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Two-phase partitioning bioreactors (TPPBs) in environmental biotechnology are based on the addition of a non-aqueous phase (NAP) into a biological process in order to overcome both mass-transfer limitations from the gas to aqueous phase and pollutant-mediated inhibitions. Despite constituting a robust and reliable technology in terms of pollutant biodegradation rates and process stability in wastewater, soil, and gas treatment applications, this superior performance only applies for a restricted number of pollutants or contamination events. Severe limitations such as high energy requirements, high costs of some NAPs, foaming, or pollutant sequestration challenge the full-scale application of this technology. The introduction of solid NAPs into this research field has opened a promising pathway for the future development of TPPBs. Finally, this work reviews fundamental aspects of NAP selection and mass transfer and identifies the niches for future research: low energy-demand bioreactor designs, experimental determination of partial mass transfers, and solid NAP tailoring.

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Concentrated animals feeding operations (CAFOs) often pose a negative environmental impact due to the uncontrolled spreading of manure into soils that ends up in the release of organic matter and nutrients into water bodies. Conventional aerobic methods treating CAFOs wastewater require intensive oxygenation, which significantly increases the operational costs. The alternative proposed in this research is the application of micro-algae based systems by taking advantage of the cost-effective in situ oxygenation via photosynthesis. A 4.9 L enclosed tubular biofilm photo-bioreactor was inoculated with an algal-bacterial consortium formed by the micro-algae Chlorella sorokiniana and a mixed bacterial culture from an activated sludge process. C. sorokiniana delivers the O(2) necessary to accomplish both organic matter and ammonium oxidation. The reactor was fed with diluted swine wastewater containing 180, 15 and 2,000 mg/L of NH(4) (+)-N, soluble P and total COD, respectively. The photo-bioreactor exhibited good and sustained nutrient removal efficiencies (up to 99% and 86% for NH(4) (+) and PO(4) (3-), respectively) while total COD was removed up to 75% when the biofilm was properly established. Liquid superficial velocities up to 0.4 m/s (achieved by culture broth recirculation) hindered the formation of a stable biofilm, while operation at velocities lower than 0.1 m/s supported stable process performance. The high shear stress imposed by the centrifugal recirculation pump disintegrated the large aggregates detached from the biofilm, which resulted in a poor settling performance and therefore poor COD removal efficiencies. Enclosed biofilm photo-bioreactors therefore offer a potentially more economical alternative to conventional tertiary treatments process.