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Article

The Problem of Selenium for Human Health—Removal of Selenium from Water and Wastewater

by
Agata Witczak
1,*,
Kamila Pokorska-Niewiada
1,
Agnieszka Tomza-Marciniak
2,
Grzegorz Witczak
3,
Jacek Cybulski
1 and
Aleksandra Aftyka
4
1
Department of Toxicology, Dairy Technology and Food Storage, Faculty of Food Sciences and Fisheries, West Pomeranian University of Technology, 70-310 Szczecin, Poland
2
Department of Animal Reproduction Biotechnology and Environmental Hygiene, Faculty of Biotechnology and Animal Husbandry, West Pomeranian University of Technology, 70-310 Szczecin, Poland
3
Department of Gynecological Surgery and Gynecological Oncology of Adults and Adolescents, Pomeranian Medical University, 70-204 Szczecin, Poland
4
Provincial Veterinary Inspectorate, 71-337 Szczecin, Poland
*
Author to whom correspondence should be addressed.
Water 2023, 15(12), 2230; https://doi.org/10.3390/w15122230
Submission received: 26 April 2023 / Revised: 31 May 2023 / Accepted: 12 June 2023 / Published: 14 June 2023
(This article belongs to the Special Issue Water Environment Pollution and Control)
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Abstract

:
Selenium is a trace element that can be poisonous in small quantities. The aim of this study was to analyze the change in the content of selenium in drinking water, raw water, as well as treated and raw wastewater in an annual cycle in the city of Szczecin. The concentration of Se in samples was determined using the spectrofluorometric method at a 518 nm emission wavelength and a 378 nm excitation wavelength. The amount of selenium in drinking water ranged from <LOD to 0.007 μg/mL, in raw water, from 0.001 to 0.006 μg/mL, in raw wastewater, from 0.001 to 0.008 μg/mL, and in treated wastewater, from 0.001 to 0.009 μg/mL. The selenium content did not exceed the maximum allowable concentration (MAC), 0.010 μg/mL, in any of the water samples tested.

1. Introduction

Selenium (Se) is a trace element that is widespread in the environment, but it is particularly found in igneous and sedimentary rocks, waters, soils, plants, and living organisms. Selenium is released from both natural and anthropogenic sources (metallurgical, glass, and pigment-producing industries [1,2]. It occurs most frequently in one of two forms—organic, including seleno-amino acids, selenopeptides, and selenoproteins—and inorganic. Inorganic forms are more toxic and less bioavailable than organic forms [3]. Selenium in waters occurs in the forms of seleno-amino acids, selenides, selenates, and dimethyl and trimethyl derivatives. The form of occurrence depends on water pH and redox potential (Eh).
Surface waters and groundwaters contain highly variable concentrations of this element. Selenium concentrations in natural marine and fresh waters ranges from 0.01 to 0.1 μg/L [4]. In some areas selenium concentrations in groundwaters can reach levels as high as 6.000 μg/L; however, in water supply networks in developed countries it occurs in quantities that do not exceed 10 μg/L [5]. Industrial wastewater can contain much higher concentrations ranging from 0.1 to 20 mg/L [6,7].
Selenium is recognized as an essential but also potentially toxic element, and the margin between selenium deficiency and toxicity is very narrow [7]. Nutritional deficiencies occur at an intake of less than 40 μg/day, and can lead to the development of many disorders, such as Keshan disease [8,9]. It is recommended to take a prophylactic dose of Se of approximately 200 µg/day to reduce the risk of cancer in humans. However, an Se dose of >400 µg/day is considered to be potentially toxic [10,11]. Excess Se can lead to the development of cancers, type II diabetes, and diseases of the circulatory and endocrine systems [7,12]. As much as 80% of this element can be absorbed in the gastrointestinal tract [13]. Concentrations of selenium in humans are determined mainly by their diet, but the intake of it can be increased by drinking water that has high concentrations of selenium [14].
Selenium requirements differ depending on age, and range from 17 to 50 μg/day, but requirements increase with excess stress, overconsumption of alcohol and nicotine, and increased physical exertion [15]. Among other things, selenium is a component of selenoproteins that are involved in antioxidant defense, DNA synthesis, and thyroid hormone production, and are essential to reproduction. Se inhibits the synthesis of osteopontin, an important protein in cancer metastasis [16]. Links have been confirmed between selenium deficiency and the occurrence of anxiety, depression, and affective disorders [13]. The recommended daily allowance (RDA) of selenium for adults is 55 µg [17].
Considering the health benefits and toxic effects of selenium in humans, the current study was undertaken with the aim of assessing changes in the selenium content of drinking water throughout the year in the city of Szczecin. The study also aimed to estimate the impact of water treatment on the selenium content of drinking water. Given that treated wastewater is discharged into surface waters and can become a secondary source of selenium in treated water, the extent to which wastewater treatment affects the final selenium content was also analyzed.

