Research On The Efficiency And Mechanism For Intensified Denitrification Of Bio-substrate In Subsurface Wastewater Infiltration System

Subsurface Wastewater Infiltration?SWI?system has good ability in removing pollution in water,but the efficiency of nitrogen is still to be improved.Therefore,three Apparatus were established in a pilot laboratory with red soil,cinder and Bio-substrate in delamination.The study focused on the physicochemical property of fillings and sewage efficiency,taking the performance and mechanism of denitrification as the mainly studied.The main conclusions are:1)The study of hydraulic permeability,absorption property and the carbohydrate of soil,cinder and Bio-substrate showed that they have suitable performance in hydraulic.Filling in the vertical direction packing could made good use of capability of them in vertical direction.,improving redox environment of the system.Soil and cinder has stable ability in adsorbing NH₄⁺-N and TP,the maximum adsorbing capability of NH₄⁺-N and TP for soil were 0.873 and 0.227 mg/g,respectively,while for cinder were 1.014 mg/g and 0.232 mg/g,respectively.Bio-substrate can release NH₄⁺-N and TP in condition of the initial concentration lower than 50 mg/L,the other pollution could release in the same time,and the sustained release time was about 20d.Different fillings can make full use of there performance for infiltration system.2)The addition of Bio-substrate were 62%,42%,0 in Apparatus?,Apparatus?,Apparatus?,respectively.The removal performance was inspected in different hydraulic loading.The result showed that the average efficiency of COD were above75%,and TP were above 98%in all Apparatus at every loading.Hydraulic loading has great influence on nitrogen removal in SWI.15 cm/d was the best operation condition for comprehensive comparison in efficiency,ability and operation time for it,the average efficiency of NH₄⁺-N were 27.55%,75.59%,80.00%,TN were 34.35%,60.63%,57.96%,respectively.3)Adding Bio-substrate intensified nitrogen removal in SWI,The best nitrogen removal efficiency at the load of 15 cm/d was in Apparatus II,then the average effluent rate reduced from 2.68 m L/min to 2.43 m L/min,hydraulic conductivity was decreased compared with Apparatus?,effluent total nitrogen contained 45.9%,46.8%for NH₄⁺-N and NO₃^--N,respectively.The intensified for nitrogen removal of Bio-substrate was improved redox environment,provided favourable environment for denitrification in SWI.4)Basis on the results of nitrogen removal effience,the mechanism of intensified denitrification of Bio-substrate was investigated for the changes rule of pollutant,enzyme activity along the deepness,the structure of microbial community.The results showed that the removal of TN was mainly completed in 60⁸0 cm layer,and then Bio-substrate released organic matter in 80 cm layer,the C/N ratio was 6.78,the organic matter could add carbon source for denitrification,enhancing enzyme activity,especially Ure and NIR.The dominant species in SWI is deformation and acid bacillus in phylum level.The relative abundance of Alphaproteobacteria in 60cm layer,Betaproteobacteria and Gammaproteobacteria in 80 cm layer were increased by 6.58%,1.19%,10.35%,respectively.The abundance of functional denitrification bacteria as Bradyrhizobium,Pseudolabrys,Rhodanobacter,Dongia,Rudaea were increased by 1.12%,1.90%,6.57%,2.55%,3.42%,respectively.for adding Bio-substrate in SWI.