1. Water quality conditions
Hardness ions: Calcium, magnesium and other ions are prone to form calcium carbonate scale, which blocks the membrane pores. In one case, when no scale inhibitor was added, the desalination rate of a system with a recovery rate of 75% dropped by 40% after one year of operation.
Organic matter and colloids: When the SDI (pollution index) exceeds 2.5, the pressure difference of the microfilter surges, resulting in the thickening of the fouling layer on the membrane surface.
Microorganisms: For systems that are not disinfected regularly, the total number of bacteria in the produced water can reach 10⁴ CFU/mL, which accelerates membrane degradation.
2. Operation management
Residual chlorine control: If the activated carbon is saturated or the dosing pump fails, the residual chlorine concentration exceeds 0.1ppm, which may oxidize the membrane material.
Pressure fluctuations: Frequent start-stopping leads to mechanical fatigue of the membrane element. In a project, the membrane curling layer separated due to sudden pressure changes, shortening the life by 60%.
Cleaning strategy: When the chemical cleaning cycle is too long (more than 3 months), the fouling layer solidifies and needs to be cleaned with a higher concentration of acid, which damages the membrane structure.
3. System design
Pretreatment matching degree: In a system without a safety filter, large particles directly impact the membrane surface, and in one case, the membrane element was scrapped in 6 months.
Recovery rate setting: A high recovery rate (such as 90%) requires a scale inhibitor, otherwise the LSI (Langelier Index) will exceed the standard and scale will form easily.