Chemical coagulation is commonly used to prevent membrane fouling in water treatment, but finding the best conditions for this process is tricky. A study looked at how pre-coagulation with aluminum salt affects membrane fouling in microfiltration. They found that acidic conditions improved water quality but led to more severe fouling. Using too much coagulant also increased fouling. Small flocs formed under acidic conditions could block the membrane pores, causing irreversible fouling. These results were confirmed in a pilot-scale test.