Application Of Activated Carbon Catalytic Ozonation In Tertiary Purification Of Biological Treatment Effluent Of Dye-making Wastewater

Dye-making wastewater possesses high chroma,salinity and organic matter concentration.The concentration of organics and chroma do not satisfy the requirements of discharge or reuse even after physicochemical and biological treatment.Tertiary purification of biological treatment effluent was performed with ozone and ozone/activated carbon oxidation.This dissertation investigates the operating parameters and catalytic ozonation mechanism.The biological treatment effluent of dye-making wastewater used in the experiment was obtained from Zhejiang dyestuff making plant.The COD,DOC and chroma were 400 mg/L,90～100 mg/L,and chroma 600 times,respectively.Initial pH value was changed and microporous membranes were used in the reactor in order to optimize the ozonation process.The main conclusions were as follows:(1)The treatment efficiency was improved as pH value increased.At initial pH 11,the removals of COD and DOC increased 13%and 20%,respectively.And 80%chroma removal efficiency was achieved after 3 min of reaction.(2)The size of ozone bubbles decreased as microporous membrane was installed at the bottom of the reactor,which increased the specific interfacial area and the retention time of ozone bubbles.Thus mass transfer was improved and the utilization ratio of ozone was increased by 10%～30%,enhancing the ozonation.Sauter diameters of ozone bubbles were 1424.34 μm,680.20μm,454.72 μm with 30 μm,20 μm,10μm pore size of membrane in the reactor.The corresponding specific interfacial areas were 115.32 mm-1,210.76 mm-1,and 210.76 mm-1.The removals of COD and TOC increased 2～12%and 4～5%as the pore size of membrane decreased.Activated carbon catalytic ozonation process was carried out for the complete mineralization of organics.The main experimental results are as follows:(1)The treatment efficency was significantly improved with the addition of saturated activated carbons as a catalyst in ozonation.The removal efficiency of COD and DOC increased by 17～35%and 17～56%for different activated carbons.The activated carbons could be used repeatedly.Catalytic effects for ozonation varied for different activated carbons,which had no correlation with adsorption capacity,but a high correlation coefficient of 0.85 with macropore volume.Alkaline functional groups were related to catalytic effects.They favoured the decomposition of ozone to hydroxyl radicals.(2)The thermal and chemical modification of activated carbon with potassium permanganate and zinc chloride increased catalytic activity,which further improved the removal efficiency of organics in biological treatment effluent.Highest removal efficiency for organics was achieved in thermal treatment in nitrogen atmosphere.The removal of COD and DOC increased by 15.77%and 40.96%.The result showed excellent pore structure and abundant alkaline functional groups were needed for catalytic oxidation.(3)The combination of micropore membrane and activated carbon improved the removal efficiency of COD and DOC due to the improvement of mass transfer.At the optimal conditions,COD and DOC were 41.47mg/L and 25.38 mg/L,respectively.It was concluded that activated carbon catalytic ozonation for tertiary purification of biological treatment effluent of dye-making wastewater can be improved by enhancing mass transfer and changing reaction pathway of ozonation.They are practical effective approaches with great application prospect.