P-nitrophenol Removal Rate Research Articles

Enhancing the microbial advanced oxidation of P-nitrophenol in sediment through accelerating extracellular respiration with electrical stimulation

Microbial advanced oxidation, a fundamental process for pollutant degradation in nature, is limited in efficiency by the weak respiration of indigenous microorganisms. In this study, an electric field was employed to enhance microbial respiration and facilitate the microbial advanced oxidation of p-nitrophenol (PNP) in simulated wetlands with alternation of anaerobic and aerobic conditions. With intermittent air aeration, an electric field of 0.8 V promoted extracellular electron transfer to increase Fe2+ generation through dissimilatory iron reduction and the production of hydroxyl radicals (•OH) through Fenton-like reactions. As a result, the PNP removal rate of the electrically-stimulated group was higher than that of the control (72.15 % vs 46.88 %). Multiple lines of evidence demonstrated that the electrically-induced polarization of respiratory enzymes expedited proton-coupled electron transfer within the respiratory chain to accelerate microbial advanced oxidation of PNP. The polarization of respiratory enzymes with the electric field hastened proton outflow to increase cell membrane potential for adenosine triphosphate (ATP) generation, which enhanced intracellular electron transportation to benefit reactive oxygen species generation. This study provided a new method to enhance microelectrochemical remediation of the contaminant in wetlands via the combination of intermittent air aeration.

Preparation of biochar-loaded nano zero-valent iron electrode material and its electrocatalytic degradation of p-nitrophenol

<p>Electrochemical treatment of wastewater containing p-nitrophenol (PNP) was carried out using a platinum electrode as an anode and biochar-loaded nano zero-valent iron material as the cathode. The prepared biochar loaded nano zero valent iron electrode materials were characterized and analyzed using SEM, XRD, and XPS. The experiment investigated the effects of current density, initial PNP concentration, electrolyte concentration, pH value, and other factors on the treatment effect of PNP. The results showed that the nZVI/BC electrode with an initial pH value of 7.0, a current density of 10mA/cm2, and an electrolyte of 1.5g/L anhydrous sodium sulfate was the optimal condition for degrading a PNP solution with an initial concentration of 20 mg/L. The PNP removal rate within 24 hours was 81.94%.BC@nZVI electrode has good stability and reusability.</p>

Enhancing the Fenton-like degradation of organic contaminants with silicate-iron in aquifer media by ascorbic acid

In this study, silicate-iron (FeSi-ox, FeAlSi-ox) in aquifer media was utilized as an original iron source in groundwater to systematically investigate the effects of ascorbic acid on the degradation of p-nitrophenol (PNP) in the in-situ Fenton-like reaction. Silicate-iron in the aquifer media increased the PNP removal rate by activing H2O2 following the addition of ascorbic acid. The optimal removal rate of PNP was nearly 89% within 40 h, which was 6.8 times higher than that without ascorbic acid. In addition to PNP, some other common pollutants, such as nitrobenzene, trichloromethane, and trichloroethylene, can also be effectively degraded and mineralized. The suitable pH range for the silicate-iron Fenton-like system with ascorbic acid was 5–9, indicating that it is feasible in near-neutral or alkaline groundwater environments. The main functional free radicals were hydroxyl free radicals (•OH), which were produced slowly but continuously. In this novel Fenton-like system, dissolved Fe played a major role in H2O2 decomposition and pollutant degradation. The main mechanism underlying the increased strength of the degradation was the ability of ascorbic acid to facilitate the dissolution of surface Fe from aquifer media and accelerate the cycling of Fe(Ⅲ)/Fe(Ⅱ) in the liquid phase.

Fe2O3/coal fly ash Fenton-like catalyst for the elimination of organic pollutants in wastewater: Kinetic, mechanism, and application feasibility