2. Materials and Methods

2.1. Materials

The study material was raw water, drinking water, and treated and raw wastewater. Raw water was collected from Lake Miedwie (Figure 1), which is the main source of water (80%) for the city of Szczecin.
Water samples were taken from an intake located 6 m above the bottom and 16–18 m below the water surface of Lake Miedwie. The wastewater tested was from the Pomorzany Wastewater Treatment Plant (Szczecin, Poland), from which raw wastewater was sampled at the grating station, and treated wastewater was collected at the outflow of the canal. The study began in March, 2018 and ran until March, 2019.

2.1.1. Drinking Water Treatment

Raw water from Lake Miedwie is treated at the Żelewo Water Treatment Plant (Stare Czarnowo, Poland) (Figure 2).
The first stage of treatment is pre-oxidation with an ozone dose of 1–2 g/m3. The highly alkaline coagulant PAX XL 1905 (Kemipol, Police, Poland, with the following properties: pH—3.6 ± 0.4; alkalinity—85 ± 5%; density—1150 kg/m3; aluminum content—6.0 ± 0.5%; chlorides—5.0 ± 1.0%) is added to the water with the ozone. Next, the water reacts with coagulants for 3 to 6 min. Then, the water flows into labyrinth chambers (20–40 min.), where a polyelectrolyte is added at a dose that depends on the current water quality and the amount of coagulant used. Sludge sedimentation can happen in the chambers, and this is washed out with an additional stream of water, after which, the water flows into horizontal settling tanks with a capacity for sedimentation of 1600 m3 each. Sludge is removed continuously to sludge funnels and discharged into a sludge canal and then into the wastewater system. The water from the settling tanks is purified on carbon filter beds and then on anthracite-sand filters. The rapid anthracite-sand filters comprise 12 filtration chambers with a surface area of 46.17 m2. The filter beds are 0.6 m layers of quartz sand and 40 cm layers of anthracite. The maximum speed of filtration is 10 m/h. Water from the filtration chamber flows into two indirect ozonation chambers where viruses and bacteria are eliminated and most pesticides are oxidized. Water is retained in the ozonation chambers for about 15 min at a flow rate of 3000 m3/h. The water is filtered through 8 carbon filters arranged in two rows between which there is an ozonation line. In the last stage, the water is disinfected with chlorine dioxide and chlorine gas. When the water is appropriately pure, it is collected in two tanks with a combined capacity of 10,000 m3, and from there, it is distributed through the water supply network to the city of Szczecin (materials from ZWiK, Department of Waterworks, Szczecin, Poland) [19].

