FW: Non combustion methods for managing PCBs
Hemantha Withanage
Poly Chlorinated Biphenyls \(PCB's\) and their Chemistry
Non-Combustion Technologies for the Destruction of PCBs and ...
Poly Chlorinated Biphenyls (PCB’s) and their destruction:
PCB’s were found to highly stable and refuse to be degraded in soil, water, algae, fungi bacteria and other oxidative mechanisms operating in environment in a natural manner. Different countries have used various methods to avoid pollution and to destroy these compounds.
Combustion: This method of destruction is the most widely used but not considered as environmentally sound technique. PCB’s get pyrolysed to water, Carbon dioxide and Hydrochloride (HCl) when burnt at temperatures 1400-1600oC. This method has potential danger of producing highly dangerous chemical species which are highly dangerous and toxic and can cause serious implications on living organisms. This is more likely when the temperature of combustion is lower than 1200oC.
Encapsulation / burial : Though this method is not a destruction method but can effectively seal the material and avoid the pollution of this compound for long periods. Concrete capsules can be made and used to bury the PCB’s and seal them off by concrete. Once this is done and when the concrete looses its capacity and witherout allowing leakage of PCB material and finally reach out and contaminate the water resources.
Chemical treatment of PCB’s with Sodium Hydroxide: The method has been tried for destruction of PCB’s. In this method sodium hydroxide is made to react with PCB’s to generate sodium chloride and biphenyl and phenolic mixtures are being generated as side products.
Though the technique appears to be more simple, the method has not acquired popularity as the side produts of the reaction are phenols and have higher solubility with water and has easy mode of spreading the toxic material by travelling in acqueous systems for long distances. This situation can be very threatening as it can cause much higher damage immediately as compared to PCB’s themselves.
Super Critical Water oxidation of PCB’s : Super critical conditions can be achieved for any material in which liquid and vapour states co-exist and are not distinguishable. Water acheives this conditon when its temperature is above 374oC & pressure at 221 bar. PCB’s, PAH’s (Poly Aromatic Hydrocarbons), Waste plastics and other materials can be converted in to simple hydrocarbons and can be reused and recycled. The technology is not yet perfected and needs lot of technological developments to meet the requirements of PCB destruction.
Sodium metal based conversion of PCB’s : In this process Sodium metal reacts with the chlorinated systems to dechlorinate the molecules at much lower temperatures than combustion.
Our country has all the options available for mitigation of this hazardous chemical in an environmentally sound manner. Among these options non combustion technologies are considered as best and efficient. Whereas combustion seems to be the alternative for much faster and cheaper method. Keeping in view of the geographical conditions we may have to use combination of technologies to get rid of this problem.