The effective filtration of source water is a prerequisite for water treatment in numerous industrial and agricultural applications. Obviously the purpose of filtration is to remove particles or “solids” from the inflowing water stream. Usually filtration efficiency is measured by various standard tests such as turbidity (NTU), total suspended solids (TSS), silt density index (SDI) and particle number and size distribution. These tests are relatively simple to do and give a good indication of how effective a given filtration step has been in removing particles. But these measurements give no “biological” information about the effect of the filtration on bacteria and other microbes that may cause trouble downstream in sensitive water treatment facilities.
This is the reason why the standard tests for filtration efficiency are inadequate, in many situations where the development of biological fouling – or bacterial “re-growth” – is problematic, such as in water treatment and desalination plants using NF or RO membranes (the image shows a membrane that has suffered from this kind of phenomenon).