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17 pages, 12025 KiB

Open AccessArticle

Spatiotemporal Analysis and Risk Prediction of Water Quality Using Copula Bayesian Networks: A Case in Qilu Lake, China

by Xiang Cheng, Shengrui Wang, Yue Dong, Zhaokui Ni and Yan Hong

Processes 2024, 12(12), 2922; https://doi.org/10.3390/pr12122922 - 20 Dec 2024

Lake water pollution under anthropogenic influences exhibits characteristics of high uncertainty, rapid evolution, and complex control challenges, presenting substantial threats to ecological systems and human health. Quantitative risk prediction provides crucial support for water quality deterioration prevention and management. This study employed the [...] Read more.

Lake water pollution under anthropogenic influences exhibits characteristics of high uncertainty, rapid evolution, and complex control challenges, presenting substantial threats to ecological systems and human health. Quantitative risk prediction provides crucial support for water quality deterioration prevention and management. This study employed the Copula Bayesian Network model to conduct a comprehensive risk assessment of water quality in Qilu Lake, China (2010–2020), incorporating inter-indicator correlations and multiple uncertainty sources. Analysis revealed generally “worse” water quality conditions (5.10 ± 1.35) according to established index classifications, with predicted probabilities of reaching “deteriorated” status ranging from 11.80% to 47.90%. Significant spatial and temporal variations in water quality and pollution risk were observed, primarily attributed to intensive agricultural non-point source loading and water resource deficiency. The study established early warning thresholds through key indicator concentration predictions, particularly for the southern region where “deteriorated” risk levels corresponded to specific ranges: TN (3.42–8.43 mg/L), TP (0.07–1.29 mg/L), and COD_Cr (27.75–67.19 mg/L). This methodology effectively characterizes lake water quality evolution while enabling risk prediction through key indicator monitoring. The findings provide substantial support for water pollution control strategies, risk management protocols, and regulatory decision-making for lake ecosystem administrators. Full article

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19 pages, 7053 KiB

Open AccessArticle

Field Study on Washing of 4-Methoxy-2-Nitroaniline from Contaminated Site by Dye Intermediates

by Zhili Wang, Kangwen Lao, Chen Chen, Hong Zhu, Yanfei Yang, Honghan Chen and Hao Pang

Processes 2024, 12(12), 2801; https://doi.org/10.3390/pr12122801 - 7 Dec 2024

Viewed by 346

Abstract

Dye intermediates are important industrial chemicals; there is a lack of systematic field experiments and relevant validation data regarding the remediation of groundwater contamination by dye intermediates. This study examines the eluting effects of alcohol eluting agents, non-ionic surfactants, and deionized water on [...] Read more.

Dye intermediates are important industrial chemicals; there is a lack of systematic field experiments and relevant validation data regarding the remediation of groundwater contamination by dye intermediates. This study examines the eluting effects of alcohol eluting agents, non-ionic surfactants, and deionized water on 4-methoxy-2-nitroaniline (4M2N) in a contaminated aquifer medium from a historically polluted dye intermediate production site in northwest China. The findings indicate that alcohol eluting agents exhibit superior eluting effects compared to non-ionic surfactants. Under optimized conditions, including 60% n-propanol concentration, a liquid-to-solid ratio of 15:1, two eluting cycles, an elution pH of 3, and a 2 h eluting duration, the eluting concentration of 4-methoxy-2-nitroaniline reached 75.49 mg/kg, exceeding that of the composite eluting agent by two times more and deionized water by three times further. Analysis revealed that the liquid-to-solid ratio and number of eluting cycles are the primary factors influencing eluting efficiency. Field trials conducted using treated groundwater involved injecting 31,560 m³ of treated groundwater over 152 days, resulting in the extraction of 38,550 m³ and the removal of about 1887 kg of 4-methoxy-2-nitroaniline. The concentrations of contaminants in both pumping wells and monitoring wells exhibited a certain degree of increase at various times. Field applications of treated groundwater washing facilitated the release of 4-methoxy-2-nitroaniline from the aquifer medium, which significantly enhances remediation efficiency. This provides theoretical support for data analysis and the promotion of similar remediation efforts. Full article

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13 pages, 2276 KiB

Open AccessArticle

Effects of Reclaimed Water Supplementation on the Occurrence and Distribution Characteristics of Antibiotic Resistance Genes in a Recipient River

by Xiaohui Zhao, Xiaofei Wang, Hang Lang, Panwei Zhang, Jie Ni and Wenqiang Wu

Processes 2024, 12(8), 1717; https://doi.org/10.3390/pr12081717 - 15 Aug 2024

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Abstract

Due to the serious scarcity of water resources and the aggravation of water pollution in northern China, replenishing reclaimed water can alleviate the water shortage problem in northern rivers to a certain extent, but has also become an important way for antibiotic resistance [...] Read more.

