Use Of Zero-valent Iron Research Articles

Biogeochemical mechanisms of zero-valent iron and biochar for synergistically mitigating antimony uptake in rice

Antimony (Sb) contamination in paddy fields can lead to its accumulation in rice grains, posing a threat to food safety. To address this issue, the combined use of zero-valent iron (ZVI) and biochar (BC) were applied to decrease the uptake of Sb in Sb-polluted soils, and their effects on Sb uptake from soil to rice grains were investigated. Our results showed that the combination treatment of 0.05 % ZVI and 0.095% BC resulted in a significant decrease (42.8%) in Sb accumulation in rice grains that was comparably more efficient than that by 0.05% ZVI (decrease of 15.8% Sb accumulation) or 0.095% BC (decrease of 12.7% Sb accumulation) alone, demonstrating the synergistic effect of ZVI and BC on mitigating Sb uptake by rice plants. ZVI presence resulted in the formation of iron oxides in the soil and on root surfaces, and the S2−/S22− ascent also increased by 58.7% on day 75 compared with that of the control, facilitating the reduction of Sb(V) to less mobile Sb(III), thereby decreasing Sb accumulation in rice plants. BC initially increased the mobility of Sb owing to its alkaline nature, whereas the electron shuttle properties of BC contributed to a decrease in Sb mobility. The abundance of the arsenite-reducing gene arrA ultimately increased by 203.2% on day 120 compared with the initial phase on day 5, and BC caused a remarkable increase in arrA gene abundance. This study revealed the synergistic mechanisms by combining ZVI and BC to mitigate Sb uptake by rice, which may be useful for the sustainable remediation of contaminated rice paddies.

Co-enhancing effects of zero valent iron and magnetite on anaerobic methanogenesis of food waste at transition temperature (45 °C) and various organic loading rates

Deoiling of food waste (FW) after hydrothermal pretreatment occurs at high temperatures, and more energy is required for substrate cooling before the anaerobic digestion (AD) process. AD at the transition temperature (for example 45 °C) is good for energy saving and carbon emission reducing when treating deoiling FW. However, the metabolic activity of methanogens must increase at the transition temperatures. This study proposes the use of zero-valent iron (Fe0) and magnetite (Fe3O4) to boost CH4 yield from deoiling FW. The results showed a co-enhancing effect on CH4 yield upgradation when using Fe0 and Fe3O4 simultaneously, and the highest CH4 yield reached 536.23 mLCH4/gVS, which was 67.5 % higher than that of Fe0 alone (320.14 mLCH4/gVS). In addition, a high organic loading was favorable for increasing the CH4 yield from deoiling FW. Microbial diversity analysis suggested that the dominant methanogenic pathway at 45 °C was hydrogenotrophic methanogenesis. Herein, a potential metabolic pathway analysis revealed that the co-enhancing effects of Fe0 and Fe3O4 enhanced syntrophic methanogenesis and possibly boosted electron transfer efficiency.

Tree-based ensemble machine learning model for nitrate reduction by zero-valent iron

The use of zero-valent iron (ZVI) for nitrate reduction has long been a topic of interest owing to its excellent reactivity compared to other inorganic electron donors. However, there is currently a lack of comprehensive and sophisticated models that can effectively integrate and analyze the dynamic data generated by this type of experiment. Such modeling is necessary to facilitate information mining and improve our understanding of the underlying mechanisms. Taking advantage of available published experimental data, a gradient-boosting decision tree and extreme gradient boosting were applied to 288 data points collected from peer-reviewed publications and compared with conventional non-tree-based models, i.e., artificial neural networks (ANN) and support vector regression (SVR). First, a predictive analysis was performed for the rate constant and the percentages of ammonium and nitrogen conversion using seven predictors related to ZVI properties, reactant concentration, and experimental parameters. Both tree-based models accurately predicted the target variables with comparable performance (R2 = 0.88–0.97) and outperformed ANN and SVR (R2 = 0.60–0.89). In addition, SHapley Additive exPlanations analysis revealed that ZVI properties (44 % average contribution) and experimental condition (68.5 % average contribution) were the key variables affecting the nitrate reduction rate constant and conversion product, respectively. Aerobic conditions were favorable for the conversion of nitrate to ammonium, with anoxic conditions being beneficial for the selectivity of nitrogen gas conversion. This study demonstrates a promising approach using machine learning with complex cross-system data for predicting the performance of water treatment and for mining valuable insights into the process by model interpretation. This method presents a new approach to revolutionize data analysis and modeling in water remediation, which can simplify the experimental operational burden.

