Studies On Denitrification Performance And Biofilm Characteristics Of The Different Solid Carbon Source-based Denitrication System

In this paper,for the treatment of low C/N wastewater,biological denitrification performances were inspected by the addition of solid carbon sources,including PCL/starch blends,polycaprolactone(PCL),polylactic acid(PLA),polybutylene succinate(PBS)and wheat straw.The effluent organic matters and microbial community evolution in denitrification system with typical solid carbon source were also investigated.Main conclusions are listed as follows:(1)Performances during and after startup of solid carbon source-based denitrification systems were probed by shake flask experiments.Results showed that biodegradability of selected solid carbon sources was in the decreasing order of PCL/starch blends,PCL6500(polycaprolactone of 6500 molecular weight),PCL6800(polycaprolactone of 6800 molecular weight),PBS,wheat straw and PLA,of which the former four carbon source-based systems were started up after 1d,16 d,16d,and43 d,while the last one failed.After startup,the denitrifying rates of systems with PCL/starch blends,PCL6500 and PCL6800 were 0.0372,0.0176 and0.01749mg/(g·h),respectively.Variation of leaching organic matter for each carbon sorces was coincident.DOCs obviously increased on day 1,and then decreased gradually until it remained unchanged.(2)By three-dimensional fluorescence spectroscopy and infrared spectroscopy,organic composition was detected for the effluents from denitrification systems with PCL/starch blend,PCL6500 and PCL6800.Results showed that polysaccharides,proteins,polycaprolactone monomers and polymers and so on constituted the main organics.(3)Microbial community evolution in the course of biofilm formation was inspected by high-throughput sequencing test.With maturation of biofilm,richness of microbial community decreased(Chao index from 196.176 to 105.500),and its diversity decreased and then increased(Shannoon from 3.003 to 2.477 and to 2.983).Uliginosibacterium and Elstera significantly increased with the formation of biofilm.In contrast,immense decrease was observed for Comamonadaceae and Dechloromonas that were aerobic denitrification bacteria.The content of denitrifying functional bacteria was gradually increased.Besides,the denitrification rate wasincreased,which was consistent with the experimental results of denitrification.Due to anoxic conditions,the content of aerobic bacteria was decreased.(4)Fishers ' exact test on family level for the comparison of microbial composition between initial sludge for inoculation and mature biofilm exhibited that debitrifiers including Rhodocyclaceae,Comamonadaceae,Xanthobacteraceae,Cytophagaceae and Sphingobacteriaceae significantly increased(p<0.005),while aerobic bacteria like norank_p_Saccharibacteria and Hydrogenophilaceae colossally decreased(P<0.005).