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Article

Trihalomethane Formation from Soil-Derived Dissolved Organic Matter During Chlorination and Chloramination: A Case Study in Cedar Lake, Illinois

by
Amin Asadollahi
*,
Asyeh Sohrabifar
and
Habibollah Fakhraei
*
School of Civil, Environmental and Infrastructure Engineering, Southern Illinois University, Carbondale, IL 62901, USA
*
Authors to whom correspondence should be addressed.
Geographies 2025, 5(1), 15; https://doi.org/10.3390/geographies5010015
Submission received: 26 February 2025 / Revised: 12 March 2025 / Accepted: 18 March 2025 / Published: 20 March 2025
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Abstract

:
Dissolved organic carbon (DOC) is a critical parameter in water quality management due to its interaction with disinfectants, leading to the formation of disinfection byproducts (DBPs) during water treatment. Forest ecosystems are key contributors of DOC to surface waters, stemming from soil leachate. This study is the first to use DOC solutions directly extracted from soil to examine the formation of trihalomethanes (THMs) during chlorination and chloramination under varying environmental conditions. For this purpose, soil samples from a densely forested upland Cedar Lake watershed in Illinois were processed to extract DOC, which was then subjected to controlled disinfection experiments under varying pH, temperature, disinfectant dose, and reaction time. The results demonstrate that chlorination produces significantly higher levels of THMs compared to chloramination, with THM concentrations ranging from 31.996 μg/L to 62.563 μg/L for chlorination and 0.508 μg/L to 0.865 μg/L for chloramination. The yields of DBPs determined by chloramination increased approximately 4, 5, and 10 times with a higher DOC concentration, disinfectant concentration, and reaction time, respectively. For chlorination, these increases were approximately 5, 8, and 3 times, respectively. The presence of bromide in the DOC solutions influenced the concentration of brominated THMs (Br-THMs). The results indicate that a high formation of THMs, during both disinfection processes, occurred in the pH range of 7–8 and temperature range of 20–25 degrees Celsius. Furthermore, all tested water quality indicators (DOC, total dissolved solids, turbidity, and UV254), except for pH and Specific Ultraviolet Absorbance (SUVA), exhibited a strong positive correlation with THM levels during chlorination. In contrast, these parameters displayed a moderate to weak correlation with THM levels in the chloramination process. These findings highlight the critical role of DOC characteristics and disinfection conditions in controlling THM formation, providing valuable insights for optimizing water treatment processes.

