Field Study on Washing of 4-Methoxy-2-Nitroaniline from Contaminated Site by Dye Intermediates
by
,
Zhili Wang
1
,
Kangwen Lao
2,
Chen Chen
3,
Hong Zhu
3,
Yanfei Yang
4,
Honghan Chen
1,* and
Hao Pang
3 1
School of Water Resources and Environment, China University of Geosciences, Beijing 100083, China
2
Advanced Institute of Natural Sciences, Beijing Normal University, Zhuhai 519087, China
3
Beijing Zhongdihongke Environmental Technology Co., Ltd., Beijing 100028, China
4
Nuclear and Radiological Safety Center of the Ministry of Ecological Environment, Beijing 100082, China
*
Author to whom correspondence should be addressed.
Processes 2024, 12(12), 2801; https://doi.org/10.3390/pr12122801
Submission received: 31 October 2024
/
Revised: 22 November 2024
/
Accepted: 6 December 2024
/
Published: 7 December 2024
(This article belongs to the Special Issue State-of-the-Art Wastewater Treatment Techniques)
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 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.
1. Introduction
China is a leading producer of dye intermediates, essential industrial chemicals extensively utilized in the dye and pharmaceutical sectors [1,2,3]. The complex production processes generate substantial by-products and waste, which, if inadequately managed, can result in severe soil and groundwater pollution. This investigation targets a historically contaminated dye intermediate production site, where primary raw materials include p-aminobenzyl ether, glacial acetic acid, and nitric acid, yielding 2-amino-4-acetamidobenzyl ether through sequential acetylation, nitration, and reduction reactions. The resultant wastewater and solid waste have severely contaminated soil and groundwater, leading to elevated CODCr concentrations in groundwater, often reaching tens of thousands of mg/L, and pH levels as low as 1–4. Notably, 4-methoxy-2-nitroaniline constitutes about 81.03% of the organic contaminants in the groundwater, accompanied by other pollutants, including 4-methoxy-3-nitroaniline, p-aminobenzyl ether, 3-chloroaniline, 4-chloroaniline, 2-amino-4-acetamidobenzyl ether, and aniline.
4-methoxy-2-nitroaniline exhibits high toxicity and intense coloration, facilitating its entry into the human body through dermal contact, inhalation, or ingestion, which severely impairs hematopoietic functions in the spleen, liver, and bone marrow. Exposure to this compound can lead to various adverse health effects, including methemoglobinemia, hepatotoxicity, hypoxia, hemorrhagic conditions, and neurotoxicity, posing significant threats to human life. The presence of nitro groups in its molecular structure enhances environmental stability by reducing the reactivity of the benzene ring, resulting in persistent toxicity and potential mutagenic and carcinogenic properties. Consequently, 4-methoxy-2-nitroaniline has been designated a priority pollutant in multiple countries [4].
Research on 4-methoxy-2-nitroaniline has primarily concentrated on its synthesis methodologies [5,6], applications as a pharmaceutical intermediate [7,8], physical properties [9,10,11,12], and toxicity assessments [13]. In contrast, remediation strategies for mitigating its contamination in groundwater and the aquifer medium have received relatively little attention, highlighting a significant knowledge gap in addressing its environmental impacts.
Considering the contaminated groundwater characteristics at this site, including diverse pollutants, high concentrations, structural stability of dye intermediates, poor biocompatibility, and pronounced toxicity, in situ remediation has incorporated extraction and treatment techniques. Long-term water extraction can lead to the development of dominant pathways, reducing solid–liquid contact in the absence of injection water disturbances. This reduction gradually decreases extraction efficiency. Furthermore, the absence of sufficient eluting agents hinders the effective removal of strongly adsorptive pollutants. Therefore, the gradual decline in extraction efficiency due to the slow release of pollutants from the aquifer medium necessitates alternative strategies. This study conducts washing experiments targeting 4-methoxy-2-nitroaniline, the primary organic pollutant in the aquifer medium, aiming to enhance extraction and treatment efficiency. The primary objective is to expedite contaminant release from the aquifer medium through targeted eluting agent injection into the aquifer, thereby mitigating the tailing and rebound phenomena commonly associated with extraction and treatment processes.
2. Materials and Methods
2.1. Aquifer Medium Sample Collection and Preservation
The study site is situated in a desert region in northwest China, where a factory operated from 1998 to 2014, producing dye intermediates (2-Amino-4-acetamino anisole). The pollution of soil and groundwater resulted from the discharge of wastewater outside the factory premises. The primary raw materials included p-anisidine, sulfuric acid, acetic acid, and nitric acid. Consequently, groundwater in the area exhibits strong acidity [14] and contains ultra-high concentrations of organic pollutants.
The experimental aquifer medium was obtained from the study site. The unconfined aquifer primarily consisted of Quaternary silty-fine sand, with the water table located at depths of 13.9 to 19.7 m below the surface. The aquifer had an approximate thickness of 25 m, and samples of the aquifer medium were collected from depths ranging between 17 and 35 m below the surface. The collected aquifer medium underwent freeze-drying using lyophilization, in order to ensure aquifer medium properties and minimize the volatilization of organic pollutants. Subsequent processing involved grinding and sieving the dried medium to achieve a uniform particle size of 0.25 mm (60 mesh), thereby ensuring homogeneity for subsequent experiments. The basic physical and chemical properties of the prepared aquifer medium samples are presented in Table 1. The moisture content of the samples was determined to be 0.2%.
2.2. Reagent and Instrument
All chemicals such as methanol (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), ethanol (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), n-propanol (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), hydrochloric acid (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), sodium hydroxide (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), polyethylene glycol sorbitan monooleate (Tween-80, C24H44O6) (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), alkyl glycoside (APG, C16H32O6) (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China), and polyethylene glycol tert-octylphenyl ether (Triton X-100, C34H62O11) (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China) were of analytical grade, and deionized water was used for experiments. The basic physical and chemical properties of non-ionic surfactants and alcohol-eluting agents are shown in Table 2.
In this study, a vacuum freeze-dryer (ZLGJ-18, Zhengzhou Huachen Instrument Co., Ltd., Zhengzhou, China), high-performance liquid chromatography (HPLC, 1220 Infinity II, Agilent, Santa Clara, CA, USA) system, ultrasonic cleaning device (KQ-50B, Kunshan Ultrasonic Instrument Co., Ltd., Kunshan, China), vortex mixer (WIGGENS Vortex3000-Elite, Germany), digital thermostatic shaker (HNY-2102C, Tianjin ONuo Instrument Co., Ltd., Tianjin, China), centrifuge (TGL-20M, Changzhou Jintan Liangyou Instrument Co., Ltd., Changzhou, China), electronic analytical balance (AL104, Mettler Toledo, Greifensee, Switzerland), and pH meter (PB-10, Sartorius, Germany) were used.
