The Escape Of Organic Compounds From Coking Wastewater Treatment Processes And Advanced Treatment Of Tail Wastewater By O₃/UV

Substances, including exhausted toxic organic compounds from coking wastewater in thebiochemical treatment process and inert components existing in the tail water afterbiochemical degradation, are very dangerous to human being and environment. Therefore, itis necessary to investigate the compositions escaping from coking wastewater treatmentprocess and further dispose the tail wastewater by using advanced treatment technology fromthe health of authorities.There are13classes of organic compounds, in general,301kinds of organic compoundsbeing detected from the escaping gas of coking wastewater treatment process. They aremainly phenols, PAHs, nitrogen heterocyclic compounds, esters, alkanes and halogenatedorganic compounds, most of them are toxic pollutants. By combination analyzing the mainpollutants VOCs and PAHs qualitatively from the pool and working area, together with theinvestigation of their escape laws and risk assessment, it shows that VOCs and PAHs mainlycome from the escape of wastewater treatment process.17types of VOCs have been detected,among them, benzenes are the most frequently detected compounds, besides, halogenatedhydrocarbons and chlorobenzenes are also found. There are17kinds of VOCs, most of whichare benzene series. Halogenated hydrocarbons and chlorobenzene class are also included. Thehighest concentration of benzene series (benzene, toluene, xylene) were selected as the targetsof health risk evaluation. Results indicate that the concentration of benzene series in thewastewater station is in the acceptable health risk level according to the requirement of U.S.EPA. The PAHs escaping from pool are mainly low molecular weight, which account for75%-90%totally. Besides, the PAHs in the air of station working area are principally lowmolecular weight, too, but their carcinogenicity is much higher than the risk level based onthe U.S. EPA rules. Those vital harm of PAHs in the air mainly exist in the particle phase. Therisk level in the working area is far more than the release significant risk level of US (10^-3),while the most risky area is the office room (2.2910^-1).The advanced treatment of coking tail wastewater was studied by using O₃/UV coupledtechnology in a self-developed fluidized bed reactor, in which the system optimal operationconditions, degradation mechanisms and kinetics of the key component in coking tailwastewater were investigated. The effects of UV catalytic and initial pH value were examinedfirstly, and then the effect of retention time of wastewater and its initial concentration underthe optimum UV and initial pH value conditions were studied. The result shows that, the UVcatalysis performing at the optimum pH value (pH=10¹1) of the solution can significantly improve the degradation efficiency of O₃. For the continuous operation experiment, the mostappropriate retention time is37min,meanwhile, COD, NH₄⁺-N, chroma, CN－and so on canmeet the requirements of industrial circulating water quality. Coking wastewater withdifferent initial COD concentrations (a maximum of291mg/L) performing in the optimumcondition can be treated to meet the requirement of reusing concentration (<40mg/L). Theinitial concentration of COD and O3consumption can be fitted by logarithm relationship withthe formula y381.6ln(x)1543(X stands for coking wastewater initial concentration ofCOD/mg/L, y represents O3consumption/g). The degradation pattern and kinetics of the keycomponent is studied. Since the SCN^―, CN^―and other nitrogenous substance exist in thewastewater, NH4+-N concentration increased firstly and then decreased after oxidation byO₃/UV. NH₄⁺-N concentration reaches a maximum time and wastewater containing nitrogencompounds The time demanded by the maximum concentration of NH₄⁺-N is positivelycorrelated to the values of nitrogen compounds in the wastewater. The COD decreasing trendof coking tail wastewater by using O₃/UV catalytic oxidation methods is consistent with afirst-order kinetics model, while the trend of NH₄⁺-N in the system is compatible withzero-order kinetics model. Results show that catalytic oxidation of coking wastewater byusing O₃/UV advanced process is effective to treat tail water, which is found dependent on thereduction activity sequence of contaminants and the mass transfer efficiency of fluidization.