| Water-qulity shortage is a key factor that restricts the development of society and economy. Wastewater recycling is an effective way to solve the water shortage problem.Potassium ferrate as an iron salt is a kind of multifunctional water treatment agent, which widely exists in nature,with its oxidation,flocculation,deodorization,sterilization.It has great potential for development.This paper used the oxidation and flocculation of potassium ferrate to study the factors, mechanism of potassium ferrate treating the domestic sewage. And the potassium ferrate was used to treat the secondary effluent for the further study.The main results of the experiment are as follows:(1)Study on the properties and the factors that affect the stability of potassium ferrate in aqueous solution. The results showed that ferrate was more stable when pH was between 8 and 10.2.The decomposition rate of potassium ferrate of which dosage was 10 mg/L was smaller than whose dosage was 40 mg/L.The smaller dosage of potassium ferrate was,the more stable the potassium ferrate was.With the increasing of time,the remaining concentration of potassium ferrate got smaller and smaller.When the dissolution time was 200 s later,the remaining concentration of potassium ferrate was basically unchanged.(2)Study on the factors influencing the oxidation of potassium ferrate which were the dosage of the potassium ferrate,the pH,the time.The results showed that when the dosage of the potassium ferrate and time were in certain conditions,the removal effect on pollutants was better in alkaline condition.The removal rate of COD,TOC respectively reached to 10.63%,10.44% when the pH was 10.31.When the pH and time were in certain conditions,the removal rate of pollutants increased with the increasing of dosage. When the dosage increased to 40 mg/L, the removal effect on pollutants was basically unchanged.The removal rate of COD,TOC respectively reached to 20.56%,19.66% at this time.When the dosage of the potassium ferrate and pH were in certain conditions,the removal rate of pollutants was basically unchanged when the time was 25 min later.The removal rate of COD,TOC respectively reached to 21.5%,19.81% at this time.Generally speaking,the potassium ferrate had better removal effect on organic matter and less removal effect on phosphorus and suspended solids in the oxidation stage.(3)Study on the factors influencing the flocculation of potassium ferrate which were the dosage of the potassium ferrate,the pH,the reaction time.The results showed that when the dosage of the potassium ferrate and time were in certain conditions,the removal rate of COD,TOC respectively reached to 8.67%,8.07% when the pH was 6.93.At this time,the removal effect on organic matter was better.The removal rate of TP,SS respectively reached to 30.01%,28.23% when the pH was 3.28.At this time,the removal effect on phosphorus and suspended solids was better.When the pH and time were in certain conditions and when the dosage increased to 40 mg/L,the removal rate of pollutants no longer increased.The removal rate of COD,TOC,TP,SS respectively reached to 14.84%,12.76%,34.38%,43.75% at this time. When the dosage of the potassium ferrate and pH were in certain conditions,the removal rate of pollutants was basically unchanged when the time was 30 min later.The removal rate of COD,TOC,TP,SS respectively reached to 23.73%,22.72%,51.96%,68.75% at this time.Generally speaking,the potassium ferrate had better removal effect on phosphorus and suspended solids and partial removal effect on organic matter in the flocculation stage.(4)The compared experiments whose water treatment agent were potassium ferrate, potassium permanganate and ferric chloride showed potassium ferrate could simultaneously remove organic matter,phosphorus and suspended solids.This indicated that the potassium ferrate was a water treatment agent which had both oxidation and flocculation.(5)Study on the variation of pollutants’ removal rate with time.The results showed that the relationship between the removal rate of COD,TOC and time respectively conformed to the polynomial equation in the oxidation stage.The COD’s equation was y=-0.0399x2+1.8496x+1.8295,and the linear correlation coefficient R2 was 0.96.The TOC’s equation was y=-0.0378x2+1.7008x+1.5778,and the R2 was 0.96. The relationship between the removal rate of TP,SS and time respectively conformed to the polynomial equation in the flocculation stage.The TP’s equation was y=-0.0437x2+3.0864x+1.594,and the R2 was 0.97.The SS’s equation was y=0.5833x2-6.3452x+21.429,and the R2 was 0.98.This indicated the fitting formulas had good linear correlation.(6)Study on the removal effect of potassium ferrate treating the secondary effluent from the sewage treatment plant.The results showed that the potassium ferrate had good removal effect on the organic matter,phosphorus and suspended solids.When the dosage was 40 mg/L,the oxidation time was 25 min,the flocculation time was 20 min,the removal rate of COD,TOC,TP,SS respectively reached to 37.45%,36.48%,23.86%,40%.This indicated that the potassium ferrate could effectively remove the organic matter,phosphorus and suspended solids in the secondary effluent from the sewage treatment plant. |
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