Evaluation of Biofilter Denitrification with Solid-State Electron Donors

Abstract

Nitrogen removal is increasingly required in the small-scale systems that treat a significant quantity of U.S. wastewater. A variety of local-scale technologies provide effective nitrification, but significant residual nitrate may be contained in effluents. Saturated biofilters with solid-state electron donors can provide effective biochemical reduction of nitrate and nitrite (denitrification), enabling small-scale systems to achieve high total nitrogen removals. An experimental study was conducted to measure the nitrate removal performance of denitrification biofilters containing various solid-state election donors. Eleven saturated biofilters were operated in parallel on nitrified municipal wastewater. Each biofilter was a 7.5 cm inner diameter vertical column containing a 91 cm depth of media. Operation was in single pass upflow mode at hydraulic loadings of 41 to 83 cm/day. Nine columns contained organic media, including southern pine, bamboo, bagasse, cypress, and other organic media (heterotrophic denitrification). Two columns contained an inorganic electron donor, elemental sulfur, which supports autotrophic denitrification. To characterize performance, nitrate, nitrite, and supporting water quality parameters were monitored in influent and effluent over a multiple month period. Solute profiles were also conducted over the biofilter media depths. Data indicate that solid-state biofilters can achieve high fractional reductions of oxidized nitrogen, using in some cases a small fraction of the total media depth. Results will be used to assess candidate media, evaluate biofilter depths, develop design loading rates, and estimate media longevity. This study will support the design of denitrification biofilters that will enable high total nitrogen removals in small-scale wastewater treatment systems.