Innovation for rapid denitrification in biofiltration systems
Biofiltration systems are an effective technology for removal of nitrogen from stormwater. It has recently been proposed to harness these systems for treatment of other water types (such as light wastewater and polluted groundwater) during dry weather periods. Light wastewater, namely greywater and secondary treated wastewater contains nitrogen at levels five to ten times higher than stormwater. At present, these systems cannot effectively attenuate nitrogen at such concentrations primarily as a result of limited denitrification rates. The objective of this study was thus to identify suitable electron donors that can promote rapid denitrification in the lower saturated zone of biofiltration systems. Eight different carbon substrates comprising both liquid and solid materials were selected, namely cracked corn, rice hulls, cotton, hardwood, softwood, brewer’s spent grain, brewery wastewater and sodium acetate. Batch scale denitrification tests were conducted to study their nitrate removal rates in a pure nutrient medium, light greywater and secondary treated wastewater. The relative removal efficiencies after 48 hours of incubation in the pure nutrient medium was: sodium acetate > cotton > spent grain > rice hulls > brewery waste > cracked corn > softwood > hardwood. The results found that light greywater possesses sufficient biological oxygen demand to induce satisfactory denitrification rates. Spent grain, cotton and rice hulls are promising candidates for promoting equally high rates in pure nitrate water and light greywater. The behaviour of cotton and rice hulls is not affected by the choice of water media.
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