2.1.2. Wastewater Treatment

Szczecin’s wastewater is treated at the Pomorzany Wastewater Treatment Plant (Figure 3).
Wastewater flows into the expansion chamber, then through a canal in which there is a sampling station, and then, to the grating station fitted with two 40 mm mesh screens and six 6 mm mesh screens. The flow rate in the grating station is 5.4 m3/s. The largest solids are removed with a screw compacting press, while the particle sizes of the solids retained on the fine screens are further reduced.
Once the largest solids are removed, the wastewater flows to the aerated grit chambers constructed of reinforced concrete with a degreasing chamber on the side. A bottom scraper collects fat and grease into the grease chamber, and then it is pumped into fermentation chambers. Minerals that sediment to the tank bottom are funneled into sand separators. From here, the wastewater flows to pre-settling tanks. The sludge that accumulates is collected with chain scrapers and is pumped into the sludge chamber. Fat and grease that rise to the surface are collected in a gutter and pumped to the fermentation chamber along with the fat and grease from the grit chambers. Mechanical treatment is followed by biological treatment. This part of the plant is equipped with devices that take measurements and steer processes such as how much air is released into the nitrification or denitrification chambers or the quantities required of iron coagulants PIX 113 (Kemipol, Poland, with the following properties: total iron 11.8 ± 0.4%; density in kg/m3 (20 °C) 1500–1570; PAX 16 (Kemipol, Poland, with the following properties: Al2O3 content 15.5 ± 0.4%; chlorides (Cl−) 19.0 ± 2.0%; alkalinity 37.0 ± 5.0%; density in kg/m3 (20 °C) 1330 ± 20; pH 1.0 ± 0.2).

2.2. Methods

High-purity analytical reagents from Merck (Darmstadt, Germany) were used in the study. Selenium concentrations in samples were determined with the spectrofluorimetric method. Water samples were digested in HNO3 for 180 min at a temperature of 230 °C and in HClO4 for 20 min at a temperature of 310 °C. After mineralization, a solution of 9% HCl was added to the samples to reduce selenate to selenite. Then, the Se was derivatized in an acidic environment (pH 1–2), which resulted in the formation of a selenodiazole complex, which was then extracted with cyclohexane. Selenium concentrations were determined with an RF-5001 PC fluorescence spectrophotometer (Shimadzu, Tokyo, Japan) at a emission wavelength of 518 nm and an excitation wavelength of 378 nm.
The accuracy of the analytical method was tested with Certified Reference Materials: Trace Metals in Drinking Water Solution A (CRM-TMDW-A; High-Purity Standards, North Charlestone, SC, USA) (for water and Certified Reference Material ERM®-CA713 (IRMM, Geel, Belgium) for sewage. The recoveries of these reference materials were, respectively, 96.3 ± 3.2% and −98.8 ± 2.9%. In addition our own standard material, selenium content was used, whose recoveries ranged from 91 to 95%. The analytical procedure was verified with blank samples (20 replicates). The relative standard deviation (RSD%) of the determinations was 2.96%, while the limit of detection (LOD, x + 3σ) was 0.001 µg/mL.
Results for the remaining parameters, including, among others, alkalinity and nitrates, were provided by the laboratories at ZWIK Szczecin (Szczecin, Poland). The results of the study were analyzed with Statistica 13.0 (StatSoft, Kraków, Poland), and they are presented as arithmetic means with standard deviations (SD) and minimum and maximum values. The significance of the differences was tested with Tukey’s post hoc test (p < 0.05).

3. Results

3.1. Analysis of Selenium in Water

The selenium content in raw water during the study period fluctuated from 0.0020 to 0.0068 μg/mL (average 0.0037 ± 0.0016 μg/mL), while in drinking water, it ranged from <LOD to 0.0052 μg/mL (average 0.0024 ± 0.0013 μg/mL) (Figure 4).
A positive significant correlation (p < 0.05) was noted in the content of Se in raw water and alkalinity, quantity of nitrates, COD, and UV absorbance m−1 (Table 1). High water alkalinity can prevent soil components from absorbing Se in aquatic ecosystems and prevent high Se concentrations in groundwater. Under these conditions, Se is predominantly present in the form of labile selenate [20]. High nitrate concentrations are known to create weak oxidation conditions that inhibit microbial Se fixation, which can also cause increased Se concentrations in water [21].
Water 15 02230 g004 550
Figure 4. Changes in selenium content in drinking water and raw water in an annual cycle. MAC—the maximum allowable concentration [22].
Figure 4. Changes in selenium content in drinking water and raw water in an annual cycle. MAC—the maximum allowable concentration [22].
Water 15 02230 g004
The differences in selenium content between raw and drinking water in individual months were statistically insignificant (p < 0.05) except in June, July, August, and October. The significance of differences (p < 0.05) in selenium content in individual months of the period analyzed is presented in Table A1 (Appendix A). Raw water treatment was shown to significantly reduce Se in drinking water by 4 to 70% (Figure 5).

