Table 1.

Factors affecting the efficiency of non-reagent membrane cleaning methods.

Method/ Membrane Configuration	Affecting Factors	Drawbacks
Ultrasound Flat sheet Tubular	Ultrasound frequency. Lower ultrasound frequencies make cleaning more efficient than higher frequencies [32,33,34,35].	Fail to provide a uniform distribution of the ultrasonic energy to the fouled membrane surface [29,36]. Damage to the ceramic membranes was observed when using high powers [37].
	Ultrasound power intensity. Sonochemical effects (amount of bubbles, hydrodynamic turbulence) boost with the increase of ultrasound power intensity [32,35].
	Temperature. The best conditions for effective cavitation were reported at 60–70 °C. When the temperature was decreased to 40 °C or raised to 85 °C, the cavitation efficiency decreased by half [29].
Electric field Flat sheetTubular	Zeta potential of a feed. Electrical field strength. The maximal efficiency (lowest fouling degree) is achieved when an electrical field strength is close to critical [38].	Intensive corrosion or expensive corrosion-resistant electrodes [39]. Potential risk of electrocoating a membrane in hard water [40].
Backwashing Flat sheet Hollow fibre Tubular	Pressure. For effective particle removal, backwash pressure has to be higher than the membrane operating pressure [29].	Intensive energy consumption [30,41]. Hard to ensure constant and uniform backflow through multichannel membranes [42].
	Composition of backwash solution. Backwashing is more effective using deionized water, rather than permeate [41,43].
Backpulsing Flat Sheet Tubular	Amplitude. An increase in amplitude allows decreasing the cleaning time [29,44].
	Frequency. The short duration of back pulses is key for effective foulant removal [44].