| The currently available comprehensive activated sludge models, ASM#1 and it successor ASM#3, do not adequately describe nitrification and denitrification with respect to ammonia oxidation inhibition, nitrite accumulation or emissions of nitric oxide and nitrous oxide. A new comprehensive activated sludge process model named ASMN (Activated Sludge Model-Nitrogen) is presented. ASMN incorporates two nitrifying populations, the ammonia oxidizing bacteria (AOB) and the nitrite oxidizing bacteria (NOB) using free ammonia (FA) and free nitrous acid (FNA) as the true substrates for the AOB and NOB, respectively. ASMN incorporates four step denitrification reduction of nitrate to nitrogen gas via nitrite, nitric oxide and nitrous oxide using individual reaction specific parameters.; Evaluations using steady state and dynamic conditions of wastewater containing high concentrations of COD, nitrogen, and an AOB inhibitor were conducted at numerous temperature, SRT, dissolved oxygen, and pH conditions as well as with moderate and high salt concentration. The nitrification operating window was defied and denitrification performance was characterized for these conditions.; Process stability studies indicate that pH and temperature are the most important variables in controlling nitrification response to upset conditions. Greatest stability was found at 15°C and a pH value of 7.2, with lower stability at higher temperatures. Greatest stability at 35°C was found at a pH value of 6.8. Contrary to accepted practice, elevated pH (7.5--8.0) is unfavorable to initiating nitrification or recovery from process upset due to FA inhibition.; Emissions of environmentally significant NO and N2O are higher than generally believed, and directly linked to depletion of electron donor in the anoxic reactor. ASMN parameter and process variable sensitivity studies along with guidelines for improved nitrification and denitrification are presented. Two new process parameters to describe mixotrophic growth by NOB and reduced heterotrophic yield under anoxic conditions are presented for the first time in a comprehensive activated sludge mode, along with an improved temperature relationship which, unlike the Arrhenius equation, accurately described the decrease in growth rate for mesophilic microorganisms as temperature exceeds 35°C.; Additional processes describe microbial growth using nitrate (or nitrite) in the absence of ammonia, as well as biodegradation of synthetic organic chemicals. |
