| Organic phosphorus pesticide wastewater does serious harm to human health andecological environment. The quality of the treated organic phosphorus pesticidewastewater by the conventional wastewater treatment processes usually can not meetthe discharge standard for its biodegradable difficulty. Therefore, it is very urgent andof great importance to investgate and develop more advanced and economic organicphosphorus pesticide wastewater treatment processes to meet the increasing stringentlegislations on water quality of the discharged effluent, the setting of the dischargecapacity limitation as well as other similar problems.This study investigated a new dephosphorization process combining membraneseparation technology and fenton oxidation technique to treat the low concentrationorganic phosphorus wastewater that is discharged from the existing wastewatertreatment plant of Xinan Chemical (Zhejiang China). After the pretreatment ofultrafiltration and softening, the low concentration organic phosphorus wastewaterwas concentrated through reverse osmosis technology by twenty times.Dephosphorization processes such as chemical precipitation, micro-electrolysis andfenton oxidation were adopted to treat the concentrated organic phosphoruswastewater and it was illustrated that fenton oxidation was the most effectivedephosphorization method. Afterwards, the influences of temperature, reaction time,drug dosage, pH, precipitation time and other fenton reaction operating conditions onthe phosphorus removal were investigated systematically. Finally, pilot-scaleexperiments were conducted with the low concentration organic phosphoruswastewater to confirm the operation parameters, demonstrate the stability, estimatethe operation cost, as well as the feasibility to the treatment of other wastewater of thedephosphorization process developed in this study. The conclusions obtained were asfollows:(1) After the pretreatment of ultrafiltration and softening using resin, the lowconcentration organic phosphorus wastewate of biodegradable difficulty could be concentrated through sequential two reverse osmosis processes by20times. The totalphosphorus content increased from2mg/L of the low contcentration organicphosphorus wastewate to about20mg/L of the concentrated wastewater, while thetotal phosphorus content of the two permeate streams from the sequential reverseosmosis processes were all much lower than0.5mg/L.(2) The better dephosphorization method for the treatment of the concentratedorganic phosphorus wastewater was fenton oxidation method under escalatedtemperarues. Under the conditions of fenton reaction temperature=50to55℃,reaction time=2.5h, reaction pH=3.0, dosage mole ratio of hydrogen peroxide toferrous iron ions=4:1, dosage of hydrogen peroxide=3000mg/L, precipitation time=2h, the total phosphorus of the concentrated organic phosphorus wastewater could bereduced from20mg/L to a value lower than3.0mg/L. The total phosphorus of thedischarged water, which was obtained by mixing one part of the dephosphorizatedconcentrated wasterwaster from reverse osmosis and6parts of the permeate streamfrom reverse osmosis, was still less than0.5mg/L.(3) The study of the thermodynamics of the fenton oxidation of the concentratedwastewater revealed that the fenton oxidation was a second order reaction with anactivative energy of about100kJ·mol-1. The constant of reaction rate of55℃wasabout40times higher than that of25.0℃(4) The treatment cost of per cubic wastewater for the dephosphorization processcombining membrane technology and fenton oxidation technique was3.81RMB,while for the dephosphorization process only using fenton oxidation technique, it washigher than10.0RMB. Additionally, part of the permeate strem of the reverse osmosisprocess of the former hybrid technology could be recyceled, showing good economicand social benefits.(5) The comparison between the treatment of the concentrated organicphosphorus wastewater from reverse osmosis and the glyphosate solution containingthe same total phosphorus indicated that the removal of the total phosphorus of theglyphosate solution was much easier. Under the condition of escalated temperarue,removal of the total phosphorus of glyphosate solution was as high as99.9%, illustrating that the main organic phosphorus presented in the low concentratedorganic phosphorus wastewater treated in this study was not glyphosate.(6) The pilot-scale experiments conducted with the phosphorus wastewater fromXinan Chemical demonstrated that the cleaning periods for the ultrafiltration andreverse osmosis systems were3and25~30days, respectively. The cost for thetreatment of one cubic of phosphorus wastewater through hybrid system was3.91RMB, indicating that the process developed in this study is cost-effective for thetreatment of wastewater of degrable difficulty. The results of the trial of the treatmentof other wastewater also indicated that the wastewater treatment process combiningmembrane technology and fenton oxidation technique possessed broad applicationprospect. |
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