Combining magnet-assisted soil washing and soil amendment with zero-valent iron to restore safe rice cultivation in real cadmium-contaminated paddy fields

Local villagers in Mae Sot District, Tak Province, Thailand are at risk of diseases related to cadmium (Cd) due to excessive consumption of rice contaminated with Cd due to zinc mining. This study verifies the hypothesis that to achieve safe rice cultivation, magnet-assisted soil washing followed by soil amendment using zero-valent iron (ZVI) is required not only for rapid remediation of the existing Cd contamination but also for the prevention of Cd recontamination caused by contaminated run-off from an upgradient contaminated paddy. Accordingly, this study conducted a pilot-scale demonstration of the combined technique to restore a real Cd-contaminated paddy (41.02 ± 5.47 mg/kg−1) and compared it with remediation using only soil amendment with ZVI or only magnet-assisted soil washing. The Cd concentration in rice grains from the contaminated rice field without treatment was 0.86 ± 0.01 mg/kg−1, and thus higher than the acceptable level of 0.4 mg/kg−1. Even though the use of magnet-assisted soil washing without amendment initially removed all the bioavailable Cd from the soil, it failed to reduce Cd uptake by the rice plants. This failure was caused by heavy off-season rain, which flooded and re-contaminated the experimental fields with Cd-contaminated run-off from an upgradient contaminated field, leading to a Cd concentration in rice grains of 1.21 ± 0.01 mg/kg−1. Similarly, the use of ZVI as a soil amendment without magnet-assisted soil washing could not ensure safe rice cultivation during the off-season flood, as Cd concentration in the rice grains was still 0.60 mg/kg−1. However, magnet-assisted soil washing followed by soil amendment using ZVI successfully removed Cd from soil and sequestered Cd from Cd-contaminated run-off, resulting in protection against Cd re-contamination in soil and the reduction of Cd content in rice grains to 0.33 mg/kg−1, representing a 60% removal efficacy. Also, this combined technique remained positive for rice growth compared to non-treatment.

Choose your amendment wisely: Zero-valent iron nanoparticles offered no advantage over microparticles in a laboratory study on metal immobilization in a contaminated soil

The potential use of zero-valent iron (ZVI) nanoparticles (i.e., <100 nm in size) for the remediation of metal-contaminated soils has sparked a flurry of research in recent years. However, even reading a large number of these papers cannot completely dispel doubts that ZVI nanoparticles are indeed superior to ZVI microparticles (e.g., iron powder or grit) in immobilizing metals and metalloids in soils. Our primary objective was to compare the adsorption properties of iron-based amendments (ZVI micro- and nanoparticles, natural iron oxides) supplied in a biochar matrix in soils contaminated by a copper-nickel (Cu/Ni) smelter on the Kola Peninsula in Russia. The following iron-containing amendments were added to the studied soil: a composite of ZVI nanoparticles and biochar (synthesized by pyrolysis of iron-impregnated biochar), a mixture of iron powder (i.e., ZVI microparticles) with biochar, and a mixture of iron oxides (from natural ferromanganese nodules) with biochar. Perennial ryegrass (Lolium perenne L.) was grown in pots on untreated and amended soils for 21 days under laboratory conditions. In our time-limited study, ZVI nanoparticles did not prove superior to ZVI microparticles or natural iron oxides at immobilizing metals in copper- and nickel-contaminated soil. In other words, ZVI particles size was irrelevant under the experimental setup of this study in its effects on exchangeable metal concentrations, foliar elemental concentrations, and plant growth.

Performance prediction of ZVI-based anaerobic digestion reactor using machine learning algorithms

