Integrating photobioreactors and constructed wetlands for paper pulp industry wastewater treatment: A nature-based system approach

Nature-based systems, such as constructed wetlands and photobioreactors, efficiently replicate natural processes for sustainable wastewater treatment. This study employed a hybrid methodology, combining a photobioreactor (NBS1) and a constructed wetland (NBS2) to enhance pollutant removal. The study was conducted over seven weeks (49 days) using raw wastewater from a paper pulp industry. Results indicated the system stabilized by the third week of operation. The system achieved the highest removal efficiencies at steady state, with 89 % for organic matter, 69 % for nitrogen, 59 % for phosphorus, and 81 % for total phenols. These results reflect the adaptive synergy between microalgae and bacteria in the photobioreactor, which facilitated the degradation of organic pollutants and nutrient cycling, combined with the contribution of wetlands plants in nutrient uptake and further pollutant removal. Biomass concentration in NBS1 stabilized from week 5 onwards at 600 mgVSS/L, suggesting that the microorganisms had reached a stationary growth phase. The values recorded for flocculation and sedimentation efficiency (89.7 ± 7.7 %) indicated that the biomass exhibited excellent sedimentation capacity, thus facilitating efficient biomass harvesting. Therefore, NBS1 and NBS2 offer viable nature-based solutions for industrial wastewater treatment, with low operating costs and environmental impacts, contributing to developing a circular economy in the paper pulp industry. • Photobioreactor-wetland system was effective in treating paper pulp mill effluent. • Achieved 89 % organic, 69 % nitrogen, 59 % phosphorus, and 81 % phenol removal rates. • Biomass shows 90 % sedimentation efficiency, which is ideal for resource recovery. • NBS1 and NBS2 enable a circular economy with low operating costs.