Study On The Preparation And Performance Of Nitrogen And Phosphorus Removal Of Non-sintered Pyrite Fillers In Constructed Wetlands

To achieve an overall improvement in the quality of China’s water environment and to control eutrophication in water bodies,stricter local standards have recently been proposed for effluent indicators such as nitrogen and phosphorus from wastewater treatment plants.To meet the stricter pollutant discharge standards,wastewater treatment plants need to be upgraded and the existing tail water treated using tertiary treatment processes such as deep denitrification.The low C/N values in the tailwater of wastewater treatment plants,of which nitrogen is predominantly nitrate nitrogen,require the addition of a large amount of carbon source material for treatment using the traditional heterotrophic denitrification technology,while the use of pyrite-driven autotrophic denitrification for wastewater treatment can reduce sludge production and reduce operating costs.In this paper,we investigated the problems limiting the application of autotrophic denitrification of pyrite and prepared a non-sintered pyrite filler with better performance at low cost.The fillers were used in constructed wetlands to compare the denitrification and phosphorus removal performance with natural pyrite fillers,and a series of studies were conducted on the purification effect,safety,economics and microbial community structure along the constructed wetlands constructed by the two fillers.The main findings of this study are as follows:(1)The compressive strength and denitrification rate of the non-sintered pyrite filler can be guaranteed when using sulphate aluminate cement as the binder.The optimum mass percentages of non-sintered pyrite filler were 31.52% binder,68.03%pyrite powder and 0.45% foaming agent.Compared to natural pyrite fillers the nonsintered pyrite fillers prepared have a high specific surface area,low bulk density,high porosity and a rough filler surface,which facilitates the denitrification rate.(2)The non-sintered pyrite filler and natural pyrite filler were used to build the constructed wetlands,the non-sintered pyrite filler constructed wetlands start-up time is 3 d shorter,both constructed wetlands start-up success nitrate-nitrogen removal rate exceeded 99%.The longer the hydraulic retention time,the better the nitrogen removal effect of the constructed wetlands.When HRT=12 h,the removal rate of total nitrogen from non-sintered pyrite filler exceeded 98%,which was better than that of natural pyrite filler,and the removal rate of total phosphorus from both exceeded 60% at this time.The constructed wetlands had the best nitrogen removal effect when the influent water was neutral,and the highest phosphorus removal effect when the p H=9 of the influent water.Both constructed wetlands achieve high levels of nitrogen and phosphorus removal within the range of influent pollutants set in the experiment.(3)The nitrate-nitrogen and total nitrogen were removed by more than 75% in the lower part of the system,while ammonia nitrogen was mainly removed in the lower part of the system and the upper surface layer,and from the middle of the system,the nitrogen removal effect of the two constructed wetlands began to show significant differences.The accumulation of nitrite nitrogen occurs in the middle of the system,with the highest accumulation of nitrite nitrogen in the non-sintered pyrite filler constructed wetlands reaching 0.223 mg/L.The sulphate concentration in the constructed wetlands system rises across the process,while the total phosphorus concentration decreases uniformly across the process.The length and biomass of all parts of Oenanthe javanica in the non-sintered pyrite-filler constructed wetlands were higher than in the natural pyrite-filler constructed wetlands,and the difference in Oenanthe javanica biomass between the two constructed wetlands was small compared to the difference in length.The heavy metal content in the effluent of both types of constructed wetlands and the planted Oenanthe javanica were both below the limit values of the relevant standards.The cost per tonne of water treated with non-sintered pyrite filler,natural pyrite filler and sulphur filler was 0.012 CNY/tonne,0.014CNY/tonne and 0.026 CNY/tonne respectively,with non-sintered pyrite filler having significant economic advantages.(4)The microbial abundance of the two constructed wetlands decreases in the order of the middle,top and bottom.The diversity of microbial communities in the middle of the non-sintered pyrite filler constructed wetlands is the lowest,while the diversity of microbial communities in the natural pyrite filler constructed wetlands is in descending order: middle,top and bottom.The number of dominant microorganisms in the non-sintered pyrite filler constructed wetlands was more concentrated.The dominant phylum in the two constructed wetlands is Proteobacteria,and the dominant classes are Betaproteobacteria 、 Alphaproteobacteria and Gammaproteobacteria contained in Proteobacteria.The dominant families were mainly Thiomonas and Sulfurimonas,with the relative abundance of both decreasing across the process within the constructed wetlands.