Study On The Preparation And Phosphorus Removing Application Of Modified Ferric Chloride

With the development of China’s economic in recent years,a large number ofwastewater discharged into rivers,lakes,oceans and other waters with rich nitrogen andphosphorus.The pollution of nitrogen and phosphorus is worsening and the problems ofwater eutrophication become apparent.In order to prevent the spreading of watereutrophication, the state implemented a series of strict effluent discharge standards,many cities in China are upgrading the sewage treatment plants which have been builtgradually. As a cost-effective method of water treatment,coagulating sedimentation hasbeen used widely in the sewage treatment plant’s upgrading.With the advantages ofsafe,effective,ferric coagulant has been used in chemical treatment of wastewatercommonly. In the ferric coagulant, Fe2+and Fe3+all have removal effect, however, theferric chloride coagulant product standard (GB4482-2006)has strict limits on the ferrouscontent, which affects control factors(such as oxidant dosage, reaction time,temperature, etc.) of production costs of the ferric chloride directly.Now,there haven’trelated research reports on whether the content of ferrous in ferric chloride coagulantaffects the coagulating sedimentation effect.Based on the effect of ferrous iron content in modification ferric chloride on thecoagulation efficiency,two new modified ferric chloride had been prepared for rawsewage and bio-chemical effluent respectively.The application research of the effect thatnew modified ferric chloride on raw sewage and bio-chemical effluent had been studiedrespectively,which can afford practical reference when these chloride used forcoagulation in the sewage treatment.Based on the raw sewage of municipal wastewater treatment plant,the effect offerrous iron content in modification ferric chloride on the coagulation efficiency hadbeen studied.In raw water,CODCrwas450mg/L, total phosphorus was5.77mg/L,pH was7.32.The results shows that when total iron dosage was32mg/L,the22%ferrous contentof Series II modification ferric chloride has the best TP removal efficiency with that TPconcentration in the supernatant was0.61mg/L,with89.4%removal rate,the CODCrconcentration was160mg/L, with64.4%removal rate and pH was7.21.The22% ferrous content of Series II modification ferric chloride was the successful modifiedferric chloride prepared for the raw water.Based on bio-chemical effluent of municipal wastewater treatment plant,the effectof ferrous iron content in modification ferric chloride on the TP removal efficiency hadbeen studied.In bio-chemical effluent,CODCrwas30mg/L, TP was1.57mg/L,pH was6.83.The results shows that when total iron dosage was16mg/L,the14%ferrous contentof Series Ⅰ modification ferric chloride has the best TP removal efficiency with that TPconcentration in the supernatant was0.14mg/L,with91.1%removal rate,pH was6.68.The14%ferrous content of Series Ⅰ modification ferric chloride was thesuccessful modified ferric chloride prepared for the raw water.Compared with the commercially available product ferric chloride,the applicationof II-modified ferric chloride on raw water TP removal efficiency had been studied.Theresults shows that,II-modified ferric chloride had a better TP removal efficiency than theferric chloride.The the optimal dosage of II-modified ferric chloride was32mg/L,whilethe TP concentration of supernatant was0.61mg/L, the CODCrconcentration was160mg/L and the residual total iron concentration was6.37mg/L.As an importantnutrient of activated sludge system,iron element has a positive effect for subsequentbiological treatment process.Without considering carbon, nitrogen and some otherfactors,the subsequent biological treatment process can make the TP concentration meetthe GB18918-2002limit.Compared with the commercially available product ferric chloride,the applicationof Ⅰ-modified ferric chloride on bio-chemical effluent TP removal efficiency had beenstudied.The results shows that,at the the dosage of12mg/L,the Ⅰ-modified ferricchloride and ferric chloride product could make the TP concentration of supernatantreduced to0.45mg/L,0.33mg/L respectively.The TP concentration meet theGB18918-2002limit.however,Ⅰ-modified ferric chloride had a relatively little effect onpH and dense precipitation.Due to the reduce of oxidant and hydrochloric acid in theproduction process,it has a lower production cost.The results showed that the modified ferric chloride with22%ferrous content hasthe best TP removal efficiency on raw water and the modified ferric chloride with14% ferrous content has the best TP removal efficiency on bio-chemical effluent.Theproduction cost was lower with the ferrous content higher.Compared with thecommercially available product ferric chloride,the modified ferric chloride has astronger market competition advantage in the economic cost with the same removalefficiency through the practical application.