A pilot-scale study of a novel two-stage denitrification filter

In this study, a pilot-scale two-stage denitrification filter (TSDNF) was developed to further remove the effluent nitrate from a cyclic activated sludge system. Sponge iron and volcanic rock were used as DNF-1 and DNF-2 filter beds, respectively. A single-stage DNF-3 filter with volcanic rock was used as the control. Most dissolved oxygen (DO) was consumed for iron oxidation in the DNF-1, and in turn denitrification rates increased in the DNF-2. In the DNF-1, 17.9 %+/- 13.6 % of the NO3--N was removed in the absence of organic carbons, resulting in a significant increase in the total NO3--N removal in the TSDNF with a COD/NO3--N ratio of about 2.6. Autotmphic denitrification should be finished by the dominant Fe(II)-oxidizing nitrate-reducing Gallionellaceae genus (21.38 %) in the DNF-1, while common denitrifying strains were dominant in both DNF-2 and DNF-3. Moreover, obvious chemical phosphorus removal (83.3 %) was found in the DNF-1. Therefore, simultaneous autotrophic denitrification and chemical P-removal can be achieved using iron ions released from sponge iron filters, which provides a new model to reshape the design of advanced removal of nitrogen and phosphorus in the secondary clarifier effluent.

Automated summary

A pilot-scale two-stage denitrification filter system was developed, using sponge iron and volcanic rock as filter media, for efficient removal of nitrate and chemical phosphorus. The experiment demonstrated that iron ions released from sponge iron filters can achieve simultaneous autotrophic denitrification and chemical P-removal, providing a new approach for nitrogen and phosphorus removal in secondary clarifier effluent.