Phosphorus recovery from phosphonate-contaminated wastewater by nonthermal plasma treatment prior to adsorption on granular iron-coated sand

Abstract

Phosphonate contamination of water resources has drawn much attention. Advanced oxidation combined with phosphorus recovery is considered as a promising solution, but the development of a cost-efficient process remains challenging. This work demonstrates an effective two-step process including a plasma-based oxidation of phosphonate, followed by phosphate adsorption on granular iron-coated sand (ICS). In the first step, a tandem reactor configuration, which consists of a dielectric barrier discharge (DBD) plasma chamber and an ozonation chamber, was used to transform 1-hydroxyethane-1,1-diphosphonic acid (HEDP) to Ortho-phosphate (Ortho-P). When lava rock was added as a packing material in the ozonation chamber, the Ortho-P production was enhanced by 10–35%, due to an increased exposure of reactive species (O3,OH and O2•-) by 120%, 20% and 30%, respectively. The use of O2 as carrier gas in the plasma reactor resulted in the highest Ortho-P production efficiency (86%), followed by Ar (48%), N2 (21%) and air (13%). Humic acids present in the wastewater can compete with phosphonates for reactive species, decreasing the Ortho-P production efficiency by 30%. In the second step, ICS granules were used to adsorb the produced Ortho-P. The final recovery efficiency of Ortho-P from synthetic and real textile wastewater was 85% and 53%, respectively. The treatment performance of this novel two-step process is better compared to that of ozone-based AOPs, while the associated operational treatment costs are still somewhat higher. This indicates that optimizing energy consumption is still the biggest challenge for further industrial applications of nonthermal plasma-based AOPs.