The Effect And Mechanism Of Weak Current On Iron And Manganese Removal Efficiency In Biofilters

Groundwater is an important water source in north China,and its safety issues should be treated seriously.Both natural and human factors can cause may all cause the iron,manganese and ammonia concentration overstandard in groundwater.Excessive groundwater can not only cause inconvenient daily life,increases water transportation costs,but also affects human health.Nowadays,there are still shortcomings on the simultaneous removal of iron,manganese,and ammonia in biofilter study: the stability of biological filters is poor and the impact of ammonia on mature biofilter’s community structure is still unclear.Since the microbial electrolysis cell has the potential to strengthen the effect of heterotrophic microorganisms,this study creatively proposes to combine the weak current with the biofilters to study the effect of weak current on the removal efficiency of iron,manganese,ammonia and the change of microbial community in different stages of the biofilters.This research mainly focuses on the removal efficiency of iron and manganese in the start-up and mature stages of the biofilters with weak current and the effect of ammonia on the removal efficiency of iron and manganese and microbial community structure,and the ammonia removal efficiency in the biofilters.The experimental results show that weak current can improve the stability of the mature biofilters during the process of manganese removal.When the water inffluent filtration rate of the mature biological filter increases from 5 mL/min to 10 mL/min,the removal rate of Mn(II)without weak current decreases from 95.68% to 91.16%,while the manganese removal rate of biofilters only decreases from 96.24% to 94.85%.The possible reason is that the abundance of the manganese-oxidizing bacteria Cupriavidus in biofilters with weak current increases.Weak current could promote the accumulation of microorganisms related to carbon and nitrogen cycle(Ampullimonas,Methylophilus,Methyloversatilis,Methanobrevibacter,Methanobacterium,Nitrosomonas,and Rhodococcus)at the electrode,indicating that the electrodes may participate in carbon and nitrogen cycle reaction in the filter through electron transfer,and has the potential of improving carbon and nitrogen cycle in the filter.The ammonia removal rate(about95%)of the biofilters in the start-up stage is higher than in mature stage(about 80%).The weak current could help improve the stability of the ammonia removal efficiency in the start-up stage of the biofilters.Ammonia has no significant effect on the removal of iron and manganese in different stages of biofilters,but makes a big change in the bacterial community structure of the mature biofilters.The dominant bacteria changes from Sphingobium with less obvious abundance advantage to Pseudomonas and Rhodococcus with extremely obvious abundance advantage.