2.3. Method of Eluting Experiment
The following non-ionic surfactants and alcohol eluting agents were selected for single eluting agent orthogonal experiments: Triton X-100, Tween-80, and APG, along with methanol, ethanol, and n-propanol. The eluting conditions employed are summarized in Table 3.
A 3.00 g prepared sample of the contaminated aquifer medium was accurately weighed and distributed among 50 mL centrifuge tubes. Eluting agents were added as specified in Table 3. The sealed tubes were vortexed for 5 s to disperse the prepared sample and then placed horizontally on a temperature-controlled shaker at 20 °C and 200 r/min for the designated duration. Upon completion, the tubes were centrifuged at 3000 r/min for 5 min. The resulting supernatant was collected with a 10 mL syringe, filtered through a 0.22 μm PES membrane, and subjected to HPLC analysis for the 4-methoxy-2-nitroaniline concentration. After decanting the supernatant, a specified volume of eluting agents was added to the sample for subsequent elution cycles, repeating the same steps as before. The concentration of 4-methoxy-2-nitroaniline in each eluent was measured and multiplied by the volume of eluent added per treatment to calculate the mass of 4-methoxy-2-nitroaniline in the eluent. The total mass of 4-methoxy-2-nitroaniline from all elution cycles was then divided by 3 g, which was the mass of the contaminated aquifer medium used in the experiment, to determine the eluted 4-methoxy-2-nitroaniline content.
Q = ∑(Ci × Vi) ÷ m
Q—eluted 4-mehoxy-2-nitroaniline content, relative to solid media, mg/kg;
C—concentration of 4-methoxy-2-nitroaniline in the eluent, mg/L;
V—volume of the eluent per treatment, L;
I—number of eluting cycles;
M—mass of the contaminated aquifer medium used in the experiment, kg.
Based on the orthogonal experiment results, the mixture experiment of non-ionic surfactants was conducted, and the eluting effect was compared with that of the alcohol eluting agent to determine the optimal eluting agents and conditions. The experimental method is detailed in Section 3.3.
In order to promote the release of pollutants on the aquifer medium and verify the applicability of washing technology in the research site, a pilot test was conducted on site, using treated groundwater for injection washing. The test conditions are detailed in Section 3.5.
2.4. Determination Method
The concentration of 4-methoxy-2-nitroaniline in the eluent was analyzed by high-performance liquid chromatography (HPLC, 1220 Infinity II, Agilent). The eluent, following filtration through a 0.22 μm PES membrane filter, was transferred into a brown glass vial for HPLC analysis using an Agilent XDB-C18 column. The mobile phase consisted of water and methanol in a 6:4 ratio, with a flow rate of 1 mL/min and an injection volume of 10 μL. The column temperature was kept at 30 °C, with detection conducted at a wavelength of 232 nm. pH measurements were carried out via the glass electrode method.
3. Results and Discussion
3.1. Alcohol Eluting Agent Eluting Experiments
The outcomes of the alcohol eluting agent eluting experiments are summarized in Table 4, Table 5 and Table 6. Comparative analysis indicates that the A7 group demonstrated optimal eluting performance in the methanol experiment, characterized by 60% methanol concentration, a 15:1 liquid-to-solid ratio, a 2 h eluting time, pH 3, and two eluting cycles, yielding a 4-methoxy-2-nitroaniline eluting content of 51.29 mg/kg. Conversely, the ethanol experiment showed the B13 group exhibiting superior performance, with 100% ethanol concentration, a 15:1 liquid-to-solid ratio, a 0.5 h eluting time, pH 4.5, and three eluting cycles, resulting in a 4-methoxy-2-nitroaniline content of 69.52 mg/kg. The n-propanol experiment revealed the C7 group as optimal, with 60% n-propanol concentration, a 15:1 liquid-to-solid ratio, a 2 h eluting time, pH 3, and two eluting cycles, yielding 75.49 mg/kg of 4-methoxy-2-nitroaniline.
These findings indicate that n-propanol is the most effective elution agent. The order of influence for n-propanol is liquid-to-solid ratio > number of eluting cycles > eluting solution pH > n-propanol concentration > eluting time. The eluting efficiency of alcohol-based agents is significantly influenced by the alcohol chain length. As the concentration of long-chain alcohols in the system increases, the system’s lipophilicity enhances, reducing the curvature of the interfacial film and increasing micelle aggregation. This leads to an improved eluting effect of the eluent. Conversely, short-chain alcohols exhibit stronger hydrophilicity, resulting in slightly lower eluting efficiency compared to that of long-chain alcohols [15,16,17]. Experimental results indicate that 4-methoxy-2-nitroaniline is more effectively transferred from the aquifer medium to the eluent when n-propyl alcohol is used as the eluting agent.
Alcohol eluting agents reduce the interfacial tension between contaminants and water through wetting, foaming, and emulsification. The optimal concentration of alcohol required must overcome the stable value of the interfacial tension. The polarity order of the tested alcohols, from highest to lowest, is methanol > ethanol > n-propanol [18]. This decrease in polarity effectively reduces interfacial tension, enhancing pollutant mobility and facilitating the transfer of 4-methoxy-2-nitroaniline from the aqueous phase to the eluent [19]. Alcohol-based eluting agents are also effective for polycyclic aromatic hydrocarbons and various nitroaniline compounds, including 4-methoxy-3-nitroaniline and similar substances. Notably, optimal alcohol concentrations decrease with decreasing polarity, attributed to achieving a stable interfacial tension value [20,21]. The liquid-to-solid ratio and number of eluting cycles are the dominant factors influencing alcohol eluting agents’ effectiveness. A higher liquid-to-solid ratio yields better outcomes, with optimal eluting cycles ranging between two and three. The optimal pH value for n-propanol eluent determined in this experiment is 3, suitable for an acid-contaminated site. For practical application and safety considerations, the use of a low-concentration n-propyl alcohol solution is recommended for field-scale operations.
