Study On The Technology Of Advanced Treatment Of Tailwater From Urban Wastewater Treatment Plants By Composite Biological Filter System

Water resources are often perceived as the the foundation for the development of social economic.At present,China is carrying tremendous burden from the shortage of water and grim situation of the water pollution.Relevant studies have indicated that water quality within a basin will be directly or indirectly affected by the performance of wastewater treatment plants?WWTPs?.For the sake of better environment,most current WWTPs in China are enforcing the first-level A or first-level B of the discharge standard of pollutants from urban wastewater treatment plants?GB18918-2002?.However,the directly discharge of tail water from these WWTPs still exposes relevant receiving water in a risky stage and might subsequently lead to eutrophication.Therefore,improvement of discharge standard and advanced treatment of tail water from WWTPs is an inevitable stream in the further development.Restricted by limited carbon resources,tail water in WWTPs is often characterized as low C/N,high loads of TP,difficult for pollutants'biodegradation and removal of nitrogen.After comprehensive consideration of aforementioned issues and recycle of agricultural wastes,corn cobs biochar and alkalized cobs are employed to serve as sustained-release carbon source in this study.Based on this,composite biological filter are built with configuration of elemental sulfur,sponge iron and some other materials for the advance removal of pollutants like phosphorus.Mechanisms,including the substrate adsorption,chemical precipitation and biodegradation will be discussed to probe into the performance of filters and pollutants'removal pathways.The main research results are as follows:?1?Selection and pretreatment of corn cob filler.In order to promote the decomposition of organic matter and release of organic or inorganic carbon sources,corn cob with complex structure requires pretreatment for the separation of materials like cellulose,hemicellulose and lignin.Different degrees of acidification,alkalization and calcination are carried out as pretreatment of corn cob at the same time.By means of observing the apparent characteristics and electron microscope scanning images,the results turn out that alkalized corn cob with pretreatment of 1.5%Na OH remains structurally sound with larger porosity.Corn cob biochar calcinated under 250?not only contains rich inorganic and organic carbon,but also possesses the greatest strength.?2?Study on the performance of composite biological filters on treating simulated tail water.Alkalized corn cob,corn cob biochar,zeolite,biological ceramsite are used as fillers in the denitrification layers.Elemental sulfur and sponge iron are used as fillers in the phosphorus removal layers.Three composite biological filters set up have been constructed with different combinations of these layers.Operation parameters,such as hydraulic loading,pollutants loading and aeration are adjusted to explore the optimum operating conditions.As the quality of inlet water satisfies level A discharge standard and hydraulic loading reaches of 2 m³·m^-2·d^-1,reactor C,filling with corn cob biochar and S/Fe mixtures,can achieve 75.80%of the TP removal rate with the average discharge concentration of 0.13 mg/L,99.08%of nitrate nitrogen removal rate with the average discharge concentration of 0.09 mg/L,71.43%of nitrate nitrogen removal rate with the average discharge concentration of 1.34 mg/L.By comparing the various nitrogen and phosphorus removal results of the three setups,the study obtained the optimal composite ways of setups as following:zeolite layer,sustained-release carbon source layer?filled with corn cob biochar and alkalized corn cob?,denitrification and phosphorus removal layer?filled with S/Fe mixtures and biological ceramic particles?,and pebble layer?serving as water collecting layer??from top to bottom?.?3?Analysis of performances of composite biological filter setup on the treatment of actual tail water treatment.To test the setup's capability on the treatment of actual tail water,the setup is constructed in a best composite way and operating under the optimal condition.The results show that average concentration of effluent COD_Cr,TP,TN,ammonia nitrogen,nitrate nitrogen are 11.23 mg/L,0.17 mg/L,1.51 mg/L,0.07mg/L,1.32 mg/L,respectively.TP,TN and ammonia nitrogen removal rate can reach66.53%,85.31%and 99.22%,respectively,basically meet the requirements of IV class in the surface water standard.?4?Analysis of diversity and functional microbial community structure.In order to explore the mechanism of nitrogen and phosphorus removal in the composite biological filters from the microscopic perspective,biofilms of each layer is tested with high-throughput sequencing.The results show that the alkalized corn cob mainly provides organic matter and exercise the function of heterotrophic denitrification.In more detailed,zeolite layer mainly enriches Streptomyces,Rhodoblastus,Nakamurella,Fodinicola and other bacteria,mainly for nitrification.The biological ceramsite layer mainly enriches Silanimonas,Hyphomicrobium,Thauera,Xanthobacter,Dechloromonas and Vogesella,playing a major role in denitrification.The S/Fe layer mainly enriches Desulfuromonas,Desulfovibrio,Desulfobulbus,Geobacter and Geothrix,exercising heterotrophic and sulfur-autotrophic denitrification functions.The composite biological filters has good capability of denitrification and dephosphorization,providing a feasible reference technology for advanced treatment of tail water from WWTPs.