Fe2O3/CFA was prepared by loading Fe2O3 on the surface of raw coal fly ash (RCFA), and then used as a Fenton-like catalyst to treat refractory organic wastewater. The characterization results of SEM-EDX, XRD, XPS, XRF, and BET test indicate that Fe2O3 is successfully loaded on the surface of RCFA, while the adsorption performance is not significantly affected. Under optimal treatment conditions of p-nitrophenol (PNP) simulated wastewater (H2O2 dosage = 8 mmol/L, Fe2O3/CFA loading = 6 g/L, pH = 3, and T = 303 K), the removal rate of PNP reaches 97.7 % at 50 min. There exist hydroxyl radicals (·OH), superoxide radicals (∙O2−) and singlet oxygen (1O2) in the Fenton-like system, and ·OH is the primary reactive oxygen species in the removal of PNP·H2O2 dosage, Fe2O3/CFA loading, and pH (i.e., [H+]) show different effects on the generation rate constant of hydroxyl radicals (k·OH), and the corresponding mathematic equation is k∙OH=6.51∙e−640.0T∙[H2O2]1.313∙[Fe2O3/CFA]1.093∙[H+]0.815. The Fenton-like process includes heterogeneous and homogeneous catalytic processes, and it is driven by the synergistic catalysis of multiple metallic elements; Fe and other metallic elements play major and auxiliary roles, respectively. In the advanced treatment of real coking wastewater, the catalytic capacity of Fe2O3/CFA can maintain 91.7 % in its 4th use, and the treatment cost is ¥4.15/ton, which can be decreased by further optimizing the preparation process of Fe2O3/CFA.

Optimization of PNP Degradation by UV-Activated Granular Activated Carbon Supported Nano-Zero-Valent-Iron-Cobalt Activated Persulfate by Response Surface Method.

Nitrophenols are toxic substances that present humans and animals with the risk of deformities, mutations, or cancer when ingested or inhaled. Traditional water treatment technologies have high costs and low p-nitrophenol (PNP) removal efficiency. Therefore, an ultraviolet (UV)-activated granular activated carbon supported nano-zero-valent-iron-cobalt (Co-nZVI/GAC) activated persulfate (PS) system was constructed to efficiently degrade PNP with Co-nZVI/GAC dosage, PS concentration, UV power, and pH as dependent variables and PNP removal rate as response values. A mathematical model between the factors and response values was developed using a central composite design (CCD) model. The model-fitting results showed that the PNP degradation rate was 96.7%, close to the predicted value of 98.05 when validation tests were performed under Co-nZVI/GAC injection conditions of 0.827 g/L, PS concentration of 3.811 mmol/L, UV power of 39.496 W, and pH of 2.838. This study demonstrates the feasibility of the response surface methodology for optimizing the UV-activated Co-nZVI/GAC-activated PS degradation of PNP.

Preparation of coal fly ash-based Fenton-like catalyst and its application for the treatment of organic wastewater under microwave assistance

In order to realize the high value-added reuse of coal fly ash (CFA), a reusable CFA catalyst (AFA) for a Fenton-like process conducted under microwave (MW) assistance was prepared by H2SO4 impregnation. The optimal AFA preparation conditions included an impregnation time of 60 min, H2SO4 dosage of 0.5 mol/L, impregnation temperature of 303 K, and solid–liquid ratio of 1 g:5 mL. In addition, several AFA critical parameters such as specific surface area, pore size distribution, particle size distribution, surface morphology, relative content, chemical states of the elements on the AFA surface, mass fractions of various AFA oxides, crystal composition, surface chemical bonds, and coordination structure of Si were determined. The dynamic treatment conditions of organic wastewater were optimised using a continuous wastewater treatment system with MW assistance, and the removal efficiency of p-nitrophenol (PNP) exceeded 90% at a hydraulic retention time of 40 min. The AFA was successfully reused three times while retaining a PNP removal efficiency of 90%. The relationship between the PNP removal rate and the utilised treatment conditions was −d[PNP]dt=0.32⋅[H2O2]0.374⋅[AFA]0.337⋅[H+]0.445⋅[PNP]0.475. Furthermore, the AFA surface played the main role and ·OH was the most reactive oxidative radical. Hence, real coking wastewater can be effectively treated by the AFA-catalysed Fenton-like process under MW assistance.

Tannic acid reinforced electro-Fenton system based on GO-Fe3O4/NF cathode for the efficient catalytic degradation of PNP