The use of zero-valent iron (ZVI) to enhance anaerobic digestion (AD) systems is widely advocated as it improves methane production and system stability. Accurate modeling of ZVI-based AD reactor is conducive to predicting methane production potential, optimizing operational strategy, and gathering reference information for industrial design in place of time-consuming and laborious tests. In this study, three machine learning (ML) algorithms, namely random forest (RF), extreme gradient boosting (XGBoost), and deep learning (DL), were evaluated for their feasibility of predicting the performance of ZVI-based AD reactors based on the operating parameters collected in 9 published articles. XGBoost demonstrated the highest accuracy in predicting total methane production, with a root mean squared error (RMSE) of 21.09, compared to 26.03 and 27.35 of RF and DL, respectively. The accuracy represented by mean absolute percentage error also showed the same trend, with 14.26%, 15.14% and 17.82% for XGBoost, RF and DL, respectively. Through the feature importance generated by XGBoost, the parameters of total solid of feedstock (TSf), sCOD, ZVI dosage and particle size were identified as the dominant parameters that affect the methane production, with feature importance weights of 0.339, 0.238, 0.158, and 0.116, respectively. The digestion time was further introduced into the above-established model to predict the cumulative methane production. With the expansion of training dataset, DL outperformed XGBoost and RF to show the lowest RMSEs of 11.83 and 5.82 in the control and ZVI-added reactors, respectively. This study demonstrates the potential of using ML algorithms to model ZVI-based AD reactors.

Oxygen Tolerant and Cytocompatible Iron(0)-Mediated ATRP Enables the Controlled Growth of Polymer Brushes from Mammalian Cell Cultures.

The use of zerovalent iron (Fe0)-coated plates, which act both as a source of catalyst and as a reducing agent during surface-initiated atom transfer radical polymerization (SI-ATRP), enables the controlled growth of a wide range of polymer brushes under ambient conditions utilizing either organic or aqueous reaction media. Thanks to its cytocompatibility, Fe0 SI-ATRP can be applied within cell cultures, providing a tool that can broadly and dynamically modify the substrate's affinity toward cells, without influencing their viability. Upon systematically assessing the application of Fe-based catalytic systems in the controlled grafting of polymers, Fe0 SI-ATRP emerges as an extremely versatile technique that could be applied to tune the physicochemical properties of a cell's microenvironments on biomaterials or within tissue engineering constructs.

Enhancement of Nitrate-Removal Efficiency Using a Combination of Organic Substrates and Zero-Valent Iron as Electron Donors

Agriculture is the most extensive source of nitrate to water resources. A high concentration of nitrate contamination in drinking water is a significant risk to human health. The aim of this study was to select the appropriate combination of organic substrates and zero-valent iron (ZVI) to use as an electron donor for denitrification in a permeable reactive barrier. From the results, a nitrate-removal efficiency of more than 85% was achieved for all the tested organic substrates at ambient temperature (25±5°C), neutral pH, and under anaerobic conditions. The initial nitrate concentration of 150 mg L−1 and the organic substrates (50 g L−1 concentration) were tested in this study. Different dosages for ZVI (10, 30, 50, and 70 g L−1) were also investigated. Using a mixture of rice husk and rice straw as an electron donor led to the highest nitrate-removal efficiency (93.3%). Using ZVI as an electron donor yielded a lower nitrate-removal efficiency than using the same amount of the organic substrate. However, the use of ZVI coupled with the organic mixture resulted in a higher nitrate-removal rate than when only the organic mixture was used. The nitrate-removal rate increased up to threefold when using ZVI wire, a type of waste from a lathe factory, mixed with the organic mixture as an electron donor.

Characterization and reactivity of novel silver/iron nanoparticles

Abstract One of critical aspects still limiting a wider use of zero-valent iron in large-scale application is the use of borohydride for the material synthesis, which is expensive and leads to the production of large quantities of hydrogen gas and toxic borates. A new bimetallic material was devised, whose synthesis employs eco-benign sulfur-based reducing agent and is of easy implementation and scalability. Our material consists of a core of zero-valent iron covered by a thin film of iron oxide, while silver is homogeneously distributed, and proved able to efficiently decolorize bromophenol blue outperforming zero-valent silver (ZVS) and nZVI obtained with the same method.

Enhanced removal of selenate from mining effluent by H2O2/HCl-pretreated zero-valent iron.

