Experiment On The Treatment Of Compound Micro-polluted Groundwater With Three-stage Contact Oxidation Filtration

Natural organic matters contained in groundwater in our country are mainly humus and polycyclic aromatic hydrocarbon compounds, there contents are generally very small. In the northern areas, part of the groundwater with high Fe and Mn is influenced by organic matter and NH4+-N. This is because the surface water is polluted by effluent discharges of industrial wastewater and sanitary sewage. After perennial infiltration, the pollution of groundwater by organic matters and NH4+-N is constantly on the rise. This not only adds to the contaminated degree of groundwater, but also increases the difficulty of Fe and Mn removal in the groundwater. Therefore, it is a technical problem of centralized water supply to seek for an economic and applicable method to deal with compound micro-polluted groundwater coexisting organic matter, NH4+-N, Fe and Mn.The experiment introduce three-stage contact oxidation filtration method to deal with compound micro-polluted groundwater using manganese sand and ceramsite as filter materials. The combination of the four filter columns system are respectively ceramsite-ceramsite ceramsite, manganese sand-ceramsite-ceramsite, ceramsite-manganese sand-ceramsite and manganese sand-ceramsite-manganese sand. The grain size of manganese sand and ceramsite is 1.25?1.60mm. The filtering layers of filter columns at all levels are all 0.5m and 1.5m in total. This can guarantee the filtration time of compound micro-polluted groundwater and provide living space and attachment for microorganisms to grow. The filter speed ranges from 1.0m/h to 3.0m/h and the experiment lasted for 242days.The water qualities are as follows:1.0?3.0mg/L for Fe,2.0?3.5mg/L for Mn,2.5?4.5mg/L for NH4+-N and 2.5?5.0mg/L for CODMn.Under the condition of adequate dissolved oxygen, the four kinds of filter column combinations all have good treatment effect on Fe, Mn and NH4+-N. When the average filtering velocity is 3.0m/h, the concentration of Fe, Mn and NH4+-N in the effluent water are less than 0.17mg/L,0.09mg/L and 0.15mg/L respectively. The removal effect of CODMn is poor when the filter column combination is ceramsite-ceramsite-ceramsite, the average concentration is 2.46mg/L when the filtering velocity is 3.0m/h.The treatment effect is the best when the filter combination is manganese sand-ceramsite-manganese sand. When the filtering velocity is 3.0m/h, the concentrations of Fe, Mn, NH4+-N and CODMn range from 0.04mg/L to 0.28mg/L, from 0.03mg/L to 0.08mg/L, from Omg/L to 0.22mg/L and from 0.5mg/L to 2.63mg/L respectively. The average values are 0.16mg/L, 0.06mg/L,0.07mg/L and 1.46mg/L respectively. The combination of ceramsite-ceramsite ceramsite, manganese sand-ceramsite-ceramsite, ceramsite-manganese sand-ceramsite with the average concenraions of Fe are 0.17mg/L, 0.11mg/L,0.14mg/L, Mn are 0.08mg/L,0.06mg/L, 0.06mg/L, NH4+-N are 0.15mg/L,0.09mg/L,0.09mg/L, CODMn are 2.46mg/L,1.52mg/L, 1.84mg/L.Within limits of the filter velocity used in the experiment, the filter velocity has little effect on the treatment effect 1.0m/h,1.5m/h,2.0m/h,3.0m/h. The concentration of the four items in the effluent water can all reach the national standards when the filtering velocities are 1.0m/h, 1.5m/h,2.0m/h and 3.0m/h. Contrastive analysis shows that the removal rate of Fe reduced slightly when the filtering velocity increased. Mn and NH4+-N are greatly influenced by dissolved oxygen. When the average values of dissolved oxygen in the first, second and third stages are 7.82mg/L,8.00mg/L and 5.97mg/L, the concentration of Fe and Mn remain unchanged when the filtering velocity ranged from 1.0m/h to 3.Om/h.The quantity of dissolved oxygen demanded is large when the NH4+-N and Mn coexist, the concentrations of Mn and NH4+-N in the effluent water are high when we used simple drop aeration under the condition that the filtering velocity is l.Om/h. When the aeration heads are added, the dissolved oxygen increased by 3.10mg/L. The average removal rates of Mn of the four groups(ceramsite-ceramsite-ceramsite, manganese sand-ceramsite-ceramsite, ceramsite-manganese sand-ceramsite and manganese sand-ceramsite-manganese sand) are respectively 97.69%,97.39%,90.91% and 96.45%; the average removal rates of NH4+-N of the four groupsare respectively 95.39%,94.44%,94.35% and 97.44%. Because of the low concentration of CODMn in the influent water, it has already reached the national standard during the drop aeration stage. The removal rate improved further with the increased of dissolved oxygen.The experiment results show that three-stage contact oxidation filtration method have good treatment effect on Fe, Mn, NH4+-N and organic matters, and the concentrations of the four items above can all meet the national drinking water standards.The best filter material combinton is manganese sand-ceramsite-manganese sand when three-stage contact oxidation filtration method is used to deal with compound micro-polluted groundwater. The filtering velocity can reach 3.0m/h with the average dissolved oxygen demand 16.29mg/L when the grain size ranges from 1.25mm to 1.60mm and the Filter layer thickness 1.5m.