Degradation Of Coking Wastewater By Synergism Of CaO And Ozone

Coking wastewater is a kind of typical toxic refractory organic wastewater,which consists of many pollutants with high concentration and difficult to be degraded. Conventional treatment of coking wastewater includes physiochemical technologies and biological treatment. However, these technologies have some shortcomings including complicated steps, long treatment time, substandard Chemical Oxygen Demand value and large dilution water consumption. Thus, it is urgent to seek a kind of economic, environmental and efficient processing approach. Ozone oxidation, a kind of advanced oxygenation with the advantages of strong oxidation ability, short reaction time, no secondary pollution, simple equipment, etc., has the great application potential in the treatment of hardly-degradable wastewater.This experiment was targeted on the high concentration coking wastewater, also named as the distilled ammonia wastewater, produced from AnGang Chemical Plant.Synergism of CaO and ozone was adoped to degrade this kind of coking wastewater in order to make the CODcr value of the treated wastewater meet the National First-degree Wastewater Discharge Standard. In this experiment,UV-visible absorption photometry and CODcr assays were used to monitor the wastewater degradation process, the effects of the reaction time, reaction temperature and CaO dosage upon the CODcr, chroma removal and pH of the coking wastewater were inspected and the reaction mechanism and the dynamics principle of CaO-Ozone oxidation were explored. Research findings showed that ozone oxidation was effective to remove CODcr and chroma of coking wastewater, adding calcium oxide in coking wastewater could speed up the degradation rate by the ozone, and that the two-step ozonation method, including degradation with CaO-ozone and filtration for the first step and degradation with ozone alone for the second step, could reduce the pH, and further improve the degradation efficiency. To degrade 200 mL coking wastewater by CaO-ozone oxidation, the optimum conditions determined by the orthogonal experiment L25(35) were that, the temperature was 45-60℃, the calcium oxide dosage 2.5-4.5g, the ozone exposure time 20-30 min, the CODcr value reduced from 3763.44 mg/L to 50 mg/L or lower, the chroma removal rate was up to 100%,and the pH was of 7-9. For the coking waste water evaporated by rotary evaporation,the CODcr dropped significantly, reducing the load on the subsequent ozone treatment.To degrade 200 mL evaporated coking wastewater by CaO-ozone oxidation, the optimum conditions determinded by the orthogonal experiment L25(35) were as follows: the temperature was 45℃, the calcium oxide dosage 1.0g, the ozone exposure time 22 min, and the corresponding results were that the CODcr value reduced from 1868.74 mg/L to 39.46 mg/L, the CODcr degradation removal rate was97.89%, and the pH was 8.24. The kinetics curves of the CaO-ozone degradation and evaporation combined with CaO-ozone degradation conformed to the apparentfirst-order kinetics models.