Paradigm Shift toward Developing a Zero Liquid Discharge Strategy for Dye-Contaminated Water Streams: A Green and Sustainable Approach Using Hydrodynamic Cavitation and Vacuum Membrane Distillation

The present study is a "first-of-its-kind" work on an integrated process consisting of a hydrodynamic cavitation (HC)-assisted advanced oxidation process and vacuum membrane distillation (VMD) for the degradation of Methylene Blue (MB) from aqueous solution as well as recovery of the water post-treatment. Experiments using HC were carried out in a systematic approach by optimizing the geometry of the cavitating device followed by studying the effect of operating parameters such as pH and inlet pressure on the degradation rate of MB. Under optimized conditions of pH 2 and 5 bar of inlet pressure, degradation of MB was found to be 23.48% in 120 min by the HC process alone with a rate constant of 2.4 x 10(-3) min(-1). Coupling HC with H2O2 and O-3 further enhanced the process, and the degradation obtained was 93.07 and 46.60%, respectively in 60 min. Moreover, a kinetic model was proposed for degradation of MB using HC coupled with oxidizing agents. Furthermore, mineralization studies were also conducted by evaluating the total organic carbon (TOC) content, and the possible intermediates involved during the process were evaluated using ex situ mass spectroscopic studies. The water from the exit of the cavitating setup was further processed through VMD to achieve zero liquid discharge. The optimized flow rate, permeate pressure, and temperature for the VMD process were 10 L/h, 20 mmHg, and 50 degrees C, respectively, and a water recovery of around 8% was achieved. Technoeconomic feasibility studies with real-life textile effluent revealed that the combined approach of HC-based advanced oxidation processes and VMD resulted in a chemical oxygen demand and TOC removal of 35.41% and 39.57%, respectively, simultaneously recovering water of similar to 90% at the economics of $18.61/m(3).