Investigating the Recovery of Phosphate from Anaerobic Digester Liquor using Ion Exchange, and its subsequent Application as a Liquid Fertilizer

Currently, practices of mining phosphate rock are not sustainable and will likely lead to the depletion of global phosphate reserves in 50-100 years. One potential option to recycle phosphorus is through ion exchange. In this research, two anion exchange resins were used in jar tests to adsorb phosphate from anaerobic digester liquor. The loaded resins were then used in column regeneration experiments in which the phosphate anions were desorbed by a regenerant solution high in concentrations of chloride, hydroxide, or a combination of the two. The result was a phosphate solution that could potentially be used as a fertilizer, eliminating the issue of brine disposal. A life cycle analysis (LCA) was also performed for two local New Hampshire farms to assess the environmental repercussions of this phosphate recovery process. The FO36 phosphate selective resin was identified as a potential option for use in ion exchange due to its advantageous recovery of phosphate. The results of the LCA showed that the production of potassium hydroxide used for the regenerant had the most significant environmental impacts. The LCA also indicated that human toxicity and fossil fuel depletion were the categories of main concern for environmental repercussions. If implemented at full scale, this process would have the ability to capture phosphate before it is released into receiving waters, having the added benefit of preventing eutrophication of drinking water sources. In addition, this process would enable local farmers to buy less commercial fertilizers thus minimizing the global impacts from that industry. This system would be ideal for small communities and small local farms