Adsorption Pretreatment Of Aromatic Petrochemical Wastewater By Coal

Petrochemical industry is the pillar industry of national economic development.Higher water consumption and water resources shortage have become importantfactors for the sustainable development of large-scale petrochemical enterprises. Theamount of discharged petrochemical wastewater is increasing day by day, which isbecoming a difficult problem to deal with. The wastewater has the characteristics ofbig chromaticity, high concentration pollutions, poor biochemistry and so on. Themain poisonous and harmful substances are Aromatic hydrocarbons and itshomologues. Hige chromaticity industry wastewater not only gives an unpleasantfeeling but also reduces transmittance of the receiving waters, so as to affect thenormal growth of aquatic creatures. Currently pretreatment technology has thedisadvantage of complex system, large aeras and high investment and operation cost.Coal as adsorbent can effectively reduce the cost and remove some toxic substancesto facilitate the subsequent biochemical treatment.Nanjing aromatics petrochemical wastewater in a chemical plant has thecharacteristics of big chromaticity, brown color and leaning neutrality. The main toxicand harmful substances are naphthalene its homologues, which are as hige as74.25%.It contains361.10mg/L of CODCr and209.78degrees of Chromaticity. This paperadopts the method of coal adsorption pretreatment of aromatic plant wastewater andstudies the adsorption effects and regularity. Results are as follows:(1) The paper had the adsorption tests under different conditions which includeddifferent coal sizes, the dosage of coal, adsorption time, vibration speed and so on.The final optimum parameters: the coal size is-0.074mm, coal concentration is75g/L,adsorption time is30min, vibration speed is120r/min. And orthogonal experimentwas carried out. Considering CODcr and chroma of the orthogonal experiment results,it can be obtained that the coal size is-0.074mm, coal concentration is75g/L,adsorption time is40min, vibration speed is120r/min. The outcomes of orthogonalexperiment results are that the removal rates of CODCris32.87%and Chromaticityremoval rates is66.94%. The final concentration of CODCris242.42mg/L andChromaticity is69.35degrees. GC-MS atlas show that adsorption process ofnaphthalene homologue drops to31.09%(2) The removal of CODCrand chroma reduces along with the increase of pHvalue. The change of pH can influence the coal pore structure. As the higher pH value,specific surface aera and total pore volume decrease first and then increase, and the average pore diameter rises continuously. GC-MS atlas show that the content ofnaphthalene homologue drops to25.59%when pH=2. After adsorption, the contentfurther reduces to11.56%.(3) The paper experiments form two aspects including adsorption isotherms andadsorption kinetic models. The results show: Adsorption reaction of CODCris wellconformed to the characteristic of second-order kinetic model. The adsorptionisotherm of CODcr is consistent with Langmuir isotherm. Δ G°is negative whichmeans it is spontaneous; Δ H°is less than zero which shows it is an exothermicreaction; Δ S°is also less than zero which indicates it is a entropy decreasing process.In practice, low temperature and hige vibration speed are beneficial to adsorptionprocess.By the means of coal adsorption, it can decrease some sewage toxic substancesand significantly reduce the chrominance. And finally it can facilitate the subsequentbiochemical treatment.