Graphical Abstract

1. Introduction

Water disinfection is a critical step in water treatment to eliminate harmful pathogens and prevent the spread of waterborne diseases [1,2]. Effective water treatment must balance the removal of pathogens with the minimization of chemical byproducts, ensuring both safety and compliance with regulatory standards [2]. The application of chlorine and chloramine as disinfectants can lead to the formation of potentially harmful DBPs, primarily through reactions with natural organic matter (NOM) present in water [3,4,5]. THMs and haloacetic acids (HAAs) are the primary disinfection byproducts formed during the chlorination of water [6]. Due to the significant health risks associated with THMs and HAAs, as well as stringent regulations imposed by the US Environmental Protection Agency (USEPA), extensive research has been conducted to develop alternative disinfection methods such as ozonation and chlorine dioxide [7]. Concurrently, a variety of pretreatment methods, including enhanced coagulation and filtration, have been implemented to reduce the levels of NOM in water [8,9,10].
While chlorine remains the most common disinfectant in water treatment, many water utilities have adopted chloramination as a secondary disinfection barrier [11]. Chloramination produces its own DBPs but generally results in much lower levels of THMs and HAAs compared to chlorination [7,12]. The DBPs formed due to chloramination include haloacetonitriles, chloramino acids, cyanogen chloride, haloketones, nitrate, nitrite, chlorate, and hydrazine aldehydes [13]. Hua and Reckhow [14] report that when iodide is present in water, iodinated THMs are more prevalent in samples treated with chloramines compared to those treated with chlorine. They also found that the organic halogens formed by chloramines are greater than those formed by chlorine. It has been shown that the main factors influencing the formation and distribution of DBPs in the water supply system include the residual chlorine dose, total organic carbon (TOC), pH, bromide concentration, temperature, and residence time [15,16,17]. Therefore, understanding the sources of NOM in surface waters and identifying key factors influencing the NOM concentration is crucial for effectively mitigating the formation of DBPs.
Surface waters, such as lakes and rivers, typically contain higher concentrations of DOC due to direct inputs from terrestrial runoff, leaf litter, algal biomass, and the decomposition of plant and animal matter [18]. In forested catchments, runoff from surrounding soils further contributes significantly to the NOM load in these water bodies [19]. Forest soil, rich in organic matter, contributes significantly to the NOM load in lakes through leaching during rainfall or snowmelt events [19,20]. This organic matter, often characterized by high aromaticity and functional groups such as hydroxyl and carboxyl, plays a critical role in DBP formation during water treatment [21]. In contrast, deeper water layers often have lower DOC concentrations due to reduced contact with organic matter sources and increased microbial degradation over time [18,22]. For drinking water production, utilities often draw from both surface and deep water sources, depending on availability and quality.
Global warming and rising intense rainfall events on watersheds can contribute to elevated levels of NOM in surface waters, as inundated soils release organic compounds [23,24]. Specifically, forest soil is rich in organic matter content, and as a result, forest catchments can release high concentrations of NOM in the water that drains out [19]. Soil acts as a major carbon reservoir, and rising atmospheric carbon dioxide levels could potentially enhance soil carbon sequestration [25]. This occurs as plants absorb increased CO2 through photosynthesis, and when they shed leaves, extend roots, or decompose after death, the organic matter they contribute enriches the soil with carbon, thereby enhancing its storage capacity [25,26]. Other factors such as an increase in the frequency of severe drought events, the mitigation of acid deposition, and changes in land use may contribute to the recent increases in the DOC concentration in natural waters [18,27]. Additionally, Previous studies have demonstrated that seasonal changes in temperature, rainfall patterns, and vegetation cycles can lead to variations in the quantity and quality of DOC in surface waters [7,22]. Chow et al. [22] showed that higher DOC concentrations are often observed during autumn due to leaf litter decomposition and during spring due to increased runoff from snowmelt, while summer droughts may reduce DOC leaching from soils. In another study, Brooks et al. found that the THM formation potential tends to be higher during wet seasons when DOC concentrations are elevated, while lower DOC levels during dry seasons may result in reduced DBP yields [28]. This would result in the growth of the quantity of carbon transferred to rivers because a strong correlation exists between DOC released and the soil carbon content in a catchment [18]. The reactivity of aromatic carbon within dissolved organic matter (DOM) molecules, determined by the positioning of functional groups such as hydroxyl and carboxyl, plays a crucial role in the formation of DBPs during water treatment [29]. Given the uneven contributions of various organic carbon fractions to DBP formation, effective pretreatment strategies to reduce DOM levels are essential for mitigating DBP formation and ensuring water quality [15,30].
While previous studies have suggested that chloramination generally produces lower levels of THMs compared to chlorination, the specific impact of these disinfection processes on soil-derived DOM under varying conditions remains unclear. Soil-derived DOM is characterized by a high content of aromatic compounds with abundant hydroxyl and carboxyl functional groups, which can significantly influence disinfection byproduct formation [8,31]. To our knowledge, this study is the first to directly compare THM formation from soil-extracted DOM solutions subjected to chlorination and chloramination, investigating the influence of various operational parameters. Our research aims to bridge critical gaps in understanding how soil-derived DOM interacts with disinfection processes, providing a scientific foundation for optimizing water treatment strategies in forested regions with high DOC concentrations.
The practical implications of this study are significant, as it offers actionable insights for water treatment facilities managing surface waters in forested areas across the US. By identifying key water quality parameters that predict THM formation, this work can help utilities minimize harmful byproducts while ensuring safe and effective disinfection. This study is particularly relevant to water quality engineers, environmental scientists, and policymakers tasked with safeguarding drinking water supplies in regions with high natural organic matter contents. Ultimately, our findings aim to contribute to safer drinking water practices and more sustainable water management strategies.

