Analysis of very-high surface area 3D-printed media in a moving bed biofilm reactor for wastewater treatment

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.

Fig 1. Images of commercial (K1) and fabricated (gyroid) biocarrier designs examined in this research.

(a) Kaldnes K1; (b) small specific surface area gyroid; (c) medium specific surface area gyroid; (d) large specific surface area gyroid.

Fig 2. Bench-scale MBBSBRs used for experimentation; (a) photograph of one system containing 6 reactors; (b) side-view schematic; (c) top-view schematic.

Fig 3. Schematic of the experimental design for the three experiments.

(a) Experiment 1, testing constant biocarrier fill ratio; (b) Experiment 2, testing constant total biocarrier surface area; (c) Experiment 3, testing constant number of biocarriers. Diagram not to scale.

Fig 4. Pooled results for total ammonia nitrogen and nitrate nitrogen concentrations over time for (a) Experiment 1, constant biocarrier fill ratio; (b) Experiment 2, constant biocarrier total surface area; (c) Experiment 3, constant biocarrier count.

Error bars represent standard deviation.

Fig 5. 8-hour total ammonia nitrogen (TAN) percentage change for each biocarrier type in each experiment (error bars represent standard deviation).

Fig 6. Total ammonia conversion for each biocarrier as a function of (a) total surface area per treatment, and (b) specific surface area of the biocarrier, for Experiment 1, constant fill ratio.