3.2. Analyses of Selenium Content in Treated and Raw Wastewater

The average selenium contents in raw and treated wastewater during the study period were 0.007 ± 0.002 μg/mL and 0.005 ± 0.002 μg/mL, respectively (Figure 6). The statistical analysis (Tukey’s test) did not reveal significant (p < 0.05) differences between the selenium contents in treated and raw wastewater.
Significantly more selenium was noted in wastewater treated in June and July, 2018 than in other months. Conversely, significantly lower Se content was noted in wastewater treated in the winter months. The significance of the differences (Tukey’s test, p < 0.05) between the selenium content in treated water and raw sewage in the different months of the period analyzed are presented in Table A2 (Appendix A). Wastewater treatment reduced selenium content significantly (Figure 7).

3.3. Selenium Consumption with Drinking Water and Consumer Safety

The permissible content of selenium in drinking water in Poland should not exceed 0.010 μg/mL [22]. Based on the results obtained, the amount of Se in drinking water was at a low level (Figure 8). In July 2018, however, the content of this element was over 40% of the maximum residue level (MAC; Figure 8).

4. Discussion

The content of selenium in surface water is influenced primarily by the geological environment of water reservoirs, e.g., selenium-rich rocks that are washed out over time. Another factor influencing Se content in water is contact with selenium-rich wastes from metallurgical, chemical, and photoelectric industries. The US EPA [23] established limits for lentic and lotic waters of 1.5 μg/L and 3.1 μg/L, respectively. According to the Regulation of the Minister of Maritime Economy and Inland Navigation [24], the permissible selenium concentration in surface waters in Poland is 10 μg/L. Given the risk of ingesting large amounts of selenium with drinking water, the process of removing this element at individual stages of water treatment was examined [6,25,26].
Selenium in drinking water, groundwater, and wastewater is a global problem. Although selenium health benefits and toxicity are well known, to date, no safe, optimal content of this element in drinking water has been established [27,28]. European standards are not uniform. The World Health Organization (WHO) standard for drinking water is 40 μg/L [29], while the US EPA [30] upper limit is 50 μg/L. The highest, permissible selenium concentration in drinking water set forth in Directive (EU) [31] is 20 µg/L. In Poland, the maximum allowable concentration (MAC) for selenium in drinking water was set forth in a regulation of the Minister of Health at 0.010 µg/mL [22].
Similar problems regarding a lack of standards are found in the selenium content of wastewater [3,28,32,33]. In most countries, Se content in drinking water is less than 10 μg/L [21,29]. Selenium content in drinking water samples from the USA, Canada, and Australia rarely exceed this value [14,34,35], but values as high as 160 μg/L have been reported in China [36]. Selenium content varies in drinking water in Europe; in Germany, values of 0.02–0.03 μg/L [37,38] have been noted, while in Slovenia, the value is 0.2 μg/L [39]. In the current study, the average content of this element in drinking water fluctuated around 2.4 μg/L, but it did not exceed the safe value for consumers. According to the WHO, selenium content in groundwater and surface water globally range from 0.06 ng/mL to 0.4 μg/mL, while in specific cases, it can reach 6 μg/mL [3,29]. The minimum and maximum values cited above do not differ from the selenium content in raw water in Szczecin.
In the current study, the slightly higher selenium content in raw water than in drinking water could have come from field and pasture fertilisers, the main component of which is selenium. This element can also reach water reservoirs with precipitation. Changes in selenium content in raw water can also be affected by the presence of other elements with which it forms compounds. Changes in selenium content in treated water could also be caused by the use of PAX aluminum coagulants that can alter water pH, among other things.
Water that is treated for drinking water usually contains less than 0.1 mg Se/L, while values in industrial water are above 1 mg/L. Wastewater that contains selenium is often associated with other substances and high salinity [40,41]. Consequently, the choice and effectiveness of treatment processes depend not only on the degree of selenium oxidation but also on the presence and concentrations of other contaminants and on other factors, including existing treatment plants and processes, treatment objectives, and concerns regarding waste treatment and costs [28]. There is no single method that ensures adequate water treatment, and, in practice, various chemical, biological, and physical methods are applied to attain the desired water quality [28,42]. For drinking water, certain local management solutions are implemented to maintain selenium below threshold levels without increasing costs to consumers. For example, groundwater can be cleaned through sand filtration combined with ion exchange resins and membrane treatments, e.g., microfiltration and nanofiltration, which can remove up to 95% of selenium [42]. However, such methods are often poorly adapted, not highly selective, and expensive. Thus, innovation is required to develop water treatment methods that are efficient, inexpensive, technologically feasible, and environmentally friendly. In France, these solutions generally aim to either request that the responsible authorities grant operational exemptions, or, most frequently, to seek other water sources [28]. When removing selenium on an industrial scale, the first possible method is to use iron co-precipitation and adsorption, and, if necessary, to combine this with coagulation–flocculation [27,28]. The principal technologies used to remove Se are the following: a nanofiltration membrane-based process [43], coagulation [44], phytoremediation [45], precipitation [46], and adsorption [6,47]. The water treatment solutions described in the present study fulfilled their roles.
Water tests were supplemented with wastewater analyses from the same study period. The highest allowable selenium concentration in all types of water is 1 mg/L [48]. At no time during the period analyzed was this limit exceeded in the current study. The causes of fluctuations in selenium content in treated wastewater could have been the PIX iron coagulant used, the components of which could have formed compounds with selenium. Coagulants are added to wastewater during treatment in various quantities depending on, among other things, oxygen and nitrogen concentrations. PAX coagulants, which can also influence Se contents in wastewater, are added when filamentous bacteria occur, which is also linked with fluctuations. The results of this study indicated that the likelihood of treated wastewater potentially increasing selenium concentrations in sources used to produce drinking water was low.
Despite the wastewater treatment, it is impossible to completely eliminate selenium, which returns to water reservoirs together with the treated wastewater. Therefore, treated wastewater may be a source of this element in the environment. Consumers and industrial plants can influence Se content. As a result of using drinking water, the level of selenium can be decreased or increased by discharging substances rich in this element.
Human requirements for water vary depending primarily on age and sex. The Institute of Food and Nutrition in Warsaw set recommended standards for H2O consumption, taking into consideration the liquid form and water consumed with foods (Table 2). The recommended daily allowance (RDA) of selenium for adults is 55 μg/day (Table 2), and the tolerable upper intake is 400 μg/day, as set by the US Institute of Medicine of the National Academy of Sciences [49], while selenium intake in excess of 5 mg/day can be fatal [50,51].

