Efficient phosphorus removal from MBR effluent with heated aluminum oxide particles (HAOPs)

Biological processes and chemical precipitation in combination with polishing by granular media or membrane filtration can remove 90-95% of the phosphorus (P) from wastewater. However, reducing the concentration to levels near those in high-quality receiving waters requires additional advanced treatment, typically including adsorption onto specialty media. These processes are often costly, they can be hard to control when the P loading varies, and their effectiveness can be compromised by the presence of competing adsorbates in the water. In this work, a novel process that might mitigate or overcome some of these challenges was explored. In the process, water is treated by passage through micron-sized adsorbent particles (Heated Aluminum Oxide Particles, HAOPs) packed in a layer that is  < 1 mm thick, thus combining the attractive features of very small particles with those of flow through packed media. In laboratory tests using both synthetic feed and the effluent from an MBR at a full-scale wastewater treatment plant, the process removed P very efficiently until the HAOPs' capacity was nearly exhausted, at which point rapid breakthrough of P occurred. The removal capacity was proportional to the thickness of the HAOPs layer and declined by only ∼20% when SO₄^2-, Cl^-, and NO₃^- were all added to the MBR effluent at concentrations of 30 mM (2880, 1065, and 1860 mg/L, respectively). Increasing the solution pH from 7.0 to 8.5 had a similar effect, and increasing the flux of water through the adsorbent layer from 200 to 600 LMH had an even smaller effect (∼10% reduction in removal capacity). In 18 days of continuous pilot-scale operation at the treatment plant, the process performed well, achieving 99.5% P removal steadily during the final seven days of testing, during which the P concentration in the feed ranged from 4 to 9 mg/L. The process also removed 52% of the organic matter in the MBR effluent, as represented by UV₂₅₄. The sludge generated by the process was extremely easy to dewater and dry.