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

Abstract

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.

Keywords: Adsorption; HAOPs; MBR; Microgranular adsorptive filtration; Phosphorus removal; Wastewater.