Key Takeaways & Executive Findings
- •• • Achieved 100% total phosphorus (TP) removal from 0.1 mmol/L PBTC within 60 min using Fe(II)/PMS/H2O2/NaCl system at pH 3.0, with Fe(II) 1.0 mmol/L, PMS and H2O2 each 0.5 mmol/L, and NaCl 10 mmol/L, enabling near-complete phosphorus recovery as FePO4 precipitate. • • Chloride (Cl−) at 10 mmol/L enhanced the generation of reactive species (•OH, SO4•−, Cl•, Cl2•−), with •OH identified as the dominant oxidant; Cl• and Cl2•− specifically targeted C–P bonds, improving phosphorus release and subsequent FePO4 formation. • • Solution pH critically governed FePO4 precipitation: acidic conditions (pH < 4.3) favored FePO4 formation, while higher pH shifted speciation, underscoring the need for pH control in practical applications. • • Coexisting HCO3− and humic acid (HA) significantly inhibited TP removal in a concentration-dependent manner, whereas Ca2+ and Mg2+ had negligible interference, indicating system robustness in hard waters but vulnerability to organic matter and alkalinity.
Abstract
Phosphonate wastewater, characterized by stable C–P bonds, poses significant environmental risks due to its resistance to degradation and potential to contribute to eutrophication. This study developed a chloride-enhanced Fe(II)/PMS/H2O2 system for the oxidative degradation of 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) and simultaneous recovery of phosphorus as iron phosphate (FePO4). Under optimal conditions (0.1 mmol/L PBTC, 1.0 mmol/L Fe(II), 0.5 mmol/L PMS, 0.5 mmol/L H2O2, 10 mmol/L NaCl, initial pH 3.0, 60 min), total phosphorus (TP) removal reached 100%, with phosphorus nearly completely recovered as FePO4 precipitate. Increasing NaCl concentration and temperature enhanced TP removal, while pH significantly influenced removal efficiency and product speciation; acidic conditions (pH < 4.3) favored FePO4 precipitation. Coexisting Ca2+ and Mg2+ had negligible effects, whereas HCO3− and humic acid (HA) inhibited TP removal in a concentration-dependent manner. Radical quenching and electron spin resonance (ESR) analyses identified hydroxyl radicals (•OH), ferryl ion (Fe(IV)=O), sulfate radicals (SO4•−), and chlorine radicals (Cl•) as primary reactive species, with •OH playing a dominant role. Chloride introduction promoted the generation of multiple reactive species, and Cl• and its derivative Cl2•− directly attacked the C–P bond and phosphonate group, facilitating phosphorus release as PO43− and subsequent FePO4 formation. The system's feasibility was validated using actual industrial circulating cooling water. This study provides a novel approach for phosphonate wastewater treatment and phosphorus recovery.
1. Introduction
Phosphonates, widely used in industrial and agricultural applications, persist in wastewater due to their stable C–P bonds, resisting conventional biological and physical treatment. Their environmental accumulation and potential to trigger eutrophication upon photolytic conversion to orthophosphate necessitate effective removal and phosphorus recovery strategies. Advanced oxidation processes (AOPs) have emerged as promising solutions, yet single-oxidant systems often suffer from incomplete mineralization and limited phosphorus recovery.
This study addresses these bottlenecks by integrating chloride ions into a Fe(II)/PMS/H2O2 system, creating a multi-radical environment that enhances the cleavage of C–P bonds and facilitates the simultaneous precipitation of FePO4. The approach not only achieves complete TP removal under optimized conditions but also recovers phosphorus as a valuable product, offering a dual-function strategy for phosphonate-laden wastewater treatment and resource recovery.
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WEN Shuozhao, LIU Xueyu, LI Jiaqian, WU Xiangyang, LING Yu, GUO Zhenjie, LI Guowen, LI Yibing, ZHANG Juanjuan (2026). Chloride-Enhanced Fe(II)/PMS/H2O2 System for Degradation of PBTC and Simultaneous Recovery of Iron Phosphate. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202510034
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Frequently Asked Questions
What is the optimal operating pH range for achieving both high PBTC degradation and FePO4 precipitation, and how does pH affect the speciation of phosphorus?
The optimal initial pH is 3.0, where 100% TP removal was achieved. Acidic conditions (pH < 4.3) favor FePO4 precipitation, as lower pH promotes the formation of Fe3+ and PO43− ions that combine to form FePO4. At higher pH, phosphorus may remain soluble or form other precipitates, reducing recovery efficiency.
How does the presence of chloride ions enhance the degradation mechanism, and what is the role of Cl• and Cl2•− in the reaction?
Chloride ions react with SO4•− and •OH to generate Cl• and Cl2•−, which are selective oxidants that attack the C–P bond in PBTC. This facilitates the cleavage of the carbon-phosphorus bond, releasing phosphorus as PO43−. This synergistic effect increases the overall TP removal efficiency compared to systems without chloride.
What are the impacts of common coexisting ions (Ca2+, Mg2+, HCO3−) and natural organic matter (HA) on the system's performance?
Ca2+ and Mg2+ at typical concentrations had negligible effects on TP removal. However, HCO3− and HA significantly inhibited TP removal, with inhibition increasing with concentration. This is likely due to scavenging of reactive radicals and complexation of iron species, reducing the availability of active oxidants.
What is the practical feasibility of this system for treating real industrial wastewater, and what are the potential scale-up challenges?
The system was validated using actual industrial circulating cooling water, achieving effective TP removal. Scale-up challenges include controlling pH in large volumes, managing the cost of reagents (PMS, H2O2, FeSO4), and mitigating the inhibitory effects of HCO3− and HA present in real wastewater. Optimization of reagent dosages and reaction conditions is necessary for economic viability.
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