Mimicking biological method with inorganic and organic compounds modified clays for continuous controlling of Microcystis aeruginosa

Although clay dispersion is one of the few techniques currently used in the field to control cyanobacterial harmful algal blooms (CyanoHABs), low flocculation efficiency and resuspension of flocculated algal cells are its main drawbacks. This study simulated the "flocculatio-lysis-degradation-nutrient regulation" model of biocontrol technique to develop a modified clay (ECRE-CS-PFS-CPL) using polyferric sulfate (PFS), chitosan (CS) and Eichhornia crassipes root extracts (ECRE) to modify the clinoptilolite (CPL). The results revealed that ECRE-CS-PFS-CPL introduced functional groups, specifically aldehyde group —CHO and amide group —CO-NH—, leading to an enhanced void structure. At 0.2 g/L concentration, ECRE-CS-PFS-CPL demonstrated a removal efficiency of 98.02 % within 30 min. ECRE-CS-PFS-CPL exhibited a positive charge in nature water, leveraging charge neutralisation to expedite the flocculation of M. aeruginosa cells. The combination of coated CS and algal cells resulted in the formation of large, dense flocs through net sweeping and bridging, which was 58.28 times larger than control. Subsequently, the loaded ECRE inhibited the algal cells via allelopathy. The inhibition activated the antioxidant system of M. aeruginosa, with significant increases in catalase (CAT) and superoxide dismutase (SOD) activities. Photosynthetic pigments (Chl-a), photosynthetic efficiency (Fv/Fm) and maximum relative photosynthetic electron transfer rate (ETRmax) were markedly reduced, indicating the damage to photosynthetic system. Furthermore, Chl-a remained consistently low during extended monitoring, registering at 4.98 % of control after 40 days. ECRE-CS-PFS-CPL effectively reduced microcystins by 81.48 % and phosphate levels in algal cultures by 91.92 % compared to control. Consequently, ECRE-CS-PFS-CPL offers an efficient, environmentally safe and sustainable solution for CyanoHABs control.