Study of hydrodynamic cavitation applied for the selective removal of Escherichia coli and Daphnia sp. present in the cultivation of microalgae in agro-industrial wastewater

The presence of undesirable microorganisms in wastewater, considered a low-cost medium, can affect the production of biomass as they take nutrients from the medium. In this sense, the present article aims to apply hydrodynamic cavitation to reduce the pollutant load of Daphnia sp. and Escherichia coli. Additionally, it aims to evaluate the impact of hydrodynamic cavitation on microalgal growth following the treatment process. The process variables were pressure, treatment time and type of organism. The results show that a pressure lower than 5 bar does not have a negative effect on the microalgal cells; however, it could have an effect of cell destruction higher than this. An E. coli removal efficiency of 99% cultivated in synthetic medium was achieved at all pressures (2-5 bar) tested; however, at lower contact times in the cavitation process with 5 bar pressure, greater removal of E. coli was achieved at a time of 20 minutes (99%), pressure 3 bar and 4 bar at a time of 30 minutes (99%) and pressure 2 bar at a time of 40 min (99%). In addition, Daphnia sp. cultivated in agroindustrial wastewater was analyzed via microscopic observation of the damage in this organism and a pressure 5 bar in a time of only 2 minutes presented a removal efficiency of 98%. It is so then hydrodynamic cavitation appears to be an interesting alternative to reduce the load of undesirable organisms in microalgal cultures.