Effect Of Plate Type Direct Current Electrolysis On Nitrogen,Phosphorus And Heavy Metals In Residual Activated Sludge Of Improved Oxidation Ditch

The increase of Chinese total economic volume has promoted the development of cities.The increasing scale of urban sewage treatment and the continuous improvement of sewage treatment capacity will inevitably lead to the production of a large amount of surplus sludge.In the process of sewage treatment,the concept of “Sludge is as important as sewage” is widely recognized.If the excess activated sludge that produced by the municipal wastewater treatment plant cannot be treated properly,it may cause harm to the environment.This study established a self-made plate type direct current electrolysis reaction system.The experiment is mainly conduct under different current parameters(3A,5A,7A)and voltage parameters(3V,5V,7V).The effects of direct current electrolysis on the content and form of nitrogen,phosphorus and heavy metals in the solid phase and liquid phase of sludge and the comprehensive toxicity of sludge mixture were studied.According to the water quality and soil testing methods of the national environmental protection standards,We measured the content of nitrogen,SCOD,phosphorus and heavy metals in the supernatant of the sludge.After the sludge solids were freeze-dried,we determined that the different forms and contents of phosphorus and heavy metals.Chlorella pyrenoidosa(CP)was taken as indicator and 96-well microplate was chosed as exposure experiment carrier,we determine the inhibition rate of sludge mixture on chlorella,the inhibition rate is used to characterize changes in overall toxicity.Through the study of the components of the remaining sludge,the main results obtained in this thesis are summarized in detail as follows:(1)direct current electrolysis has lysis effect on microbial cells,Under different current and voltage parameters treatment,analysis the content changes of SCOD and total nitrogen in the supernatant of the sludge,it is the best parameters that 7A,7V.for self-made plate type direct current electrolysis instrument.At the same time,the treatment effect of that different plate spacings of 2cm and 4cm was characterized by the release of SCOD in the supernatant.It can be seen that the lysis effect is best when the plate spacing is 2 cm.(2)direct current electrolysis has a better effect on the removal of total phosphorus in the sludge supernatant,under the best parameters,the removal rate was 95% at a treatment time of 5 min.For phosphorus in sludge,direct current electrolysis treatment affects its form distribution.With the treatment time prolongs,the content of that calcium phosphorus increases,and iron phosphorus and organic phosphorus decreases in the sludge.Direct current electrolysis treatment reduces the potential for environmental hazards during sludge application.(3)That direct current electrolysis treat sludge,under optimal parameters,can effectively reduce the heavy metal content in the sludge mixture.The content of Zn decreased from 106.2 mg/kg to 55.1 mg/kg,and the content of Cu decreased from 276.45 mg/kg to 106.2 mg/kg.The content of exchangeable Cd,Pb and Ni in the sludge did not change significantly,and the influence on other heavy metal forms was obvious.It is decreasing that the content of exchangeable state Mn,Zn and Cu in the sludge,especially under the 7A,7V parameter treatment,the content was reduced from 77.65mg/kg,49.85mg/kg,55.2mg/kg to 56.2mg/kg,27.1mg/kg,30.25mg/kg.(4)With processing time increasing,the overall toxicity of the sludge mixture decreases.That the comprehensive toxicity removal effect is the best After treatment for 15 minutes under the parameters of 7A and 7V,and the inhibition rate of 24 H for chlorella decreased from 46.6% to 22.1%.Comparing electron microscopy scan photo of original sludge samples with the sludge samples that treat under 7A,7V parameters,it can be seen that direct current electrolysis treatment has a better effect that destruct microbial cell.The comprehensive cost of sludge treatment under the optimal parameters of the plate type DC electrolysis reaction system is 326.12 yuan,and the economic benefit is better.In summary,the plate type direct current electrolysis system processes sludge,dissolves microorganisms,releases nutrients,removes phosphorus and heavy metals,and decomposes organic pollutants,thereby achieving stabilization,reduction,harmlessness,and resource utilization of sludge treatment.