The denitrification sludge from high-efficiency denitrification reactor in laboratory was utilized as inoculation sludge to start autotrophic sodium hexametaphosphate-Fe2+ denitrification reactor.The nitrogen removal efficiency and microbiological characteristics of the iron salt nitrogen removal process was investigated through a 88-day continuous operation using simulated wastewater.The results showed that,at a nitrate nitrogen volumetric load of 0.42 kg/(m3·d),the maximum stable nitrogen removal load was 0.41 kg/(m3·d);similarly,at a Fe2+ volumetric load of 4.92 kg/(m3·d),the maximum iron removal load was 2.77 kg/(m3·d).The reactor exhibited a nitrate and Fe2+ removal rates of 94.6%and 52.6%respectively during stable operation,maintaining optimal performance for 28 days.By the 82th day of the operation,the color of granular sludge changed from yellow to grayish brown,accompanied by particle disintegration.The specific activity of the sludge gradually increased,the specific denitrification activity increased from 0.71 to 2.3 mg[N]/(g[VSS]·h),showed a significant increase of 224%,and the specifica iron oxidation activity increased from 7.3 to 15 mg[Fe]/(g[VSS]·h),showed a notable increase of 105%.As a new autotrophic denitrification technology,sodium hexametaphos-phate-Fe2+nitrogen removal technology not only enhances the biological activity and denitrification activity of living bacteria,but also prolongs the efficient denitrification period of ferric denitrized sludge.
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