Denitrification behavior in a woodchip-packed bioreactor with gradient filling for nitrate-contaminated water treatment

Abstract

Woodchip solid-phase denitrification bioreactors (SPDRs) are widely applied to remove NO3− from water. In this study, two SPDRs with different woodchip filling patterns, namely a gradient filling bioreactor (G-SPDR) and a uniform filling bioreactor (U-SPDR), were constructed and their denitrification performances were investigated. Analysis of the NO3− removal pathway along the water flow path showed that NO3− removal rates could be enhanced using the G-SPDR (35.66–174.55 mg N·L−1·d−1) compared to the U-SPDR (25.17–111.72 mg N·L−1·d−1) at an appropriate flow rate (0.3–1.8 mL·min−1). In addition, the G-SPDR promoted complete denitrification with low NO2− accumulation. Chamber model analysis showed that the maximum NO3− removal rate was closer to the inlet in the G-SPDR. Furthermore, the optimum reaction height was 25 cm for the G-SPDR and 35 cm for the U-SPDR, implying that gradient filling could reduce the size of the bioreactor. Therefore, gradient filling is a promising and cost-saving method to construct SPDRs for the bioremediation of NO3− contaminated water.