5. Conclusions

The selenium content in surface waters is influenced, among others, by the type of geochemical environment, leaching processes from rocks, and environmental pollution. Lake Miedwie, which was the source of the tested water, is characterized by a high content of organic matter, which affects the amount of nitrates in the water. In addition, the catchment area of Lake Miedwie is mainly agricultural land, where, among others, nitrogen fertilizers are also used. These compounds, as well as other polluting chemicals, may enter the waters of Lake Miedwie as a result of soil leachate and surface runoff of rainwater.
The amount of precipitation during the year also affects the presence of selenium in the analyzed water reservoir.
Selenium content in raw water was the highest in summer, which correlated with higher contents of nitrates (III). Usually in the summer period (June–August), there is also the largest leachate from the soil to the lake caused by heavier rainfall, which is short and very intense.
The removal of selenium from raw water and wastewater is difficult because the metalloid is often present in various complex forms and can also form various compounds with other elements.
The higher content of Se in raw water may be caused by fertilizing fields and pastures with fertilizers whose main component is selenium.
The water treatment process lowered selenium content in drinking water by a range of 4 to 70%.
The processes used during water treatment affect the reduction in the selenium content in the water. The changes in the selenium content in water after treatment could also be caused by the use of PAX aluminum coagulants, causing, among others, changes in water pH.
As a results of treatment process, the selenium content in drinking water was low and ranged from 14 to 43% of the MAC value.
Treated wastewater can be a source of selenium in the environment and, discharged into surface waters, can become a secondary source of selenium in treated water. In our study, treating wastewater resulted in lowering selenium content in treated wastewater by as much as 47%.

