Boron promoted Fe3+/peracetic acid process for sulfamethazine degradation: Efficiency, role of boron, and identification of the reactive species

Odorant production surges induced by exogenous oxidative stress: An overlooked risk in PAA-based moderate preoxidation for algal-laden water

Moderate preoxidation is feasible for odor-producing algae treatments, usually requiring trade-offs in algal removal and integrity maintenance. However, dosing oxidants may cause internal oxidative homeostasis imbalances and secondary odorous metabolite responses, adding new trade-offs for moderate treatments. Peracetic acid (PAA)/Fe processes are promising strategies in moderate treatments and thus were applied to examine how to achieve the following three trade-offs: good algal removal, no odorant increases and no releases. For algal removal, the highest removal efficiency was 71.1 %, 87.0 % and 98.1 %, respectively, in PAA/Fe(Ⅲ) separate, PAA/Fe(Ⅱ) separate and PAA/Fe(Ⅱ) simultaneous process. Odorant responses always followed a pattern of "promotion-low dosages, inhibition-high dosages", with the highest production reaching 3.91-fold of the control without PAA addition, well above odorant threshold concentrations (500 ng/L). Instant releases did not occur, yet with delayed releases observed during sludge retention in sedimentation tanks (5, 16 h). It was verified that exogenous oxidative stress stimulated odorant generation with multiple reactive species. Among them, PAA oxidant was crucial in algal removal and odorant promotion; R-O· and ·OH caused odorant generation and degradation, respectively. Overall, PAA/Fe(Ⅱ) processes were more suitable for moderate treatments, simultaneously avoiding odorant increases and allowing sludge retention. This work provides a novel perspective for moderate preoxidation, highlighting instant odorant generation and delayed releases triggered by exogenous PAA stressors.

Removal of sulfamethoxazole by Fe(III)-activated peracetic acid combined with ascorbic acid

Ascorbic acid (AA) was used as a reducing agent to improve the Fe(III)-activated peracetic acid (PAA) system for the removal of sulfamethoxazole (SMX) in this work. The efficiency, influencing factors and mechanism of SMX elimination in the AA/Fe(III)/PAA process were studied. The results exhibited that AA facilitated the reduction of Fe(III) to Fe(II) and subsequently improved the activation of PAA and H2O2. Various radicals, including organic radicals (e.g. CH3C(O)O• and CH3C(O)OO•) and hydroxyl radical (HO•), were rapidly formed from the activated PAA and H2O2, resulting in SMX removal. Increasing dosages of PAA and Fe(III) contributed to enhanced SMX degradation, while excessive PAA and Fe(III) did not further promote SMX degradation. Due to the radicals' quenching effect, excess AA hindered SMX elimination in the AA/Fe(III)/PAA process. The presence of HCO 3 - and Cl- inhibited SMX removal in this system, whereas NO 3 - , SO 4 2 - and natural organic matter had little impact on SMX degradation. The transformation pathways of SMX in the AA/Fe(III)/PAA system included hydroxylation, bond cleavage and amino oxidation. This research provides a strategy to enhance the Fe(III)-activated PAA system for the elimination of refractory organic pollutants.

Persulfate catalyst synthesized with waterworks sludge for degrading Safranine T in the presence of boron

Energy conservation and emission reduction are the general trend of the present world. In this study, a catalyst of 3WSH based on the waste recycle of waterworks sludge (WS) and Chinese herbs was prepared using one-step calcination treatment and then characterized by SEM, XRD, XPS, FTIR and BET. The catalytic performance of 3WSHB for activating potassium persulfate (PDS) was evaluated through the degradation of Safranine T (ST) in the presence of boron powder (B). The effects of vital parameters on ST removal were systematically studied, including PDS concentration, 3WSHB dosage, initial solution pH, B dosage, temperature and coexisting cations. The highest efficiency of ST removal was up to 93.0% under the optimal condition with 1.85 mM of PDS, 0.3 g/L of 3WSHB, 0.35g/L of B, 7 of pH. EPR and free radical quenching experiments demonstrated that •OH was the dominant reactive oxygen species for ST degradation in the PDS/3WSHB/B system. Moreover, the intermediates determined by HPLC-MS indicated that the oxidization of benzene ring substituents in ST and a hydrogen abstraction by electron transfer might occur during ST degradation. The dissatisfied reuse performance of 3WSHB might be attributed to its low Fe content and simple reusing way. The results demonstrate the effectiveness of WS recycling and reuse in the field of pollutant remediation.

