Unraveling encapsulated growth of Nitrosomonas europaea in alginate: An experimental and modeling study.

Encapsulation is a promising technology to retain and protect autotrophs for biological nitrogen removal. One-dimensional biofilm models have been used to describe encapsulated systems; they do not, however, incorporate chemical sorption to the encapsulant nor do they adequately describe cell growth and distribution within the encapsulant. In this research we developed a new model to describe encapsulated growth and activity of Nitrosomonas europaea, incorporating ammonium sorption to the alginate encapsulant. Batch and continuous flow reactors were used to verify the simulation results. Quantitative PCR and cross-section fluorescence in situ hybridization were used to analyze the growth and spatial distribution of the encapsulated cells within alginate. Preferential growth of Nitrosomonas near the surface of the encapsulant was predicted by the model and confirmed by experiments. The modeling and experimental results also suggested that smaller encapsulants with a larger surface area to volume ratio would improve ammonia oxidation. Excessive aeration caused the breakage of the encapsulant, resulting in unpredicted microbial release and washout. Overall, our modeling approach is flexible and can be used to engineer and optimize encapsulated systems for enhanced biological nitrogen removal. Similar modeling approaches can be used to incorporate sorption of additional species within an encapsulant, additional nitrogen-converting microorganisms, and the use of other encapsulation materials.