An evaluation of biological aerated filtration for wastewater treatment through pilot and laboratory scale experiments

In order to seek a reliable and cost-effective secondary process for the upgrade of existing treatment plants; a pilot scale testing and a laboratory scale experiment were conducted individually to evaluate the performance and investigate the treatment mechanisms of Biological Aerated Filtration (BAF) process with respect to treatment efficiency, comparison of two pilot BAF systems (BiostyrRTM and Biofor(TM)), physical properties of filtration media, effects of operational parameters and kinetics study.; In the pilot testing at Ravensview Water Pollution Control Plant (WPCP), both BAF pilot plants demonstrated excellent ability to eliminate substrate and nitrogen in the wastewater. The design objectives could be achieved for more than 95% of the testing period. Compared to Biofor(TM) system, Biostyr RTM performed better for TSS, BOD5, COD and TN removal and showed a stronger resistance to low temperature environments, while Biofor(TM) had an advantage over BiostyrRTM for ammonia nitrogen and TKN removal. The solids yield from Biofor(TM) was about three times as high as that from BiostyrRTM.; The laboratory scale experiment was carried out by simulating a Biostyr RTM system at Queen's University. During the laboratory scale experiment, a quick start-up of the biological aerated filter was observed and the single stage BAF process demonstrated good capacity for the removal of high strength organic matter (COD) and NH3-N. The increase in hydraulic loading reduced the treatment efficiency for COD, NH3-N and TN. The effluent COD of less than 90 mg/L could be reached at the COD loading of up to 8 kgCOD/m 3.d. The annual average compliance limit for NH3-N (11 mg/L) could be obtained at the applied NH3-N loading of up to 0.5 kgNH3-N/m3.d. Under the test conditions, the recommended ratio of process air to water was found to be 5:1 and the backwash rate of 10 L/m2.s was recommended for both water flush and air scouring in the laboratory scale BiostyrRTM column. In the kinetics study, the soluble COD removal followed the first order reaction very well. The reaction rates at three levels of hydraulic loadings verified that the high water velocity negatively affected the substrate removal.; Based on the results from the pilot testing and laboratory scale experiment, it was concluded that the combination of biological oxidation, physical filtration and flocculation of micro organisms contributed to substrate and nutrient removal in the BAF process. Its small footprint and stable performance for wastewater treatment makes BAF a promising alternative to the conventional activated sludge process for the expansion and upgrade of existing primary wastewater treatment plants.