| Coking wastewater is generated from coal coking, coal gas purification, andby-product recovery processes of coking. It contains lots of inorganic pollutants andorganic pollutants, such as ammonium, sulfate, cyanide, thiocyanate, phenoliccompounds, polycyclic aromatic hydrocarbons (PAHs), nitrogen-, oxygen, andsulfur-containing heterocyclic compounds. Most of these compounds are refractory,toxic mutative, and carcinogenic, thus the pollution caused by coking wastewater is aserous problem in the world. Although the coking wastewater effluent meet thenational discharge standard after a multistage water treatment process, the TOCremains always about30mg·L-1. For the residual toxicity, active substance in cokingwastewater discharge, because of the limitation of environmental regulations andanalysis technique, it is a lack of comprehensive understanding of the environmentalbehavior of it. Therefore, the treatment of coking wastewater discharge is a challengetask in coking industry and a better understanding of the the composition of theindustrial wastewater and the behaviors and fate of specific compounds during thewastewater treatment will be helpful to optimize the system for controlling andminimizing the amount of PAHs discharged to environment.On the basis of the analysis of the conventional control indicators, the residualorganic compounds were adopted for separating by XAD-8, Dowex50and Amb-R900resin separation technology and ultrafiltration method. It is the first time to use thedisinifection by-products formation potential to evaluate the environmental risk oftoxicants in coking wastewater discharge. The high risk of disinfection by-productsprecursors was screen by coupling the solid phase extraction enrichment method withsilica-alumina extraction technology and GC-MS analysis. Results showed thatorganic matter>100kDa and <1kDa parts have a higher trihalomethanes (THMs) andhalogen acetonitrile (HANs) formation potential. The hydrophilic acidic organicmatters in coking wastewater have the highest proportion. According to the threedimensional flurescence spectrum and GC-MS analysis, microbial metabolitesexhibited high fluorescence response though not high in concentration. Among <1kDaarganic matter, about120kinds of disinfection by-product precursors were indentified, including nitrile, amine, nitrogen heterocyclic nitrogen, phenols, hydrocarbons, esters,acids, alcohols, polycyclic aromatic hydrocarbons and oxygen heterocyclic organiccompounds.Ozonation significantly reduced the amount of precursors of DBPs in cokingwastewater effluent. Furthermore, it was found that higher concentration of O3resulted in lower amounts of precursors. The results of DOC, UV254and SUVAshowed that O3preferentially decomposed DOM that had unsaturated and aromaticcomponents. The results of MW and3DEEM showed that small MW (<1kDa) DOMwas more easily degraded by O3as compared to large MW (>1kDa) DOM. Thespecies of organic compounds in effluent have been changed by ozonation.Nitrogenous orginc compounds such as nitrogen-containing heterocylic compoundsand nitrile can be oxidated fastly. Amine presented a trend that increased at thebeginning and than decreased. Olefin and phenol which contain unsaturatedfunctional groups can be also oxidated selectively by ozonation. On the other hand,organic acids and alkane have been formed in the process of ozonation. But theseintermediate compounds showed relatively low formation potential of HAN and THM.Therefore, precursors of HAN and THM can be mineralization or be converted toorganic compounds which have lower disinfection byproducts formation potential. Allthe results provided evidence that treatment of coking wastewater effluent byozonation was effective in minimizing the disinfection byproducts formation potential(DBPFP). Ozonation can reduce the environmental risk of the effluent of cokingwastewater treatment plants, and improve the security of water supply.Coking wastewater treatment plant (CWWTP) represents a point source ofpolycyclic aromatic hydrocarbons (PAHs) to environment. A pilot-scale O3/ultraviolet(UV) fluidized bed reactor (O3/UV FBR) was designed to enhance the removal ofresidual PAHs. Different operation factors including UV irradiation intensity, pH,initial concentration, contact time, and hydraulic retention times (HRTs) wereinvestigated at an ozone level of240g·h-1and25±3℃. The health risk evaluationand cost analysis were studied under the continuous-flow mode. Results indicated that18target PAHs were effectively removed in O3/UV FBR due to synergistic effects.Either increased reaction time or increased pH was beneficial for the removal of PAHs.The degradation of the target PAHs within8h can be well fitted by the pseudo first-order kinetics (R2>0.920). The reaction rate was also positively correlated withthe initial concentration of PAH. The health risk assessment showed that the totalamount of carcinogenic substance exposure to surface water was reduced by0.432g·d-1. The economic analysis showed that the O3/UV FBR was able to remove18target PAHs at a cost of0.16USD per cubic meter. These results suggest that O3/UVFBR is efficient in removing residuals from WWTP, thus reducing the accumulationof persistent pollutant in surface water.Activated coking wastewater sludge is a significant problem, due to thehydrophobic organic micro-pollutants which are adsorbed on it. This work discussesan O3fluidized bed reactor (FBR) process to stabilize and reduce coking sludge andremove16target polycyclic aromatic hydrocarbons (PAHs) adsorbed onto the sludgeduring this process. The degradation efficiencies and influential factors affectingsludge ozonation were investigated. The results indicated that the target PAHs presentin activated coking sludge can be effectively removed by O3, especially the highmolecular weight PAHs. However, the dose of O3that is applied should be carefullycontrolled, because a low dose (e.g.,300mg O3g-1SS) can lead to an increase in theconcentrations of PAHs in the liquid phase of activated coking sludge. Furthermore,the addition of H2O2or an increase in pH can improve the removal of most of thetarget PAHs, because of a synergistic effect (S>0). The degradation kinetics of thetarget PAHs were assigned to a pseudo first-order model. By this process it becamepossible to reduce the amount of activated coking sludge, as well as achieve removalof PAHs adsorbed on it, with a minimal O3dosage.The results from this study enrich the knowledge of coking wastewater discharge,which promises to be useful for the research of advanced treatment technology. Theidentification of DBPFP can be applied as an index for the environment behaviors ofcoking wastewater discharge. The assessment of removal of residual PAHs in thedischarge and sludge of coking wastewater by O3fluidized bed reactor provideprospectives for advanced treatment of WWTP. |
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