Advanced Treatment Of Deinking Wastewater By Ozonation/Catalytic Ozonation

Deinking wastewater has the characteristic of complicated pollution constituents, low biodegradability, and varying wastewater quantities. Normally, the effluent from the secondary treatment processes for deinking wastewater could not consistently meet the discharge standards, resulting in a troublesome problem in the field of industrial wastewater treatment. In recent years, advanced treatment by catalytic ozonation process (COP) has extensively attracted the water scientists’attention, owing to its high treatment efficiency, strong versatility and no secondary contaminations. COP is also convenient to integrate into existing wastewater treatment plants. In this study, the biological treatment effluent from a waste paper mill in Shandong was chosen as the wastewater to be studied. After coagulation pretreatment, the wastewater was treated by three advanced treatment processes with the use of ozone, i.e. Ozonation, activated carbon catalyzed ozonation and metal-loaded activated carbon catalyzed ozonation, respectively. The results are listed as follows:(1) In the coagulation pretreatment, the main objective is to remove the dissolved inorganic carbon (DIC) and hardness in the deinking wastewater, to reduce the dosage of ozone in the subsequent advanced treatment. pH was proved to be an important influencing parameter for the removal of hardness and total inorganic carbon. Coagulation accelerated the sedimentation rate of dissolved and slightly soluble calcium and magnesium salts. Under the conditions of PACl dosage of 300 mg/L, pH of 10, and 1 mg/L PAM, the removal efficiencies of DIC, hardness and dissolved organic carbon (DOC) were 39.3%,84.8% and 28.9%, respectively. The removal of hardness and total inorganic carbon could be enhanced by 12.7% and 4.1% by changing the sequence of PACl dosage and, then pH adjustment.(2) In the ozonation process, the removal of DOC increased with the increasing amount of ozone. Ozone oxidation had a higher treatment efficacy under alkaline condition. Under the experimental conditions, the optimal ozone dosage was 3.0 g/(L·h), pH of 10 and reaction time of 60 min, leading to DOC removal of 45.5%. The deinking wastewater was completely de-colored in 30 minutes. (3) In the activated carbon catalyzed ozonation process, the optimal gas flow rate was determined to be 1 L/min by CFD stimulation and reactor fluidization demonstrations. Compared to direct ozonation, the DOC removal could be further improved upto 12.4% by adding 5 g/L granular activated carbon (GAC). The de-colorization time required was reduced to 20 minutes and the treated effluent COD was 69.2mg/L.(4) Catalyzing ozonation by GAC loaded with Cu, Fe or Mn could improve the treatment performance of the deinking wastewater. By comparing the effects of various metals and loading amount on the DOC removal efficiency, the GAC loaded with 0.1 mmol/g Fe showed the best de-contamination performance. The DOC removal rate was 72.1%. The decolorization time for deinking wastewater was only 15 minutes.(5) Scanning electron microscope (SEM) showed that Fe present on activated carbon in the form of amorphous crystal. X-ray diffraction (XRD) showed that the morphology of Fe on the catalyst was Fe2O3, Fe3O4 and FeOOH, while elemental Cu for Cu-loaded GAC, and MnO for Mn-loaded GAC, respectively.(6) Ozonation alone and catalytic ozonation reactions were conformed the quasi-kinetic model. Ozone utilization of activated carbon contained iron catalyzed reaction was significantly higher than ozonation and activated carbon catalyzed ozonation. Ozone unit utilization were 0.044,0.051 and 0.066 mgDOC/mgO3, respectively.