Biological Purification Of Iron, Manganese And Ammonia With High Concentration In Groundwater And Engineering Application

The purification of groundwater containing manganese has been solved well by biological technology of manganese removal. The typical process flow has been widely used to remove iron and manganese by single filter. But it should be improved by further study to adapt diverse groundwater quality and to be used throughout the country. It is reported that the required start-up period of biofilter for the removal of Mn is typically 1-2 months, but when water contains ammonia, biological Mn removal can take place only after complete nitrification, and when water contains high concentration of Fe2+, the start-up period may be 6-8 months. So in this work we study in the effect of high concentration of Fe2+ and ammonia on the biological removal of manganese in order to shorten the start-up period of biofilter and build demonstration plant for the removal of Fe2+, Mn2+ and ammonia in a single biofilter.According to the research of redox relationship between Fe and Mn in the biofilter, the reduction of biological manganese oxide takes place under high concentration of Fe2+ (>3mg/L), inducing the release of Mn2+ and the destruction of Mn-removal biofilm. Fe2+ and Mn2+ can be removed in a single biofilter, but the efficient manganese removal can only take place in the middle-lower part of the filter after the complete oxidation of Fe2+, so a thick layer is needed for the biofilter. Considering the destruction of Mn-removal biofilm by high concentration of Fe2+, we suppose that: in the culture process of single-media biofilter for Mn-removal, partly formed Mn-removal biofilm would be destroyed by contacting high concentration of Fe2+ in the raw water because of mixed-layer structure of biofilter after backwashing, which would delay the accumulation of biofilm and prolong the start-up period. And dual-media filter is put forward to solve this problem, the result of the filter-column experiment proves that: the start-up period of the dual-media biofilter for the removal of Fe2+ and Mn2+ is shortened to 2 months when the concentration of Fe2+ and Mn2+ is respectively 15mg/L and 1.5mg/L in the raw groundwater.The DO in the influent should be raised above 7.5mg/L for the simultaneous removal of Fe2+, Mn2+ and NH4+-N from groundwater( Fe2+ about 15mg/L, Mn2+ about 1.5mg/L, NH4+-N about 1mg/L). The dissolved oxygen is mostly consumed at the upper part of the filter for oxidization of Fe2+, NH4+-N and other reducing agents. The residual dissolved oxygen concentration in the middle and lower part of the biofilter determines the result of the biological removal of manganese. The aeration system, even the process flow for the biological purification of groundwater should be taken fully into account according to the concentration of NH4+-N in raw water. When the weak cascaded aeration couldn't afford enough dissolved oxygen for the purification, strong aeration technology should be adopted, for example, spray aeration and mechanical aeration. With the further increasing of NH4+-N, one-stage aeration couldn't supply adequate dissolved oxygen due to the limitation of saturation of dissolved oxygen, and we try the two-stage filtration process which has two-stage aeration and the aerated biofilter process.The accumulation of NO2--N inhibits the culture process of Mn-removal biofilter and until it disappears, the complete removal of Mn could come true. The accumulation of nitrifying bacteria is the key part for the rapid start-up of biofilter for Mn-removal from groundwater containing NH4+-N. So we try cycling culture for rapid start-up of the biofilter, the result turns out that: the period is shortened to 20 days.In the end, the two-stage filtration process is transformed to one-stage filtration after transformation of aeration system, adjustment of filter structure and culture of biofilm in Songbei water plant, and the concentration of iron, manganese and NH4+-N in the filtrate is lower than 0.2mg/L, 0.05mg/L and 0.2mg/L. Structure and dynamics analysis of microbial community from biofilters indicate that the variation of the structure is inapparent, and Zooglowa has a role to the stability of the biofilter for its wide distribution and great adaptability. A strain Chryseobacterium sp.MSB-4 is isolated, which is efficient for the Mn-removal under low temperature and has close relationship with sheathed bacteria (Sphingobacterium).