Characteristics And Mechanism Of Advance Removal Nitrogen By Volcanic Rock Substrate In Simulated Constructed Wetland

Constructed wetland is an economical and efficient advance denitrification treatment technology,and wetland substrate is the key to affecting denitrification efficiency.Studies have found that Volcanic Rock(VR)are good substrates for denitrification,but current researches mostly use simulated wastewater as experimental water,and studies using actual domestic wastewater are rarely reported.In this paper,the secondary treatment effluent of a sewage treatment plant is used as experimental water,and the denitrification performance of VR in 8 different regions of my country is evaluated through analysis systems such as shake flask experiment research and TOPSIS evaluation model;Denitrification and phosphorus removal performance and nitrogen transformation characteristics of the constructed wetland substrate system within 206 days;combined with Optical Microscope(OM),Scanning Electron Microscope(SEM),X-ray fluorescence diffraction(XRD)characterization,clarified the nitrogen removal mechanism of the substrate system,research results Provide theoretical reference for the application of VR substrate.The main conclusions are as follows:(1)At three temperatures(5,15 and 25°C),the removal of ammonia nitrogen by VR is a rapid process.The ammonia nitrogen removal rate can reach 84.6% in the first 1 hour,and the ammonia nitrogen concentration can reach the surface level V water after 2 hours(Except Baoshan VR).The sorption effect of VR on ammonia nitrogen is better at low temperature.As temperature increases,the equilibrium sorption capacity of ammonia nitrogen decreases.The sorption of ammonia nitrogen by VR is mainly between the sorption between single-layer molecules and multilayer molecules.According to the evaluation of TOPSIS model,the Ulanqab VR has the best comprehensive denitrification performance among the eight VRs.(2)Within 206 days,the average removal rate of ammonia nitrogen for the single gravel packing system was 66.8%,slightly higher than that of VR packing 49.8%;the single VR packing system the average removal rate of total nitrogen was 13.5%,which was significantly higher than that of gravel packing 6.1%.The combined VR substrate system(VR-gravel)has good removal of ammonia nitrogen and total nitrogen,and its average removal rate is 37.6% and 16%,respectively.The average removal rate of ammonia nitrogen and total nitrogen of the combined gravel packing(gravel-gravel)is 51.4% and 12.6%,respectively.It can be seen that in the actual sewage treatment,compared with the classic gravel packing,the VR packing has no outstanding advantages;the nitrification and denitrification performance of the gravel packing is more prominent,and the denitrification effect of the VR packing is slightly stronger.In view of this,the mixed use of the two substrates is expected to improve the removal of ammonia nitrogen and total nitrogen in the system.(3)Through OM and SEM,it was found that a series of short rod-shaped bacteria developed on the surface of VR and gravel.The biofilm on the surface of gravel is dominated by white crystals,while the biofilm on the surface of VR shows white(mineral surface)and yellow particles(in honeycomb pores).XRD analysis found that VR and gravel substrates are rich in iron,aluminum,calcium and other metal elements.After long-term use,the element composition and structure of the substrates change,indicating that the substrate itself participates in the sorption reaction during the sorption process.