Successful Evaluation of Ten IFAS and MMBR Facilities by Applying the Unified Model to Quantify Biofilm Surface Area Requirements for Nitrification, Determine Its Accuracy in Predicting Effluent Characteristics, and Understand the Contribution of Media...

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The performance of ten full scale wastewater treatment facilities applying IFAS and MBBR systems was evaluated using the Unified Model for Activated Sludge, IFAS and MBBR systems. At each facility, the model was applied to compute the biofilm surface area required to achieve nitrification based on the plant loading, mixed liquor temperature and aerobic mixed liquor MCRT. The effluent ammonium-N was then computed for the amount of biofilm surface area
installed and compared to the plant effluent. The analysis showed that the model was able to accurately predict the performance of the facilities (9 out of 9 for which data exists for average loads, 6 out of 6 for peak loads). When the quantity of media installed exceeded the amount computed by the model (% of Media Required that is Installed is > 100%), the observed data showed that the plant was able to achieve less than 2 mg/L under average flow and less than 3 mg/L under diurnal peak load. What is significant is that when the quantity of media installed was less than the amount computed by the model, the plant was not able to nitrify adequately. This was observed at two out of the ten facilities where the model showed that the effluent ammonium-N would exceed 5 mg/L. The results of the model can be applied to determine the additional amount of biofilm surface area (and media) that is required to achieve satisfactory nitrification. Alternatively, for IFAS systems, the model shows how much the aerobic mixed liquor MCRT would have to be increased in lieu of increasing the amount of biofilm surface area. A series of nomographs were generated to enable a designer to determine the biofilm surface area based on temperatures, 4 hour peak to diurnal average loadings and BOD5:TKN ratios.

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