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Start-up and monitoring data from the first 13 months of operation of a full-scale MBBR for nitrification indicated that the system was capable of achieving the effluent NH3-N objective of 6 mg/L at influent loadings exceeding the design loading (0.84 g/[m2-d]) and an average detention time just under five hours. During warm weather operation, with an average effluent temperature of 18.9°C, the influent concentration and loading were 20.4 mg/L and 0.93 g/(m2-d). The corresponding effluent concentration and removal rate were 3.5 mg/L and 0.77 g/(m2-d). During cold weather operation, with an average effluent temperature of 11.8°C, the influent concentration and loading were 23.4 mg/L and 0.96 g/(m2-d). The corresponding effluent concentration and removal rate were 6.1 mg/L and 0.71 g/(m2-d). Removal rates observed for summer and winter operation indicate only a slight reduction in performance between the two temperature regimes. The reduction in performance associated with colder water temperatures appears to be, to some extent, offset by increased DO concentrations.

By visual observation, a minimum air flow rate of 0.12 standard m3/(m2-min) (0.4 scfm/ft2) was required to thoroughly mix the media throughout the basin. Hydraulic evaluation and in-basin monitoring indicated that performance might be enhanced by improving influent dispersion and minimizing short-circuiting in the MBBR. The data also imply that, for any MBBR, the basin configuration, inlet piping, and mixing system can be optimized. Increasing the basin length-towidth ratio, using multiple inlet points, increasing mixing intensities (aeration or mechanical mixing) at the inlet point, or baffles may be beneficial.

Document Type: Research Article


Publication date: January 1, 2004

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