3.2. Non-Ionic Surfactant Eluting Experiments
The results of non-ionic surfactant eluting experiments are presented in Table 7, Table 8 and Table 9. Comparative analysis reveals optimal eluting performance was achieved by the D4 group in the APG experiment, characterized by an APG concentration of 0.5 g/L, a liquid-to-solid ratio of 15:1, an eluting time of 3 h, a pH of 7, and four eluting cycles, resulting in a 4-methoxy-2-nitroaniline eluting content of 34.80 mg/kg. Similarly, the E4 group exhibited optimal results in the Triton X-100 experiment, with conditions including a 0.5 g/L Triton X-100 concentration, a liquid-to-solid ratio of 15:1, an eluting time of 3 h, an eluting pH of 7, and four eluting cycles, yielding 32.40 mg/kg of 4-methoxy-2-nitroaniline. The Tween-80 experiment showed the F4 group achieved optimal performance, corresponding to a Tween-80 concentration of 0.5 g/L, a liquid-to-solid ratio of 15:1, an eluting time of 3 h, a pH of 7, and four eluting cycles, with an eluting content of 31.20 mg/kg of 4-methoxy-2-nitroaniline.
The experimental results demonstrate that APG exhibited superior eluting performance among the three non-ionic surfactants tested. The factors influencing the effectiveness of APG follow the order as follows: solid-to-liquid ratio > number of eluting cycles > APG concentration > elution pH > eluting time. The unique hydrophilic and oleophilic structure of surfactants allows the formation of a layer of non-polar hydrocarbon chains on the water surface, reducing the interfacial tension between phases. When the concentration of surfactant in water surpasses the critical micelle concentration, monomer adsorption at the interface saturates, minimizing interfacial tension. Excess surfactant molecules aggregate in solution, forming micelles with hydrophilic groups oriented outward, facilitating pollutant desorption from soil surfaces and dispersing them into the aqueous phase for enhanced dissolution [22]. Non-ionic surfactants, characterized by lower critical micelle concentrations compared to those of anionic surfactants, exhibit greater solubilization capacity and superior pollutant elution efficiency [23]. In this study, non-ionic surfactants were utilized due to these advantages. While differences in solubilization effects among the three non-ionic surfactants studied were minimal, APG stands out for its superior environmental compatibility, non-toxicity, biodegradability, and enhanced pollutant solubilization. These properties make APG a suitable alternative for on-site applications [24].
The eluting effect of a single surfactant was positively correlated with the liquid–solid ratio and the eluting cycles. With the increase in the liquid–solid ratio and the eluting cycles, the eluting amount of 4-methoxy-2-nitroaniline gradually increased. This finding aligns with previous studies indicating favorable eluting of hydrophobic organic compounds at liquid-to-solid ratios between 4:1 and 20:1 [25]. The optimal liquid-to-solid ratio of 15:1 obtained in this study falls within this recommended range.
The primary mechanisms (Figure 1) governing surfactant interactions with pollutants on the aquifer medium include [26] (1) the incorporation of pollutants into surfactant micelles, reducing aquifer medium surface adsorption; (2) competition between surfactants and pollutants for aquifer medium adsorption sites, decreasing pollutant adsorption; (3) the dispersion of aquifer medium particles by surfactants, increasing available adsorption sites and enhancing pollutant adsorption; and (4) the formation of a secondary adsorption layer through surfactant adsorption on aquifer medium surfaces, re-adsorbing pollutants.
However, increasing surfactant concentration does not enhance eluting effectiveness. At lower concentrations, micelles are not formed or are present in low concentrations, effectively reducing interfacial tension and facilitating eluent entry into pore spaces, thereby promoting 4-methoxy-2-nitroaniline removal. However, as surfactant concentration increases, the number of micelles rises, leading to increased adsorption of the aquifer medium onto micelles, resulting in heightened surfactant loss due to adsorption. Furthermore, micelle adsorption on the medium surface can cause re-adsorption of 4-methoxy-2-nitroaniline, ultimately diminishing eluting effectiveness.
3.3. Determination of Optimal Eluting Agents and Conditions
APG and Triton X-100 were selected for blending due to their superior eluting performance. The surfactant concentration was standardized at 0.5 g/L, with a fixed liquid-to-solid ratio of 15:1, a pH of 7, and an eluting duration of 3 h, divided into four cycles. Various volume proportions of APG solution were evaluated: 0%, 20%, 40%, 50%, 60%, 80%, and 100%. Three control groups were also established, as detailed in Table 10. The outcomes of these experiments are presented in Figure 2.
The experimental results revealed variations in the effectiveness of combined eluting agents with different APG to Triton X-100 ratios. Optimal eluting occurred when the APG solution comprised 80% of the volume, resulting in a 4-methoxy-2-nitroaniline concentration of 42.01 mg/kg. The APG and Triton X-100 mixture outperformed individual non-ionic surfactants. The likely explanation is that the combination of surfactants leads to the formation of mixed micelles and adsorption layers. The critical micelle concentration of the resulting complex surfactants is lower than that of individual surfactants [27], enhancing the distribution coefficient of pollutants within the micelles and increasing the interaction opportunities between pollutants and micelles. The composite eluting agents exhibit a synergistic enhancement effect among their various components, which demonstrates greater adaptability to different remediation environments and conditions. This synergy can neutralize potential adverse effects caused by individual components, which thus enhances the efficiency of contaminant desorption.
Compared to the control group, significant differences in eluting performance were observed between the combined eluting agent and alcohol-based eluting agents. Under optimal conditions, the eluting efficiency of n-propyl alcohol surpasses that of compound eluting agents, making it the most effective eluent. However, its usage should be carefully evaluated with regard to dosage and potential impacts on human health and the environment. For on-site applications, it is essential to ensure that its use does not pose safety risks or lead to secondary pollution, and it should only be implemented under conditions that guarantee these considerations.
3.4. Deionized Water Washing Experiments
The experimental results indicate that the liquid-to-solid ratio and the number of eluting cycles are the two primary factors influencing eluting effectiveness. The liquid-to-solid ratio directly affects the contact area and contact time between the eluting agent and the contaminants in the aquifer medium, which thus impacts the effectiveness of a single eluting cycle. In contrast, the number of eluting cycles influences the cumulative removal of contaminants. Considering practical feasibility, safety, and economic factors, deionized water was used for washing tests to compare the washing effect of alcohol eluting agents and surfactants. The results are shown in Table 11. Comparative analysis reveals the G4 group achieved optimal washing performance, characterized by a liquid-to-solid ratio of 15:1, a washing time of 3 h, an elution pH of 7, and four washing cycles, yielding 32.40 mg/kg of 4-methoxy-2-nitroaniline. The influencing factors for deionized water washing rank as follows: liquid-to-solid ratio > number of washing cycles > elution pH > washing time.
