| At present,water source reservoirs have become the main surface drinking water source in most cities and towns,and play an important role in urban water supply.However,with the development of society,the pollution of reservoirs has intensified,resulting in eutrophication,algae blooms and causes a series of water pollution problems in summer,which seriously endanger the safety of drinking water.Nitrogen is one of the most critical factors leading to water quality problems.In this study,in order to explore an economical and feasible method to solve the problem of excessive nitrogen concentration in source water.By monitored the water quality indicators of Lijiahe Reservoir for one year,analyzed the pollution status of the reservoir,designed the reactor according to the key nitrogen pollutants in the reservoir.Simulated the aerobic conditions,and carried out the laboratory scale experiment,to explored the feasibility and sustainability of microbial immobilization technology combined with inorganic electron donor materials(iron powder,manganese powder)to strengthen the biological aerobic denitrification,analyzed the changes of organic matter components,iron and manganese powder materials and microbial community,preliminarily explored the mechanism of strengthen biological denitrification.The main conclusions were as follows :(1)During the study period from September 2020 to September 2021,under the operating conditions of natural mixing and Water-lifting aerator in Lijiahe Reservoir,the thermal stratification in summer was significantly weakened and the water remains aerobic,but the reservoir still had the problem of the surface anaerobic zone caused by algal blooms;the total nitrogen concentration was kept above 2.5 mg/L during the study period,excessive nitrogen concentration is the main water quality problem in reservoir;with the heavy rainfall and runoff,the nutrient salt in the reservoir appeared at a high concentration for a short time,total nitrogen,nitrate nitrogen,ammonia concentration up to 5.43 mg/L,4.13 mg/L,0.42 mg/L;in the high incidence period of algae,algae assimilation led to the increase of organic matter concentration,the highest concentration was 5.16 mg/L;during the formation period of thermal stratification,the release of iron and manganese exceeded the standard temporarily,and the concentrations of total iron and total manganese exceeded 0.3 mg/L and 0.1 mg/L respectively.(2)Laboratory scale experiments showed that the use of polyurethane foam to fix microbial growth combined with iron and manganese materials can significantly improve the efficiency of microbial aerobic denitrification.After the reaction,the concentration of total nitrogen was lower than 1.0 mg/L,the total nitrogen removal rates of B–F in the experimental group were 80.6%,72.3%,79.5%,79.6% and 69.4%,respectively,and other pollutants(organic matter and total phosphorus)were also well removed;denitrification and nitrification occurred simultaneously in the reaction process,but nitrogen was removed by aerobic denitrification.In the second and third cycles,the iron powder material group continued to maintain the enhanced denitrification effect,the total nitrogen removal rates in the second and third cycles were 74.72% and 69.81%,respectively,while the denitrification effect of other groups decreased;iron powder and manganese powder material have dissolution in the reaction process,especially manganese powder material has the risk of concentration exceeding standard,and the total manganese concentration is up to 0.15 mg/L.(3)The change of organic matter components showed that the microbial metabolic activity showed a strong first and then weak change rule in the reaction process,and microbial assimilation was not the main way to remove organic matter.Through the comparison of the characterization of iron powder and manganese powder before and after the experiment,it was found that the oxidation corrosion of iron powder and manganese powder could provide inorganic electron donor for denitrification microorganisms,and it would not adsorb and remove nitrogen in water.The electrochemical reaction of iron and manganese mixture accelerated the corrosion,and new high-valence oxides were generated.The microbial community structure changed significantly before and after the reaction,and the proportion of aerobic denitrification and nitrogen cycle functional bacteria(Acidovorax,Comamonadaceae,Hydrogenophaga and Limnohabitans)decreased,which was the reason for the low nitrogen removal efficiency of control group A.In the experimental group B～F,the dominant phyla such as actinomycetes and Firmicutes coexisted after the reaction,and the denitrification efficiency was improved under the combined action of various mixed functional bacteria. |
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