Hybrid process of coagulation/flocculation with Moringa oleifera followed by ultrafiltration to remove Microcystis sp. cells from water supply

摘要

In Brazil and other countries, the large biomass of monospecific crops and the need to enhance plant growth by the extensive use of fertilizers have caused a fast eutrophication of rivers and reservoirs that has resulted in a high growth in the population of cyanobacteria, of which several species have been described as producers of toxins capable of causing death of domestic and wild animals, in addition to problems to human health. The objective of the present work was then to evaluate the efficiency of Moringa oleifera seeds as coagulant in removing cells of the cyanobacterium Microcystis sp., apparent color, and turbidity from water in association with ultrafiltration. For the experiments, deionized water was artificially contaminated with Microcystis sp. cells from a culture. Mixing was carried out until samples with initial turbidity of 350 and 450 NTU were obtained to simulate high turbidity water with bloom of cyanobacteria. After being prepared, the samples were subjected to the processes of (1) coagulation/flocculation with moringa seeds (CFM), (2) UF, and (3) combined coagulation/flocculation with moringa solution followed by ultrafiltration (CFM-UF). The CFM process was carried out with a solution of 1% moringa seeds at concentrations of 25 to 300 mg/L. Mixing was promoted in a jar test device. Poly(ether sulfone) membrane with retention of 50 kDa and operating pressure of 2 bar was used for the UF process. In the CFM process, turbidity removal ranged from 49 to 97.4%, color removal varied between 39 and 99.2%, and removal of Microcystis sp. cells ranged from 20 to 91%. Applying the analysis of variance to the results, optimal moringa concentrations of 175 and 250 mg/L were obtained for water samples of 350 and 450 NTU respectively. These concentrations were used in the combined CFM-UF process. Microcystis sp. cells were not detected in treated water after UF and CFM-UF processes. Color and turbidity removal was above 99% for both processes. For the permeate flux, the combined CFM-UF process and the UF process alone presented average relative fluxes of 40% and 29.4%, respectively. Membrane fouling was 78.5% for UF and 70% for CFM-UF. This way, it can be said that coagulation/flocculation with moringa can be applied to high turbidity water, with high removal of color, turbidity, and Microcystis sp. cells, reaching more than 99% when this process was combined with ultrafiltration. In addition, the combined process showed higher permeate flux and slightly lower fouling percentage when compared with the UF process alone.