Footprints and Capital Costs Reduction for Onsite Wastewater Treatment Systems - a Novel Dual Media Recirculating Biofilters

The purpose of this study was to develop a dual media filter bed design for recirculating biofilters (RBFs) for achieving high level treatment to meet the strict wastewater discharge regulations. Five types of filter media were applied in the bench scale RBFs, including two single media (crushed glass or CG, geotextile or GT), and three dual media with CG and GT at different volume ratios (3CG:1GT, 2CG:2GT, and 1CG:3GT). These five types of RBFs were dosed with both low and high hydraulic loading rates (HLR) of 0.20 and 0.80m3 /m2/day, respectively. The effluent parameters including BOD5, NH4+-N, NO3-N, TN, TSS, pH, and fecal coliform were measured and statistically analyzed. The results showed that the dual media RBF of 3CG:1GT dosed with both low and high hydraulic loading rates (HLRs) provided the highest removal for BOD and TSS amongst six dual media RBFs in this study. More importantly, the dual media RBF of 3CG:1GT dosed with the high HLR produced effluents with BOD concentrations even lower than the CG biofilter dosed with a low HLR. However, three clogging occurrences were observed for the CG biofilter dosed with the high HLR during the experimental period, while no clogging problem was found for all the dual media RBFs. This conclusion indicated that the dual media RBF of 3CG:1GT could decrease the footprints for RBFs significantly since HLRs and daily flow rates determine the size of filter beds.