Direct use of zero-valent iron (ZVI) in reductive removal of selenate (Se(VI)) is inefficient due to the intrinsic passive layer of ZVI. Here we observed that ZVI pretreated with H2O2 (P-ZVI-O) performs much better in Se(VI) removal from a mining effluent than other three modes of ZVI alone, acid washing ZVI (P-ZVI-A), and simultaneous addition of H2O2 and ZVI (ZVI-O) as well. The P-ZVI-O exhibits exceptionally high Se(VI) removal at a low dosage, wide pH range, with Se dropping down from 93.5 mg/L to <0.4 μg/L after 7-h reaction. Interestingly, the initial pH (2-6) of the mining effluent exerted little influence on the final Se(VI) removal. H2O2/HCl pretreatment results in the formation of various reducing corrosion products (e.g. Fe3O4, FeO and Fe2+), which greatly favors the efficient Se(VI) removal. In addition, surface-bound Fe2+ ions participated in the reduction of Se(VI). Combined with the influence of Se valence as well as pH and Fe2+ (whether dissolved or surface bound), it is deduced that the P-ZVI-O mode induced efficient Se(VI) removal via the adsorption-reduction and/or co-precipitation. This study demonstrates that H2O2/HCl pretreatment of ZVI is a very promising option to enhance the efficiency of reductive removal of Se(VI) from real effluents.

Effect of pH on Zero Valent Iron Performance in Heterogeneous Fenton and Fenton-Like Processes: A Review.

Heterogeneous Fenton processes with solid catalysts have gained much attention for water and wastewater treatment in recent years. In the field of solid catalysts, zero valent iron (ZVI) is among the most applicable due to its stability, activity, pollutant degradation properties and environmental friendliness. The main limitation in the use of ZVI in heterogeneous Fenton systems is due to its deactivation in neutral and alkaline conditions, and Fenton-like processes have been developed to overcome this difficulty. In this review, the effect of solution pH on the ZVI-Fenton performance is discussed. In addition, the pH trend of ZVI efficiency towards contaminants removal is also considered in oxic solutions (i.e., in the presence of dissolved O2 but without H2O2), as well as in magnetic-field assisted Fenton, sono-Fenton, photo-Fenton and microwave-Fenton processes at different pH values. The comparison of the effect of pH on ZVI performance, taking into account both heterogeneous Fenton and different Fenton-like processes, can guide future studies for developing ZVI applications in water and wastewater treatment.

CO2 conversion to CH4 using Zero Valent Iron (ZVI) and anaerobic granular sludge: Optimum batch conditions and microbial pathways

Abstract This study investigates a new approach for carbon dioxide (CO2) conversion to methane (CH4) by using Zero Valent Iron (ZVI) and anaerobic granular sludge under aquatic mild conditions. Numerous studies have used ZVI to stimulate the anaerobic digestion of waste and wastewater. Up to date however, little research has been done on the use of ZVI and anaerobic granular sludge for the conversion of CO2 as a sole carbon substrate to CH4. The results showed that 75 g L−1 ZVI, 2 gVS L−1 anaerobic granular sludge at initial pH of 6 under daily pH regulation contributed to substantial CH4 production. It was pointed out that the initial ZVI (50 g L−1), with anaerobic granular sludge, was sufficient for the production of the same amount of CH4 over 2 CO2 re-feedings for a total of 67 days. To identify the microbial pathways for CO2 conversion to CH4, the following inhibitors were independently added: antibiotics for bacteria inhibition, 2-Bromoethanesulphonate (BES) for methanogens inhibition and Trichloromethane (CHCl3) for inhibition of bacteria and methanogens. Results showed that when antibiotics were added, they did not have any negative effect on CO2 conversion to CH4. This demonstrates that CO2 is converted to CH4 mainly through hydrogenotrophic methanogens and the contribution of homoacetogens was minor. Under these conditions of anaerobic granular sludge and ZVI the addition of BES and CHCl3 resulted in a high generation of H2, no production of CH4 and generation of 1110 mg L−1 and 730 mg L−1 in 8 days respectively.

Combined Use of Zero Valent Iron and Magnetic Separation for ex-situ Removal of Bioavailable Metals from Contaminated Sediments