2. Materials and Methods

2.1. Study Area

The Cedar Lake watershed in southern Illinois covers 514 km2 and is designated as a 10-unit Hydrologic Unit Code (HUC 0714010612). The study area extends from 37°38′23.64″ N to 41°57′00″ N latitude and 89°16′46.92″ W longitude. It predominantly features upland forests as a major land-cover type (31% of the land) and possesses fine-grained soil with a moderate water transmission rate [32]. The annual average precipitation in the watershed is about 1100 mm, and the average monthly air temperatures range from −4 °C in January to 32 °C in July [33]. The water quality in Cedar Lake is exceptionally pure, exhibiting an average turbidity value of 5.0 nephelometric turbidity units (NTU). Turbidity levels range from 2.0 NTU to 30.0 NTU, with no discernible contaminants detected in the raw water, as confirmed by the Illinois Environmental Protection Agency (IEPA) [32]. The reservoir spans an expansive surface area of 7.3 km2 and maintains an average depth of 9 m [34]. The water from Cedar Lake is primarily used for drinking water, irrigation, and industrial purposes [32]. Based on population growth projections from the Illinois State Water Survey and anticipated economic development in the region, water demand is expected to increase by approximately 20% over the next decade [35]. This growth is driven by rising residential needs and expanded industrial activities in the watershed area [32].

2.2. Soil Sample Preparation

The soil samples were collected from six different spots in the upland forest area surrounding Cedar Lake. The samples were collected from both organic and mineral horizons within 0 to 30 cm depth at each sampling spot based on previous studies [36]. This zone represents the most biologically active and organic-rich layer in forest ecosystems [19]. Sampling within this depth ensures that the extracted DOM is representative of the organic matter most likely to be transported into aquatic systems during rainfall or runoff events. In the laboratory, soil samples were air-dried, crushed into finer particles, and then sieved (<2 mm) to eliminate coarse particles. Then, a homogenized mixture of 1200 g of sample was prepared by taking 200 g from each spot [22]. After that, the extracted DOC from the soil samples was soaked in deionized (DI) water overnight while stirring gently at room temperature, and then it was left to settle for another 24 h. In this study, DI water was used for DOC extraction, rather than a typical alkaline solution, to simulate surface runoff and prevent the oxidation of alkaline extraction [19]. Finally, the soil solution was poured off and filtered with 0.45 μm nylon membrane filters to obtain the DOC stock solution, and the resulting DOC stock was stored at 4 °C for analysis.

2.3. Water Quality Parameters

Before conducting disinfection in different conditions, some preliminary water quality parameters of the DOC solution were measured for each test in the laboratory. Turbidity measurements were conducted using a calibrated Hach 2100N Turbidimeter (Hach Company, Loveland, CO, USA). A Thermo Fisher Scientific Orion Star A211 (Thermo Fisher Scientific, Waltham, MA, USA) was used for the pH measurement, and the pH meter was standardized using standard solutions before the measurements. Total dissolved solids (TDSs) were measured using an E-1 Portable TDS & EC Meter (Hanna Instruments, Woonsocket, USA). Approximately 50 mL of sample was transferred to a glass beaker, and the reading was recorded once the meter stabi-lized. The UV absorbance (UVA) and specific UVA (SUVA) of all samples were meas-ured with the Thermoscientific Biomate 3S at the full spectrum within the range of wavelengths from 190 nm to 840 nm at 1 nm intervals (Hua et al., 2015) [37]. Bromide was analyzed in this study by following the Ion Chromatography Dionex SM4110B Meth-od. The DOC measurement was conducted using a Shimadzu TOC-L Analyzer (Shi-madzu Corporation, Kyoto, Japan). Residual chlorine levels were determined for each sample using the DPD-ferrous titrimetric method at the conclusion of the disinfection reaction.

2.4. Disinfection Process

In this research, the disinfection of the DOC solution was conducted using chlorine and chloramine under various conditions, based on a document published by the EPA [38]. The EPA guidelines were instrumental in ensuring that the experimental design aligned with standardized methods for evaluating the DBP formation potential. The parameters included the DOC concentration, reaction time, chlorine to DOC ratio, bromine level, pH, and temperature. Only a single condition was varied at a time for each set of reactions, while the rest of the conditions were maintained at the baseline levels as mentioned in Table 1. Additionally, Table 2 presents the chlorination and chloramination processes for the samples, executed according to methodologies established in prior studies [13,35]. After disinfection, 5 mL aliquots were extracted from a total sample volume of 20 mL and placed into new 20 mL headspace vials. To halt the reaction, 4 drops of 10% sodium thiosulfate were added to each sample. The headspace vials were then sealed with Microliter 20 mm Aluminum Crimp Top Headspace Vial Seals and stored in a refrigerator at 4 °C until they were analyzed for THMs within 24 h. Subsequently, the data obtained from the analysis were monitored and reported using the Thermo Scientific™ Chromeleon™ Chromatography Data System (CDS) software, version 7.3.

