Abstract
Moving Bed Biofilm Reactors (MBBRs) can efficiently treat wastewater by incorporating suspended biocarriers that provide attachment surfaces for active microorganisms. The performance of MBBRs for wastewater treatment is, among other factors, contingent upon the characteristics of the surface area of the biocarriers. Thus, novel biocarrier topology designs can potentially increase MBBR performance in a significant manner. The goal of this work is to assess the performance of 3-D-printed biofilter media biocarriers with varying surface area designs for use in nitrifying MBBRs for wastewater treatment. Mathematical models, rendering, and 3D printing were used to design and fabricate gyroid-shaped biocarriers with a high degree of complexity at three different levels of specific surface area (SSA), generally providing greater specific surface areas than currently available commercial designs. The biocarriers were inoculated with a nitrifying bacteria community, and tested in a series of batch reactors for ammonia conversion to nitrate, in three different experimental configurations: constant fill ratio, constant total surface area, and constant biocarrier media count. Results showed that large and medium SSA gyroid biocarriers delivered the best ammonia conversion performance of all designs, and significantly better than that of a standard commercial design. The percentage of ammonia nitrogen conversion at 8 hours for the best performing biocarrier design was: 99.33% (large SSA gyroid, constant fill ratio), 94.74% (medium SSA gyroid, constant total surface area), and 92.73% (large SSA gyroid, constant biocarrier media count). Additionally, it is shown that the ammonia conversion performance was correlated to the specific surface area of the biocarrier, with the greatest rates of ammonia conversion (99.33%) and nitrate production (2.7 mg/L) for manufactured gyroid biocarriers with a specific surface area greater than 1980.5 m2/m3. The results suggest that the performance of commercial MBBRs for wastewater treatment can be greatly improved by manipulation of media design through topology optimization.
Highlights
Moving Bed Biofilm Reactors (MBBRs) are used for nutrient removal and recovery applications in secondary and tertiary levels of wastewater treatment
The results suggest that the performance of commercial MBBRs for wastewater treatment can be greatly improved by manipulation of media design through topology optimization
The results from Experiment 1, constant Fill Ratio of biocarriers, are presented in Fig 4a, with parameters expressed as pooled Total Ammonia Nitrogen (TAN) and Nitrate Nitrogen concentrations over time
Summary
Moving Bed Biofilm Reactors (MBBRs) are used for nutrient removal and recovery applications in secondary and tertiary levels of wastewater treatment. These applications include pharmaceutical wastewater [1, 2], petroleum contaminated waters [3, 4], pulp and paper industry waste streams [5, 6], piggery wastewater treatment [7], and sustainable nutrient remediation in municipal wastewater treatment [8]. The biocarrier media in MBBRs provide a surface on which a functional microbial biofilm attaches, and mixing in the reactor replenishes nutrient-rich wastewater to the active biofilm surface on each biocarrier. The rate of reaction, determining the overall performance of the reactor, is determined in part by the surface area characteristics of the biocarrier media, including the media size, shape, surface area per unit volume (the specific surface area, or SSA), and the fill ratio in the reactor vessel [9, 11]
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