Response mechanisms of microalgal-bacterial granular sludge to different loading strategies of copper oxide nanoparticles
Alfonz Kedves, Zoltán Kónya
Abstract
This study investigated the effects of copper oxide nanoparticles (CuO NPs) at concentrations of 1–50 mg/L on the microalgal-bacterial granular sludge (MBGS) wastewater treatment process, comparing two nanoparticle addition methods: shock-load (SL) and stepwise (SW) increases. The results demonstrated that the chemical oxygen demand (COD) and ammonia‑nitrogen (NH 3 -N) removal were more sensitive in the reactor with shock-load (R SL ), phosphate concentrations were higher in the effluent from the reactor with stepwise increases (R SW ). Accumulation of nitrate‑nitrogen was observed only in the SW method at CuO NP concentrations ≥20 mg/L, likely due to the nanoparticles becoming entrapped within the granule interiors, as evidenced by scanning electron microscopy coupled with energy-dispersive X-ray (SEM-EDX) mapping. Although total EPS levels were highest in both reactors at 20 mg/L CuO NP dosage, the levels were significantly higher in the RSW sludge (191.1 mg/g MLVSS in R SL vs. 218.3 mg/g MLVSS in R SW ), primarily due to the long-term exposure leading to increased loosely-bound EPS (LB-EPS) content (75.7 mg/g MLVSS in R SL vs. 102.9 mg/g MLVSS in R SW ). Furthermore, CuO NPs interacted with EPS, binding to N H, C N, C O, and C-O-C groups in protein (PN) and polysaccharide (PS) structures. • 1 and 5 mg/L of copper oxide nanoparticles did not impair nutrient removal. • Sudden nanoparticle exposure impaired carbon and ammonia removal more severely. • Only long-term nanoparticle accumulation influenced nitrate removal efficiency. • Gradual exposure increased production of extracellular polymeric substances.