Key Takeaways & Executive Findings
- •• • Coupling pretreatments (coagulation, adsorption, biological oxidation) with ionizing radiation (IR) increased COD removal by 19%–42% and CTX removal by 8.4%–19% compared to direct IR at 5 kGy, demonstrating enhanced overall treatment efficiency. • • Adsorption pretreatment using activated carbon reduced the matrix effect by 17%, the highest among the three pretreatments, while biological oxidation and coagulation sedimentation reduced it by 11% and 9%, respectively, indicating selective removal of radical scavengers. • • Biological oxidation achieved the highest COD removal (47.3% after 12 h) but showed limited CTX removal (<20%), whereas coagulation with PFS removed 27.4% of COD but <2% of CTX, highlighting the need for process selection based on target pollutant and matrix composition. • • The optimal conditions were: PFS as coagulant, activated carbon as adsorbent, and 6 h aeration for biological oxidation; these parameters are critical for scaling up pretreatment-IR systems for real pharmaceutical wastewater.
Abstract
Ionizing radiation (IR) is an emerging advanced oxidation process for degrading recalcitrant organic pollutants in water, but its efficiency is often hampered by matrix effects from coexisting substances in real wastewater. This study coupled three pretreatments—coagulation sedimentation, adsorption, and biological oxidation—with electron beam IR to treat a model cephalosporin wastewater containing cefotaxime sodium (CTX) and typical coexisting components. The results showed that all coupled systems significantly improved treatment performance compared to direct IR: COD removal increased by 19%–42% and CTX removal by 8.4%–19%. Under the tested conditions, the optimal coagulant was polymeric ferric sulfate (PFS), the optimal adsorbent was activated carbon, and the optimal aeration time for biological oxidation was 6 h. All three pretreatments reduced matrix effects, with adsorption, biological oxidation, and coagulation sedimentation lowering the matrix effect by 17%, 11%, and 9%, respectively. Quantum chemical calculations and LC-MS analysis predicted radical reaction sites on CTX and revealed five possible degradation pathways. The study demonstrates that pretreatment-IR coupling is an effective strategy to mitigate matrix effects and enhance the targeted degradation of antibiotics in complex wastewater matrices.
1. Introduction
Ionizing radiation (IR) offers rapid and energy-efficient degradation of recalcitrant pollutants, but its application to real wastewater is hindered by matrix effects: non-target constituents such as natural organic matter and suspended solids scavenge reactive radicals, reducing the degradation efficiency of target contaminants. For instance, the presence of coexisting substances lowered the radiolytic degradation of cefotaxime sodium (CTX) by 11.8% compared to pure aqueous solutions, necessitating higher absorbed doses and increased energy costs. Existing approaches often rely on increasing radiation dose, which is economically and practically suboptimal.
This study addresses this bottleneck by integrating three pretreatments—coagulation sedimentation, adsorption, and biological oxidation—prior to IR. These pretreatments selectively remove or transform matrix components, thereby mitigating their radical-scavenging effects and enhancing the targeted degradation of CTX. By systematically evaluating the coupled systems, the research identifies optimal pretreatment conditions and quantifies their contributions to matrix effect elimination, providing a practical strategy for improving the efficiency and cost-effectiveness of IR-based wastewater treatment.
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ZHANG Yanru, ZHAO Zhen, XIA Tao, QI Buriju (2026). Elimination of Matrix Effects in Ionizing Radiation Treatment of Cephalosporin Wastewater by Pretreatment Coupling. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202511034
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Frequently Asked Questions
What is the quantitative impact of each pretreatment on reducing the matrix effect in IR treatment?
Adsorption with activated carbon reduced the matrix effect by 17%, biological oxidation by 11%, and coagulation sedimentation by 9%, as measured by the change in the relative degradation rate (ΔRp) at 5 kGy.
Which pretreatment is most effective for COD removal, and what are the trade-offs?
Biological oxidation achieved the highest COD removal (47.3% after 12 h), but it removed less than 20% of CTX. Coagulation with PFS removed 27.4% of COD but less than 2% of CTX. Adsorption with activated carbon provided the best overall improvement in CTX degradation, increasing CTX removal by 19%.
What are the optimal operating parameters for each pretreatment?
For coagulation, PFS at a dose of 4 g per 100 mL with 0.4 mL added to 100 mL wastewater and 2 mL of 0.1 g/L PAM, stirred for 15 min and settled for 20 min. For adsorption, 5 g/L of activated carbon (iodine value 1000 mg/g) with 6 h contact time. For biological oxidation, activated sludge at MLSS 1.2 g/L with aeration for 6 h (optimal for matrix effect reduction).
How does the coupled system affect energy consumption compared to direct IR?
By reducing matrix effects, the coupled systems achieve higher removal efficiencies at the same absorbed dose (5 kGy), thereby lowering the dose required to meet discharge standards. This translates to reduced energy consumption per cubic meter of wastewater treated, as IR energy demand is directly proportional to dose.
What are the main degradation pathways of CTX under IR, and how were they identified?
DFT calculations and LC-MS analysis identified five possible degradation pathways, primarily involving C-S bond cleavage, aromatic ring opening, and hydroxylation. Nine transformation products (TP1–TP9) were detected with m/z values ranging from 105.04810 to 472.05193, indicating stepwise breakdown into simpler molecules.
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