Water Reuse Microfiltration

Physical separation with membranes with pores of about 0.1 to 10 µm that retains suspended solids and bacteria so water can be reused or treated.

Microfiltration is a pressure-driven membrane process. Water passes through the membrane and particles larger than the pore are retained: suspended solids, turbidity, large colloids and most bacteria and protozoa. It does not retain dissolved salts or most dissolved organic matter, and its effect on viruses is limited; for that, ultrafiltration, nanofiltration or reverse osmosis are used, processes for which microfiltration often acts as pretreatment. It can operate in dead-end mode, in which all the water passes through the membrane, or in cross-flow mode, in which the water flows parallel to the surface and carries away part of what is retained.

In water reuse it is used to clarify treated effluents, wash water or process water before reusing it for purposes that do not require drinking water, such as irrigation, cleaning of facilities or auxiliary circuits, often followed by disinfection. If the end use requires removing salts or dissolved contaminants, microfiltration alone is not enough. In the European Union, Regulation (EU) 2020/741 sets the minimum quality requirements for reclaimed water for agricultural irrigation.

With use, membranes become fouled by the build-up of particles, organic matter, mineral scale and biofilm, and the flow rate drops. To recover it, periodic backwashes and chemical cleans are carried out, usually alkaline for organic fouling and acid for scale, following the membrane manufacturer's instructions on products, concentrations and temperatures compatible with its material.

More information: Industrial reverse osmosis · Biofilm