Peroxyphosphoric acid as an oxidant for antibiotics removal in agricultural waters

Peroxide-based oxidants are widely used in water treatment, yet their application in agricultural wastewater reuse is often limited by insufficient reactivity, instability, and undesirable secondary impacts. Here, we report the application of peroxyphosphoric acid (PPA), an inorganic peroxy acid, for antibiotic abatement in agricultural waters, integrating oxidative performance with environmental compatibility. PPA was synthesized via a controlled biphasic oxidation route and systematically characterized using Raman spectroscopy, ³¹P NMR, UV-vis spectrophotometry, and density functional theory (DFT) calculations, which collectively confirmed its structure and electronic properties. Acid dissociation constants (pK_a1 = 1.5, pK_a2 = 5.5, pK_a3 = 11.7) and stability assessments revealed that PPA exhibits remarkable resistance to self-decomposition over a wide pH and temperature range. The oxidation capacity of unactivated PPA exhibited a trend of increasing, then decreasing, and increasing again with rising pH. Among the various metal ions tested, only Co²⁺ demonstrated superior activation efficiency. Two mixtures containing potassium peroxomonophosphate salts were prepared, with active oxygen contents of 3.5 % and 2.2 %, respectively. The aqueous solutions of both mixtures exhibited higher pH values than those of peroxymonosulfate (PMS) at the same mass concentration. Compared with PMS and peracetic acid (PAA), PPA achieves superior antibiotic removal, a moderate decomposition rate, and significantly lower acute toxicity. Notably, PPA shows no adverse effects on wheat germination in simulated agricultural irrigation water. These findings highlight PPA as a promising oxidant for agricultural water treatment, offering a unique combination of reactivity, stability, and agronomic compatibility.