• fouling index
• low-pressure membranes
• membrane fouling
• MFI
• SDI

The considerable improvements and the corresponding decrease in treatment cost, the significant stress to meet the ever increasing water demand, and the increasingly stringent water quality regulation have brought to a more and more increasingly popular microfiltration (MF) and ultrafiltration (UF) membrane processes.
Microfiltration and ultrafiltration are key elements in many fields as: biotech, medical, food&beverage, industrial, electronics, water and wastewater, including polishing and membrane bioreactors (MBR).
A major problem for these membrane processes is fouling, which causes a decrease of membrane permeability. Fouling is an accumulation of colloidal and particulate matter, organic macromolecules (organic fouling), soluble inorganic compounds (scaling), and microorganisms (biofouling) on the membranes.
Membrane fouling can lead to reduced productivity, deteriorated permeate quality, increased energy consumption and treatment cost, as well as shorter membrane life span.
Earlier studies on fouling have focused on fouling indices such as silt density index (SDI) and modified fouling index (MFI), but these indices offer little mechanistic view of the factors governing membrane fouling.
The literature on RO and NF colloidal fouling is expanding at an exponential rate and indices developed for these latter processes have started to be used also for MF and UF processes. Is it viable?
This thesis summarizes the existing literature fouling indices and makes a comparison between them. Furthermore the thesis investigates and tries to understand if it is reliable or not to apply indices developed for RO and NF also to MF and UF.
The goals of the use of these indices are to estimate the fouling potential of a feed water and to assess the advantage of employing or not a membrane filtration system in a given place.
For this reason, the thesis analyses if the use of the earlier simply and fast field indices is really useful or if it is better to entrust the estimation of the fouling potential to more accurate measuring technologies which need laboratory instruments.