Study On The Process And Mechanism Of PCB Organic Wastewater With Catalytic Ozonation

With the rapid development of industry,significant number of chemical factories have come up,resulting in discharging a large amount of industrial wastewater.Industrial effluents contain a large number of organic contaminants,which are refractory,toxic and with high concentration,creating a large concern on the quality of water resources and the human health.The organic wastewater produced in the printed circuit board(PCB)manufacturing factories belongs to typical high-concentration and refractory organic wastewater.There are some limitations in the current treatment methods,such as high cost and incomplete degradation.Catalytic Oxidation technology is an advanced oxidation treatment technology that can degrade refractory organic wastewater efficiently and quickly,which has a good prospect for the treatment of PCB organic wastewater.In this paper,PCB organic wastewater was used as the research sample.The study mainly focused on the catalytic performance of the degradation of PCB organic wastewater by catalytic ozonation in the presence of calcium oxide.Firstly,the experimental factors were optimized to degrade organic contaminants efficiently and low-costly in the catalytic ozonation system.Secondly,the degradation mechanism and possible degradation pathways were explored.Finally,the cycle performance of calcium oxide which used as catalyst was studied.The main experimental conclusions are as follows.(1)PCB organic wastewater is typical high-concentration and refractory organic wastewater with high COD concentration up to 20246.4 mg/L.The wastewater contains 20 organic compounds,including n-hexane,2-butoxyethanol,isopropyl alcohol,1,2-ethanediol,isosorbide,2-(2-ethoxyethoxy)ethanol and so on.(2)Catalytic ozonation with calcium oxide can efficiently degrade PCB organic wastewater.Under the condition of pH value of 13.0,calcium oxide mass of 4.0 g,the solution depth of 13 cm,treatment time of 180 min and the ozone dosage of 200 mg/min,the COD removal ratio of PCB organic wastewater can reach 96.72%.(3)The optimum conditions from simplex optimization experiments are pH value of 12.97,calcium oxide mass of 1.0 g,the solution depth of 11 cm,treatment time of 150 min,the ozone dosage of 120 mg/min.The COD removal ratio of the wastewater can reach 90.045% under this optimized conditions,which can achieve the purpose of degrading organic matter efficiently with low cost and shorter treatment time.(4)The results of t-butanol quenching experiment and salicylic acid tracer test prove that ozonation of organic contaminants in the presence of calcium oxide involves hydroxyl radicals,namely,calcium oxide can be used as catalyst to promote the degradation of organic contaminants.(5)The intermediate products of PCB organic wastewater during catalytic ozonation process shows that the organic contaminants are directly oxidized to small molecules or oxidized to small molecules after forming hydroxyl products by the combination with hydroxyl radicals,then are decomposed to acetic acid and finally mineralized to carbon dioxide and water by hydroxyl radicals.(6)Calcium oxide has good cyclic performance in the catalytic ozonation system.After five cycles,the COD removal ratio of organic wastewater decreases insignificantly,which changes from 92.78% to 84.04%.The catalyst is partially deactivated after several cycles due to agglomeration,the conversion of catalyst to calcium carbonate,the increasing and uneven distribution of pore size.