In addressing the challenges of deep purification of cadmium (Cd) heavy metal
contamination and membrane fouling control in spacecraft drinking water sources
and recirculation systems, this study adopts a coagulation-ultrafiltration
coupled process, with polyaluminium chloride (PACl) as the coagulant and sodium
polyacrylate (PAANa) as the complexing agent. A systematic investigation was
carried out to examine the effects of key operating parameters—including
coagulant dosage, complexing agent dosage, and humic acid (HA) concentration—on
Cd removal efficiency, floc morphological characteristics, and ultrafiltration
membrane resistance distribution.
The results indicate that for simulated raw water containing 0.05 mg/L Cd and (50
± 0.5) NTU turbidity, under the optimized conditions of 20 mg/L PACl, 20 mg/L
PAANa, and pH = 7, the Cd concentration in the effluent treated by the
coagulation-ultrafiltration coupled process is reduced to as low as 0.004 mg/L,
which meets and even exceeds the hygiene standard limits for both spacecraft
drinking water and domestic drinking water. HA was found to promote floc growth
and enhance the complexation-based removal of Cd, yet it exacerbates membrane
surface adsorption and gel layer fouling. Membrane resistance analysis reveals
that gel layer resistance and concentration polarization resistance are the
primary sources of fouling, and membrane fouling can be effectively mitigated
through rational regulation of operating parameters.
This coagulation-ultrafiltration coupled process is characterized by high
purification efficiency, stable effluent quality, and strong modularity. It is
well adapted to the requirements for closed-loop circulation of spacecraft water
resources and drinking water safety assurance, and can provide technical support
for water circulation systems in manned spacecraft, drinking water purification
at launch sites, and in-situ water treatment during deep space exploration.