Due to the serious scarcity of water resources and the aggravation of water pollution in northern China, replenishing reclaimed water can alleviate the water shortage problem in northern rivers to a certain extent, but has also become an important way for antibiotic resistance genes (ARGs) to spread into rivers. In order to study the characteristics of ARGs in reclaimed water recharge rivers (Wenyu River), the abundance and distribution of ARGs in a typical reclaimed water replenishment river were analyzed by metagenomic sequencing technology combined with river water quality. The results showed that: due to the input of reclaimed water, the water quality characteristics of downstream sampling points of the river were significantly different from those upstream. Water quality factors such as total organic carbon, chemical oxygen demand, chlorophyll, and total nitrogen tended to increase gradually. Quinolones and macrolides were the main types of antibiotics. A total of 1217 ARGs were detected in the reclaimed water river system, including multidrug resistance, macrolide-lincosamide-streptogramin (MLS), tetracycline, glycopeptide, peptide, aminocoumarin, etc. The average abundance of ARGs in reclaimed water was higher than that in rivers. Among them, multidrug ARGs existed most widely, which may gradually become the main trend of ARGs’ evolutionary variation. RDA results revealed that the environmental factors EC and DO, as well as tetracycline antibiotics (TCs), may be important environmental factors affecting the distribution of ARGs. Full article

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17 pages, 2592 KiB

Open AccessArticle

Effects of Irrigation with Slightly Algae-Contaminated Water on Soil Moisture, Nutrient Redistribution, and Microbial Community

by Han Zheng, Xiaofei Wang, Chen Huang, Zhe Bao, Xiaohui Zhao, Zhanming Tan and En Xie

Processes 2024, 12(8), 1639; https://doi.org/10.3390/pr12081639 - 4 Aug 2024

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Abstract

The presence of excessive algae in water is always considered as a negative factor in irrigation. However, the optimal balance between algal removal and retention in irrigation water when the algal biomass is controllable remains unknown. Therefore, this study explores the impact of [...] Read more.

The presence of excessive algae in water is always considered as a negative factor in irrigation. However, the optimal balance between algal removal and retention in irrigation water when the algal biomass is controllable remains unknown. Therefore, this study explores the impact of low-level algal presence (Scytonema javanicum) on soil and microbial activity through controlled soil column experiments. Soil moisture was measured, and 16S rRNA gene amplicons sequencing was applied to characterize the microbial community. Slight community changes indicated no negative impact on the local microbial community of S. javanicum. Enzyme assays and quantitative polymerase chain reaction (qPCR) revealed that algae improved soil moisture retention, and enhanced the nutrient content of the topsoil. The decrease in moisture in the treatment group (from 27.53% to 26.42%) was significantly reduced (p < 0.05) compared to the control (from 27.55% to 25.17%), while the contents of ammonium (NH₃-N) and total nitrogen (TN) in the treatment (0.70 mg/kg and 0.54 g/kg) were also higher (p < 0.05) than that of the control (0.43 mg/kg and 0.49 g/kg). The results of the abundance of functional gene suggested algae facilitated nitrogen fixation and nitrification. This research offers innovative insights for diversifying the sources of irrigation water. Full article

(This article belongs to the Special Issue State-of-the-Art Wastewater Treatment Techniques)

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22 pages, 3831 KiB

Open AccessArticle

Candida parapsilosis CMGB-YT Biosurfactant for Treatment of Heavy Metal- and Microbial-Contaminated Wastewater

by Ortansa Elisabeta Csutak, Nicoleta-Oana Nicula, Eduard-Marius Lungulescu, Virgil Emanuel Marinescu, Ioana Catalina Gifu and Viorica Maria Corbu

Processes 2024, 12(7), 1471; https://doi.org/10.3390/pr12071471 - 13 Jul 2024

Cited by 1 | Viewed by 1045

Abstract

During the last few decades, water pollution has become a growing concern at international level. To date, only a few Candida parapsilosis strains were successfully used in environmental remediation. In the present article, the strain C. parapsilosis CMGB-YT was studied for its ability [...] Read more.

