Performance of a ceramsite-enhanced gravity-driven ceramic membrane (GDCM) for simultaneous manganese ion and ammonia removal

Rapid population and economic growth have led to increased discharge of industrial wastewater into the aquatic environment. Multiple contaminants, such as ammonia and manganese ion in groundwater, may pose a significant risk to our drinking water safety. In this work, a novel groundwater purification system (i.e., a ceramsite-dosed gravity-driven ceramic membrane (GDCM)) has been applied to simultaneously remove manganese ion and ammonia for 60 days. The GDCM showed excellent ammonia and manganese ion removal; this performance was attributed to the degradation by enriched bacteria (5.2 × 10⁶ CFU/mL), along with highly catalytic birnessite that enhanced both biotic and abiotic oxidation of ammonia and manganese ion. The proportions of heterotrophic nitrifying and aerobic denitrifying bacteria (HN-AD) and manganese oxidizing bacteria (MnOB) (Hyphomicrobium) existing in the GDCM were 81.51% and 0.24%, respectively. Besides, the mixture/separate/deposit of PAC-MnOx (powdered activated carbon) and ceramsite provided favorable ecological conditions for the efficient removals of manganese ion (<0.1 mg/L) and ammonia (not detected) in the later stage. The flux of mixture-mode and separation-mode were stabilized at 13.9 LMH and 10.9 LMH, respectively, owing to the decreased porosity of fouling layer after the long-term operation, as confirmed by the BET analysis. Additionally, divalent manganese ion still existed in the PAC-MnOx and the peak intensity of birnessite increased significantly over time, as demonstrated by SEM-EDS mapping, Raman analysis, X-ray diffraction (XRD), and X-ray Photoelectron Spectroscopy (XPS) analysis. From the perspective of real application, inoculation of cycled raw water (GDCM 3#) and transfer of mature filter material (GDCM 4#) into a new GDCM tank significantly reduce the ripening time (Not even needed), while the purification effect of manganese ion and ammonia can also be satisfactory. It was particularly noted that the membrane fouling control effect of mixture-filled mode (GDCM 1-1#) was the most significant, that was, the minimum irreversible fouling was 4.8 × 10⁸ m⁻¹. At the same time, the ripen period of the mixture-filled mode was 5 days earlier than that of the separation-mode, and the final stable flux was slightly larger (17.25 LMH>16.25 LMH). In conclusion, the novel strategy, PAC-MnOx filled ceramsite composite GDCM system, was satisfactory in treating manganese ion and ammonia-containing groundwater as well as encouraging extensive applications of membrane technologies for drinking water supply.