Discussion On The Efficiency And Mechanism Of Modified Zeolite For Treating Manganese-containing Groundwater

Although China is rich in total water resources,many areas are still facing with the shortage of drinking water,owing to the large and increasing urban population and the great spatial and temporal variations of water resources.Groundwater,as an important source of alternative drinking water production,has been widely exploited in recent years.Iron and manganese ions are major contaminants of groundwater.At present,iron and manganese contaminated groundwater are conventionally treated by sand filtration.However,the long ripening time ranging from 3-6 months even a year required for the filter media to become mature is a major concern.On the other hand,water quality parameters,especially the concentration of iron and manganese,vary obviously in different areas.Besides,the type of filter material also has a significant effect on the removal of iron and manganese.In the current study,modified silica alumina sand was selected as the filter medium for the contact oxidation sand filter process and the adsorption characteristics of which was investigated.On the basis of actual groundwater in Durbat monggol village,Daqing,the effect of modified silica alumina sand on the removal of iron and manganese was evaluated.Then,the pre-oxidative effect of sodium hypochlorite on the acceleration of ripening sand filter was studied.In particular,the effect of iron ion on the characteristics of matured active manganese oxides and the subsequent affecting on the manganese removal performance.Eventually,the effect of sodium hypochlorite on the emergency removal of manganese was in comparison to potassium permanganate.In order to understand the adsorption characteristics of modified silica alumina sand,the static adsorption test was carried out.It was found that modified silica alumina sand presented excellent adsorption performance for manganese and the corresponding adsorption equilibrium period was 8h.However,the competitive adsorption between calcium and manganese occurred in the presence of large amounts of calcium ions,resulting in decreased removal efficiency of manganese.It was found in the dynamic filtration tests that the concentration of calcium had a great effect on the adsorption of manganese.The modified silica alumina sand presented good adsorption efficiency on manganese when the concentration of calcium was less than 40 mg/L.However,it only took three days for the content of manganese in the effluent exceed the standard(0.1mg/L)as long as the concentration of calcium was above 200 mg/L.In the case ofcalcium content reached 700 mg/L,there was barely any removal effect on manganese remained.Based on the aforementioned findings,a pilot study with modified silica alumina sand as filter media of a single rapid sand filtration was performed under controlled conditions.Both of the sand filters exhibited excellent removal efficiency on iron with the effluent meets the quality standards for drinking water recommended by China.However,due to the effect of hardness in the actual groundwater on the modified silica alumina sand,the manganese content in the effluent exceeded the threshold throughout the experiment.In addition,the formed manganese oxide was insufficient to oxidize ammonia effectively and efficiently,owing to the long ripening time required for the sand media to mature.On the other hand,the presence of manganese dioxide in the original manganese sand was capable to absorb and oxidize manganese rapidly and effectively.Besides,the formation of manganese oxide acted as the carrier,enhancing the oxidation of manganese and ammonia.A study was carried out to investigate the effect of sodium hypochlorite pre-oxidation on the formation of manganese oxide,with the aim to shorten or eliminate the ripening time and ensure the drinking water safety of manganese concentrations varying on a seasonal basis.The results showed that even though sodium hypochlorite pre-oxidation could be of help in the removal of manganese,the formed manganese oxide coating on sand had a temporary removal effect on manganese.Moreover,the high content of ferrous ions in the influent could lead to manganese oxide reduction leading to the release of divalent manganese.Both the impact of ferrous ions and the reducing conditions trigged the high concentrations in dissolved manganese during periods of lake stratification especially in summer.For the purpose to solve the seasonal or abrupt manganese leakage phenomenon,the effect of pre-oxidation by potassium permanganate and sodium hypochlorite on manganese removal performances were investigated.The resulted indicated that the reaction of potassium permanganate with manganese leading to the formation of in-site manganese dioxide,which contributed to the adsorption behavior of manganese in the formed manganese oxides.Moreover,manganese oxides acted as reactant or catalyst accelerating the oxidation of manganese and further promoting the removal of manganese.In brief,potassium permanganate exhibited better manganese removal performance than sodium hypochlorite in the case of emergency manganese leakage.Therefore,the use of sodium hypochlorite pre-oxidation can effectively shorten the maturity time of the contact oxidation filter,but does not have long-term manganese removal capacity.When the raw water quality changes and the effluent manganese concentration exceeds the standard,potassium permanganate has more efficient emergency manganese removal capacity.