ABSTRACTSandy and organic sediments characterized by different heavy metal binding capacities (HMBC), and contaminated with Copper (Cu), mercury (Hg), or zinc (Zn) were treated ex-situ using a remediation approach consisting of (i) sorption onto oxidized zero-valent iron (ZVI) surfaces and (ii) retrieval of formed metal-ZVI complexes from sediment matrices by magnetic separation. The research focused on the reduction/elimination of the bioavailable fractions of metals, and the efficiency of the method assessed by a combination of a bacterial (MetPLATE™) and an invertebrate (the 48-h Ceriodaphnia dubia acute toxicity test) based bioassays. In sandy sediments, characterized by low HMBC (20.8, 23.5, and 39.6 for Hg, Cu, and Zn, respectively), the determined toxicity units (TU) prior to sediment treatment increased in the order Hg < Cu < Zn, regardless of the bioassay used. The use of ZVI and magnetic separation in these sandy sediments resulted in up to 97% TU reduction. In organic-rich sediments, the affinity of the studied metals for organic matter (OM) resulted in much higher HMBC values (83.9, 108.3, and 136.2 for Cu, Zn, and Hg, respectively) and much lower TU values before sediment treatment with ZVI. The use of MetPLATE™ on non-treated sediments resulted in TU values increasing in the order Hg < Cu < Zn, with TU removal efficiencies ranging from 83% to 97% after treatment. The TU values measured with the 48-h C. dubia assay were higher than those obtained with MetPLATE™, and in this case, sediments contaminated with Zn exhibited the lowest percentage of TU removal, with only 81.7% and 80.5% TU removal for sediments with contamination levels of 400 and 800 mg/kg, respectively. For organic sediments contaminated with Cu and Hg, the TU removal exceeded 95%. Overall, this study showed that the proposed remediation method has great potentials with regard to the elimination of the bioavailable metal fractions in contaminated sediments.

The use of zero-valent iron (ZVI)–microbe technology for wastewater treatment with special attention to the factors influencing performance: A critical review

ABSTRACTIn recent years, the use of zero-valent iron (ZVI) coupled with microorganisms has attracted considerable attention for the removal of diverse contaminants from wastewater, and the performance of bio-ZVI systems under diverse conditions is of particular interest. This paper comprehensively reviews the recent developments related to (1) the effects of the iron surface area, operating conditions, coexisting ions, and contaminant concentrations on the performance of bio-ZVI systems; (2) the potential mechanisms of the major factors affecting the ZVI–microbe performance; and (3) the effects of ZVI on the characteristics of the microorganisms, including both enhancing and deteriorating effects. All these factors can have notable impacts, which are contaminant-specific and highly dependent on the removal mechanisms of the respective pollutants, and on the performance of the bio-ZVI system in terms of contaminant removal. Additionally, the stimulating effects of ZVI on the growth and diversity of microorganisms are reasonable considering the synergistic effects of the combined system on pollutant removal, although inhibitory effects of ZVI on bacterial activity have also been proposed. Based on these findings, further efforts should be made to establish feasible strategies to improve the engineering design and performance of integrated ZVI–microbe systems.

Pulsed Electrochemical Deposited Nano-Iron for Water Treatment

The application of nanotechnology in drinking water treatment and pollution cleanup is promising, as demonstrated by a number of field-based (pilot and full scale) and bench scale studies. In recent years, the use of zero-valent iron (ZVI) for the treatment of toxic contaminants in groundwater and wastewater has received wide attention and encouraging treatment efficiencies have been documented. In this review, nanoscale iron was prepared by pulse electrodeposition of nano iron by chemical reduction of iron chloride and iron sulfate. Our research focuses on iron nanoparticles preparation and its use for aqueous Cr(VI) reduction. The Cr(VI) reduction by the nFe0 prepared by electrochemical and blasting method at neutral pH were carried. The results show that blasting-nFe0 show lower reaction than the electrochemical-nFe0. It is because the blasting-nFe0 surface contains more Fe2O3 than the other one.

Enhancement of aerobic granulation by zero-valent iron in sequencing batch airlift reactor

This study elucidates the enhancement of aerobic granulation by zero-valent iron (ZVI). A reactor augmented with ZVI had a start-up time of aerobic granulation (43 days) that was notably less than that for a reactor without augmentation (64 days). The former reactor also had better removal efficiencies for chemical oxygen demand and ammonium. Moreover, the mature granules augmented with ZVI had better physical characteristics and produced more extracellular polymeric substances (especially of protein). Three-dimensional-excitation emission matrix fluorescence showed that ZVI enhanced organic material diversity. Additionally, ZVI enhanced the diversity of the microbial community. Fe2+ dissolution from ZVI helped reduce the start-up time of aerobic granulation and increased the extracellular polymeric substance content. Conclusively, the use of ZVI effectively enhanced aerobic granulation.