The eluting effect of deionized water is slightly lower compared to that of n-propanol. However, its washing efficiency shows no significant difference when compared with the effects of single or compound surfactants. This outcome is likely due to the lithology of the contaminated aquifer medium, which primarily consists of silty-fine sand with poor adsorption properties, facilitating the desorption of pollutants. These findings underscore the effectiveness of deionized water washing under optimized conditions, providing valuable insights for potential field applications.
3.5. On-Site Washing Pilot Test
A pilot-scale test was conducted at a high-concentration pollution area within the contaminated site to validate washing effectiveness. The site configuration is illustrated in Figure 3. The test setup consisted of one injection well for washing, five monitoring wells, and five extraction wells. The distances of the extraction wells and the monitoring wells from the injection well and the slotting locations of the wells are shown in Table 12.
In consideration of the planned implementation of Groundwater Monitored Natural Attenuation (MNA) at the experimental site, the potential impact of n-propanol, despite its low toxicity and environmentally friendly properties [28], on indigenous microorganisms remains uncertain. To ensure construction safety, reduce costs, and minimize adverse effects on native microbial populations, an on-site pilot test was conducted using treated groundwater. After undergoing physicochemical and biochemical treatments (Figure 4), a substantial reduction in pollutant concentrations was observed in the treated groundwater, as shown in Table 13, with the pH value adjusted to approximately 7.0.
This treated groundwater was injected into the aquifer as the eluent. It utilizes physical flushing, dissolution, and the promotion of contaminant migration to transfer contaminants adhered to aquifer medium particle surfaces into the aqueous solution, and they are then removed with pumping, which makes it both economical and environmentally friendly. Continuous steady pressure was applied to the injection well, while the extraction wells operated continuously. Water meters were installed on the extraction wells to measure the flow rate of each well.
Subsequent to water injection initiation, pressure (Figure 5) increased gradually from 0 to 0.88 MPa over the first 15 days. The flow rate (Figure 5) initially peaked at 6.5 m3/h and then decreased to about 2 m3/h, before increasing again. By day 31, the flow rate stabilized at around 5 m3/h, with pressure fluctuating between 0.7 and 0.75 MPa. A rapid pressure decrease to 0.3–0.46 MPa was observed on day 68, accompanied by a flow rate increase to 14–17 m3/h, which then stabilized. Fluctuations in both flow rate and pressure occurred after 133 days. The water injection period lasted 152 days, with a cumulative injection volume of 31,560 m3.
Daily extraction volumes from individual wells showed fluctuations that stabilized after 80 days (Figure 6). Wells DC1 and DC2, positioned closer to the injection well, yielded higher extraction volumes, spanning 58–881 m3/d. Conversely, DC3 and DC5, located farther from the injection well, displayed lower extraction volumes, ranging from 1 to 36 m3/d. DC4 exhibited intermediate daily extraction volumes of 5–155 m3/d. Over the 140-day period, the cumulative extraction volume from all five wells totaled 38,550 m3, surpassing the total injection volume.
Water quality monitoring data from the extraction wells (Figure 7) revealed that DC4, situated closest to the injection well (16.3 m) and downstream of the groundwater flow direction, was most affected by the water injection washing. Pollutant concentrations in DC4 exhibited significant fluctuations, with notable increases observed during days 7–18, 60–74, and 90–122. The maximum concentration reached 116.84 mg/L, exceeding the initial concentration of 45.33 mg/L. After day 90, pollutant concentrations in DC4 remained elevated above initial levels. Calculations based on the average concentration of 4-methoxy-2-nitroaniline extracted from DC4 and the total extraction volume yielded an estimated mass of about 241 kg of 4-methoxy-2-nitroaniline removed during the pilot test period.
Extraction wells DC3 and DC5, located at greater distances from the injection well (32.4 m and 30 m, respectively), exhibited a general decline in pollutant concentration, accompanied by fluctuations. Transient increases were observed in DC5 on days 11 and 50, with concentrations reaching 71.87 mg/L and 75.48 mg/L. Between days 54 and 108, concentrations fluctuated minimally, stabilizing between 15.5 and 19.5 mg/L. A gradual decrease occurred from days 116 to 154, with concentrations ranging from 7.4 to 10.85 mg/L. After day 54, DC3 displayed relatively stable fluctuations, averaging about 19.4 mg/L. Over the pilot test period, the cumulative mass of 4-methoxy-2-nitroaniline extracted from DC3 and DC5 was calculated to be 5.26 kg and 3.34 kg, respectively.
Extraction wells DC1 and DC2, situated closer to the injection well (17 m and 18.1 m), were positioned upstream and displayed a declining trend in pollutant concentration, accompanied by fluctuations. DC2 exhibited a gradual increase in pollutant concentration during the initial 16 days, followed by fluctuating levels. A notable spike in pollutant concentration occurred on day 138, reaching 98.36 mg/L. Over the duration of the pilot test, the cumulative mass of 4-methoxy-2-nitroaniline extracted from DC1 and DC2 was calculated to be 518 kg and 1120 kg, respectively.
Water quality monitoring data from the monitoring wells (Figure 8) revealed that upstream monitoring well G2, positioned closest to the injection well (9 m), experienced a substantial increase in pollutant concentration during the initial operational phase (days 1–64), rising from 39.36 mg/L to 158.88 mg/L. This was followed by a notable decrease and stabilization around 18.5 mg/L in the later phase. The side monitoring wells G1, G3, and G5, located progressively further from the injection well, displayed corresponding delays in pollutant concentration increases. Peak concentrations were observed in G1 on day 26 (85.24 mg/L), G3 on day 88 (100.94 mg/L), and G5 on day 112 (512.88 mg/L). Downstream monitoring well G4, situated 18 m from the injection well, exhibited minimal variation in pollutant concentration during the first 104 days, stabilizing around 37.5 mg/L. After day 104, concentrations increased sharply, peaking on day 142 at 390.96 mg/L.
