The intensive use of antibiotics in hospitals, poultry, and other industries has led to the emergence of bacteria resistant to most commercially available antibiotics. These antibiotic-resistant bacteria (ARB) are being released into the aquatic environment and could cause serious health issues. In this study, multidrug-resistant bacteria (MDR) were isolated from the effluent of secondary process (activated sludge) in full-scale hospital wastewater treatment plants (HWWTPs). These bacterial isolates were tested against commercially available antibiotics to explore their resistance profile. Sulfonated hafnium oxide-doped CuO nanoparticles (Cu/SHfNP) were synthesized to improve the antibacterial and antibiofilm activities of hafnium against Gram-negative (Enterobacter asburiae, Escherichia coli, and Pseudomonas aeruginosa PA01) and Gram-positive (Staphylococcus aureus ATCC6538) bacterial strains. The combined effects of CuO and SHfNP at 0.5 mM and 1 mM exhibited strong antibacterial and antibiofilm activities against MDR bacteria. The results showed that Cu/SHfNP was an effective alternative agent inhibiting persister cells, planktonic cells, and mixed-species biofilm formation on polystyrene, nylon, and glass surfaces. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) showed that the biofilm thickness and cell attachment were reduced significantly when exposed to Cu/SHfNP. The photocatalytic activity of Cu/SHfNP revealed the maximum reduction of cell growth by 6.1 log CFU mL⁻¹ under visible light irradiation for 180 min. Cu/SHfNP was nontoxic to human cells, meaning that it can be used as a self-healing agent to combat MDR and prevent membrane biofouling in membrane-based bioreactors.