In order to overcome the sluggish kinetics of the redox conversion between Fe3+ and Fe2+ in Fenton process, we established a novel electro-Fenton system based on GO-Fe3O4 cathode and tannic acid (TA) for the efficient degradation of p-nitrophenol (PNP). Under the optimal degradation parameters (including the initial PNP concentration of 20 mg L−1, pH = 5, current density of 30 mA cm−2 and feeding ratio of PNP: TA = 1:2), the TA reinforced GO-Fe3O4 electro-Fenton system exhibited the removal rate of PNP over 90.1 ± 0.2%, the COD removal rate of 69.5 ± 0.84% and satisfactory reusability (with the removal rate of ∼80% after 5 recycles). The excellent degradation performance of the proposed TA reinforced GO-Fe3O4 electro-Fenton system was partly attributed to the optimized morphology (with the particle size of Fe3O4 reduced to tens of nanometers, pore size decreased by ∼80% and pore volume increased by 24.3 times) and larger specific surface area (increased by 72.7 times) after compositing GO with Fe3O4, which exposed more active sites. In return, the electron transfer process, the two-electron oxygen reduction reaction (ORR) and the degradation efficiency were promoted in the cooperation of GO and Fe3O4. Moreover, the incorporated TA would form a TA-Fe(III) complex to promote the reduction reaction from Fe3+ to Fe2+, which strengthened the self-circulation of Fe2+ and Fe3+ and indirectly enhanced the conversion of H2O2 to ROS to decompose PNP into smaller organic fragments or mineralize into CO2, H2O, NO2− or NO3−, etc. Obviously, the incorporation of TA provided a promising strategy to improve the electro-Fenton efficiency and realize the efficient removal of PNP in wastewater.

Photoelectrocatalytic PNP removal using C3N4 nanosheets/α-Fe2O3 nanoarrays photoanode: Performance, mechanism and degradation pathways

The massive discharge of p-nitrophenol (PNP) has adversely affected ecosystem and human health. In this work, the g-C3N4 nanosheets was integrated with α-Fe2O3 nanorod arrays (C3N4 NSs/Fe2O3 NRAs) through simple in-situ hydrothermal and electrochemical deposition, and applied for the photoelectrocatalytic degradation of PNP. At the optimum experiment conditions at PNP initial concentration of 10 mg/L, pH value of 6.1, electrolyte concentration of 0.2 mol/L, and bias voltage of 1.5 V, the optimized photoanode displayed the highest PNP removal rate. This improvement was attributed to the synergistic effect between photocatalysis and electrocatalysis, a synergy factor of 1.6 was achieved during this C3N4 NSs/Fe2O3 NRAs photoelectrocatalytic system. The C3N4/Fe2O3 heterojunction and bias voltage facilitated the generation, separation and transfer of electron/hole pairs. The electrolysis also provided rich active species, hydroxyl radicals, etc., which cooperated with the reactive oxygen species derived from enhanced photocatalysis to achieve rapid pollutants decomposition. Based on the intermediates detection and analysis, two PNP degradation pathways, namely direct oxidation and reduction–oxidation path, were proposed, that matched well the existence form and transformation rule of inorganic nitrogen. The radical capture experiments demonstrated that electrons, hydroxyl radicals and holes were the main species responsible for PNP photoelectrocatalytic removal.

Isotypic heterojunction based on Fe-doped and terephthalaldehyde-modified carbon nitride for improving photocatalytic degradation with simultaneous hydrogen production

To achieve an efficient photocatalytic for clean energy production and environmental remediation, the highly active Fe-doped and terephthalaldehyde-modified carbon nitride (Fe-CN/NTE) isotypic heterojunction photocatalyst is constructed via a simple annealing method for degradation of organic pollutants with simultaneous resource recovery. The Fe-CN/NTE catalyst exhibits a 93% removal rate of p-nitrophenol (4-NP) and a 1.72 mmol/g H2 evolution rate in 2 h simultaneously under visible light irradiation, which are higher than those of pristine CN, Fe-CN, and NTE, respectively. Photoelectrochemical tests show that the excellent photocatalytic performance of Fe-CN/NTE comes from the improved migration, transportation, and separation of photoinduced charge carriers and expanded light-harvesting range. Moreover, hydroxyl radical (OH), electron (e−), and hole (h+) are the main active species and the rational mechanism of 4-NP photodegradation was proposed based on scavenger measurements and liquid chromatography-mass spectrometry (LC–MS), respectively. Isotypic heterojunction Fe-CN/NTE photocatalyst possesses excellent stability in the H2 evolution and 4-NP degradation during five-run cycle tests, posing as a promising candidate in practical works for organic pollution and energy challenges.

