Study On Pre-treatment Of Metronidazole Pharmaceutical Wastewater By Iron-carbon Microelectrolysis&Fenton

Recent years,the water environment pollution is still very serious in China.Numbers of water pollution accidents occur frequently,including the most serious situation that industrial pharmaceutical wastewater pollutant exceeding thesewage discharge standard.The reasons including:firstly,it is very difficult to treat the industrial pharmaceutical wastewater,and the traditional wastewater treatment method is not sufficiently effective to meet the standard;Secondly,the operation cost of some new wastewater treatment technologies is high and it is difficult to apply the new technology to practical engineering.However,metronidazole pharmaceutical wastewater treatment is one of the most difficult example in pharmaceutical wastewater treatment,which is characterized by high COD_crr concentration and poor biodegradable ability.The traditional biological treatment method adopted by pharmaceutical factories is difficult to meet the discharge requirement,therefore,it is necessary to improve the biodegradability of wastewater through pre-treatment so that it is possible to improve the subsequent biochemical treatment effieiency.Taking metronidazole as a treatment traget,in this study we chose iron carbon micro electrolysis,Fenton oxidation process,iron carbon micro electrolysis coupled Fenton oxidation process as a treatment,and investigate the two kinds of process and two joint after pre-treatment of wastewater and wastewater biochemical treatment effect using two water quality indexes including the COD_crr removal rate and the biochemical BOD₅/COD_cr.The major research contents and conclusions are as follows:?1?Iron-carbon Micro-electrolysis pre-treatmentThe optimal process parameters for Fe-C micro-electrolysis pre-treatment of metronidazole pharmaceutical wastewater were obtained as:initial pH value of wastewater:3.0;solid-liquid ratio:250 g/L;mass ratio of iron to carbon:2:3;aeration:15 L/min,At this time,the removal rate of CODcr reached the maximum:34.1%.?2?Fenton Oxidation pre-treatmentThe optimal process parameters for Fe-C micro-electrolysis pre-treatment of metronidazole pharmaceutical wastewater were obtained as:initial pH value of wastewater:3.0;dosage of H₂O₂:50 mL/L;H₂O₂/Fe²⁺molar ratio:60:1.Results showed that the highest COD_crr removal rate reached as 13.1%.Comparing the removal efficiency of COD_crr with results of iron-carbon micro-electrolysis pre-treatment of metronidazole pharmaceutical wastewater,At this time,the removal rate of CODcr reached the maximum:13.1%.?3?Iron-carbon Micro-electrolysis&Fenton ProcessStep One:Plackett-Burman experiment was applied to select three factors that had significant influence on the removal rate of COD_cr,namely,H₂O₂ dosage,solid-liquid ratio and iron-carbon mass ratio.Subsequently,the response surface optimization experiment was carried out,with COD_crr removal rate,BOD₅/COD_crr as dependent variables,and three key influencing factors as independent variables,to conduct quadric surface equation fitting.The fitting model had a good correlation with the measured values and could be used for optimal value prediction.When analyzing the pairwise interaction of the three key factors through the model surface graph,it is found that the pairwise interaction of the three factors is not significant.In addition,by calculating and solving the optimal value of the simulation equation,the theoretical optimal process parameters were obtained:hydrogen peroxide dosage was 40.4 ml/L,solid-liquid ratio was 449.2 g/L,and Fe-C mass ratio was 1.4:1.At this time,the model predicted that the removal rate of COD_crr reached the maximum,which was 42.5%,and BOD₅/COD_crr was 0.33.By comparing,the removal efficiency of COD_crr of the combined process was significantly higher than that of the single process.Step Two:Dynamic continuous experiment was used to verify the best predicted value obtained by response surface optimization method.It was found that under the optimal process parameters,the COD_crr removal rate of metronidazole pharmaceutical wastewater pretreated by Fe-C micro-electrolysis coupled Fenton oxidation method reached to 40.8%,and the biochemical index BOD₅/COD_crr of this wastewater was as high as 0.31.This indicates that the combined process can effectively remove COD_crr from wastewater and improve the biodegradability of wastewater.Step Three:Through the UV-Visible spectrum analysis of metronidazole pharmaceutical wastewater before and after pre-treatment of ferrocarbon micro-electrolysis coupled Fenton oxidation method,it was found that the absorption peak of metronidazole at the wavelength position of 225 and 319 nm had a slight red shift.Comparing ultraviolet-visible spectra before and after the pre-treatment of wastewater we found that corresponding to the two absorption peaks of metronidazole 230 nm wavelength location of absorption peaks disappeared,320 nm position of absorption peak at 322 nm,and peak area size has obviously decreased,indicating that the iron carbon micro electrolysis&Fenton oxidation process in the pre-treatment of metronidazole pharmaceutical wastewater can effectively remove the main organic matter:metronidazole.And in cost accounting,it was found that each 1.0L wastewater treatment cost 0.76 yuan,indicating that this coupling process is an economical pretreatment method.In summary,it is considered that the coupled process is an efficient,stable and economically feasible pretreatment method for metronidazole pharmaceutical wastewater.