Production of photosynthetic bacteria using organic wastewater in photobioreactors in lieu of a culture medium in fermenters: From lab to pilot scale

Photosynthetic bacteria (PSB), used as fish feed and as raw materials for producing bio-active substances, are normally cultivated in fermenter using culture medium. This work investigated a novel, cleaner PSB production method using non-toxic organic wastewater as culture medium in photobioreactors (PBRs). The scale was enlarged from lab to bench and finally to pilot scale. Results showed that brewery wastewater with nitrogen supplement could substitute traditional culture medium with a comparable biomass output. At the lab scale, biomass production reached 1886.9 mg/L. Plexiglass cylindrical PBRs with mechanical agitation were selected to ensure good mixing to avoid the biomass wall-attachment. Finally, the scale was successfully enlarged 667-fold and the reactor was steadily operated outdoors for 80 days without temperature control and artificial light at the pilot scale. The biomass, protein, carotenoids, bacteriochlorophyll and Coenzyme Q10 values reached 1786.7, 1014.4, 4.9, 23.0, and 67.3 mg/L with a biomass yield of 0.53 g/g-COD-removal, respectively. PSB cells generated from brewery wastewater exhibited no acute toxicity. Culturing PSB with non-toxic wastewater can reduce the cost of culture medium, eliminate the necessity of fermentation broth treatment, and partially saves the cost of wastewater treatment. The challenges/practical barriers, such as chronic toxicity and management, should be further studied. The findings in this study might lead to the establishment of a cleaner PSB production technology with no residual liquid and wastewater resourcization.