The Study Of Extraction Displacement-Biodegradable Coupling Technique To Remove COD From Coking Wastewater

The components of coking wastewater are very complex. It is a sort of industrial wastewater which is difficult to be treated. Dealing with coking wastewater by activated sludge process, the value of CODcr and NH3-N in effluent can hardly meet the national discharge standard. So, the advanced treatment of coking wastewater, especially the removal of refractory organics has become an urgent environmental problem. Based on analyzing organic components of coking wastewater and finding out the refractory organics, this paper aims at looking for a suitable way to improve the biodegradability of coking wastewater and recycling refractory organics in order to provide a new idea for the treatment.Based on analyzing the sources, characteristics, composition and research status at home and abroad of coking wastewater, extraction displacement-biodegraded coupling technique was used to deal with coking wastewater, and GC-MS was adopted to do qualitative analysis. This thesis studied the extraction features of different organics in ways of treating coking wastewater with extraction displacement by different extractants. Through the analysis of the organic components and biodegradability of coking wastewater before and after extracted, the proper solvent was selected. SBR biological treatment systems was adopted to treat coking wastewater after extracted to definite its biodegradability and to test the actual application results of extraction displacement-biodegraded coupling technique.(1) Study on the extraction displacement of coking wastewater by different organic solvents. The analytical results of GC-MS and COD obtained differ in different solvents. The removal effects of organics from coking wastewater followed the order of cyclohexane> heptane> di-n-buty 1 ether> xylene> 1 octanol. The rise of COD caused by organic solvents residue followed the order of> di-n-buty 1 ether> xylene> cyclohexane> heptane. The experimental results indicated that octanol can displace the refractory organics of coking wastewater by extraction effectively. However, because of the higher solubility of 1 octanol in water, the value of COD of the coking wastewater extracted by it was significantly increased.(2) Selecting the Operating Conditions of Extraction. Combined with octanol, cyclohexane used as a diluent was adopted to extract coking wastewater in order to reduce the loss of 1 octanol during extraction process. The results show that cyclohexane can reduce the loss of 1 octanol effectively and the mixed solvents consisted of 1 octanol and cyclohexane in the ratio of 5/5 and 7/3 can displace the refractory organics of coking wastewater. According to the results and economics of experimental research, the mixed solvent in the ratio of 5/5 between cyclohexane and octanol was adopted as the proper extractant to remove COD from coking wastewater. The proper extraction time was 5 min and the proper ration between the amount of extractant and coking wastewater was 1:1.(3) Study on the treatment of coking wastewater by SBR. Two identical SBR experimental systems were used to deal with coking wastewater before and after extracted, when these systems were running steadily after the activated sludge were acclimated for one week respectively. The experimental results indicated that the value of COD of coking wastewater before extracted in effluent was reduced to 246.79mg/L from 1864mg/L, while the other was reduced to123.34mg/L from 2148.7mg/L meeting the national discharge standard. The analytical results of GC-MS showed that the types and contents of refractory organics in coking wastewater after extracted such as benzene, pyridine, quinoline and so on were reduced significantly, while the contents of alcohols and hydrocarbon compounds with the substituent of methyl and ethyl groups were increased to some extent.The economic feasibility analysis of this technology was discussed in the paper and the result showed that extraction displacement-biodegraded coupling technique could reduce the running cost in the long run and achieve the high efficiency and economics for the treatment of coking wastewater.