2.5. THM Analysis

The research employed two widely recognized USEPA methods (5021A and 8260) to assess the levels of THMs in both chlorinated and chloraminated water samples [38]. These methods are based on using gas chromatography (GC) followed by detection through mass spectrometry (MS) or an electron capture detector (ECD). The analysis was conducted using the Thermo Scientific™ TRACE™ 1300 Helium gas chromatograph (Thermo Fisher Scien-tific, Waltham, USA) equipped with a split flow of 30 mL/min. This system was cou-pled with a Thermo Scientific™ ISQ™ 7000 single quadrupole mass spectrometer (Thermo Fisher Scientific, Waltham, USA), operating within a mass range of 35–300 m/z. VOC extraction and sampling into the GC/MS system were performed using the Thermo Scientific™ TriPlus™ 500 valve and loop headspace autosampler ((Thermo Fisher Scientific, Waltham, MA, USA), based on the study by Lee and Cojocariu [26].

3. Results and Discussion

3.1. DOC Variation

Dissolved organic carbon includes a complex mixture of organic compounds, such as humic and fulvic acids, carbohydrates, proteins, and other organic molecules derived from plant and microbial decomposition [39]. To investigate the influence of DOC concentration variation on disinfection byproduct formation, the initial DOC solution was diluted with DI water to create solutions with 10 different DOC concentrations. These solutions were then subjected to chlorination and chloramination under identical experimental conditions to evaluate their DBP formation potential. Figure 1a,b demonstrates that during disinfection, the concentration of THMs increased with rising DOC levels for both the chlorination and chloramination processes. During the chlorination process, THM concentrations peaked at 35.6 μg/L at a DOC level of 22.97 mg/L, while the lowest concentration observed was approximately 7.319 μg/L at a DOC level of 2.3 mg/L. The correlation between elevated DOC levels and increased humic acid concentration, coupled with the provision of chloride ions from increased chlorine doses, likely contributes to the heightened formation of THMs [13]. An increase in the free residual chlorine (FRC) concentration was observed with increasing DOC levels. This phenomenon may be attributed to the consumption of chlorine by various water constituents, including bacteria and certain microorganisms. Furthermore, chloroform (CHCl3) and dichlorobromomethane (CHCl2Br) were identified as the predominant THM species formed during the disinfection process [34]. As with chlorination, chloramination resulted in an increase in THM formation. However, a more pronounced increase in THM concentration, from approximately 0.2 to 0.8 μg/L, was observed at DOC levels exceeding 13.8 to 23 mg/L. Concurrently, an increase in residual chlorine levels was noted. However, chlorination resulted in approximately 40 to 140 times more THMs than chloramination at similar DOC concentrations. This difference can be attributed to the fact that chlorine possesses greater oxidation potential than chloramine [23].

3.2. Disinfectant Dose Variation

The formation of DBPs is notably influenced by the disinfectant dose, with higher doses and extended reaction times leading to increased concentrations of THMs and HAAs [40]. Figure 2a,b demonstrates that the chlorination dose directly impacts the formation of THMs in both chloramination and chlorination processes. During chlorination, the THM concentrations range from 35.657 μg/L to 398.745 μg/L, with higher THM levels observed at increased chlorination doses. This finding is consistent with studies by Koltsova et al. and Liu et al. [10,13], who also reported elevated concentrations of DBPs, including chloroform, DCAA, and TCAA, with higher chlorine doses. Regarding the FRC values, a relatively stable level of approximately 3–4 mg Cl2/L is observed. However, a significant increase occurs, with the concentration suddenly doubling to 8 mg Cl2/L when the Cl2/DOC ratio reaches 3. The concentration of THMs increased significantly from 0.536 μg/L to 3.108 μg/L as the Cl2/DOC ratio increased from 0.5 to 3 due to chloramination. Concurrently, the FRC levels also rose with the chloramine dose, increasing from 3 mg/L to 8 mg/L at Cl2/DOC ratios of 0.5 and 3, respectively. The predominant THM observed was chloroform (CHCl3). This increase can be attributed to the further reaction of intermediate DBPs with chlorine and chloramine, resulting in the formation of THMs as final products [41]. The main difference noted between them is that the THM concentration increased by 8.66 times during chlorination and by 5.37 times during chloramination, with an increase in the Cl2/DOC ratio.

