DYNAMICS WITHIN A YARD-WASTE COMPOST BIOFILTER DURING AMMONIA BIOTRANSFORMATION

Laboratory-scale biofilters were made with oven-dried compost and inoculated with: 1) a wastewater activated sludge (WW); 2) a diluted wastewater treatment plant nitrifying seed culture, NitroBac 100G (NB); or, 3) mixed with distilled, deionized H2O. The biofilters were fed an air stream with NH3 gas at between 15 to 130 ppm concentration. Observing concentrations of total ammoniacal nitrogen (TAN), nitrate (NO3−) and pH, indicate that dissolved and adsorbed TAN did not always reach equilibrium with the gas phase suggesting that the microbial activity was capable TAN removal faster than the loading rate.Constants for a Michaelis-Menten kinetic model were determined using inlet and outlet gas measurements. For inoculated biofilters, KS=100 mg N/ kg dry compost and Rmax=679 mg N/ kg dry compost-day while the uninoculated compost showed constants of KS=48 mg N/ kg dry compost and Rmax=415 mg N/ kg dry compost-day.As NO3− ions increased, the measured compost pH was observed to decrease. This decrease was correlated with increasing NO3− concentration resulting from the nitrification process. With the use of a titration curve and a factor needed to correct for other reactions which may be occurring, the pH changes were modeled.Liquid media tests were used to assess relative nitrification and TAN degradation reaction rates when inoculated with biofilter material. Generally, TAN degradation rates within liquid media decreased slightly when the biofilter was exposed to NH3 gas. On the other hand, NO3− production rates increased suggesting that the microbial nitrifying population was increasing.