Submerged membrane photocatalytic reactor for advanced treatment of p-nitrophenol wastewater through visible-light-driven photo-Fenton reactions

A submerged membrane photocatalytic reactor (SMPR) was constructed for the advanced treatment of p-nitrophenol (PNP) wastewater and rapid recycling of powdery catalyst, including a suspended photocatalytic system and a submerged microfiltration (MF) membrane system. To evaluate the performance of the SMPR, a visible-light responsive Fe(III)-ZnS/g-C3N4 photo-Fenton catalyst was successfully synthesized by the microwave hydrothermal method, and several techniques were used to characterize the resulting catalyst. The key operation factors on the wastewater treatment efficiency were successively optimized. When the influent PNP concentration was 10 mg·L−1, initial pH was 5, catalyst dosage was 1.0 g·L−1, H2O2 concentration was 170 mg·L−1, aeration rate was 0.50 m3·h−1, and operation time was 4 h, the PNP removal rate was 91.6% by the SMPR under simulated solar light irradiation. The rejection rate of the catalyst by the MF membrane was 100%, which realized the rapid separation and recycling of the suspended catalyst powders and avoided the catalyst loss and secondary pollution. The toxicity calculation results of PNP and its possible degradation products indicated that the toxicity of PNP wastewater decreased overall after the visible-light-driven photo-Fenton reactions. This study provided a combined photocatalysis-membrane filtration process that had a high treatment efficiency of refractory wastewater and solved the problem about the separation and recycling of the powdery catalyst synchronously.

Optimization of microelectrolysis process for treatment ofPNP wastewater by response surface methodology

The simulated p-nitrophenol (PNP) wastewater was treated by micro-electrolysis. The Box-Behnken experimental design model in response surface method was adopted with iron-carbon as a micro-electrolytic filler. Factors such as iron chip dosage, initial pH value of solution and reaction time were used as investigation indexes to study the influence of single factors and their interactions on the PNP wastewater removal rate. The final optimization results show that the experiment has a good removal rate of PNP, with only a small difference from the predicted value. It can be seen that the response surface method is feasible and suitable forthe process optimizion of p-nitrophenol wastewatertreatment by micro-electrolysis, which can be applied to engineering practice through further research and improvement.

Photo-assisted heterogeneous Fenton-like process for treatment of PNP wastewater

Abstract The purpose of this study was to investigate the effect of photo-assisted heterogeneous Fenton on p-nitrophenol (PNP) wastewater treatment by a homemade reactor. Supported Fe-Ce/Al2O3 was used as a catalyst and H2O2 as an oxidant to treat simulated p-nitrophenol wastewater under ultraviolet light. The effects of H2O2 dosage, catalyst dosage, initial solution pH value, reaction temperature and reaction time on the removal rate of p-nitrophenol in a photo-assisted heterogeneous Fenton system were determined. According to the relation between the concentration of each component and time, the relation curve is fitted, and then the kinetic equation is established. Finally, we obtained the optimum process conditions to achieve the PNP wastewater removal rate of 98.7%. The degradation of the photo-assisted heterogeneous Fenton method conforms to the first-order kinetic model, and the kinetic equation is . Therefore, photo-assisted heterogeneous Fenton treatment of PNP wastewater is effective and can be used in the treatment of refractory wastewater.

Role of radical and non-radical pathway in activating persulfate for degradation of p-nitrophenol by sulfur-doped ordered mesoporous carbon

A new application of heteroatom doped ordered mesoporous carbon as metal-free catalyst was proposed in this study. Sulfur-doped ordered mesoporous carbons (S-OMCs) with different sulfur doping amount were synthesized to activate persulfate (PS) for p-nitrophenol (PNP) degradation. Thereinto, the activation effect of 2.0 wt% S-OMC improved most significantly after it reached the adsorption equilibrium, and the removal rate of PNP was 82.02%. The optimal experimental effect can be achieved at room temperature and unadjusted pH (pH = 6), retrenching energy and chemical input for practical applications. Higher temperatures could cause radical quenching, while electrostatic repulsion existed between S-OMC and PNP at pH > 6.03, which led to a reduction of PNP removal. Moreover, the structural features and surface characters of S-OMC were studied and found that the defect structure and surface functional groups had noticeable influence on the reusability of S-OMC. More importantly, both radical activation and non-radical activation were detected, and non-radical activation predominated in the S-OMC/PS system. The radical pathway oxidized pollutant by generating OH, SO4−, and O2−. Among them, OH was dominated. While the non-radical pathway attacked contaminant by continuous electron transport between PNP, S-OMC and PS. This research provided a new perspective on the application of heteroatom doped ordered mesoporous carbon and presented an easy and effectual way for the removal of organic contaminants.

Study on dynamic adsorption of p-nitrophenol by multi-walled carbon nanotubes dispersed cyclodextrin.

