Study On NO Removal Via Anammox In Tower Biological Filter

Nitrogen oxides (mainly composed of NO) are major atmospheric pollutants, which are harmful to ecological environment and human health. Existing physical and chemical technologies for NO removal have some disadvantages, such as, requirement of rigorous condition, deactivation of expensive catalyst, generation of secondary wastes. However, biological NO removal technologies have advantagies of easy operation and low capital cost. Compared with NO removal technology via denitrification, anaerobic ammonium oxidation (anammox) technology has no external carbon demond and no greenhouse gas emission. Therefore, NO biological removal technology via anammox could provide a new method for NO removal, meanwhile increases the variety of substrate for anammox bacteria.In this study, tower biological filter was adopted for NO removal, using volcanic rock as biofilm carrier. Using NH4+-N and NO2- -N as substrates, the anammox biofilm was formed successfully after initial 31 days. Afterwards, NO with different concentration was induced from the bottom of filter, while artificial nutriuent containing NH4+-N and NO2--N (no NO2-N in final experimental period) was pumped from the top of filter. The effect of diffirent influent and NO concentrations on NO removal was investigated. The main experimental results are as follows:(1) Anammox was fulfilled directly by using NO as electron acceptor, and NH4+-N as electron donor. The reaction ratio of NH4+-N consumption:NO-N consumption:NO3--N production was 1:1.12:0.11.(2) With NO level was increased from 4018 mg/m3 to 8,036 mg/m3, the biofilm color changed to black. Meanwhile, the anammox activity deterioriated with TN removal load and NO removal rate decreased by 47.1% and 69.6%, respectively. The proportion of NO-N in electron acceptor decreased from 78.8% to 43.1%. Subsequently, by increasing influent NO2--N concentration from 20 mg/L to 60 mg/L, the anammox activity recovered with TN removal load and NO removal rate increased by 2.4 and 2.1 times, respectively.(3) When influent NO2--N was 20 mg/L, NO concentration was 4018 mg/m3, gas empty tower retention time was 2.3 min, temperature was 38℃, the maximum NO removal load reached 165.8 g NO-N/(m3d) with NO removal efficiency of 54.2%. While without NO2--N in influent and with same other operational conditions, the maximum NO removal load reached 132 g NO-N/(m3d) with NO removal efficiency of 43.1%. (4) The 16S rDNA results show that the percentage of anammox bacteria among whole bacteria community of biofilm was 80.9%, while the major population of anammox was Candidatus Kuenenia stuttgartiensis whose proportions was 89.1%.