Enhancing starch hydrolysate syrup purification: long-term ultrafiltration membrane performance under industrial conditions

Abstract

Ultrafiltration (UF) membranes based on Polyethersulfone (PES) are extensively used in food and bioprocessing industries for their good mechanical robustness and chemical resistance. In starch and sweetener production, these membranes play a vital role in clarifying and purifying carbohydrate-rich syrups. However, sustaining membrane performance under industrial conditions, characterised by elevated temperatures, high pressures, and chemically complex feed solutions, remains a significant challenge due to progressive fouling, membrane ageing, and irreversible performance decline. This study investigates the long-term performance (32h) of the GR90PP tight PES UF membrane (5 kDa cut-off) from Alfa Laval, operated under representative industrial conditions (60 °C, 8 bar) and using a real DE40 starch hydrolysate syrup. The study focuses on quantifying operational stability and fouling–cleaning behaviour across four filtration-cleaning cycles, including analysis of flux evolution, cleaning efficiency, solute rejection, and membrane integrity. Results revelaled a progressive Relative Flux Reduction (RFR), averaging 44 %, alongside a significant Flux Recovery Ratio (FRR) after cleaning, peaking at 80 % after the last alkaline rinse. Scanning Electron Microscopy (SEM) analysis confirmed a gradual build-up of fouling layer, predominantly organic in nature, contributing to reduced permeability and moderate irreversible fouling (average 21 %). Alkaline cleaning proved significantly more effective than acidic cleaning, highlighting the dominance of organic fouling mechanisms. Overall, the GR90PP membrane demonstrated strong operational stability, chemical compatibility, and cleaning resilience under extended high-temperature UF operation, supporting its suitability for processing of carbohydrate-rich products. These findings provide practical insights for optimising cleaning protocols, defining cleaning frequency, and adjusting operational parameters to sustain membrane performance in industrial food applications.