Study On Removal Of Manganese And Ammonia Nitrogen From Drinking Water By Preoxidation Enhanced Coagulation

In the China Environmental Status Bulletin 2017,manganese and ammonia nitrogen are the main pollutants in surface and groundwater sources.This project is aimed at the problem that manganese and ammonia nitrogen in the surface water of an overseas water supply project exceeded the standard,and the conventional process has the limited effect of removing manganese and ammonia nitrogen.The effects of pre-oxidation enhanced coagulation when manganese pollution,ammonia nitrogen pollution,manganese and ammonia nitrogen combined pollution are studied respectively.For the raw water contaminated by manganese,the optimum dosages,pH value,pre-oxidation time of potassium oxymanganate,sodium hypochlorite and potassium ferrate were studied,and investigated the effect of manganese removal by pre-oxidation enhanced coagulation in the presence of iron contamination in raw water.For the raw water contaminated by ammonia nitrogen,the optimum dosages,pH value,pre-oxidation time of potassium oxymanganate,sodium hypochlorite and potassium ferrate were studied.For the raw water contaminated by manganese and ammonia nitrogen,the optimum dosages,pH value,pre-oxidation time of potassium oxymanganate,sodium hypochlorite and potassium ferrate were studied.When sodium hypochlorite was combined with potassium ferrate,the effects of the addition sequence,iron pollution on manganese and ammonia nitrogen removal were investigated,and orthogonal experiments were conducted to investigate the influence order of various influencing factors on the removal rate of manganese and ammonia nitrogen.Comparing the amount of disinfection by-products by three pre-oxidation enhanced coagulation methods of sodium hypochlorite alone,sodium hypochlorite combined with potassium ferrate and potassium ferrate alone.The results showed that when manganese concentration is 1.0mg/L,at the pH value of raw water,1.2mg/L potassium permanganate oxidation for 3⁵min,6mg/L sodium hypochlorite oxidation for 10min,6mg/L potassium ferrate oxidation for3⁵min,the three pre-oxidation enhanced coagulation treatment methods can make the manganese concentration in effluent less than 0.1mg/L.Under the corresponding dosage,when there is 0¹.5mg/L Fe²⁺in raw water,the manganese concentration in effluent can be less than 0.1mg/L.The dosage of potassium permanganate should be determined according to the concentration of manganese in the raw water,when the potassium permanganate concentration is too low,the manganese concentration can not reach the standard,when too high,due to manganese reverse dissolution,manganese concentration in effluent would exceed the standard again.The reaction between sodium hypochlorite and divalent manganese is slow,so it is necessary to increase the dosage of sodium hypochlorite to reduce the concentration of manganese in effluent.When the raw water is contaminated by organic matter,it is not recommended to use pre-oxidation of sodium hypochlorite to remove manganese.Removing manganesel by potassium ferrate pre-oxidation enhanced coagulation has the characteristics of good effect and high speed.Potassium ferrate is a green oxidant,it does not produce disinfection by-products during oxidation.Therefore,it is recommended to use potassium ferrate to pre-oxidize manganese.When ammonia nitrogen concentration in the raw water is 0.8mg/L,the sodium hypochlorite pre-oxidation enhanced coagulation can make the ammonia nitrogen concentration in effluent less than 0.5mg/L,but potassium permanganate and potassium ferrate pre-oxidation can not make the ammonia nitrogen concentration in effluent meet the standard.For the water quality of this test,the suitable operating parameters are:8mg/L the effective chlorine of sodium hypochlorite,5¹0min pre-oxidation time,7⁸.5 pH.When manganese and ammonia nitrogen concentration in the raw water is1.0mg/L and 0.8mg/L,respectively,under the pH value of raw water,12mg/L sodium hypochlorite is pre-oxidized for 10min,6mg/L sodium hypochlorite combined with6mg/L potassium ferrate is pre-oxidized for 10min.This two kinds of pre-oxidation enhanced coagulation methods can make the manganese and ammonia nitrogen in effluent reach the standard,but the pre-oxidation of potassium ferrate alone can only make the manganese in effluent reach the standard,and can not make the ammonia nitrogen meet the standard.The order of factors affecting the removal rate of manganese in combination by orthogonal test is pH value>potassium ferrate dosage>sodium hypochlorite dosage>pre-oxidation time,and the order of factors affecting the removal rate of ammonia nitrogen is sodium hypochlorite dosage>pH>Potassium ferrate dosage>pre-oxidation time.The removal rates of manganese and ammonia-nitrogen so high as up to 98.0%and 45.9%under the condition of 8.0 mg/L effective chlorine,6.0 mg/L potassium ferrate,at pH=7,through 10 minutes of pre-oxidation.8mg/L sodium hypochlorite combined with 6mg/L potassium ferrate pre-oxidation compared with 12mg/L sodium hypochlorite alone,the concentrations of trichloromethane,trichloroacetonitrile and bromodichloromethane decreased by59.6%,56.7%,53.1%.Therefore,the combination of sodium hypochlorite and potassium ferrate can give full play to their respective advantages.the production of disinfection by-products can be greatly reduced while simultaneously removing manganese and ammonia nitrogen.