Study On Function Of Carbon Release And Enhanced Microbial Denitrification Process Of Multi-Carbon Source Composite Carriers

The successful denitrification requires to provide enough carbon source as electron donor.Among the existing solid carbon sources,the content of cellulose water-soluble organic matter in agricultural carbon source was high,which was easy to cause secondary pollution of water;the period of artificially synthesized carbon release was long,but it was mainly used as a microbial carrier material in the later stage.However,the research on composite carbon sources mostly focused on carbon release and denitrification efficiency.There were relatively few studies on the mechanism of the carbon release amount and denitrification utilization of carbon sources.In this study,a complementary cellulose-based agricultural carbon source and a synthetic carbon source were coated by a freeze-crosslinking method into a coagulating synthetic material,polyvinyl alcohol-sodium alginate(PVA-SA),to prepare a multi-carbon source.The multi-carbon source(NCC),its carbon release mechanism and carbon source utilization pathway,denitrification process and microbial community structure were alse studied.The main research results were as follows.(1)The multi-carbon source composite carrier combined solid carbon sources with complementary performance to improve the carbon release amount and cycle.During the 20d carbon release cycle,the cumulative release TOC of from PCL,PBS,PVA-SA,CC,and PS were 3.19mg/g,3.49mg/g,5.42mg/g,29.44mg/g,and 26.95mg/g,respectively.In the rapid carbon release stage,the N of PCL and PBS was 0.3-0.45 and the carbon source release process depended mainly on the diffusion;The N of PVA-SA was 0.6632 and the carbon source release process included diffusion corrosion and skeleton;The N of CC and PS was more than 1 and the carbon source release process depended skeleton corrosion;In the slow carbon release stage,the release index N of all carbon sources was less than 0.12,and the release process of carbon source depended on diffusion.Considering the combination of PCL and CC,PCL and PS,PBS and CC,PBS and PS,which were complementary in performance,as a carbon source material.And they were coated into PVA-SA by freeze-crosslinking method to prepare a multi-carbon source composite NCC-I,NCC-II,NCC-III,NCC-IV.(2)The performance improvement of NCC was evaluated by carbon release,structure and other indicators.The results showed that? The maximum carbon release amount of NCC-I,NCC-II,NCC-III and NCC-IV in 7d were 3.92mg/g,4.68mg/g,4.87 mg/g,4.86 mg/g,respectively.And the stability and durability of carbon release were optimized compared to the constituent materials.?The carbon release process followed the first-order equation,Higuchi and Ritger-Peppas equations.In the fast carbon release stage,the value of N was ranging from 0.54 to 0.59,while in the slow carbon release stage was ranging from 0.11 to 0.16.?The released amount of carbon source increased as the ambient temperature increasing.(3)NCC-I was used to reinforce the denitrification process.The results showed that:?The removal rate of nitrate nitrogen in the DK group(without supplemental carbon source)was 46.7%.The nitrate nitrogen was completely removed after adding NCC-I.?the utilization rate of dissimilated denitrifying carbon source was 13.24%,while that of assimilated denitrifying carbon source is 17.21%.?In a certain range,the temperature affected the carbon source release and activated sludge activity of NCC-I.The higher the temperature,the higher the denitrification denitrification efficiency.Hydraulic conditions affect the aggregation and growth of activated sludge,and the smaller the hydraulic disturbance,the higher the denitrification eff-iciency.(4)The removal rate of TN was increased by more than 60%after NCC-I was used in biological denitrification.The activated sludge was closely related to the smooth progress of the denitrification process.Therefore,the high-throughput sequencing was used to study the composition of the activated sludge community.The results showed that:?NCC-I promoted the growth of hypoxia or anaerobic bacteria such as Denittrasoma and Thauera,and the growth of hoterotrophic bacteria using carbon source organic matter as nutrients such as Acidovorax.Their increase were beneficial to the smooth progress of denitrification.?As the DO condition of the denitrification system was below 2mg/L,which was not conducive to the growth of aerobic bacteria such as Nitrosomonas and Nitrospira.?By comparing Shannon and Simpson,the abundance and diversity of activated sludge species were improved after NCC-I was used as a carbon source for denitrification.