| In recent years,China's pharmaceutical industry has flourished,which has inevitably produced a large amount of pharmaceutical wastewater while bringing economic benefits.Due to the characteristics of pharmaceutical wastewater and the stringent emission standards in China,conventional biochemical secondary treatment is difficult to achieve emission standards.Subsequent advanced treatment is imperative.Coagulation is widely used because of its simplicity,effectiveness and economic feasibility.Based on the conditions and effects of several coagulants and coagulant aids that is used for advanced treatment of pharmaceutical wastewater,this paper optimized the treatment conditions of polyaluminum sludge reflux enhanced coagulation process,explored the changes of floc characteristics,and discussed the economy and adaptability of this process.The experiment found that the dosage,the pH and the temperature of the wastewater have an effect on the COD and SS removal rate,but the influence degree of temperature is small.At the same time,the increase of dosage will also lower the pH of the solution,the reduction of the iron-based coagulant can reach about 5.0,while the impact of aluminum-based coagulant is much bigger,which can reach about 3.4.Under the same conditions,the treatment effect of low molecular weight coagulant like FS and AS is not as good as that of polymer coagulant like PFS and PAC.PFS has better removal ability of COD and PAC has better removal ability of SS.After the coagulant aids was used in the coagulation process,PAM had the best improvement of the SS removal rate,which can reach 11%.While the powdered activated carbon can improve the COD removal rate better,which is 20%~25%.Polyaluminum sludge reflux enhanced coagulation process has three forms: polyaluminum sludge reflux process,powdered activated carbon + polyaluminum sludge reflux process and PAM + powdered activated carbon + polyaluminum sludge reflux process.The experimental results show that the addition of reflux sludge can improve the removal efficiency of pollutants by 7%~10%,and the best removal rate appears near the Zeta potential is 0,indicating that the main mechanism of enhanced coagulation is adsorption-electroneutralization.With the powdered activated carbon,the organic compound removal rate of the polyaluminum sludge reflux process can be further improved by 11%~30%,and the effect on the SS removal rate is not significant.The PAM+ powder activated carbon + sludge reflow process can achieve the best removal rate of pollutants among these processes,which is related to the adsorption of powdered activated carbon,the adsorption-electroneutralization of coagulant and reflux sludge,and the bridging effect of PAM.The results of floc characteristics change experiment show that the floc growth rate of polyaluminum sludge reflux process is the fastest,which is 124?m/min.The powdered activated carbon can be used as the floc core to enhance the strength of flocs.PAM can exert the effect of adsorption-bridging to help floc recover better.On the other hand,the fractal dimension increases when the flocs break up,the size decreases and the compactness increases.Polyaluminum sludge reflux enhanced coagulation process has strong adaptability to the change of COD and SS.The qualities of treated water can all meet the national standard.The removal rate increases first and then decreases with the increase of pollutant concentration.Research on Economy shows that although PAM+powdered activated carbon+ polyaluminum sludge refluxing process has the best removal rate of pollutants,the unit COD removal cost of polyaluminum sludge reflux process are the lowest,which are 1.41 yuan/kg. |
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