Development of a photoheterotrophic biofilm in a packed-bed reactor for the polishing of wastewater contaminated with parabens

An innovative photoheterotrophic biofilm composed of Chlorella vulgaris and Rhodococcus fascians was established in a packed-bed bioreactor containing K5 carriers of high-density polyethylene for the polishing of synthetic wastewater (SWW) contaminated with methylparaben (MetP). Single- and dual-species biofilms were formed and characterized for the production of extracellular polymeric substances (EPS) and their effectiveness in the removal of nutrients (nitrogen and phosphorous) and MetP from a SWW. The presence of the bacterium increased the cellular growth of C. vulgaris from 863.6 ± 135.1 cells/mm 2 , under axenic conditions, to 1905.0 ± 483.5 cells/mm 2 in the consortium, representing close to 25% of the community present on the carriers. The presence of the MetP positively affected the planktonic cellular growth of axenic R. fascians , while axenic C. vulgaris did not grow in the presence of MetP. The consortium increased the EPS production in both suspension (113.7 μg/L on the 4th day with MetP) and on the carriers (60.5 μg/L). Regarding WW bioremediation, the consortium successfully removed N (87.6 to 96.4%), P (49.4 to 73.7%), and MetP (82.2%). While axenic R. fascians was also able to remove the contaminant, the removal of N and P was negligible. The consortium developed benefits from the cooperation between both microorganisms for the establishment of a functional and synergistic photoheterotrophic biofilm of relevance for wastewater polishing.