Author Contributions

Conceptualization, A.W., K.P.-N. and G.W.; methodology, A.T.-M.; validation, A.W.; formal analysis, A.W. and K.P.-N.; investigation, A.W., A.T.-M. and J.C.; writing—A.W., K.P.-N. and A.A.; visualization, A.W. and K.P.-N. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Data available on request.

Conflicts of Interest

The authors declare no conflict of interest.

Appendix A

Table
Table A1. Significant differences (in bold type) in selenium content in raw and drinking water among sampling periods (p < 0.05)—Tukey’s test.
Table A1. Significant differences (in bold type) in selenium content in raw and drinking water among sampling periods (p < 0.05)—Tukey’s test.
Sampling PeriodRaw Water
03.1804.1805.1806.1807.1808.1809.1810.1811.1812.1801.1902.19
03.18
04.180.9947
05.180.88711.0000
06.180.73020.99110.9998
07.180.08260.62100.75271.0000
08.180.30200.93830.99121.00000.9999
09.180.15600.79710.91661.00001.00001.0000
10.180.03200.37500.74251.00001.00000.99831.0000
11.181.00000.99990.98550.88590.20820.56500.34750.0923
12.181.00000.99470.88710.73020.08260.30200.15600.03201.0000
01.191.00000.98940.84560.68810.06580.25480.12720.02491.00001.0000
02.191.00000.88710.55740.46610.01920.09470.04090.00660.99851.00001.0000
Sampling PeriodDrinking Water
03.1804.1805.1806.1807.1808.1809.1810.1811.1812.1801.1902.19
03.18
04.181.0000
05.180.99651.0000
06.181.00001.00001.0000
07.180.09990.31550.33210.8034
08.180.77380.97560.99760.99890.9276
09.180.42690.79290.88890.97830.99921.0000
10.181.00001.00000.99981.00000.18510.90750.6151
11.180.96600.99971.00001.00000.84221.00000.99750.9945
12.181.00001.00000.99981.00000.18510.90750.61511.00000.9945
01.191.00000.99990.98971.00000.07150.68660.34161.00000.93341.0000
02.191.00001.00000.99771.00000.11130.80030.45711.00000.97371.00001.0000
Table
Table A2. Significant differences (in bold type) in selenium content in treated and raw wastewater among sampling periods (p < 0.05).
Table A2. Significant differences (in bold type) in selenium content in treated and raw wastewater among sampling periods (p < 0.05).
Sampling PeriodTreated Wastewater
03.1804.1805.1806.1807.1808.1809.1810.1811.1812.1801.1902.19
03.18
04.180.9592
05.180.98171.0000
06.180.55620.98870.9784
07.180.01400.38840.08891.0000
08.180.43420.99840.97011.00000.8040
09.180.95921.00001.00000.98870.13320.9900
10.181.00000.99310.99800.69320.03110.62760.9931
11.181.00000.99310.99800.69320.03110.62760.99311.0000
12.181.00000.70640.79340.30170.00260.15110.70640.99960.9996
01.190.99530.35960.44920.14420.00060.04280.35960.96820.96821.0000
02.190.95920.19390.25670.08380.00030.01720.19390.86610.86610.99961.0000
03.190.96210.42100.48740.02970.00640.11070.42100.90610.90610.99781.00001.0000
Sampling PeriodRaw Wastewater
03.1804.1805.1806.1807.1808.1809.1810.1811.1812.1801.1902.19
03.18
04.181.0000
05.181.00001.0000
06.180.99950.99990.9995
07.180.99870.99990.99191.0000
08.181.00001.00001.00001.00001.0000
09.180.99970.99760.99800.95650.59640.9357
10.181.00001.00001.00000.99780.99251.00001.0000
11.180.98780.95950.98780.85900.58910.89221.00000.9976
12.180.80580.68120.80580.59750.22360.52740.99760.90071.0000
01.190.12590.07800.12590.13480.01040.04410.54240.19510.80580.9878
02.190.07800.04670.07800.09690.00570.02550.40700.12590.68120.95951.0000