Simultaneous removal of CUII, NIII and ZNII by a granular mixture of zero-valent iron and pumice in column systems

The granular mixtures between zero-valent iron (ZVI) and other materials (e.g. sand, pumice) have been recently proposed to overcome the problems (e.g. clogging) related to the use of ZVI alone in treatment systems such as permeable reactive barriers or individual potabilisation systems. This paper presents the results of the research activity, carried out by column tests, aimed at comparing the performance of a granular mixture between ZVI and pumice (weight ratio 30:70) and of pure ZVI for the individual and combined removal of CuII, NiII and ZnII. The specific objective was to verify the occurrence of phenomena of mutual interaction and/or competition among contaminants. In fact, although metal removal by ZVI has been extensively documented in the past, the great majority of studies examined either very simple systems (i.e. single metal solutions) or very complicated ones (e.g. real acid mine drainage). In both cases, and for different reasons, the occurrence of mutual interactions (positive or negative) among the chemical species present in water is impossible to detect. For these reasons, this paper compares column experiments carried out in similar conditions using both monocontaminant and pluricontaminant solutions. The concentration values used for the three contaminants were of 500 or 50 mg/l for CuII and 50 mg/l for NiII and ZnII. In monocontaminant systems, in both reactive media the removal sequence observed is Cu > Zn > Ni. In pluricontaminant solutions, CuII removal is unaffected by the presence of the other metals while the removal efficiencies of Ni and Zn decrease in respect to monocontaminant tests. In the mixture ZVI/pumice, the long-term removal efficiency reduction is higher for Zn (about 58% in respect to the experiment carried out with the solution containing Zn only) than for Ni (reduction of about 33%), leading to the removal sequence Cu > Ni > Zn for the test with the highest CuII concentration. This behaviour has been explained, hypothesising the possible spontaneous formation of a bimetallic system between ZVI and Cu capable of enhancing Ni removal especially in the short term.

Removal of heavy metals from groundwater affected by acid mine drainage

Batch tests have been used to assess the level of the removal of metals (copper, nickel, cobalt, zinc, and chromium, in cationic and in anionic forms) from water at low pH values affected by acid mine drainage. The predominant processes which result in the removal with the use of zero-valent iron (Fe0) in Permeable Reactive Barrier Technology were evaluated. The most probable processes for each metal have been presented in drawings. There are: reductive precipitation leading to the metallic form, co- precipitation mainly with iron in the form of oxides and/or hydroxides and adsorption on the surface of iron corrosion products or on the surface of zero-valent iron.

Rapid decoloration of Reactive Black 5 by an advanced Fenton process in conjunction with ultrasound

The decoloration of reactive azo dye, Reactive Black 5 (RB5), by an advanced Fenton process in conjunction with ultrasound (Fenton/US) was investigated. The Fenton/US process using zero-valent iron (ZVI) aggregates as catalyst could achieve synergistic degradation of RB5, as compared to Fe(0)/US and Fenton systems. A synergy factor of 22.9 based on the first-order rate constant (k) was found. The decoloration efficiency was strongly influenced by initial pH, ZVI dose, H2O2 dose, ultrasonic input power, and the presence of salts in reaction solution. Experimental results showed that the optimum conditions for the decoloration of RB5 were ZVI 1g/L, initial pH 3.0, and H2O2 1.03×10−2mol/L with acoustic power of 120W/L at 60kHz. These conditions yielded 99% decoloration of 5.0×10−4M RB5 (ADMI 5605) solution within 10min treatment and the operation cost was only 2.25USD/m3. The dye solutions containing inorganic anions could retard the decoloration. The inhibitory effect of various inorganic anions on decoloration of RB5 followed the sequence of H2PO4-≫Cl->ClO4-≈NO3-≈SO42-. High acoustic power accelerated the reaction rate and increased decoloration efficiency. ZVI aggregates were reusable and the decoloration efficiency did not decrease substantially with repeated use of ZVI. Findings showed that the Fenton/US process could effectively decolor the reactive azo dye RB5 in wastewater.

Degradation and toxicity changes in aqueous solutions of chloroacetic acids by Fenton-like treatment using zero-valent iron

AbstractThree priority pollutants, i.e. mono-, di-, and trichloroacetic acids, were degraded by the conventional Fenton AOP system (Fe2+ and H2O2). The results obtained suggest that the degradation decreased in the order: monochloroacetic, dichloroacetic, and trichloroacetic acid. The best of advanced oxidation processes (AOPs) for the degradation of trichloroacetic acid was reductive dechlorination with the use of zero-valent iron (Fe°). The results of Escherichia coli toxicity tests revealed that the reagents’ toxicity after the Fenton treatment process was decreased.