3.3. Reaction Time Variation

Prominent DBPs such as THMs and HAAs have higher concentrations with increased reaction times [40,42]. In this study, seven identical samples were prepared to investigate the effect of various reaction times on THM formation. After each reaction time, four drops of 10% sodium thiosulfate were added to the chlorinated samples to stop the reaction. As shown in Figure 3a,b, the THM levels generally increased with longer reaction times. The concentration of THMs rose more than three-fold, from 45.2 μg/L at 24 h to 173.02 μg/L at 168 h. This trend aligns with the findings of previous studies [13,34]. In contrast, the FRC levels show a decreasing trend, dropping from 6 mg/L to 2 mg/L over the 168 h period. This decline can be attributed to the fact that initially, most of the chlorine does not react immediately with the DOC solution. As the reaction time progresses, chlorine gradually interacts with the DOC, leading to the formation of THMs and other DBPs [43]. In chloramination, the THM concentration ranged from 0.17 μg/L at 0 h to 1.88 μg/L at 168 h of reaction time. Concurrently, the FRC level decreased from 6 mg Cl2/L to 2 mg Cl2/L. The initial lack of immediate interaction between chlorine and the DOC solution can explain this pattern. Over time, chlorine reacts with DOC as the reaction progresses, leading to the formation of THMs and other DBPs [43]. The trend in THM concentration over the first 24 h varied between chlorination and chloramination. During chlorination, THM levels appeared stable in the initial 24 h. In contrast, during chloramination, there was a rapid increase in the THM concentration starting after just 2 h.

3.4. Bromide Variation

Bromide and iodide precursors significantly influence DBP formation, with higher bromide levels in raw water increasing the risk of hazardous DBPs [13,44,45]. It is evident from Figure 4a,b that the concentration of THMs increases with rising bromide levels following disinfection with chlorine. During chlorination, the range of THMs formed varied from 31.99 μg/L to 62.56 μg/L at bromide concentrations of 0.038 mg/L and 0.338 mg/L, respectively, whereas during chloramination, these values ranged from 0.51 μg/L to 0.86 μg/L. The THM concentrations observed during chlorination exceed the US Environmental Protection Agency (USEPA) maximum contaminant level (MCL) of 80 μg/L for total THMs [35]. Chronic exposure to THMs at these levels has been linked to increased risks of bladder cancer, reproductive issues, and developmental problems [46,47]. Similarly, while chloramination resulted in significantly lower THM concentrations (0.508 μg/L to 0.865 μg/L), even low-level exposure to certain THM species, such as brominated THMs, may pose health risks due to their higher toxicity compared to chlorinated THMs [13,46,48]. The FRC level decreased from 4 mg/L to 1 mg/L with increasing bromine levels during chlorination, while it decreased from 6 mg/L to 4 mg/L during chloramination. The main difference between the impact of the bromide concentration during chlorination and chloramination is the proportion of Br-THMs formed. The bromide concentration significantly affects the formation of Br-THM species during chlorination, while it has a negligible impact during chloramination. This discrepancy is likely due to free chlorine being a stronger oxidizing agent, leading to a faster reaction with bromide to form HOBr compared to chloramine [41].

3.5. Temperature Variation

In this study, the DOC solutions were subjected to incubation at three different temperature conditions after disinfection to analyze the impact of temperature on THM formation. Figure 5a,b shows that the THM concentration during chlorination increases from 31.99 μg/L to 48.63 μg/L as the temperature rises from room temperature (22 °C) to 30 °C, while in chloramination, the THM concentration ranges from 0.71 μg/L to 0.8 μg/L. The decrease in FRC levels complements these observations, with FRC dropping from 4 mg-Cl2/L at room temperature to 2 mg-Cl2/L at 30 °C during chlorination and from 6 mg-Cl2/L at room temperature to 3 mg-Cl2/L at 30 °C during chloramination. In this process, the concentration of Br-THMs was lower compared to CHCl3, and their rate of decrease was even greater than that of CHCl3. This could be due to the fact that, with the increase in temperature, the concentration of stable products such as CHCl₃ increases, while the concentration of bromine-containing species becomes thermally unstable [41].

