Nitrogen discharges from decentralized wastewater treatment (DWT) systems contribute to surface and groundwater contamination. However, the high variability in loading rates, long idle periods and lack of regular maintenance presents a challenge for biological nitrogen removal in DWT. A Tire-Sulfur Hybrid Adsorption Denitrification (T-SHAD) process was developed that combines nitrate (NO3(-)) adsorption to scrap tire chips with sulfur-oxidizing denitrification. This allows the tire chips to adsorb NO3(-) when the influent loading exceeds the denitrification capacity of the biofilm and release it when NO3(-) loading rates are low (e.g. at night). Three waste products, scrap tire chips, elemental sulfur pellets and crushed oyster shells, were used as a medium in adsorption, leaching, microcosm and up-flow packed bed bioreactor studies of NO3(-) removal from synthetic nitrified DWT wastewater. Adsorption isotherms showed that scrap tire chips have an adsorption capacity of 0.66 g NO3(-)-N kg(-1) of scrap tires. Leaching and microcosm studies showed that scrap tires leach bioavailable organic carbon that can support mixotrophic metabolism, resulting in lower effluent SO4(2-) concentrations than sulfur oxidizing denitrification alone. In column studies, the T-SHAD process achieved high NO3(-)-N removal efficiencies under steady state (90%), variable flow (89%) and variable concentration (94%) conditions.

Department of Civil and Environmental Engineering University of South Florida 4202 E Fowler Ave ENB 118 Tampa FL 33620 USA

Department of Civil and Environmental Engineering University of South Florida 4202 E Fowler Ave ENB 118 Tampa FL 33620 USA; Department of Civil Engineering University of Jordan Amman 11942 Jordan

Department of Water Technology and Environmental Engineering Institute of Chemical Technology Prague Technicka 5 166 28 Prague 6 Czech Republic

Department of Water Technology and Environmental Engineering Institute of Chemical Technology Prague Technicka 5 166 28 Prague 6 Czech Republic; Department of Civil and Environmental Engineering University of South Florida 4202 E Fowler Ave ENB 118 Tampa FL 33620 USA

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