During the last few decades, water pollution has become a growing concern at international level. To date, only a few Candida parapsilosis strains were successfully used in environmental remediation. In the present article, the strain C. parapsilosis CMGB-YT was studied for its ability to assimilate hydrophobic substrates and to produce biosurfactants with antimicrobial activity and positive effects on heavy metal removal from contaminated wastewaters. The strain C. parapsilosis CMGB-YT was grown on yeast peptone (YP) media with 1% n-decane, n-dodecane, n-tetradecane, n-hexadecane, as well as commercial sunflower and olive oils. The production of the biosurfactant was evaluated using the emulsification index (E_24%). The surface properties and emulsifying stability of the biosurfactant were determined. The effect of the biosurfactant on the cell growth of two strains of Rhodotorula mucilaginosa and on their removal capacity of lead (0.032 g/L) and cadmium (0.030 g/L) ions from synthetic wastewater were also studied. The antimicrobial potential of 20 mg/mL and 40 mg/mL biosurfactant was established in the presence of pathogenic Candida krusei strains. C. parapsilosis CMGB-YT assimilated n-hexadecane with good rates over 216 h and produced an anionic glycolipidic biosurfactant with stable E_24% towards long-chain carbon compounds at different temperatures, with an alkaline pH and high salinity (10% NaCl). The biosurfactant reduced the surface tension to 53.58 ± 0.42 mN/m, while the critical micellar concentration (CMC) was reached at 4.2% biosurfactant. The crude biosurfactant (5%) enhanced R. mucilaginosa growth in heavy metal-contaminated wastewater, increased chemical oxygen demand (COD) removal of up to 80%, and improved Cd²⁺ removal by 10%. Additionally, the concentrated biosurfactant effectively prevented Candida krusei biofilm formation. In conclusion, the biosurfactant produced by C. parapsilosis CMGB-YT demonstrates promising potential for the efficient treatment of wastewater contaminated with heavy metals and microbial pathogens. Full article

(This article belongs to the Special Issue State-of-the-Art Wastewater Treatment Techniques)

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20 pages, 11336 KiB

Open AccessArticle

Improved Dujiangyan Irrigation System Optimization (IDISO): A Novel Metaheuristic Algorithm for Hydrochar Characteristics

by Jingyuan Shi, Dapeng Zhang, Zifeng Sui, Jie Wu, Zifeng Zhang, Wenjie Hu, Zhanpeng Huo and Yongfu Wu

Processes 2024, 12(7), 1321; https://doi.org/10.3390/pr12071321 - 26 Jun 2024

Viewed by 1268

Abstract

Hyperparameter tuning is crucial in the development of machine learning models. This study introduces the nonlinear shrinking factor and the Cauchy mutation mechanism to improve the Dujiangyan Irrigation System Optimization (DISO), proposing the improved Dujiangyan Irrigation System Optimization algorithm (IDISO) for hyperparameter tuning [...] Read more.

Hyperparameter tuning is crucial in the development of machine learning models. This study introduces the nonlinear shrinking factor and the Cauchy mutation mechanism to improve the Dujiangyan Irrigation System Optimization (DISO), proposing the improved Dujiangyan Irrigation System Optimization algorithm (IDISO) for hyperparameter tuning in machine learning. The optimization capabilities and convergence performance of IDISO were validated on 87 CEC2017 benchmark functions of varying dimensions and nine real-world engineering problems, demonstrating that it significantly outperforms DISO in terms of convergence speed and accuracy, and ranks first in overall performance among the seventeen advanced metaheuristic algorithms being compared. To construct a robust and generalizable prediction model for hydrochar element characteristics, this study utilized IDISO and DISO algorithms to fine-tune the parameters of the XGBoost model. The experimental results show that the IDISO-XGBoost model achieved an average prediction performance of 0.95, which represents a 4% improvement over the DISO-XGBoost model. These results indicate that the IDISO algorithm has significant potential and value in practical applications. Full article

(This article belongs to the Special Issue State-of-the-Art Wastewater Treatment Techniques)

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13 pages, 10711 KiB

Open AccessArticle

Preparation of Bioaerogel from Iron-Rich Microalgae for the Removal of Water Pollutants

by Xinqi Niu, Junhui Si, Binyi Chen, Qianting Wang, Sen Zeng and Zhixiang Cui

Processes 2024, 12(7), 1313; https://doi.org/10.3390/pr12071313 - 24 Jun 2024

Cited by 1 | Viewed by 1189

Abstract

Microalgae-based materials have gained significant attention considering their rich resources, cost-effectiveness, and environmental friendliness. Herein, iron-rich microalgae (Chlorella pyrenoidosa, CP) were treated by hydrothermal reaction under alkaline conditions to remove the protoplast and obtain a hollow shell with an Fe_xO_y [...] Read more.

