BACKGROUNDMembrane fouling is the main limiting factor for the application of ultrafiltration (UF) to wastewater treatment as tertiary treatment or in membrane bioreactors. Soluble microbial products (SMP) play the more important role on membrane fouling. In this work, four sequencing batch reactors were operated in parallel using two different simulated wastewaters under operating conditions maximizing and minimizing SMP production. The aim was to study the influence of the wastewater type, which until now has hardly been considered, on SMP production and, consequently, on membrane fouling. RESULTS AND CONCLUSIONResults showed that organic matter (OM) type in wastewater greatly influenced SMP production and composition (protein : carbohydrate ratio). The food-to-microorganisms (F : M) ratio also significantly influenced SMP production. The lowest protein : carbohydrate ratio was achieved for wastewater containing sodium acetate as OM source at a F : M=0.2. Finally, both mixed liquor and treated effluent were subjected to an ultrafiltration (UF) process and it was confirmed that the carbohydrate concentration in SMP was the main parameter influencing membrane fouling when the reactor effluent was fed to the UF process. (c) 2018 Society of Chemical Industry