4. Conclusions
- (1)
- The alcohol-based eluting agents applied to leach 4-methoxy-2-nitroaniline (4M2N) from the contaminated aquifer medium showed the following effectiveness: n-propanol > ethanol > methanol. This efficacy is closely related to the polarity of the alcohol eluting agents. The eluting agents reduce the interfacial tension between contaminants and water through wetting, foaming, and emulsification effects, with the optimal concentration of alcohol needed to overcome the stable value of interfacial tension. N-propanol’s optimal conditions involve 60% concentration, a 15:1 liquid-to-solid ratio, two eluting cycles, pH 3, and a 2 h eluting duration. Notably, n-propanol exhibited the most effective eluting, achieving a 4-methoxy-2-nitroaniline concentration of 75.49 mg/kg. The liquid-to-solid ratio and number of eluting cycles emerged as the primary factors influencing the efficacy of alcohol-based eluting agents.
- (2)
- The non-ionic surfactants used to leach 4-methoxy-2-nitroaniline from the contaminated aquifer medium exhibited the following effectiveness: APG > Triton X-100 > Tween-80. The optimal concentration of APG was found to be 0.5 g/L, with a liquid-to-solid ratio of 15:1, eluting conducted four times, an elution pH of 7, and an eluting duration of 3 h. The liquid-to-solid ratio and the number of eluting cycles are the two primary factors influencing the efficacy of non-ionic surfactant eluting. The liquid-to-solid ratio directly affects the contact area and contact time between the eluting agent and the contaminants in the aquifer medium, which thus influences the effectiveness of a single eluting event, while the number of eluting cycles affects the cumulative removal of contaminants.
- (3)
- The blending of APG and Triton X-100 as an eluting agent enhances the eluting effect compared to individual non-ionic surfactants. The blended eluting agents exhibited a synergistic enhancement effect among their various components, which demonstrates greater adaptability to different remediation environments and conditions. This synergy can neutralize potential adverse effects associated with individual components, which can enhance the efficiency of contaminant elution. The optimal blending ratio of APG to Triton X-100 was determined to be 4:1.
- (4)
- n-propanol has been identified as the optimal eluting agent for removing 4-methoxy-2-nitroaniline from the aquifer medium. Optimal eluting conditions were determined as a 15:1 liquid-to-solid ratio, two eluting cycles, an elution pH of 3, 60% n-propanol concentration, and a 2 h eluting duration. Under these conditions, n-propanol exhibits significantly enhanced performance, surpassing that of the blended non-ionic surfactant agent by two times more and deionized water eluting by three times further, thereby establishing its efficacy as a superior eluting agent for 4-methoxy-2-nitroaniline removal. This is also suitable for polycyclic aromatic hydrocarbons and other nitroaniline compounds such as 4-methoxy-3-nitroaniline, etc.
- (5)
- Field pilot tests were conducted using treated groundwater washing, which revealed a significant increase in contaminant concentrations in the pumping wells and monitoring wells located downstream of the washing injection well. In contrast, in the upstream and lateral monitoring wells, the time for contaminant concentration increases was correspondingly delayed with increasing distance from the injection well. Water washing facilitates the transfer of contaminants adhering to aquifer medium particle surfaces into the aqueous solution through mechanisms such as physical washing, partial dissolution, and the promotion of contaminant migration. This approach is both cost-effective and environmentally friendly.
Author Contributions
Conceptualization and writing, Z.W.; data curation, K.L. and C.C.; methodology and project administration, Z.W., H.C. and H.Z.; visualization, Z.W. and K.L.; investigation, Y.Y. and H.P. All authors have read and agreed to the published version of the manuscript.
Funding
This work was supported by Ningxia Hui Autonomous Region 2024 Annual Special Project for Central Guiding Local Science and Technology Development: Green and Low-carbon Integrated Technology Research and Demonstration for High-salt Strong Acid Organic Polluted Groundwater Remediation in Zhongwei Industrial Park [grant number 2024FRD05070].
Data Availability Statement
The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.
Acknowledgments
The authors would like to thank the editor and reviewers for their constructive and valuable comments and suggestions, which significantly improved the quality of this work.
Conflicts of Interest
Authors Chen Chen, Hong Zhu and Hao Pang were employed by Beijing Zhongdihongke Environmental Technology Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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Figure 1.
Schematic diagram of alcohol eluting agents and surfactant eluting principles.
Figure 2.
Relationship between 4-methoxy-2-nitroaniline extraction and compound ratio.
Figure 3.
Site location and well layout.
Figure 4.
Treatment process for contaminated groundwater.
Figure 5.
Water injection status.
Figure 6.
Water extraction status.
Figure 7.
Changes in 4-methoxy-2-nitroaniline concentration in extraction wells.
Figure 8.
4-methoxy-2-nitroaniline concentration and water level changes in monitoring wells.
Table 1.
Basic physical and chemical properties of prepared aquifer medium samples.
| Indicators | Conductivity | pH | Organic Matter | Moisture Content |
|---|---|---|---|---|
| Prepared Aquifer Medium Samples | 81.3 mS/m | 7.4 | 7.58 g/kg | 0.2% |
Table 2.
Basic physical and chemical properties of reagents used.
| Name | CAS | Molecular Formula | Structural Formula | Molecular Weight | Melting Point (°C) | Boiling Point (°C) | Property Description |
|---|---|---|---|---|---|---|---|
| 4-methoxy-2-nitroaniline | 97-52-9 | C7H8N2O3 |  | 168.15 | 123–126 | 338 | Orange-red powder. Slightly soluble in water, soluble in ethanol and ether, and slightly soluble in benzene. |
| methanol | 67-56-1 | CH4O |  | 32.04 | −97.8 | 64.7 | Colorless transparent liquid with an irritating odor. Soluble in water and miscible with most organic solvents such as alcohols and ethers. |
| ethanol | 64-17-5 | C2H5OH |  | 46.07 | −114 | 78 | Colorless liquid with a fruity aroma. Miscible with water and most organic solvents, including ethers, chloroform, glycerol, and methanol. |
| n-propanol | 71-23-8 | C3H8O |  | 60.1 | −127 | 97 | Colorless transparent liquid with an ethanol-like odor. Miscible with water and most organic solvents such as alcohols and ethers. |
| Tween-80 | 9005-65-6 | C24H44O6 | 428.60 | Exhibits high hydrophilicity, unaffected by environmental pH. Easily soluble in water, ethanol, vegetable oils, ethyl acetate, methanol, and toluene. Insoluble in mineral oils. | |||
| APG | 141464-42-8 | C16H32O6 | 320.42 | Low surface tension, fully biodegradable in nature, non-toxic, and harmless. Resistant to strong bases, strong acids, hard water, and has strong salt tolerance. | |||
| Triton X-100 | 9002-93-1 | C34H62O11 | 646.85 | Colorless or nearly colorless transparent viscous liquid. Soluble in water, toluene, xylene, and ethanol. Insoluble in petroleum ether. |
Table 3.
