Membrane fouling is an unavoidable issue in the operation of reverse osmosis (RO) systems, and cleaning is the primary means of restoring performance. However, some seemingly reasonable practices during cleaning can actually cause subtle damage to membrane elements. Based on practical experience from Dalton Membrane Technology in industrial and municipal water treatment projects, this article summarizes four of the most common cleaning misconceptions for your reference.

Misconception 1: The more frequent the cleaning, the better

• Phenomenon
  Some users schedule regular cleanings to ensure system stability, even when differential pressure and permeate flow remain within normal ranges. Each cleaning is carried out strictly according to procedures, which appears unobjectionable on the surface.
• Consequences
  Excessive cleaning accelerates the aging of the membrane's separation layer, leading to a gradual decline in salt rejection and significantly shortening the overall membrane lifespan. Frequent exposure to chemical agents also increases the risk of membrane material fatigue and mechanical damage.
• Correct approach
  The timing of cleaning should be determined based on trends in differential pressure, permeate flow, and salt rejection. Typically, cleaning should be initiated when the single-stage differential pressure increases by 15% over the initial value, or exceeds 0.25 MPa, combined with a normalized permeate flow decline of more than 10%. Keeping thorough records and conducting trend analysis on a daily basis is more scientific than cleaning at fixed intervals.

Misconception 2: The higher the cleaning solution concentration, the better the effect

• Phenomenon
  When cleaning results are unsatisfactory, some operators directly increase the cleaning agent concentration, believing that "stronger is better than weaker," and even treat high-concentration cleaning as a shortcut to deep cleaning.
• Consequences
  Overly high concentrations of cleaning agents can directly attack the membrane's separation layer, causing irreversible loss of salt rejection. Over time, cleaning at high concentrations may shorten the effective service life of membrane elements by 20% to 30%, and the damage often accumulates silently and imperceptibly.
• Correct approach
  Strictly prepare cleaning solutions according to the concentration range recommended by the membrane manufacturer. If the effect is insufficient, prioritize extending the cleaning circulation time appropriately or raising the cleaning temperature within permissible limits, rather than simply increasing the chemical concentration. Any parameter adjustment should be based on sound justification, not on intuition.

Misconception 3: The higher the cleaning solution temperature, the better the effect

• Phenomenon
  To achieve better cleaning results, some operators heat the cleaning solution, thinking that "hotter cleans more thoroughly," especially when dealing with organic fouling and grease/oil contamination.
• Consequences
  Excessive temperatures can significantly damage most industrial RO membranes. In particular, polyamide composite membranes have very limited tolerance under high-temperature alkaline conditions, and overheating may cause hydrolysis of the membrane sheet, leading to permanent loss of salt rejection.

Important distinction: Different membrane elements have different temperature tolerance limits. For conventional industrial RO membranes, the cleaning temperature generally should not exceed 45°C.

Dalton Membrane's sanitary-grade thermally disinfectable membrane elements, however, are manufactured with special materials and processes that can withstand hot water disinfection up to 85°C, making them suitable for pharmaceutical, food, beverage, and other industries with strict microbiological requirements. Before cleaning, always confirm the temperature tolerance range of the membrane elements in use to avoid damage from improper temperature control.

• Correct approach
  Strictly control the cleaning solution temperature within the allowable range for the membrane elements. For conventional industrial membranes, it is generally not advisable to exceed 45°C; for thermally disinfectable membranes, follow the temperatures specified in the product manual. Avoid pushing both temperature and concentration to their upper limits simultaneously, as their combined effect greatly increases the risk of membrane damage.

Misconception 4: One cleaning protocol fits all types of fouling

• Phenomenon
  Regardless of the fouling type, operators apply a standard "alkaline wash + acid wash" package, proceeding directly to cleaning without any diagnosis of the fouling. Some sites even establish a fixed template of "alkaline wash → water rinse → acid wash" and repeat it mechanically for every cleaning.
• Consequences
  When the cleaning protocol does not match the fouling type, the effectiveness is greatly compromised, and the contaminants cannot be properly removed. Repeated cleaning attempts that still yield poor results not only waste chemicals and time but also expose the membrane elements to the combined effects of fouling and chemical attack, eventually leading to premature failure.
• Correct approach
  First diagnose the fouling type, which generally falls into categories such as inorganic scaling, organic fouling, microbial fouling, and colloidal fouling, and then select the corresponding cleaning protocol. Preliminary diagnosis is not complicated: you can open the end cap of the first membrane element to observe the color, morphology, and odor of the deposits, or refer to patterns in system operating data. If in-house diagnostic capabilities are insufficient, consult technical professionals to avoid blind cleaning.

Cleaning is a necessary maintenance measure, but excessive or improper cleaning can damage membranes more than no cleaning at all. Taking an extra step to diagnose before cleaning may add months to the service life of your membrane elements.