Ammonia Removal and Degradation Within Laboratory-Scale Yard-Waste Compost Biofilters

摘要

Yard-waste compost, a common ingredient for biofilter solid media, was investigated as a biofilter solid material for ammonia (NH3) adsorption and microbial support. A gas source was generated by combining humid air with anhydrous NH3 for controlled concentrations of between 5 and 180 ppm NH3. Oven-dried compost was mixed with 3 separate supplements: distilled, deionized H2O; a wastewater activated sludge inoculum (WW); or, a diluted wastewater treatment plant nitrifying seed culture, NitroBac 100G (NB). Concentrations of total ammoniacal nitrogen (TAN) and pH were measured at various times to analyze NH3 adsorption equilibrium after H2O addition, and microbial activity after inoculation. Using Henry's law and an NH3 acid dissociation constant, TAN concentrations in H2O (TAN_(H2O)) were calculated and subtracted from measured TAN resulting in values for TAN associated with solids (TAN_(SOL)). In equilibrium studies, initial compost pH was altered from 5.0 to 11.0 by addition of either HCl or NaOH. Exposure to 50 ppm NH3 gas resulted in a pH shift which is described by the equation triangle openpH = -0.6(pHi) + 5.85. Wet compost with initial pH values ranging from 5.0 to 10.0 were exposed to between 5 to 180 ppm NH3 gas. TAN_(SOL) values were correlated with TAN_(H2O) values to establish a solid-liquid partitioning relationship. A Langmuir isotherm model was fit to data and resulted in the relationship TAN_(SOL) = 4148(TAN_(H2O))/(477+TAN_(H2O)), where TANsol and TAN_(H2O) are mg N/ kg dry compost and mg N/ L H2O, respectively. Microbial degradation of NH_4~+ in compost was observed with and without inoculation at several NH3 gas concentrations under steady-state conditions during 4 week-long experiments. Compost with H2O (no inoculum) showed minimal NH3 degradation with no measurable nitrification. A WW and NB inoculum demonstrated nitrification with an NH3 removal efficiency of up to 90% and 99%, respectively. Microbial activity was substantially reduced when NH3 gas concentrations reached near 160 ppm. A Michaelis-Menten kinetic model was used to describe NH_4~+ degradation.