The optimisation of hydrodynamic cavitation as an advanced oxidation option for the removal of persistent contaminants in wastewater

Abstract

Wastewater is growing into a scarce commodity as more and more demand upon it in urban city is placed. The presence of persistent contaminant such as dye and perfluorinated compounds from industries is placing a demand on the need to design technique of removal of these chemicals from water as they induce adverse effects on life. This study investigated an approach to solving this problem of water scarcity using the hydrodynamic cavitation pilot plant. This work thus explores the application of the hydrodynamic cavitation plant combined with the venturi to suggest a way to clean water. The evaluation of the cost of implementation and investment was also explored. The study begun with the optimisation of the processes of removal by exploring the effect of orifices of size 2, 3, 4, 5 and 6 mm on the decolouration of orange II dye. The impact of catalyst: Iron II, oxidising agent: hydrogen peroxide, contact time were evaluated to suggest the ideal conditions under which the removal of perfluorooctanoic acid were to be removed from wastewater. It turned out that the decolouration of 20 ppm of orange II dye in simulated industrial textile wastewater was achieved at 90% efficiency under the following conditons: the pressure at the inlet was maintained at 300 KPa, the temperature at 34°C, the pH at 2 and the orifice size at 2 mm of diameter. The system had an energy efficiency of 38% or 1.36×10−4𝑚𝑔/𝐽 cavitational yield. The material as well as the energy balance showed the law of conservation was observed. The energy of the system was found to be 839 Watt. The kinetic study proved the decolouration reaction was pseudo first order and the rate of decolourisation of orange II was 0.23 𝑚𝑖𝑛−1. The total capital investment to acquire the HC pilot plant was 𝑅 27 305 and the total operating cost for a 10 𝐿 sample run on the HC pilot plant over a period of 10 min was 𝑅 8.82. The technique proved that the combination of venturi and orifice requires the throat size of the venturi to be similar or equal to that of the orifice for better efficiency.