In this paper, the modified multi-walled carbon nanotubes were prepared by β-cyclodextrin denoted as β-CD-MWNTs. The structure and morphology of β-CD-MWNTs was characterized by TEM and the dynamic adsorption of p-nitrophenol on β-CD-MWNTs was studied by the Thomas model. Some affecting factors of dynamic adsorption and the adsorbent regeneration process such as the sewage concentration, the amount of absorbent in column, including the type of reagent, solid-liquid ratio, regeneration time, and regeneration times were investigated and optimized. The results indicated that the p-nitrophenol removal rate could reach 84% under stuffing 2g β-CD-MWNTs. The curves of p-nitrophenol's dynamic adsorption conformed to the Thomas model. Moreover, the adsorption capacity of regenerated β-CD-MWNTs was similar to the fresh β-CD-MWNT column. The optimal conditions of regenerations of β-CD-MWNTs were shown as follows: the type of reagent is anhydrous ethanol, the solid-liquid ratio is 200:40 (mg/mL) and the regeneration time is 120min.

Bioaugmented soil aquifer treatment for P-nitrophenol removal in wastewater unique for cold regions

P-nitrophenol (PNP) is a toxic and recalcitrant organic pollutant and a usual intermediate in the production of fine chemicals, which has posed a significant threat to subsurface environment safety. Soil aquifer treatment (SAT) is a promising method to remove and remediate contamination in vadose zone with low cost and high efficiency. However, there are still research gaps for the treatment of recalcitrant contaminants by SAT in cold regions, such as un-robust indigenous microbes and low temperature constraint in vadose zone. The bioaugmentation technology was first introduced into SAT in order to enhance the removal ability of PNP by SAT operated in cold regions in this study. A high-efficiency PNP-degrading bacterium was successfully isolated, which can efficiently degrade PNP below 200 mg L−1 with a degradation rate above 99% at 15 °C close to the real subsurface temperature in cold regions, and added into SAT for bioaugmentation. The feasibility of bioaugmented SAT and associated PNP removal process were investigated by laboratory sand columns, along with effects of the SAT operative parameters (namely PNP loading concentration, flow rate and soil saturation level of SAT). Within the range of PNP loading stresses tested (1–200 mg L−1), PNP removal efficiency was optimal at constant flow rate of 219 mL d−1 in unsaturated operating condition of SAT under 15 °C among all the investigated experimental conditions. Longer hydraulic residence time increased the PNP removal rate, although the accumulated mass removed reduced and the removal efficiencies remained constant in unsaturated operating condition of SAT. It is found from the comparison between the PNP removals via both unsaturated and saturated columns that slight difference only in the removal rate of PNP was observed and the highly efficient bioaugmented SAT can completely degrade PNP of 10 mg L−1 within 5 wetting/drying cycles under both scenarios.

Facile and rapid microwave-assisted preparation of Cu/Fe-AO-PAN fiber for PNP degradation in a photo-Fenton system under visible light irradiation

A visible-light responsive Cu-Fe bimetallic amidoxime-modified polyacrylonitrile (denoted by Cu/Fe-AO-PAN) fiber was prepared using a facile and rapid microwave-assisted synthesis method. Several microscopic and spectroscopic techniques were adopted to characterize the morphology, structure, thermal and optical properties of the Cu/Fe-AO-PAN fiber. The results indicated that Cu2+ and Fe3+ ions were successfully coordinated with AO-PAN without causing distinct damage to the fiber and that chelation with metal ions extended the light absorption into the visible-light region. P-nitrophenol (PNP) was used to investigate the photocatalytic performance of the Cu/Fe-AO-PAN fiber in a photo-Fenton system under visible light irradiation. Various parameters that affected PNP removal were discussed, including the microwave heating temperature, irradiation time, Cu/Fe molar ratio, and photo-Fenton reaction conditions, such as the pH, H2O2 concentration and fiber dosage. Under the optimal conditions, a PNP removal rate of approximately 100% was achieved within 150 min under visible light irradiation. The bimetallic Cu/Fe-AO-PAN exhibited improved pH tolerance, photocatalytic performance and stability compared to the monometallic Fe-AO-PAN fiber. In addition, a mechanism for PNP degradation induced by the Cu/Fe-AO-PAN fiber in the photo-Fenton system under visible light irradiation was proposed.

