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This research looked at how three different light intensities (1600, 4300, and 7200 lx) affect the biomass development, treatment of fuel synthesis wastewater and the recovery of valuable bioproducts between biofilm and suspended growth in a purple-bacteria enriched photobioreactor. Each condition was run in duplicate using an agricultural shade cloth as the biofilm support media in a continuously mixed batch reactor. The results showed that the highest chemical oxygen demand (COD) removal rate (56.8 ± 0.9 %) was found under the highest light intensity (7200 lx), which also led to the most biofilm formation and highest biofilm biomass production (1225 ± 95.7 mg). The maximum carotenoids (Crts) and bacteriochlorophylls (BChls) content occurred in the suspended growth of the 7200 lx reactor. BChls decreased with light intensity in suspended growth, while in biofilm both Crts and BChls were relatively stable between light conditions, likely due to an averaging effect as biofilm thickened at higher light intensity. Light intensity did not affect protein content of the biomass, however, biofilm showed a lower average (41.2 % to 43.7 %) than suspended biomass (45.4 % to 47.7 %). For polyhydroxybutyrate (PHB) the highest cell concentration in biofilm occurred at 1600 lx (11.4 ± 2.4 %), while for suspended growth it occurred at 7200 lx (22.7 ± 0.3 %), though total PHB productivity remained similar between reactors. Shading effects from the externally located biofilm could explain most variations in bioproduct distribution. Overall, these findings suggest that controlling light intensity can effectively influence the treatment of fuel synthesis wastewater and the recovery of valuable bioproducts in a biofilm photobioreactor.

In the current era of wastewater treatment, integrating reusable water production with resource recovery is a key goal. This study aims to treat fuel-synthesis wastewater (FSW), intending to recover various resources, including polyhydroxybutyrate (PHBs), single cell protein, bacteriochlorophylls, carotenoids, and coenzyme Q10 from suspended and biofilm growth to decrease the harvesting costs. The study considered the treatment process, biofilm growth, and resource recovery potential in a mixed-culture system enriched with purple non-sulfur bacteria for treating FSW. Specifically, the effects of four different FSW strengths (25–100 %) and nitrogen sufficiency (N+) or deficiency (N−) were evaluated in eight biofilm photobioreactors. This study observed a direct correlation between the concentration of FSW and PHB content; specifically, as the FSW content decreased from 100 % (undiluted) to 25 % the PHB content decreased. The undiluted condition achieved 17 % dry cell weight as PHB in the suspended growth and 22.6 % in the biofilm growth under N− condition. The protein content ranged between 33 and 44 %, and the presence of nitrogen had a slight positive effect on higher protein content. No trend was observed for carotenoids or bacteriochlorophylls in the N− condition. In contrast, for the N+ condition, the concentration of bacteriochlorophylls increased with decreasing wastewater concentration under suspended growth, while it decreased with decreasing wastewater concentration under biofilm growth. Coenzyme Q10 concentration was enhanced under the most growth-limited condition (25 %, N−). PHB and protein content of these resources seem most promising when using N− and N+ conditions, respectively.

This review paper provides an overview of various types of photobioreactors (PBRs) that could be used for the production of polyhydroxyalkanoates (PHAs) using anoxygenic photoheterotrophs, with a focus on the design and operation of these systems. The paper highlights the potential of different PBRs based on reactor geometry and growth mode, and also examines the advantages and disadvantages of each PBR type and summarizes their suitability for PNSB-PHA production. The optimization of reactor design and operation is crucial for maximizing PNSB growth and PHA productivity. The self-immobilization of bacteria in granular sludge is a promising technology for wastewater treatment and the production of PHAs, while grooved-surface PBRs and porous-substrate PBRs have limitations due to difficult biomass harvesting in the former and the presence of aerobic conditions incongruent with PNSB culturing in the latter. Limitations exist with all solutions for maximizing rapid growth and maintaining high biomass concentrations due to the requirements of phototrophic growth.