Nutrient Removal and Biomass Production in an Outdoor Pilot-Scale Phototrophic Biofilm Reactor for Effluent Polishing
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An innovative pilot-scale phototrophic biofilm reactor was evaluated over a 5-month period to determine its capacity to remove nitrogen and phosphorus from Dutch municipal wastewater effluents. The areal biomass production rate ranged between 2.7 and 4.5 g dry weight/m2/day. The areal nitrogen and phosphorus removal rates averaged 0.13 g N/m2/day and 0.023 g P/m2/day, which are low compared to removal rates achieved in laboratory biofilm reactors. Nutrient removal increased during the day, decreased with decreasing light intensity and no removal occurred during the night. Additional carbon dioxide supply was not requisite as the wastewater was comprised of enough inorganic carbon to sustain microalgal growth. The study was not conclusive for the limiting factor that caused the low nutrient removal rate, possibly the process was limited by light and temperature, in combination with pH increases above pH 9 during the daytime. This pilot-scale study demonstrated that the proposed phototrophic biofilm reactor is not a viable post-treatment of municipal wastewater effluents under Dutch climate conditions. However, the reactor performance may be improved when controlling the pH and the temperatures in the morning. With these adaptations, a phototrophic biofilm reactor could be feasible at lower latitudes with higher irradiance levels.
KeywordsMicroalgae Biofilm Wastewater treatment Nitrogen removal Phosphorus removal
This work was performed in the TTIW-cooperation framework of Wetsus, Centre of Excellence for Sustainable Water Technology (www.wetsus.nl). Wetsus is funded by the Dutch Ministry of Economic Affairs, the European Union Regional Development Fund, the Province of Fryslân, the City of Leeuwarden and the EZ/Kompas program of the “Samenwerkingsverband Noord-Nederland”. The authors like to thank the participants of the research theme “Advanced waste water treatment” and the steering committee of STOWA for the fruitful discussions and their financial support. The authors also thank J. Tuinstra and W. Borgonje for their help building the pilot, R. Loos, R. Khiewwijit, J. Tessiaut, and L. Taparavičiūtė for their help operating the pilot and K. Sukacova for the taxonomical analysis.
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