Microalgae-based materials have gained significant attention considering their rich resources, cost-effectiveness, and environmental friendliness. Herein, iron-rich microalgae (Chlorella pyrenoidosa, CP) were treated by hydrothermal reaction under alkaline conditions to remove the protoplast and obtain a hollow shell with an Fe_xO_y core inside. Then, the iron-rich microalgae-based aerogel (Fe-CP aerogel) was fabricated through a freeze-drying process. The as-prepared Fe-CP aerogel exhibited superior adsorption performance, and the maximum adsorption quantity for Cu²⁺ could reach 208.3 mg/g due to the synergistic adsorption of the hollow shell of CP cells and Fe_xO_y core. The Fe-CP aerogel also possessed super-hydrophilicity and displayed high separation efficiency (over 99%) when used for separating different oil/water emulsions. Moreover, the existence of Fe_xO_y endowed the Fe-CP aerogel with photo-Fenton activity, thus exhibiting excellent antifouling performance. The prepared Fe-CP aerogel could be considered an ideal adsorbent, with green, efficient, low-cost, and regenerative properties, and has the potential for the practical treatment of wastewater. Full article

(This article belongs to the Special Issue State-of-the-Art Wastewater Treatment Techniques)

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18 pages, 3483 KiB

Open AccessArticle

Effects of Vegetation Cover Varying along the Hydrological Gradient on Microbial Community and N-Cycling Gene Abundance in a Plateau Lake Littoral Zone

by Jing Yuan, Jing Cao, Wanxue Liao, Feng Zhu, Zeying Hou and Zhaosheng Chu

Processes 2024, 12(6), 1276; https://doi.org/10.3390/pr12061276 - 20 Jun 2024

Cited by 1 | Viewed by 979

Abstract

The lake littoral zone is periodically exposed to water due to water level fluctuations, driving the succession and distribution of littoral vegetation covers, which complexly affect nutrient biogeochemical transformation. However, the combined effects of water level fluctuations and other environmental factors on microbial [...] Read more.

The lake littoral zone is periodically exposed to water due to water level fluctuations, driving the succession and distribution of littoral vegetation covers, which complexly affect nutrient biogeochemical transformation. However, the combined effects of water level fluctuations and other environmental factors on microbial characteristics and functions at the regional scale remain unclear. In this study, typical vegetation cover types along various water levels were chosen to investigate the effects of water level and vegetation cover on the microbial community and functional genes in the Lake Erhai littoral zone. The results showed that water level fluctuations influenced oxygen and nitrogen compound contents due to oxic–anoxic alternations and intensive material exchange. Meanwhile, vegetation cover affected the organic matter and total nitrogen content through plant residues and root exudation supplying exogenous carbon and nitrogen. Along the hydrological gradient, the high microbial diversity and abundant microbes related to nitrogen cycling were observed in interface sediments. It was attributed to the alternating aerobic–anaerobic environments, which filtered adaptable dominant phyla and genera. The abundances of amoA AOA, nirS, and amx were higher than those of the other genes and were strongly related to flooding days and water content. In conclusion, water level fluctuations and vegetation type jointly affect microbial community structure and nitrogen-related functional genes. Full article

(This article belongs to the Special Issue State-of-the-Art Wastewater Treatment Techniques)

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16 pages, 2934 KiB

Open AccessEditor’s ChoiceArticle

Controlling Eutrophication of Aquaculture Production Water Using Biochar: Correlation of Molecular Composition with Adsorption Characteristics as Revealed by FT-ICR Mass Spectrometry

by William F. Rance Bare, Ethan Struhs, Amin Mirkouei, Kenneth Overturf, Martha L. Chacón-Patiño, Amy M. McKenna, Huan Chen and Krishnan S. Raja

Processes 2023, 11(10), 2883; https://doi.org/10.3390/pr11102883 - 30 Sep 2023

Cited by 1 | Viewed by 1897

Abstract

This study aims to construct a novel and sustainable approach for remediating aquaculture-generated water contamination using various engineered biochars. Particularly, this study focuses on capturing nitrogen and phosphorus from downstream water of commercial fish farms in Magic Valley, Idaho, containing approximately 2.26 mg/L [...] Read more.