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Water 15 02230 g001 550
Figure 1. Location of the study area: 1: area supplied with water from Lake Miedwie—left-bank part of Szczecin (north, west, and downtown districts); 2: pumping stations; 3: water treatment plant; 4: water sampling sites at the Żelewo Water Treatment Plant [18].
Figure 1. Location of the study area: 1: area supplied with water from Lake Miedwie—left-bank part of Szczecin (north, west, and downtown districts); 2: pumping stations; 3: water treatment plant; 4: water sampling sites at the Żelewo Water Treatment Plant [18].
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Figure 2. Model of the water treatment process in the Water Treatment Plant, Żelewo.
Figure 2. Model of the water treatment process in the Water Treatment Plant, Żelewo.
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Figure 3. Model of mechanical and biological treatment at the Pomorzany wastewater treatment plant.
Figure 3. Model of mechanical and biological treatment at the Pomorzany wastewater treatment plant.
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Figure 5. Changes in selenium content in water after treatment.
Figure 5. Changes in selenium content in water after treatment.
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Figure 6. Selenium content in raw and treated wastewater in an annual cycle.
Figure 6. Selenium content in raw and treated wastewater in an annual cycle.
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Figure 7. Changes in wastewater selenium content after treatment.
Figure 7. Changes in wastewater selenium content after treatment.
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Figure 8. Selenium content in drinking water compared to MAC values.
Figure 8. Selenium content in drinking water compared to MAC values.
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Table
Table 1. Correlations between selenium content and selected parameters and chemical compounds in drinking water and raw water.
Table 1. Correlations between selenium content and selected parameters and chemical compounds in drinking water and raw water.
Drinking WaterRaw Water
ParameterPearson’s Correlation Coefficient p < 0.05ParameterPearson’s Correlation Coefficient p < 0.05
pH−0.440Absorbance in UV m−10.314
alkalinity (mmol/L)0.353alkalinity (mmol/L)0.762
nitrates (NO3/L)0.362nitrates (NO3/L)0.350
chlorine dioxide (mg ClO2/L)0.502COD with the permanganate method mg O2/L0.287
Table
Table 2. Selenium requirements in different age categories [52].
Table 2. Selenium requirements in different age categories [52].
AgeRDA—Recommended Daily Allowance for Selenium (μg/Day) *Recommended Water Consumption mL/DayDaily Se Requirement Met by Drinking the Water Tested (%)
1–320125015
4–9301600 (4 YOA)–1750 (9 YOA)13 (4 YOA)–14 (9 YOA)
10–12401900 ♀; 2100 ♂11 ♀; 13 ♂
13–15551950 ♀; 2350 ♂9 ♀; 10 ♂
≥16552000 ♀; 2500 ♂9 ♀; 11 ♂
Pregnant women6023009
Breastfeeding women7027009
Note(s): * nutrition standards for the Polish population according to Jarosz et al. [52].
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Witczak, A.; Pokorska-Niewiada, K.; Tomza-Marciniak, A.; Witczak, G.; Cybulski, J.; Aftyka, A. The Problem of Selenium for Human Health—Removal of Selenium from Water and Wastewater. Water 2023, 15, 2230. https://doi.org/10.3390/w15122230

AMA Style

Witczak A, Pokorska-Niewiada K, Tomza-Marciniak A, Witczak G, Cybulski J, Aftyka A. The Problem of Selenium for Human Health—Removal of Selenium from Water and Wastewater. Water. 2023; 15(12):2230. https://doi.org/10.3390/w15122230

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Witczak, Agata, Kamila Pokorska-Niewiada, Agnieszka Tomza-Marciniak, Grzegorz Witczak, Jacek Cybulski, and Aleksandra Aftyka. 2023. "The Problem of Selenium for Human Health—Removal of Selenium from Water and Wastewater" Water 15, no. 12: 2230. https://doi.org/10.3390/w15122230

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