Advanced Treatment Of Coking Wastewater Effluent With Ozone And The Utilization Of Residual Ozone

In the real coking wastewater treatment plant, the effluent after bio-treatment and coagulation still contains a particular proportion of biorefractory organics and inorganics. It will contaminate the water environment if discharged directly and induce technical difficulties in water reuse. The advanced treatment of coking wastewater effluent becomes imperative since the new national standard of COD emission of 80 mg/L is required. Exploring the reducing process of pollutants in coking wastewater effluent can provide guidance and basis for the optimal design of advanced treatment of coking wastewater effluent.This paper firstly studied the advanced treatment of coking wastewater effluent with ozone-fluidized bed reactor, the effect of ozone dosage, pH, hydraulic retention time (HRT) on the reaction process was analyzed. The results indicated that, the COD concentration of coking wastewater effluent decreased with the ozone dosage and tended to stable when the ozone dosage was more than 430 g under intermittent condition. The pH value had little influence on the ozonation of coking wastewater effluent, the removal efficiencies of COD> UV254 and color intensity in alkaline condition were 51.5%、87.3% and 85% respectively, slightly larger than those obtained in acidic and neutral conditions. The COD concentration of coking wastewater effluent decreased with HRT, and the COD value is below 40 mg/L with a HRT of 2 h. The COD and chromaticity degradation curves over time obeyed the pseudo first order reaction kinetics equation in 0-30 min and 45-120 min.The variation in organic composition was further analyzed by ultraviolet and visible spectrophotometer, three-dimensional fluorescence spectrometer and Gas Chromatography Mass Spectrometry (GC/MS). The results indicated that, Major organics in coking wastewater effluent included Alkanes, N-heterocyclic carbenes, Alcohols, Acids, Esters, and a small quantity of Ethers and polycyclic aromatic hydrocarbons (PAHs), etc. After ozonation, some of the non-biodegradable organics in effluent have been removed partially or completely, and have been turned into some new organics, such as, Alkane, Phenylcarbinol, Hexanoic acid, etc and the molecular weight decreased. The materials with fluorescence response can be effective decomposed, and the decomposition rate of order is tryptophan-like> soluble microbial products-like> humic acid-like> tyrosine-like. There existed strong ultraviolet absorption at 200～250 nm in coking wastewater effluent and ozonated effluent, and the intensity of ultraviolet absorption decreased with the reaction time. The concentration of 16 kinds of PAHs in wastewater effluent was about 3.518μg/L, after 2 h ozonation, the removal rate reached 51.1%. Among them, the removal rate of PAHs with ring number of 5 or more reached 70.3%, higher than the lower ring PAHs removal effect.Considering the residual ozone in advanced treatment with ozone, this paper further attempted the advanced treatment of coking wastewater effluent and produced polymeric ferric sulfate (PFS) with off-gas ozone at the same time. The results showed that, compared with the direct release of off-gas ozone, the utilization rate of ozone increased to more than 3 times by the absorption of off-gas ozone with ferrous sulfate solution. The performance indicators of PFS synthesized with off-gas ozone meet or exceed the requirements of national standard (GB 14591-2006). The basicity of PFS decreased with increasing sulfuric acid dosage, and it reached maximum when the reaction temperature was 50℃...