Ageing of ultrafiltration membranes in contact with sodium hypochlorite and commercial oxidant: experimental designs as a new ageing protocol
Résumé
In drinking water production plants using membrane processes, contact with cleaning chemicals is believed to play an important role in membrane ageing. In this article, polysulfone membranes were used to simulate the industrial cleaning in static conditions. Ageing of the membrane was mimicked by immersing samples in solutions containing sodium hypochlorite and commercial oxidants with various concentrations, temperatures and soaking times defined by experimental designs. For the first time in the chemical membranes ageing research, an approach based on methodological tools has been realized. The main interest is to achieve a relevant ageing pattern without using an accelerated ageing protocol (high concentrations and short contact times). The macroscopic changes were monitored by permeability measurement and mechanical strength tests coupled with a microscopic characterization by ATR-FTIR (to identify the chemical functional groups affected by ageing) and SEM (to visualize qualitatively the surface changes and deteriorations). The present work details the comparison between NaOCl and another oxidant: P3-Oxysan ZS (composed of peracetic and peroctanoic acid). The comparison of the macroscopic and microscopic properties of hypochlorite-aged membranes and P3-Oxysan ZS-aged membrane indicate NaOCl is far more detrimental for membrane integrity than P3-Oxysan ZS. The latter might give an alternative solution to the use of chlorine on industrial plant. The obtained results let to consider less harmful cleaning products on membranes. Then, the present study based on experimental designs let to underline that the most commonly used parameter "concentration × time of exposure" (c × t) was not a representative tool to predict membrane ageing.