HDC in Wastewater Treatment
Many industrial, agricultural, medical, and other domestic activities produce wastewater composed of organic and inorganic compounds such as pesticides, drugs, textile dyes, etc. Many conventional techniques such as adsorption, coagulation, ion exchange, membrane filtration, and other biological methods have been used to overcome this pollution caused to the environment.
However, most of these techniques can only remove these pollutants by means of physical separation, thereby causing a secondary load on the environment. Conventional biological methods are not able to completely mineralize many organic pollutants known as biorefractory pollutants. Cavitation is a promising technique that is found to be efficient in mineralizing these pollutants present in wastewater.
In the HDC induced effects, such as high temperature and high pressure (hot spots) and high-velocity liquid jets can degrade various organic substances and simultaneously generate hydroxyl radicals that oxidize these pollutants present in wastewater The hydroxyl radicals (˙OH) generated by the fragmentation of water molecule under the HDC effects have high oxidation potential as compared with the other oxidants and are efficient in degrading these complex substances in wastewater.
The effective use of HDC in wastewater treatment requires rigorous optimization of several geometrical as well as operating parameters. During the treatment of wastewater, the geometry of a cavitating device, operating conditions such as inlet pressure and cavitation number, and the physicochemical properties of the liquid significantly affect the course of degradation.
We have successfully applied HDC to destroy COD in textile dyeing wastewater.
We have also studied HDC on the biodegradability of distillery wastewater. In the sample we received, even after the conventional anaerobic treatment, there was no satisfactory reduction in chemical oxygen demand (COD), and also the Biodegradability Index (BI = Biochemical Oxygen Demand [BOD5]/ Chemical Oxygen Demand [COD]) was very low, i.e. 0.14, which shows the inapplicability of an anaerobic digester to further treat such effluent. With HDC treatment, we were able to r aise the BI to 0.38, which made the material suitable for further anaerobic digestion.
We have used HDC to increase the methane yield of dairy farm wastewater. With HDC as a pretreatment, the suspended solids were pulverized creating higher surface area. Methane yield increased by several folds.