Eluting conditions for single eluting agents.
| Level Factor | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| Non-ionic surfactant concentration (g/L) | 0.5 | 1 | 2 | 5 |
| Alcohol eluent concentration (%) | 30 | 60 | 80 | 100 |
| Liquid-to-solid ratio (single, non-cumulative) | 2.5:1 | 5:1 | 10:1 | 15:1 |
| Eluent time | 0.5 h | 1 h | 2 h | 3 h |
| Eluent pH (hydrochloric acid adjustment) | 3 | 4.5 | 6 | 7 |
| Eluting cycles | 1 | 2 | 3 | 4 |
Table 4.
Orthogonal experiment results for methanol eluting.
| Experiment No. | Methanol Concentration (%) | Liquid-to-Solid Ratio | Eluting Time (h) | Eluting Solution pH | Eluting Cycles | Elution 4-methoxy-2-nitroaniline Content (mg/kg) |
|---|---|---|---|---|---|---|
| A1 | 30 | 2.5:1 | 0.5 | 3 | 1 | 10.79 |
| A2 | 30 | 5:1 | 1 | 4.5 | 2 | 16.14 |
| A3 | 30 | 10:1 | 2 | 6 | 3 | 22.93 |
| A4 | 30 | 15:1 | 3 | 7 | 4 | 32.46 |
| A5 | 60 | 5:1 | 0.5 | 6 | 4 | 10.91 |
| A6 | 60 | 2.5:1 | 1 | 7 | 3 | 7.92 |
| A7 | 60 | 15:1 | 2 | 3 | 2 | 51.29 |
| A8 | 60 | 10:1 | 3 | 4.5 | 1 | 8.49 |
| A9 | 80 | 10:1 | 0.5 | 7 | 2 | 32.93 |
| A10 | 80 | 15:1 | 1 | 6 | 1 | 18.86 |
| A11 | 80 | 2.5:1 | 2 | 4.5 | 4 | 22.09 |
| A12 | 80 | 5:1 | 3 | 3 | 3 | 22.57 |
| A13 | 100 | 15:1 | 0.5 | 4.5 | 3 | 31.42 |
| A14 | 100 | 10:1 | 1 | 3 | 4 | 28.29 |
| A15 | 100 | 5:1 | 2 | 7 | 1 | 16.88 |
| A16 | 100 | 2.5:1 | 3 | 6 | 2 | 10.44 |
| k1 | 20.58 | 12.81 | 21.51 | 28.24 | 13.75 | |
| k2 | 19.65 | 16.63 | 17.80 | 19.53 | 27.70 | |
| k3 | 24.11 | 23.16 | 28.30 | 15.78 | 21.21 | |
| k4 | 21.76 | 33.51 | 18.49 | 22.55 | 23.44 | |
| R | 4.46 | 20.70 | 10.49 | 12.45 | 13.95 |
Table 5.
Orthogonal experiment results for ethanol eluting.
| Experiment No. | Ethanol Concentration (%) | Liquid-to-Solid Ratio | Eluting Time (h) | Eluting Solution pH | Eluting Cycles | Elution 4-methoxy-2-nitroaniline Content (mg/kg) |
|---|---|---|---|---|---|---|
| B1 | 30 | 2.5:1 | 0.5 | 3 | 1 | 11.49 |
| B2 | 30 | 5:1 | 1 | 4.5 | 2 | 15.79 |
| B3 | 30 | 10:1 | 2 | 6 | 3 | 29.67 |
| B4 | 30 | 15:1 | 3 | 7 | 4 | 32.65 |
| B5 | 60 | 5:1 | 0.5 | 6 | 4 | 22.89 |
| B6 | 60 | 2.5:1 | 1 | 7 | 3 | 15.66 |
| B7 | 60 | 15:1 | 2 | 3 | 2 | 26.02 |
| B8 | 60 | 10:1 | 3 | 4.5 | 1 | 14.02 |
| B9 | 80 | 10:1 | 0.5 | 7 | 2 | 32.13 |
| B10 | 80 | 15:1 | 1 | 6 | 1 | 21.67 |
| B11 | 80 | 2.5:1 | 2 | 4.5 | 4 | 27.29 |
| B12 | 80 | 5:1 | 3 | 3 | 3 | 23.15 |
| B13 | 100 | 15:1 | 0.5 | 4.5 | 3 | 69.52 |
| B14 | 100 | 10:1 | 1 | 3 | 4 | 29.77 |
| B15 | 100 | 5:1 | 2 | 7 | 1 | 16.26 |
| B16 | 100 | 2.5:1 | 3 | 6 | 2 | 19.72 |
| k1 | 22.40 | 18.54 | 34.01 | 22.61 | 15.86 | |
| k2 | 19.65 | 19.52 | 20.72 | 31.65 | 23.42 | |
| k3 | 26.06 | 26.40 | 24.81 | 23.49 | 34.50 | |
| k4 | 33.82 | 37.47 | 22.38 | 24.18 | 28.15 | |
| R | 14.17 | 18.93 | 13.28 | 9.04 | 18.64 |
Table 6.
Orthogonal experiment results for n-propanol eluting.
