| dc.description | The overall objective of this thesis was to develop an improved understanding of recirculating biofilters that would lead to a more robust design approach for the sustainable implementation of these on-site systems. To obtain this objective, this study involved the use of bench-, pilot- and full-scale RBF systems in a series of controlled and uncontrolled experiments to analyze various impact factors on RBF performance. At the bench-scale, the factors investigated included hydraulic loading rate, dosing frequency, recycle ratio and filter media. The results showed that dosing frequency had a significant impact on RBF performance in terms of BOD5 removal. Based on this conclusion, a target study compared five different dosing frequencies (including 48, 96, 144, 192 and 240 times per day) for municipal wastewater treatment. The results of the bench-scale experiments showed that a dosing frequency of 192 times per day could provide improved performance as compared to other dosing frequencies tested in this study. In addition, this research also conducted a series pilot-scale RBF experiments to examine the impact of ventilation locations on RBF performance. The experimental results showed that the RBF ventilated from both the top and the bottom sidewall of the filter bed could provide better performance than the RBFs ventilated from the only the top or the bottom sidewall of the filter beds. Four field-scale RBF systems were evaluated in this study to compare the long-term performance of RBFs treating multi-residential wastewater. Both bench- and field-scale studies found that crushed glass could be applied as an effective RBF medium. It was also found that geotextile could be another effective medium for RBFs. Although peat is widely applied in single-pass packed bed filters for domestic wastewater treatment, this study found that peat could not provide satisfactory performance as a RBF medium based on poorer removals of BOD5 and ammonium (NH 4+-N). Finally, this study investigated a dual-media RBF for treating municipal wastewater with geotextile and crushed glass as filter media. The filter beds were filled with these two types of media at five different volume ratios. Specifically, a crushed glass to geotextile volume ratio of 100:0, 75:25, 50:50 and 25:75 were evaluated at the bench-scale. The dual media RBFs were operated at both a low hydraulic loading rate (HLR) (i.e., 0.12 m3/m2/day) and a high (i.e., 0.40 m3/m2/day) HLR. The results showed that the dual media RBF with the geotextile volume percentage of 25% could provide better performance than the other RBFs tested in this study under both the low and the high HLRs. | en_US |
