Particle counting as surrogate measurement of membrane integrity loss and assessment tool for particle growth and regrowth in the permeate of membrane bioreactors

Normalized particle counting data for permeate samples with no apparent membrane leakage or significant growth and aggregation. [Display omitted] •MBR membrane integrity successfully checked by particle counting.•One single particle counter applied to 8 full- and pilot scale MBRs.•No problems detected with air bubbles or flow variations.•Unified methodology to assess membrane integrity, growth/regrowth in the permeate.•Particle size distribution “decides” cleaning of the permeate collection system. Wastewater is increasingly used as a viable water source. Reclamation schemes rely on membranes technologies, such as Membrane Bioreactors (MBR) and subsequent membrane filtration steps to achieve the discharge or reuse limits. However, membrane technology is only effective if the membranes are intact. Moreover, growth or regrowth of particles between membrane filtration steps should be restricted, to guarantee a stable water production. Membrane integrity tools are being developed for the drinking water industry with high sensitivity and accuracy. However, such standards are not required for MBRs, where the produced permeate is not used for consumption without further treatment. In this research, we focused on permeate quality and particle counting measurements in the range 2–100μm. A total of 433 samples of permeate and process water were measured at 8 full-scale and pilot-scale MBR locations, which were compared with 43 de-mineralized water samples measured at TU Delft. Only at one full-scale MBR the membrane integrity was compromised, which was successfully assessed by counts and shapes of the permeate particle counting distributions. All permeate samples had particles about a 100 times larger than the membrane pore size. Our results allowed us to define the relevant steps of a methodology to assess membrane integrity, particle or biomass growth and aggregation in MBR permeate. The latter two are of particular interest to determine whether growth in permeate lines is still acceptable or whether a cleaning action of the permeate collection system is required.