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A novel reactor design, coined a high density bioreactor (HDBR), is presented for the cultivation and study of high density microbial communities. Past studies have evaluated the performance of the reactor for the removal of COD(1) and nitrogen species(2-4) by heterotrophic and chemoautotrophic bacteria, respectively. The HDBR design eliminates the requirement for external flocculation/sedimentation processes while still yielding effluent containing low suspended solids. In this study, the HDBR is applied as a photobioreactor (PBR) in order to characterize the nitrogen removal characteristics of an algae-based photosynthetic microbial community. As previously reported for this HDBR design, a stable biomass zone was established with a clear delineation between the biologically active portion of the reactor and the recycling reactor fluid, which resulted in a low suspended solid effluent. The algal community in the HDBR was observed to remove 18.4% of total nitrogen species in the influent. Varying NH4(+) and NO3(-) concentrations in the feed did not have an effect on NH4(+) removal (n=44, p=0.993 and n=44, p=0.610 respectively) while NH4(+) feed concentration was found to be negatively related with NO3(-) removal (n=44, p=0.000) and NO3(-) feed concentration was found to be positively correlated with NO3(-) removal (n=44, p=0.000). Consistent removal of NH4(+), combined with the accumulation of oxidized nitrogen species at high NH4(+) fluxes indicates the presence of ammonia- and nitrite-oxidizing bacteria within the microbial community.

Data collected from experiments conducted at a flask scale are regularly used as input data for life cycle assessments and techno-economic analyses for predicting the potential productivities of large-scale commercial facilities. This study measures and compares nitrogen removal and biomass growth rates in treatment systems that utilize an algae-bacteria consortium to remediate landfill leachate at three scales: small (0.25 L), medium (100 L), and large (1000 L). The medium- and large-scale vessels were run for 52 consecutive weeks as semibatch reactors under variable environmental conditions. The small-scale experiments were conducted in flasks as batch experiments under controlled environmental conditions. Kolomogov-Smirnov statistical tests, which compare the distributions of entire data sets, were used to determine if the ammonia removal, total nitrogen removal, and biomass growth rates at each scale were statistically different. Results from the Kolmogov-Smirnov comparison indicate that there is a significant difference between all rates determined in the large-scale vessels compared to those in the small-scale vessels. These results suggest that small-scale experiments may not be appropriate as input data in predictive analyses of full scale algal processes. The accumulation of nitrite and nitrate within the reactor, observed midway through the experimental process, is attributed to high relative abundances of ammonia- and nitrite-oxidizing bacteria, identified via metagenomic analysis.

Metabolic kinetics, microscopy, metagenomic analysis, and real-time PCR are applied to characterize nitrogen species transformation and identify and quantify the organisms key to these transformational processes.