Two-stage algal cultivation for the biotransformation of urban wastewater’s pollutants into multiple bioproducts in a circular bioeconomy paradigm

Abstract

Resource recovery and recycling of urban wastewater have become essential due to rapidly depleting water resources. Here, a newly isolated cyanobacterium Pseudoscillatoria coralii BERC01 was employed for the biotreatment of urban wastewater (UWW) via a two-stage cultivation system followed by biotransformation of the biomass into multiple bioproducts. During the stage-I, the cyanobacterial strain BERC01 removed 100 % suspended solids (9–27 g/L) from the UWW within 3–7 days via biosorption, and the resultant biomass was used as a soil amender which improved the phosphate availability, microbial carbon biomass, and nitrate-nitrogen of the soil by 2.65–5.86-fold, 2.27–3.65-fold, and 3.20–6.57-fold, respectively. During stage-II, re-culturing the BERC01 in the recycled water improved the productivities of carbohydrates and proteins by 10-fold and 3-fold, respectively, when compared to the control. Cultivation of BERC01 also improved the pH of UWW (9.47 ± 0.2 – 10.93 ± 0.16) to reduce the bacterial and/or fungal contamination. The two-stage cultivation of BERC01 in the UWW lowered the total nitrogen, total phosphorous, chemical oxygen demand, and biological oxygen demand of the UWW by 41.94 %, 95 %, 79 %, and 89.64 %, respectively, bringing the quality of treated water within the WHO’s safety limits of agricultural purposes. Cascading processing of the stage-II biomass yielded food-grade pigments (phycocyanin = 148.95 ± 1.81 mg/g, allophycocyanin = 51.92 ± 0.51 mg/g), and 470–490 mg/g of lipids which contained compounds of pharmaceutical interest such as undecanoic acid, pentadecanoic acid, and eicosanoic acid. Finally, the pigment-free and de-oiled residual biomass (PDRB) was completely valorized to mycoprotein and α-amylase through fungal fermentation using 10–50 g/L PDRB as a sole source of nutrition. Resultantly, Aspergillus niger and Aspergillus oryzae produced 98.44 U/mL and 118.56 U/mL of α-amylase in 96 h of incubation, respectively, whereas the protein content of the fermented biomass was improved by 10.42-fold and 7.34-fold, respectively. This novel approach could help in achieving the economic and environmental sustainability of the algal biorefineries.