| Experiment No. | n-Propanol Concentration (%) | Liquid-to-Solid Ratio | Eluting Time (h) | Eluting Solution pH | Eluting Cycles | Elution 4-methoxy-2-nitroaniline Content (mg/kg) |
|---|---|---|---|---|---|---|
| C1 | 30 | 2.5:1 | 0.5 | 3 | 1 | 2.78 |
| C2 | 30 | 5:1 | 1 | 4.5 | 2 | 18.74 |
| C3 | 30 | 10:1 | 2 | 6 | 3 | 25.19 |
| C4 | 30 | 15:1 | 3 | 7 | 4 | 54.36 |
| C5 | 60 | 5:1 | 0.5 | 6 | 4 | 23.57 |
| C6 | 60 | 2.5:1 | 1 | 7 | 3 | 19.12 |
| C7 | 60 | 15:1 | 2 | 3 | 2 | 75.49 |
| C8 | 60 | 10:1 | 3 | 4.5 | 1 | 9.94 |
| C9 | 80 | 10:1 | 0.5 | 7 | 2 | 23.11 |
| C10 | 80 | 15:1 | 1 | 6 | 1 | 17.91 |
| C11 | 80 | 2.5:1 | 2 | 4.5 | 4 | 4.82 |
| C12 | 80 | 5:1 | 3 | 3 | 3 | 29.06 |
| C13 | 100 | 15:1 | 0.5 | 4.5 | 3 | 40.28 |
| C14 | 100 | 10:1 | 1 | 3 | 4 | 41.41 |
| C15 | 100 | 5:1 | 2 | 7 | 1 | 12.79 |
| C16 | 100 | 2.5:1 | 3 | 6 | 2 | 12.94 |
| k1 | 25.27 | 9.91 | 22.44 | 37.19 | 10.85 | |
| k2 | 32.03 | 21.04 | 24.30 | 18.45 | 32.57 | |
| k3 | 18.73 | 24.91 | 29.57 | 19.90 | 28.41 | |
| k4 | 26.86 | 47.01 | 26.57 | 27.34 | 31.04 | |
| R | 13.30 | 37.10 | 7.14 | 18.74 | 21.72 |
Table 7.
Orthogonal experiment results for APG eluting.
| Factors | APG Concentration (g/L) | Elution Time (h) | Liquid-to-Solid Ratio | Elution pH | Eluting Cycles | Elution 4-methoxy-2-nitroaniline Content (mg/kg) |
|---|---|---|---|---|---|---|
| D1 | 0.5 | 0.5 | 2.5:1 | 3 | 1 | 7.95 |
| D2 | 0.5 | 1 | 5:1 | 4.5 | 2 | 12.20 |
| D3 | 0.5 | 2 | 10:1 | 6 | 3 | 20.70 |
| D4 | 0.5 | 3 | 15:1 | 7 | 4 | 34.80 |
| D5 | 1 | 1 | 2.5:1 | 6 | 4 | 12.80 |
| D6 | 1 | 0.5 | 5:1 | 7 | 3 | 14.25 |
| D7 | 1 | 3 | 10:1 | 3 | 2 | 15.40 |
| D8 | 1 | 2 | 15:1 | 4.5 | 1 | 16.05 |
| D9 | 2 | 2 | 2.5:1 | 7 | 2 | 7.85 |
| D10 | 2 | 3 | 5:1 | 6 | 1 | 6.65 |
| D11 | 2 | 0.5 | 10:1 | 4.5 | 4 | 24.00 |
| D12 | 2 | 1 | 15:1 | 3 | 3 | 25.65 |
| D13 | 5 | 3 | 2.5:1 | 4.5 | 3 | 9.68 |
| D14 | 5 | 2 | 5:1 | 3 | 4 | 16.00 |
| D15 | 5 | 1 | 10:1 | 7 | 1 | 11.30 |
| D16 | 5 | 0.5 | 15:1 | 6 | 2 | 19.50 |
| k1 | 18.91 | 16.43 | 9.57 | 16.25 | 10.49 | |
| k2 | 14.63 | 15.49 | 12.28 | 15.48 | 13.74 | |
| k3 | 16.04 | 15.15 | 17.85 | 14.91 | 17.57 | |
| k4 | 14.12 | 16.63 | 24.00 | 17.05 | 21.90 | |
| R | 4.79 | 1.48 | 14.43 | 2.14 | 11.41 |
Table 8.
Orthogonal experiment results for Triton X-100 eluting.
| Factors | Triton X-100 Concentration (g/L) | Elution Time (h) | Liquid-to-Solid Ratio | Elution pH | Eluting Cycles | Elution 4-methoxy-2-nitroaniline Content (mg/kg) |
|---|---|---|---|---|---|---|
| E1 | 0.5 | 0.5 | 2.5:1 | 3 | 1 | 9.43 |
| E2 | 0.5 | 1 | 5:1 | 4.5 | 2 | 15.60 |
| E3 | 0.5 | 2 | 10:1 | 6 | 3 | 21.00 |
| E4 | 0.5 | 3 | 15:1 | 7 | 4 | 32.40 |
| E5 | 1 | 1 | 2.5:1 | 6 | 4 | 15.50 |
| E6 | 1 | 0.5 | 5:1 | 7 | 3 | 16.65 |
| E7 | 1 | 3 | 10:1 | 3 | 2 | 17.60 |
| E8 | 1 | 2 | 15:1 | 4.5 | 1 | 15.30 |
| E9 | 2 | 2 | 2.5:1 | 7 | 2 | 11.25 |
| E10 | 2 | 3 | 5:1 | 6 | 1 | 11.30 |
| E11 | 2 | 0.5 | 10:1 | 4.5 | 4 | 24.00 |
| E12 | 2 | 1 | 15:1 | 3 | 3 | 26.10 |
| E13 | 5 | 3 | 2.5:1 | 4.5 | 3 | 11.18 |
| E14 | 5 | 2 | 5:1 | 3 | 4 | 17.80 |
| E15 | 5 | 1 | 10:1 | 7 | 1 | 12.80 |
| E16 | 5 | 0.5 | 15:1 | 6 | 2 | 22.20 |
| k1 | 19.61 | 18.07 | 11.84 | 17.73 | 12.21 | |
| k2 | 16.26 | 17.50 | 15.34 | 16.52 | 16.66 | |
| k3 | 18.16 | 16.34 | 18.85 | 17.50 | 18.73 | |
| k4 | 15.99 | 18.12 | 24.00 | 18.28 | 22.43 | |
| R | 3.61 | 1.78 | 12.16 | 1.76 | 10.22 |
Table 9.