Exploring the viability of peracetic acid-mediated antibiotic degradation in wastewater through activation with electrogenerated HClO

Electrochemical advanced oxidation processes (EAOPs) face challenging conditions in chloride media, owing to the co-generation of undesirable Cl-disinfection byproducts (Cl-DBPs). Herein, the synergistic activation between in-situ electrogenerated HClO and peracetic acid (PAA)-based reactive species in actual wastewater is discussed. A metal-free graphene-modified graphite felt (graphene/GF) cathode is used for the first time to achieve the electrochemically-mediated activation of PAA. The PAA/Cl- system allowed a near-complete sulfamethoxazole (SMX) degradation (kobs =0.49 min-1) in only 5 min in a model solution, inducing 32.7- and 8.2-fold rise in kobs as compared to single PAA and Cl- systems, respectively. Such enhancement is attributed to the occurrence of 1O2 (25.5 μmol L-1 after 5 min of electrolysis) from the thermodynamically favored reaction between HClO and PAA-based reactive species. The antibiotic degradation in a complex water matrix was further considered. The SMX removal is slightly susceptible to the coexisting natural organic matter, with both the acute cytotoxicity (ACT) and the yield of 12 DBPs decreasing by 29.4 % and 37.3 %, respectively. According to calculations, HClO accumulation and organic Cl-addition reactions are thermodynamically unfavored. This study provides a scenario-oriented paradigm for PAA-based electrochemical treatment technology, being particularly appealing for treating wastewater rich in Cl- ion, which may derive in toxic Cl-DBPs.

Infancy of peracetic acid activation by iron, a new Fenton-based process: A review

The exacerbated global water scarcity and stricter water directives are leading to an increment in the recycled water use, requiring the development of new cost-effective advanced water treatments to provide safe water to the population. In this sense, peracetic acid (PAA, CH3C(O)OOH) is an environmentally friendly disinfectant with the potential to challenge the dominance of chlorine in large wastewater treatment plants in the near future. PAA can be used as an alternative oxidant to H2O2 to carry out the Fenton reaction, and it has recently been proven as more effective than H2O2 towards emerging pollutants degradation at circumneutral pH values and in the presence of anions. PAA activation by homogeneous and heterogeneous iron-based materials generates - besides HO• and FeO2+ - more selective CH3C(O)O• and CH3C(O)OO• radicals, slightly scavenged by typical HO• quenchers (e.g., bicarbonates), which extends PAA use to complex water matrices. This is reflected in an exponential progress of iron-PAA publications during the last few years. Although some reviews of PAA general properties and uses in water treatment were recently published, there is no account on the research and environmental applications of PAA activation by Fe-based materials, in spite of its gratifying progress. In view of these statements, here we provide a holistic review of the types of iron-based PAA activation systems and analyse the diverse iron compounds employed to date (e.g., ferrous and ferric salts, ferrate(VI), spinel ferrites), the use of external ferric reducing/chelating agents (e.g., picolinic acid, l-cysteine, boron) and of UV-visible irradiation systems, analysing the mechanisms involved in each case. Comparison of PAA activation by iron vs. other transition metals (particularly cobalt) is also discussed. This work aims at providing a thorough understanding of the Fe/PAA-based processes, facilitating useful insights into its advantages and limitations, overlooked issues, and prospects, leading to its popularisation and know-how increment.

Peracetic acid-based electrochemical treatment of sulfamethoxazole and real antibiotic wastewater: Different role of anode and cathode

Although has high oxidation capacity and low toxic by-product formation potential, the feasibility, mechanism, and antibiotic treatment performance of peracetic acid (PAA)-based electrochemical system remains unknown. This work systematically studied the electro-activation process of PAA, and distinguished the different mechanisms of anode and cathode. In the PAA-based electrochemical system, the anode mainly produces BDD(•OH), and the cathode is mainly the R-O• (especially CH3CO3•). These differences lead to different degradation pathway and toxicity evolution of sulfamethoxazole (SMX). The anode transformation products (TPs) show negative toxicity and are difficult to be further removed, while TPs from PAA-dominated cathode posed electron-donating effect and a tapering ecological risk. The BDD(•OH) can well mineralize the TPs produced from cathode. Moreover, the active chlorine produced by the anode can effectively avoid the accumulation of NH4+- N released by antibiotic degradation. In an undivided cell, PAA-based treatment for real antibiotic wastewater achieved 73.9%, 59.4%, 76.9%, and 31.7% of COD, TOC, NH4+- N, and TN removal, respectively. More importantly, when PAA existed in this system, the active chlorine and AOCl accumulation are inhibited (inhibition ratio 83.5% and 82.7%, respectively). This study provides theoretical and technical support for the practical application of PAA-based electrochemical system.