Effects of pH, soluble organic materials, and hydraulic loading rates on orthophosphate recovery from organic wastes using ion exchange

Abstract

Phosphorus recovery from organic wastes attracts more and more attentions because of the phosphorus sustainability challenges. Ion exchange (IX) was used in this study to recover orthophosphate (ortho-P) from the anaerobic digester (ADs) supernatant of an organic waste. The effects of pH, soluble organic materials (SOM), and hydraulic loading rates (HLR) on phosphate recovery were investigated by column tests. The results of tests with model water showed that the IX capacities were 64.2 mg P/g and 36.7 mg P/g at pH of 4.5 and 9.0, respectively. The desired HLR of ortho-P capture was 0.69 m/H (3 BV/h), with ortho-P capture efficiency and recovery efficiency of about 90% and 80%, respectively. The ortho-P desorption efficiencies with NaOH and KNO3 brines as eluents were investigated, finding that both NaOH and KNO3 could be substitutions of officially recommended NaCl to reduce the harmful effect on soil or plants in applications. The results of tests with ADs supernatant showed that the ortho-P capture capacity decreased to 14.3 mg P/g, with great disruption of SOM. Both ortho-P and SOM were desorbed well with over 85% ortho-P recovery efficiency and no detrimental effect on resin reuse. Regenerate with KNO3 could create mobile nutrients solution containing a N/ortho-P/K mass ratio of 17:8:75, which could balance deficient fertilizer. This research promotes the current understanding of phosphate recovery from organic wastes for fertilizer application.