Abstract <p>Ceramic microfiltration membranes based on fly ash microspheres were used for the separation of diesel fuel (DF) in water emulsions. The membranes were characterized by an average pore size of 0.451 µm and a water permeability of 0.255 m³/(m² h bar). Filtration experiments in a dead-end configuration were conducted for emulsions with hydrocarbon phase concentrations from 100 to 1000 mg/L at a transmembrane pressure of 3 bar. The steady-state DF rejection was 97–98%, independent of concentration, while steady-state flux values ranged from 0.057 to 0.309 m³/(m² h). Lower flux values corresponded to higher DF concentrations. The decline in permeate flux over time due to membrane fouling was best described by the intermediate pore blocking model, which implies that the droplet size is comparable to the pore size, allowing droplets to deposit on top of each other. This conclusion is supported by droplet size distribution measurements, showing an average droplet size of 0.31–0.46 µm. The retention mechanism is determined by the formation of a hydrocarbon phase layer on the membrane surface, as well as electrostatic repulsion of droplets from the negatively charged surface. The obtained results can be used for the development and improvement of technologies for treating wastewater and produced water from oil and petroleum products.</p>