This study aims to construct a novel and sustainable approach for remediating aquaculture-generated water contamination using various engineered biochars. Particularly, this study focuses on capturing nitrogen and phosphorus from downstream water of commercial fish farms in Magic Valley, Idaho, containing approximately 2.26 mg/L of nitrogen and 0.15 mg/L of phosphorous. The results indicate that the proposed approach can improve downstream waters by adsorbing micronutrients (e.g., nitrogen-ammonia, nitrate-n + nitrite-n, and total phosphorus). Water treatment time and biochar pH are two key parameters strongly associated with adsorbed compounds. Molecular-level characterization of solvent-extracted organics from biochar materials (before and after water treatment) suggests increased levels of highly oxygenated molecules as a function of increasing water treatment time. Also, the results show the enrichment in organic species with higher molecular weight and increased double bond equivalents, with a compositional range similar to that of dissolved organic matter. Upon water treatment, extracted organics revealed higher abundances of compounds with higher H/C and O/C ratios. The engineered biochars, after water treatment, can be reused as nutrient-rich fertilizers. This study concluded that the engineered biochars could sequester more nitrogen and phosphorous over time. Also, the proposed approach can simultaneously increase fish production capacity and support the aquaculture industry in different regions by improving water quality and enabling aquaculture expansion. Full article

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16 pages, 2525 KiB

Open AccessArticle

Response of Nitrogen Removal Performance and Microbial Distribution to Seasonal Shock Nutrients Load in a Lakeshore Multicell Constructed Wetland

by Jing Yuan, Bin Wang, Zeying Hou, Jiayu Peng, Dan Li and Zhaosheng Chu

Processes 2023, 11(9), 2781; https://doi.org/10.3390/pr11092781 - 18 Sep 2023

Cited by 3 | Viewed by 1227

Abstract

Multicell constructed wetlands (MCWs) on lakeshores are a prospective treatment technique. However, the factors affecting the nutrient removal performance of lakeshore MCWs at the field scale are unclear. This study chose a field-scale lakeshore MCW with the highest mass removal efficiency (approximately 49,175.12 [...] Read more.

Multicell constructed wetlands (MCWs) on lakeshores are a prospective treatment technique. However, the factors affecting the nutrient removal performance of lakeshore MCWs at the field scale are unclear. This study chose a field-scale lakeshore MCW with the highest mass removal efficiency (approximately 49,175.12 mg m⁻² day⁻¹) for total nitrogen removal in the wet season to investigate the response of nitrogen removal and microbial distribution to seasonal shock nutrients load. The mass loading rates in the wet season were as high as 43~72 times over those in the dry season. Hence, a storage pond (SP), as a forebay retention cell, was necessary to mitigate the shock loads of the influent, which is beneficial to nitrogen removal of the MCW system. The two major genera in the sediments are heterotrophic nitrification–aerobic denitrification bacteria, and the abundance and species of the nitrogen-related functional genera were higher in the wet season than the dry season. According to the results of redundancy analysis, the hydraulic residence time (29.4%, F = 2.2, p < 0.1) and hydraulic loading rate (85.9, F = 36.5, p < 0.05) were the major factors explaining microbial community variation, instead of environmental factors (temperature, pH, and dissolved oxygen). The shock loads of influent and the periodic saturation in sediments contributed to a complicated oxygen and nitrogen nutrient exchange environment resulting in higher abundance and species of nitrogen-related microbes, which is beneficial to nitrogen removal in lakeshore MCWs. The results provided a scientific basis for the optimal design of constructed wetlands on lakeshores. Full article

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14 pages, 3235 KiB

Open AccessArticle

Surface Runoff and Diffuse Nitrogen Loss Dynamics in a Mixed Land Use Watershed with a Subtropical Monsoon Climate

by Congyu Hou, Zhifeng Yang and Wei Ouyang

Processes 2023, 11(7), 1910; https://doi.org/10.3390/pr11071910 - 25 Jun 2023

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Abstract

The surface hydrology and diffuse pollution loading is hypothesized based on the unique characteristics under different rainfall types in watersheds with a subtropical monsoon climate. This study evaluated the effects of different rainfall event intensity on surface runoff and diffuse nitrogen loss in [...] Read more.