3.6. pH Variation

One of the main parameters that is known to impact the production, stability, and speciation of DBPs is pH [49]. In this study, the DOC solutions were subjected to five different pH conditions ranging from 6.5 to 8.5 to examine the influence of pH on THM formation. Previous studies have shown that pH values outside this range are less common in practical water treatment scenarios and may lead to less stable disinfection conditions or uncommon DBP formation patterns [16,35]. Figure 6a,b illustrates a general increase in THM formation during both chlorination and chloramination, ranging from 30.791 μg/L to 46.736 μg/L and from 0.58 to 1.7 μg/L, respectively, at higher pH levels. This phenomenon is attributed to the fact that elevated pH conditions can induce the hydrolysis of various intermediate DBPs, such as trihalopropanones and trihaloacetonitriles, leading to the formation of THMs [21,41]. This increase in FRC from 2 to 3 mg/L during chlorination seems inversely related to the rising pattern observed in the THM concentration as the pH increases. Similarly, during chloramination, the FRC generally increased from 3 mg/L to 5 mg/L as the pH rose from 6.5 to 8.5. It can be stated that an increase in pH caused the concentration of THMs to increase during chlorination.

3.7. Correlation Between THMs and Water Quality Parameters

Building on the earlier discussion of the relationship between various disinfection conditions and THM formation, this section focuses on examining the connection between the water quality parameters of the DOC solution and the resulting THM levels produced during disinfection with chlorine and chloramine. To understand the relationship, two statistical analytical methods were applied. By utilizing the Data Analysis tool in Excel, a high coefficient of determination (R2) and p-value between THMs and water quality parameters were determined through analysis of variance (ANOVA). Figure 7a indicates a strong positive correlation (R2 = 0.84 and p = 0.00019) between turbidity and THMs formed during chlorination. The highest THM concentration of 39.68 μg/L corresponded to a turbidity of 3.63 NTU, while the lowest THM concentration of 7.32 μg/L corresponded to a turbidity of 0.86 NTU. Meanwhile, during chloramination, the R2 and p-value are 0.37 and 0.06445, respectively. These values indicate a relatively less significant correlation between turbidity and THM formation during chloramination. Based on Figure 7b, it is apparent that there is a strong positive correlation between TDSs and TTHM formation during chlorination, with an R2 and p-value of 0.89 and 0.00005, respectively. On the other hand, during chloramination, the R2 and p-value of 0.58 and 0.01014, respectively, indicate a comparatively less significant correlation between TDSs and THM formation, which aligns with the results of Aleid et al.’s research [50].
The change in the SUVA value showed a significant variation with the changes in DOC concentration. While SUVA fluctuated considerably for most of the DOC solutions, it increased notably at lower DOC concentrations (Figure 7c). For both chlorination and chloramination, there is an opposite trend between the value of SUVA and the concentration of THMs. The R2 and p-value are 0.4 and 0.05031, respectively, during chlorination, and the R2 and p-value are 0.24 and 0.16916, respectively, during chloramination. These values indicate a weak correlation between SUVA and THM formation. However, Koltsova 2019 [13] observed a positive and decent correlation between SUVA and THMs. This difference in findings could be attributed to the fact that they used surface waters for disinfection, which inherently had higher aromatic contents. From Figure 7d, the value of UV254 closely followed the concentration of THMs during chlorination (R2 = 0.90 and p = 0.00003). Meanwhile, during chloramination, it is evident that there is a correlation, as the values of R2 and p-value are 0.64 and 0.00528, respectively. So, it can be asserted that there is a direct relationship between UV254 and TTHMs formed during chlorination. However, the measurement of UV254 might not be as useful during chloramination due to a moderate correlation between UV254 and the THMs formed.

