Phosphorus Recovery by Liquid-Liquid Extraction

It is acknowledged that phosphorus removal is more crucial in comparison with nitrogen removal for preventing algae glooming and eutrophication. Chemical and biological methods are common methods for the P removal. Excessive sludge production and difficulties of recovering phosphorus are concerns in terms of sustainable waste management. A liquid-liquid extraction (LLE) process is thus considered for the study aiming at recovering phosphorus from wastewater in a sustainable way. The results revealed that the best extractant is a mixture of kerosene and benzyl-di-methyl-amine (BDMA) at a volume ratio of 2:1. Under the study conditions, one part of extractant can react with four parts of wastewater to transfer 97% of P to the organic phase. In addition, in the stripping step, a 1:1 ratio of extract to recycled acid can result in 96% recovered P, implying an overall 93% phosphorus recovery efficiency can be achieved by the LLE process. Most importantly, the extractant can be recycled and reused at least 5 times if the residual P concentration should be less than 4mg/L vs. the original P concentration of 21mg/L. A complexion between amine groups in BDMA and phosphates and the positive charge of the micelles surface when the extractant (composed of kerosene and BDMA) mixed with P containing wastewater would contribute to the P recovery and this is a novel approach to recover P from wastewater.