF, showing that PDT and DAF tests are a simple, reliable means to monitor membrane integrity under field conditions. Indirect integrity monitoring using turbidity and particle counting, however, responded poorly to changes in membrane integrity. Microbial challenge study demonstrated that microfiltration was capable of removing various pathogens including Cryptosporidium, at the level required by drinking water regulations, under even adverse operating conditions. Finally, PDT and DAF tests showed a better correlation with actual microbial removal efficiency of microfiltration than turbidity and particle counting. The turbidity and particle counting grossly underestimated the removal of pathogen larger than MF membrane pore size due to poor sensitivity.

Drivers of Microbial Risk for Direct Potable Reuse and de Facto Reuse Treatment Schemes: The Impacts of Source Water Quality and Blending

“…Microfiltration log removal values of 4.6 ± 0.96 were reported by Hong et al [31] for Cryptosporidium from a pilot-plant with 0.2 µm nominal pore size polypropylene filter in Tampa, Florida. This is consistent with a 4–7 log removal range reported by Reardon et al [53] for protozoa.…”

“…For the DPR advanced treatment processes, microfiltration (MF), reverse osmosis (RO), UV, ozone, biological activated carbon filtration (BAC or BAF), membrane bioreactors (MBR), and nanofiltration (NF) were the processes considered. Microfiltration log removal values of 4.6 ± 0.96 were reported by Hong et al [ 31 ] for Cryptosporidium from a pilot-plant with 0.2 µm nominal pore size polypropylene filter in Tampa, Florida. This is consistent with a 4–7 log removal range reported by Reardon et al [ 53 ] for protozoa.…”

Pyrosequencing Demonstrated Complex Microbial Communities in a Membrane Filtration System for a Drinking Water Treatment Plant

“…Because the membranes used to purify drinking water have pores that are smaller (typically 0.04-0.2 μm) than microorganisms (typically 0.5-5.0 μm), microorganisms are effectively rejected through a sieving mechanism (30), although some microorganisms (e.g., ultramicrobacteria (28)) can pass through the membranes. However, defects on a membrane's surface can decrease sieving efficiency, allow pathogens to pass through the membrane, and affect public health, and it is important to test the integrity of membranes during the filtration process (1,9,10). A membrane integrity test is frequently conducted by counting particles in filtered water and/or checking pressure-induced decay by applying high pressure to the membranes.…”

Monitoring the Integrity of low‐pressure membranes

“…What is not clear is whether the fouling layer reduces the sensitivity or reliability of direct integrity tests in signaling a breach of membrane integrity. However, a recent study showed that membrane fouling had little to no effect on the sensitivity of pressure decay and diffusive airflow tests (Hong et al, 2001). Nonetheless, further work should be conducted to verify this finding.…”

“…A more recent study (Hong et al, 2001) attempted to establish correlations between microbial removal efficiency of a pilot‐scale microfilter and results of direct integrity monitoring tests (pressure decay and diffusive airflow tests). Cryptosporidium spp.…”