Phosphate recovery from wastewater via reversible adsorption

Eutrophication and the resulting formation of harmful algal blooms causes huge economic and environmental damages. Phosphorus (P) has been identified as a major limiting nutrient for eutrophication. Phosphorous concentration greater than 100 µg P/L is usually considered high enough for causing eutrophication. The strictest regulations however aim to restrict the concentration below 10 µg P/L. Orthophosphate (or phosphate) is the bioavailable form of phosphorus. Adsorption is often suggested as technology to reduce phosphate to concentrations less than 100 and even 10 µg P/L with the advantages of a low-footprint, minimal waste generation and the option to recover the phosphate.
In this thesis, the optimum properties of a phosphate adsorbent are identified and studied. Limitations of porous adsorbents having high surface areas are discussed and the optimum pore size distribution for phosphate adsorbents is determined. The role and mechanism of biogenic iron oxides in phosphate removal is discussed. Optimum methods for regenerating the adsorbent and improving the adsorbent reusability is studied. An economic assessment for phosphate adsorption is done, highlighting the main cost factors and identifying the research gaps needed to better understand these factors. A scenario analysis comparing the economics of low-cost one-time use adsorbents vs more expensive reusable adsorbents is made. A cost comparison of different technologies and the conditions where adsorption is favorable is highlighted. Suggestions for future studies are made based on the current findings.