3.8. Broader Implications for Other Regions and Alternative Treatment Methods

While this study focused on Cedar Lake, Illinois, as a representative forested upland catchment, the findings provide valuable insights that can be contextualized for other regions with differing soil compositions and climatic conditions. The key factors influencing DOM leaching and DBP formation, such as the soil organic carbon content, aromaticity of DOM, and the presence of functional groups including hydroxyl and carboxyl, are universal, though their magnitudes may vary [22]. Similarly, climatic conditions such as higher rainfall intensity or prolonged drought periods can alter DOM concentrations and characteristics in surface waters [7,23]. In tropical regions, higher temperatures and microbial activity may accelerate organic matter decomposition, leading to DOM with different reactivity compared to temperate regions [22]. While the specific DBP yields and formation pathways observed in this study are tied to the conditions at Cedar Lake, the methodological framework and key relationships identified—such as the influence of pH, temperature, and disinfectant dose on DBP formation—can be applied to other regions. In addition, other alternative treatment methods such as Ozone Treatment, which is highly effective at degrading organic matter and reducing DBP precursors, or advanced oxidation processes (AOPs), which often combine ozone, hydrogen peroxide, or UV light, can further enhance the breakdown of complex organic compounds [5]. However, they may also introduce other challenges, such as the formation of bromate during ozonation or higher operational costs [5,37,50].
Future studies should explore the integration of these alternative methods with traditional disinfection processes to optimize water treatment strategies and further mitigate DBP risks. Additionally, expanding the study to other geographic regions with varying soil compositions, land use practices, and climatic conditions would help assess the generalizability of the findings. Investigating long-term patterns of THM formation under varying climatic conditions, such as seasonal fluctuations in temperature and rainfall, would provide valuable insights into the dynamic nature of DBP formation in real-world water systems. Furthermore, examining other classes of disinfection byproducts, such as haloacetic acids (HAAs) and nitrogen-containing DBPs, is critical, as these compounds may pose additional health risks and require tailored mitigation strategies. By addressing these research gaps, future studies can contribute to the development of more effective and adaptable water treatment practices.

4. Conclusions

This study investigated THM formation during the disinfection (chlorination and chloramination) of soil-derived dissolved organic matter. Key water quality parameters influencing THM formation were evaluated under controlled conditions. The results showed that chloramination produced significantly lower THM concentrations compared to chlorination but resulted in a higher proportion of brominated disinfection byproducts. This suggests that combining chlorine as a primary disinfectant with chloramine as a secondary disinfectant could be an effective strategy for water treatment in the Cedar Lake Watershed. THM formation was strongly influenced by reaction time, DOC concentration, and disinfectant dosage, with THM levels increasing five- to ten-fold as the disinfectant doses rose. The bromide concentration directly impacted Br-DBP formation during chlorination but had minimal effect during chloramination. Temperature and pH variations had a modest influence on THM formation in both processes. Minimizing DBP precursors (e.g., DOC and bromide) and optimizing disinfectant doses can effectively reduce THM formation. During chlorination, most water quality parameters (except SUVA) showed strong positive correlations with THMs, while the correlations were weaker during chloramination.
This study is the first to examine THM formation from soil-extracted DOM in a watershed setting. The findings revealed that organic soil layers produced nearly double the DOC levels of mineral layers, while initial bromide concentrations in the DOC solutions were low. Future research should explore seasonal and temperature effects on DBP formation, investigate nitrogenous DBPs (N-DBPs), and evaluate alternative disinfection methods such as UV irradiation, ozonation, and chlorine dioxide.

Author Contributions

Conceptualization, H.F. and A.A.; Methodology, A.A.; Software, A.A. and A.S.; Validation, A.A. and H.F.; Formal analysis, A.A. and A.S.; Writing—original draft, A.A. and H.F.; Writing—review and editing, A.A., H.F. and A.S.; Supervision, H.F. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

All data generated or analyzed during this study are included in this published article.

Acknowledgments

The author expresses his or her thanks to the people helping with this work and acknowledges the valuable suggestions from the peer reviewers. Special thanks go to Sajjan Nhuchhen Pradhan for his invaluable time, dedication, and unwavering efforts throughout the development of this research.

Conflicts of Interest

The author declares no conflicts of interest.

