[Nitrogen Removal and the Characteristics of Denitrification Bacteria Using NUA-DAS Ecofilter]

A small-scale combined ecofilter was constructed using neutralized-used acid residue (NUA) and dewatered alum sludge (DAS), and the nitrogen removal for wastewater treatment and characteristics of denitrification bacteria using the NUA-DAS ecofilter were studied. After the system was stabilized, the average removal rates of COD, TN, NO₃^--N in the final effluents were 60%, 70% and 95%, respectively, and the range of NO₃^--N concentration in the effluents was only 0.02-0.55 mg·L^-1. Furthermore, the richness and similarity of three types of functional genes (nirS, nirK and nosZ) for denitrification in different substrates during the operation period were analyzed using PCR-DGGE method. These results showed that the richness of all denitrification bacteria at NUA and DAS increased remarkably after operation for 30 and 60 days compared to that in fresh substrate, and the richness was basically the same for the same kind of gene at the identical substrate regardless of depth gradient and operation period. The richness of nirS, nirK and nosZ detected in the NUA and DAS followed the order of nosZ > nirK > nirS. It was also revealed that spatial location had an apparent influence on the community structure of denitrifying bacteria (nirS, nirK and nosZ) but operation time had no obvious effect. Finally, nirK might be the most suitable for the environment in the system, and the adaptive capacity of denitrification bacteria (nirS, nirK and nosZ) in NUA could be superior to that in DAS.