The surface hydrology and diffuse pollution loading is hypothesized based on the unique characteristics under different rainfall types in watersheds with a subtropical monsoon climate. This study evaluated the effects of different rainfall event intensity on surface runoff and diffuse nitrogen loss in a subtropical watershed located in the latitude range between 22.5° north and 25° north in southern China by adapting the hydrological model SWAT (Soil and Water Assessment Tool). The rainfall events were classified into four categories including light rainfall (LR), moderate rainfall (MR), intense rainfall (IR), and extreme rainfall (ER). Our results showed that the ER events had the lowest occurrences of 7 days per year, but they contributed the most to total surface runoff (54.29%) and TN losses (57.63%) in the subtropical watershed researched. Although forests and pastures had a better effect on reducing diffuse pollution, their surface runoff and nitrogen loss were still proved to be serious under ER events. As for the nitrogen loss form, water-soluble nitrogen oxides nitrogen (ON-N) loss was the dominant form of total nitrogen (TN) loss, which accounted for 90% of the total loss in the simulated watershed in the subtropical monsoon climate region. Under LR events, however, nitrate nitrogen (NO₃-N) accounted for 74.54% and 55.59% of TN losses from paddy fields and dry lands, respectively. The effects of antecedent soil water content (ASW) on surface runoff and TN loss were higher under ER events. The surface runoff and TN loss in the high-ASW condition were 1.17–3.86 times and 1.34–1.76 times higher, respectively, than in the low-ASW condition. These findings highlighted the important influence of ER events on diffuse pollution and have significant implications for controlling diffuse pollution under different rainfall types. This conclusion proved that extra attention and efforts are required in handling non-point-source pollution in subtropical monsoon watersheds than the watersheds in cooler regions because the natural systems including forest and pastures are no longer effective enough in controlling surface runoff and TN loss during ER. Full article

(This article belongs to the Special Issue State-of-the-Art Wastewater Treatment Techniques)

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Review

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17 pages, 6613 KiB

Open AccessReview

A Mini-Review on the Use of Chelating or Reducing Agents to Improve Fe(II)-Fe(III) Cycles in Persulfate/Fe(II) Systems

by Lanbing Feng, Yun Zeng, Pan Wang, Na Duan, Haodong Ji and Xiao Zhao

Processes 2024, 12(11), 2361; https://doi.org/10.3390/pr12112361 - 28 Oct 2024

Viewed by 671

Abstract

Persulfates (PSs) have recently gained recognition as strong oxidants notably for soil and groundwater remediation. Ferrous iron (Fe(II)) has been extensively employed in activating PS. However, the PS/Fe(II) system still suffers from some inherent drawbacks, including the fast accumulation of ferric ion (Fe(III)) [...] Read more.

Persulfates (PSs) have recently gained recognition as strong oxidants notably for soil and groundwater remediation. Ferrous iron (Fe(II)) has been extensively employed in activating PS. However, the PS/Fe(II) system still suffers from some inherent drawbacks, including the fast accumulation of ferric ion (Fe(III)) or precipitation of Fe(III), sluggish conversion from Fe(III) to Fe(II), and the unwanted scavenging of SO₄^•− by excess Fe(II). To overcome these issues, the following two types of reagents are usually used: chelating agents and reducing agents. There are 11 chelating agents mentioned in this paper (EDTA, CA, etc.) and 3 reducing agents (HA, thiosulfate and A-Boron). This review extracted data from studies to give a data-based overview on how the added agents can improve the PS/Fe(II) system under varied conditions. The mechanisms of improvement by chelating agents could be classified into the following three categories: to control excess Fe(II), reduce Fe(III) to Fe(II), and inhibit Fe precipitation. The data analysis suggested an optimal working agent/Fe(II) ratio of 0–2 with acidic and neutral pH. The mechanism of using a reducing agent for PS/Fe(II) system improvement is simply reducing Fe(III) to Fe(II), using hydroxylamine, thiosulfate, etc. The improvement was significant at a hydroxylamine/Fe (II) molar ratio between 0 and 10, yet overdosed hydroxylamine can scavenge the reactive radicals, resulting in negative effects. The future research trend was also proposed in this review. Full article

(This article belongs to the Special Issue State-of-the-Art Wastewater Treatment Techniques)

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