Mechanisms for removal of p-nitrophenol from aqueous solution using zero-valent iron

Batch experiments were conducted to examine mechanisms for removal of p-nitrophenol (PNP) from aqueous solution using zero-valent iron (ZVI). Removal of PNP using ZVI was mainly attributed to three mechanisms: degradation, precipitation and adsorption. A complete removal of 30 mg L−1 PNP with ZVI dosage of 1000 mg L−1 achieved within 30 min at pH 3. The PNP removal rate in the acidic solutions was significantly suppressed at higher pH. The modified Langmuir–Hinshelwood kinetic model could successfully describe the PNP removal process using ZVI at different pH conditions. Total organic carbon (TOC) removal efficiencies were found to be almost independent of pH. While the TOC removal at lower pH was profoundly affected by the reductive and/or oxidative degradation, the adsorption was favorable at higher pH. The effect of dissolved oxygen on PNP removal was investigated at pH 3 where a maximum contribution of oxidative degradation could be expected. The PNP removal in the anoxic system purged with nitrogen gas was quick as well as that in the system being open to the air. However, the TOC removal under the anoxic condition was negligible as compared with that in the oxic system. The profiles of the intermediates formed during the PNP degradation indicated that the reductive degradation was predominant in the initial phase of the removal and subsequently the oxidative degradation occurred.

Removal of high concentration p-nitrophenol in aqueous solution by zero valent iron with ultrasonic irradiation (US–ZVI)

In this study, the US–ZVI system was used to produce the strong reductants including H and nascent Fe2+ ions to eliminate the toxicity of the high concentration p-nitrophenol (PNP) wastewater. The effect of the reactor structure, initial pH, ZVI dosage, ultrasonic power and initial PNP concentration on the removal efficiency of PNP from water was investigated intensively. The results show that a higher removal rate can be obtained by using a conical structure reactor, and the lower initial pH can aid the acceleration of PNP removal rate by using US–ZVI system. Furthermore, the removal efficiencies of PNP increased obviously with the increase of initial ZVI concentration from 0 to 15gL−1. Also, the treatment capacity of ZVI was enhanced remarkably by the ultrasonic irradiation, and the US–ZVI system can maintain high treatment efficiency for the high concentration PNP wastewater (500–10,000mgL−1). Meanwhile, the high removal efficiency of PNP was mainly resulted from the synergistic reaction of ZVI and US. At last, the main degradation product (i.e., p-aminophenol) was detected by gas chromatography–mass spectrum (GC–MS). Thus, the reaction pathway of PNP in the US–ZVI system is proposed as a reducing process by the H and nascent Fe2+ ions.

Bioelectrochemical system for recalcitrant p-nitrophenol removal

Bioelectrochemical system (BES) for recalcitrant p-nitrophenol (PNP) removal was investigated in this study. Effective removal of PNP at rates up to 9.14±0.48molm−3d−1 was achieved at an energy consumption as low as 0.010±0.002kWhmol−1 PNP. PNP removal rate was enhanced with negative cathode potential, increased influent PNP concentration and shortened hydraulic retention time (HRT). Although the coulombic efficiencies at the anode did not exceed 40%, coulombic efficiencies for PNP removal at the cathode were above 70% at various cathode potentials. Compared with conventional anaerobic process, the cosubstrate dosage in BES was significantly reduced due to the high coulombic efficiencies at the cathode. p-Aminophenol (PAP) was identified as the dominant product of PNP reduction at the abiotic graphite cathode of BESs. This study demonstrated that the BES had a potential for efficient removal of nitrophenol pollutants from wastewater.

Kinetics of Ultrasound-Enhanced Oxidation of p-Nitrophenol by Fenton's Reagent

Aqueous solutions of p-Nitrophenol (PNP) were oxidized by Fenton's reagent assisted by ultrasound (US) irradiation. The effects of operating parameters such as initial medium pH, initial concentration of PNP, the molar ratio of Fe2+/H2O2, the temperature and the type of saturating gas on the degradation rates of PNP were investigated. The results showed that both pH value and PNP concentration altered noticeably the reaction rates, with preferred operation conditions at low pH, and low PNP concentration. Among the four different saturating gases (namely Ar, O2, air and N2), PNP degradation in an oxygen-saturated solution was the fastest. The addition of Fenton's reagent could increase the PNP removal rate. PNP degradation followed apparent pseudo-first-order kinetics under US irradiation, Fenton's reagent oxidation and the combined US/Fenton's reagent oxidation process. The overall reaction rates were significantly enhanced in the US/Fenton's reagent oxidation system, most likely because ultrasound could accelerate Fenton's reagent to generate hydroxyl radical (.OH) and other reactive oxygen intermediates. There was an obvious synergetic effect in the combined US-Fenton's reagent process. The observed synergetic effects of the US/Fenton's reagent system resulted in an increase in the net PNP degradation rate by a factor of 2.06.