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Figure 1. Effect of DOC on THM and FRC levels due to (a) chlorination (b) and chloramination.
Figure 1. Effect of DOC on THM and FRC levels due to (a) chlorination (b) and chloramination.
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Figure 2. Effect of Cl2/DOC ratio on THM and FRC levels due to (a) chlorination and (b) chloramination.
Figure 2. Effect of Cl2/DOC ratio on THM and FRC levels due to (a) chlorination and (b) chloramination.
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Figure 3. Effect of reaction time on THM and FRC levels due to (a) chlorination and (b) chloramination.
Figure 3. Effect of reaction time on THM and FRC levels due to (a) chlorination and (b) chloramination.
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Figure 4. Effect of bromide level on THM and FRC levels due to (a) chlorination and (b) chloramination.
Figure 4. Effect of bromide level on THM and FRC levels due to (a) chlorination and (b) chloramination.
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Figure 5. Effect of incubation temperature on THM and FRC levels due to (a) chlorination and (b) chloramination.
Figure 5. Effect of incubation temperature on THM and FRC levels due to (a) chlorination and (b) chloramination.
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Figure 6. Effect of pH on THM and FRC levels due to (a) chlorination and (b) chloramination.
Figure 6. Effect of pH on THM and FRC levels due to (a) chlorination and (b) chloramination.
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Figure 7. Correlation between TTHM and water quality parameters for chlorination and chloramination. (a) Turbidity. (b) TDSs. (c) SUVA. (d) UV254 (The red and blue lines represent trendlines for the correlation between TTHM and water quality parameters. The red line corresponds to chloramination, and the blue line corresponds to chlorination).
Figure 7. Correlation between TTHM and water quality parameters for chlorination and chloramination. (a) Turbidity. (b) TDSs. (c) SUVA. (d) UV254 (The red and blue lines represent trendlines for the correlation between TTHM and water quality parameters. The red line corresponds to chloramination, and the blue line corresponds to chlorination).
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Table 1. Baseline and various conditions applied to study.
Table 1. Baseline and various conditions applied to study.
ParameterBaseline ConditionCondition
DOC concentration22.97 mg/L0% DI to 90% DI
Reaction time24 h0, 2, 12, 24, 48, 96, and 168 h
Bromine levelAmbient (0.038 mg/L)0.038, 0.18, 0.28, and 0.38 mg/L
pH7.56.5, 7, 7.5, 8, 8.5
Chlorine to DOC ratio1:10.5:1, 1:1, 1.5:1, 2:1, 3:1
TemperatureRoom temperature (22 °C)22 °C, 25 °C, 30 °C
Table 2. Steps to perform chlorination and chloramination.
Table 2. Steps to perform chlorination and chloramination.
ChlorinationChloramination
  • Preparing the standardized sodium hypochlorite solution.
  • Adjusting the pH of samples based on requirements.
  • Adding chlorine to samples.
  • Putting samples in dark and required temperature for the required duration.
  • Determining the free residual chlorine using the DPD titrimetric method.
  • Adding 4 drops of 10% sodium thiosulfate solution for THM analysis.
  • Preparing the standardized sodium hypochlorite solution along with a standard aqueous ammonium chloride solution.
  • Adjusting the pH of samples based on requirements.
  • Adding chloramine according to the following relation.
  • Putting samples in the dark and required temperature for the required duration.
  • Determining the free residual chlorine using the DPD titrimetric method.
  • Adding 4 drops of 10% sodium thiosulfate solution for THM analysis.
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Asadollahi, A.; Sohrabifar, A.; Fakhraei, H. Trihalomethane Formation from Soil-Derived Dissolved Organic Matter During Chlorination and Chloramination: A Case Study in Cedar Lake, Illinois. Geographies 2025, 5, 15. https://doi.org/10.3390/geographies5010015

AMA Style

Asadollahi A, Sohrabifar A, Fakhraei H. Trihalomethane Formation from Soil-Derived Dissolved Organic Matter During Chlorination and Chloramination: A Case Study in Cedar Lake, Illinois. Geographies. 2025; 5(1):15. https://doi.org/10.3390/geographies5010015

Chicago/Turabian Style

Asadollahi, Amin, Asyeh Sohrabifar, and Habibollah Fakhraei. 2025. "Trihalomethane Formation from Soil-Derived Dissolved Organic Matter During Chlorination and Chloramination: A Case Study in Cedar Lake, Illinois" Geographies 5, no. 1: 15. https://doi.org/10.3390/geographies5010015

APA Style

Asadollahi, A., Sohrabifar, A., & Fakhraei, H. (2025). Trihalomethane Formation from Soil-Derived Dissolved Organic Matter During Chlorination and Chloramination: A Case Study in Cedar Lake, Illinois. Geographies, 5(1), 15. https://doi.org/10.3390/geographies5010015

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