Evaluation of an Algal Turf Scrubber (ATS) for Nitrogen Removal from High Strength Nitrate Wastewater

The production of plastics, nitric acid, nitrogen-based fertilizers as well as fuel and explosive components often results in the generation of wastewater volumes with high levels of inorganic nitrogen, often in the form of nitrate. The nitrate removal is a challenge of particular significance for traditional physical-chemical treatment technologies as the processes are often energy intensive with little ability to recover viable resources for further valorization of the original waste. In this scenario, microalgae treatment systems (MTSs) are gaining increasing attention as industrial ecology based technology; in fact, MTSs allows to achieve resource recovery in the form biomass revealing the inherent value of waste streams. Among MTSs, algal turf scrubber (ATS) represent a resilient and feasible technology with high efficacy for remediation of a variety of wastewater. ATS rely on the artificial composition of wastewaters to stimulate microalgal productivity, which leads to nutrients (C,P,N) assimilation into the biomass. In this study, an indoor bench scale ATS set up was inoculated with a filamentous algae consortium and utilized for treatment of high strength nitrate wastewater. Changes in the algae consortium were observed over time with the filamentous genus Ulothrix sp. rapidly becoming the dominant alga strain; the filamentous genus resulted in ease in harvesting and resistance to predation. Batch tests were conducted according to different nitrogen to phosphorous ratio (N:P) and recirculation rates. Nutrients uptake as well as biomass productivity were determined for each of the conditions tested and used to estimate the performance of the system at larger scale. Overall, the system was able to achieve up to 50% of the influent nitrogen load with biomass productivity in the range of 3-10 g_dryweight m^-2 d^-1. In addition, the recirculation rate showed to have higher effect on the nitrogen removal as well as biomass production compared to the initial N:P ratio.