Removal of organic phosphorus and formaldehyde in glyphosate wastewater by CWO and the lime-catalyzed formose reaction

Glyphosate (PMG) wastewater with 40–600 mg/L organic phosphorus (OP) and 1–4% CH₂O was treated by catalytic wet oxidation (CWO) and the lime-catalyzed formose reaction to remove total phosphorus (TP) and improve biodegradability. Activated carbons (ACs) modified by H₂O₂ oxidation and thermal treatment with melamine were used as CWO catalysts and characterized by N₂ adsorption/desorption and XPS. The CWO experiments were performed in an autoclave reactor at 110–130 °C and 1.0 MPa. The modified AC showed higher catalytic activity than the parent AC due to the introduction of nitrogen-containing functional groups, exhibited over 90% OP removal for various real PMG wastewaters, and had good stability for 20 consecutive CWO runs. The CWO effluents were further treated by lime at 80 °C to remove TP and CH₂O. The treated effluents, containing 0.5–12 mg/L TP and 20–60 mg/L CH₂O, showed good biodegradability with a BOD₅/COD ratio of 0.31–0.41. The combination of CWO and lime is an effective treatment method prior to biological treatment for solving the problems of OP and CH₂O encountered by the glyphosate industry.