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Excessive growth of microalgae due to use of fertilizers, detergents, and discharge of domestic waste results in the eutrophication and degradation of the water quality of lakes and ponds. The present study aimed to improve the quality of pond water by harvesting mixed cultures of microalgae grown in a pond using Moringa oleifera (MO) extract as a coagulant. The study comprises evaluating the effects of coagulant dose, pH, mixing time, mixing rate, settling time, temperature, and algal biomass concentration on nutrient and microalgae cell removal. The pond water quality restoration was assessed by characterization of raw and MO‐treated water. The MO was found to be very effective for mixed culture microalgae harvesting with flocculation efficiency of 92.97% at dose of 15 ml/L of MO extract, pH 8, mixing time 5 min, mixing rate 30 rpm, and 20‐min settling time. The results have shown significant improvement in pond water quality with reduction in turbidity from 388.16 ± 48.23 to 8.39 ± 1.0 NTU, chlorophyll‐a from 635.01 ± 86.20 to 15.03 ± 1.5 mg/m3, total nitrogen (TN) from 20.37 ± 4.64 to 12.10 ± 1.19 mg/L, and total phosphorus (TP) from 2.05 ± 0.10 to 1.61 ± 0.24 mg/L. Practitioner points Production of biomass and water quality improvement of the pond at the same time MO extract shows better removal efficiency at a lower dose with fast kinetics Cost‐effective flocculant saves time and energy during flocculation Common bioflocculant to remove both microalgae and nutrients.

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The presence of microalgae affects water quality and beneficial uses of surface freshwaters. Chitosan with proven potential for harvesting specific microalgae species from their culture medium for producing biofuels and bioproducts appears promising for efficient removal of mixed microalgae species from surface freshwaters also. The main thrust of the present study was on removal of mixed microalgae species using chitosan as a coagulant to help improve water quality. Important operational parameters were optimized for economical microalgae removal. The microalgae cells, chlorophyll-a, TN and TP removal efficiency were 82.06, 89.90, 69.32 and 44.01%, respectively at an optimum chitosan dose of 10 mg/L, pH 8, slow mixing time 7 min, slow mixing rate 30 rpm and settling time of 15 min. The results have shown that chitosan coagulation efficiently removed the mixed microalgae species from surface freshwater with significant improvement in water quality and recovery of algal biomass for other beneficial applications.