Orthogonal experiment results for Tween-80 eluting.
| Factors | Tween-80 Concentration (g/L) | Elution Time (h) | Liquid-to-Solid Ratio | Elution pH | Eluting Cycles | Elution 4-methoxy-2-nitroaniline Content (mg/kg) |
|---|---|---|---|---|---|---|
| F1 | 0.5 | 0.5 | 2.5:1 | 3 | 1 | 8.23 |
| F2 | 0.5 | 1 | 5:1 | 4.5 | 2 | 13.30 |
| F3 | 0.5 | 2 | 10:1 | 6 | 3 | 21.60 |
| F4 | 0.5 | 3 | 15:1 | 7 | 4 | 31.20 |
| F5 | 1 | 1 | 2.5:1 | 6 | 4 | 11.90 |
| F6 | 1 | 0.5 | 5:1 | 7 | 3 | 15.30 |
| F7 | 1 | 3 | 10:1 | 3 | 2 | 17.80 |
| F8 | 1 | 2 | 15:1 | 4.5 | 1 | 15.90 |
| F9 | 2 | 2 | 2.5:1 | 7 | 2 | 10.00 |
| F10 | 2 | 3 | 5:1 | 6 | 1 | 7.00 |
| F11 | 2 | 0.5 | 10:1 | 4.5 | 4 | 22.40 |
| F12 | 2 | 1 | 15:1 | 3 | 3 | 26.55 |
| F13 | 5 | 3 | 2.5:1 | 4.5 | 3 | 7.13 |
| F14 | 5 | 2 | 5:1 | 3 | 4 | 16.80 |
| F15 | 5 | 1 | 10:1 | 7 | 1 | 12.00 |
| F16 | 5 | 0.5 | 15:1 | 6 | 2 | 21.00 |
| k1 | 18.58 | 16.73 | 9.31 | 17.34 | 10.78 | |
| k2 | 15.23 | 15.94 | 13.10 | 14.68 | 15.53 | |
| k3 | 16.49 | 16.08 | 18.45 | 15.38 | 17.64 | |
| k4 | 14.23 | 15.78 | 23.66 | 17.13 | 20.58 | |
| R | 4.35 | 0.95 | 14.35 | 2.66 | 9.79 |
Table 10.
Control group experimental conditions.
| No. | Eluent | Concentration | Liquid-to-Solid Ratio | pH | Elution Time | Eluting Cycles |
|---|---|---|---|---|---|---|
| A | deionized water | / | 15:1 | 7 | 3 h | 4 |
| B | deionized water | / | 15:1 | 3 | 2 h | 2 |
| C | n-propanol | 60% | 15:1 | 3 | 2 h | 2 |
Table 11.
Orthogonal experiment results for deionized water washing.
| Factors | Elution Time (h) | Liquid-to-Solid Ratio | Elution pH | Washing Cycles | Elution 4-methoxy-2-nitroaniline Content (mg/kg) |
|---|---|---|---|---|---|
| G1 | 0.5 | 2.5:1 | 3 | 1 | 7.425 |
| G2 | 1 | 5:1 | 4.5 | 2 | 9.5 |
| G3 | 2 | 10:1 | 6 | 3 | 20.4 |
| G4 | 3 | 15:1 | 7 | 4 | 32.4 |
| G5 | 1 | 2.5:1 | 6 | 4 | 10.5 |
| G6 | 0.5 | 5:1 | 7 | 3 | 16.8 |
| G7 | 3 | 10:1 | 3 | 2 | 16.6 |
| G8 | 2 | 15:1 | 4.5 | 1 | 15.3 |
| G9 | 2 | 2.5:1 | 7 | 2 | 6.65 |
| G10 | 3 | 5:1 | 6 | 1 | 7.3 |
| G11 | 0.5 | 10:1 | 4.5 | 4 | 20.4 |
| G12 | 1 | 15:1 | 3 | 3 | 24.3 |
| G13 | 3 | 2.5:1 | 4.5 | 3 | 7.425 |
| G14 | 2 | 5:1 | 3 | 4 | 14.6 |
| G15 | 1 | 10:1 | 7 | 1 | 9.9 |
| G16 | 0.5 | 15:1 | 6 | 2 | 19.2 |
| k1 | 15.96 | 8.00 | 15.73 | 9.98 | |
| k2 | 13.55 | 12.05 | 13.16 | 12.99 | |
| k3 | 14.24 | 16.83 | 14.35 | 17.23 | |
| k4 | 15.93 | 22.80 | 16.44 | 19.48 | |
| R | 2.41 | 14.80 | 3.28 | 9.49 |
Table 12.
Distance to test wells and slotting locations.
| Type | Number | Distance from an Injection Well | Screening Location |
|---|---|---|---|
| Washing injection well | GZ | / | 8m above the bottom |
| Monitoring well | G1 | 10.9 m | Full sieve |
| G2 | 9 m | Full sieve | |
| G3 | 14 m | Full sieve | |
| G4 | 18 m | Full sieve | |
| G5 | 26.2 m | 15 m above the bottom | |
| Extraction well | DC1 | 17 m | 3 m above the bottom |
| DC2 | 18.1 m | 3 m above the bottom | |
| DC3 | 32.4 m | 3 m above the bottom | |
| DC4 | 16.3 m | 3 m above the bottom | |
| DC5 | 30 m | 3 m above the bottom |
Table 13.
Water quality of injecting water (treated groundwater).
| Index | pH | ORP (mV) | CON (μs/cm) | DO (mg/L) | Sulfate (mg/L) | CODCr (mg/L) | 4-chloroaniline (µg/L) | 4-methoxy-2-nitroaniline (µg/L) | 4-methoxy-3-nitroaniline (µg/L) | 3-chloroaniline (µg/L) |
|---|---|---|---|---|---|---|---|---|---|---|
| Injection Water (Average Value) | 6.98 | 75 | 6048 | 6.68 | 4500 | 24 | 10 | 28.6 | 292 | 2.6 |
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Wang, Z.; Lao, K.; Chen, C.; Zhu, H.; Yang, Y.; Chen, H.; Pang, H. Field Study on Washing of 4-Methoxy-2-Nitroaniline from Contaminated Site by Dye Intermediates. Processes 2024, 12, 2801. https://doi.org/10.3390/pr12122801
AMA Style
Wang Z, Lao K, Chen C, Zhu H, Yang Y, Chen H, Pang H. Field Study on Washing of 4-Methoxy-2-Nitroaniline from Contaminated Site by Dye Intermediates. Processes. 2024; 12(12):2801. https://doi.org/10.3390/pr12122801
Chicago/Turabian StyleWang, Zhili, Kangwen Lao, Chen Chen, Hong Zhu, Yanfei Yang, Honghan Chen, and Hao Pang. 2024. "Field Study on Washing of 4-Methoxy-2-Nitroaniline from Contaminated Site by Dye Intermediates" Processes 12, no. 12: 2801. https://doi.org/10.3390/pr12122801
APA StyleWang, Z., Lao, K., Chen, C., Zhu, H., Yang, Y., Chen, H., & Pang, H. (2024). Field Study on Washing of 4-Methoxy-2-Nitroaniline from Contaminated Site by Dye Intermediates. Processes, 12(12), 2801. https://doi.org/10.3390/pr12122801
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