Microbial photosynthetic carriers in biofilm bioreactors: a systematic review and quantitative synthesis

Microbial photosynthetic biofilm systems have emerged as a promising alternative to suspended cultivation, providing efficient nutrient removal and concentrated biomass production. This study analyses the effect of carriers, under different cultivation conditions, in wastewater treatment and biomass production. A systematic literature review method is adopted to evaluate publication and patent trends. Data obtained is systematically categorised, based on carrier biodegradability, and analysed via a multivariate analysis to identify correlations and highlight key parameters that influence the systems' efficiency. Quantitative synthesis of the available studies revealed comparable treatment efficiencies among horizontal, vertical, inclined, and rotating biofilm systems, suggesting that operational conditions exert a greater influence on performance than reactor orientation. Consequently, reactor configuration should be selected based on its ability to support optimal operating conditions for a specific application. The COD, Total Nitrogen, and Total Phosphate removal efficiencies ranged from 53 to 98%, 25-100%, and 64-99% with overall mean removals of 82%,78% and 88%, respectively. Median reference values of 7.8 for pH, 14 h for light duration, 9 days for HRT, and 26 °C for temperature are derived from global biofilm cultivation systems. Multivariate regression analysis identified illumination (p = 0.002) and cultivation area (p = 0.005), as factors explaining biomass yield (R² = 79.76%). Microbial photosynthetic carriers help improve wastewater treatment efficiency whilst producing valuable biomass for bioenergy or bioproducts. This has driven commercialisation efforts and created future opportunities to scale algal biofilm systems.