Study On Nitrogen Removal Performance Of Low C/N Acclimated Bio-floc

Microorganism in bio-floc decompose organic and inorganic nitrogen in aquaculture water mainly through metabolic pathway of ammonification,assimilation,nitrification and denitrification.At present,aquaculture system based on Bio-floc technology?BFT?,adds a lot of carbon source to promote the rapid growth of heterotrophic microorganisms,which is to ensure rapid degradation of harmful substances.Carbon sources are consumed a lot,and the dissolved oxygen fluctuates violently,in which way may lead to high cost of the aqaaculture.The nitrogen load of aquaculture drainage is closely relate to the breeding density,feeding amount and the biological nitrogen budget of culture.Meanwhile,the treatment performance of bio-floc on the harmful nitrogen in aquaculture water directly affects the production of the aquaculture system.Through sequencing batch method in a way of aerobic and anoxic operation,the study acclimated bio-floc at low C/N,then analysed the microbial community structure and related nitrogen metabolism pathway for acclimated bio-floc,and study on the removal performance of inorganic nitrogen.Finally,the effect of the organic nitrogen load of aquaculture water on the removal performance of bio-floc was preliminary studied.The research results have important practical significance for the application of bio-floc in aquaculture water treatment.The main results are as follows:The bio-floc was acclimated at low C/N ratio through SBR during 240days,in the process of which the amount of carbon source was gradually reduced,C/N ratio adjusted from 15 to 7.9.The water quality results showed that,NH₄⁺-N and NO₂^--N concentration in effluent was remained below 0.5 mg/L and 0.1 mg/L respectively,coupled with NO₃^--N below 57mg/L,and sludge volume index was no higher than 60 mL/g during 240days cultivation and acclimation,which illustrated the bio-floc had high activity and good sedimentation property.From the metagenome data with 431534 high-quality DNA sequences,obtained from high-throughput sequencing technology at the bio-floc that C/N ratio was kept at 7.9,and water quality stable.Amazing biodiversity was showed in the bio-floc,which included 39 phyla,48 class and 233genera.Proteobacteria was the most abundant phylum,whose proportion was up to 48.72%.In low C/N ratio acclimated bio-floc,the ratio of functional genes for nitrogen metabolism was 0.9%.Among five processes of nitrogen metabolism,the most abundant genes was ammonification,which was 37.77%,followed by denitrification was 28.99%,assimilation was 20.92%,nitrification was 11.14%,and nitrogen fixation was 1.18%.Low C/N acclimated bio-floc with abundant carbon source and without additional carbon source.Based on this,autotrophic nitrification?AN?,heterotrophic nitrification and aerobic denitrification?HN-AD?and anaerobic denitrification?An-D?performances were studied to evaluate the existence of these three biochemical processes and their removal efficiencies of inorganic nitrogen.The results showed that,bio-floc had the characteristics of high autotrophic and heterotrophic nitrification activities after acclimating under low C/N ratio condition,with NH₄⁺-N removal percentages of 97.10%and 100.00%,respectively.Ammonia oxidation stage was the rate-determining step in AN process,and special ammonia oxidation rate of AN process achieved 13.17 mg/?gVSS.d?,slower than special nitrite oxidation rate of 29.20 mg/?gVSS.d?.Heterotrophic special ammonia oxidation rate was 40.28 mg/?gVSS.d?,about 3 times of autotrophic special ammonia oxidation rate.Due to the existence of simultaneous nitrification and denitrification?SND?,consumption of alkalinity and removal of TIN in HN-AD process were both higher in comparison with heterotrophic nitrification.In HN-AD process,3.34 g alkalinity was required with per g NH₄⁺-N removed?calculated as CaCO₃?,while 4.30 g alkalinity was needed in AN process.TIN removal in heterotrophic nitrification was 53.69%.HN-AD process appeared higher nitrite accumulation phenomenon,and the highest accumulation rate of nitrite reached 46.37%,while mass concentration of NO₂^--N was 2.62mg·L^-1.In AN process,nitrite accumulation rate was only 3.31%,and mass concentration of NO₂^--N was 0.47 mg·L^-1.The study on AN and HN-AD process of bio-floc which was acclimated by low C/N ration which would provide some theoretical preference for bacterial orientational cultivation and its application in aquaculture water treatment.Bio-floc,that was inoculated in SBR,where bio-floc was acclimated with low C/N,was put into runway system with effective volume 2 m³,and have gradually improved the amount of organic nitrogen?feed?in the runway system.In this study,the effect of the nitrogen removal performance on the runway bio-floc system was studied,with the organic nitrogen load gradually increased from 7.91 gTON/kgMLSS·d to 78.47gTON/kgMLSS·d.The results illustrated that NH₄⁺-N was 0.5mg/L up and down fluctuation,NO₂^--N concentration in effluent was remained below0.1 mg/L,and NO₃^--N was less than 6mg/L.In the process of study,the highest consumption of COD and alkalinity were 279.44 mg/L and 38.54mg/L respectively,while its rate accounting for 64.45%and 18.93.With the increase of organic nitrogen load,the water treatment time was prolonged,and the water quality could reach a stable state within 7 h,which could meet the culture requirement of tilapia.