Investigation of the Impact of Water Quality in Central Water Supply Systems on Human Health and the Environment

Introduction. Providing the population with high-quality drinking water is a global challenge. This challenge is caused by a combination of factors, with access to clean water sources being a key one. However, due to the global anthropogenic impact on the environment, there are virtually no natural sources that provide water suitable for drinking without treatment. The qualitative and quantitative composition of water in natural sources of drinking water supply is an important factor determining the state of the environment and the sanitary and epidemiological well-being of the population. A study by the UN Special Committee found that human disease burden is largely determined by the quality of water from natural sources. With the development of urban areas and industrial agglomerations, the anthropogenic load on water bodies increases, which leads to their pollution [1]. In this regard, water treatment technologies come to the fore, the choice of which should be justified taking into account sanitary, hygienic, environmental, technological, and economic considerations.

The documents of the World Health Organization (WHO) and the national regulatory documents of the Russian Federation establish drinking water quality standards aimed at ensuring safety and maintaining human health. According to WHO’s recommendations, the quality of water treatment is assessed by the following groups of factors: microbiological, chemical, radiological, and sensory (or organoleptic in Russian terminology). WHO also emphasizes the importance of monitoring and regular verification of water quality at all stages of the supply chain, from source to end user. This approach guarantees timely identification of deviations and adoption of appropriate measures to reduce risks to public health and maintain public well-being.

Insufficient water treatment leads to the emergence and spread of infectious diseases (cholera, dysentery, typhoid fever, hepatitis A, poliomyelitis) [2], which cause deaths of up to 1.4 million people every year around the world [3]. Prolonged consumption of drinking water containing chemical pollutants in concentrations exceeding the maximum permissible limits leads to the development of pathologies of the digestive system [4], urinary [5], endocrine [6], and cardiovascular systems: disruption of the heart muscle [7], hypertension and high blood pressure [8], ischemic cardiomyopathy [9]. In addition, high nitrate content in the water leads to stomach cancer [10]. The presence of heavy metals causes neurological diseases in children: lead — damage to the brain and central nervous system [11], mercury — impaired concentration, memory loss, nerve damage [12], and skin cancer noted by domestic [13] and foreign [14] researchers. Increased water hardness contributes to the accumulation of salts in the human body, which causes joint diseases and kidney stone disease [15].

In this regard, the improvement of water treatment and water purification technologies, as well as systems for monitoring the parameters of natural and drinking water, is of paramount importance. This requires a reasonable choice of these technologies and the determination of a set of parameters for their comparative evaluation. Methodological recommendations MR 2.1.4.0289–22⁴ propose a methodology for assessing the effectiveness of measures aimed at improving the quality of drinking water in centralized water supply systems. A comparative assessment is conducted based on such parameters as the potential risk to human health and the efficiency of water treatment.

Despite the availability of approved methods for assessing the risk to public health from drinking water quality, the existing studies focus on individual pollutants or evaluate the effectiveness of specific purification stages. A comprehensive assessment of various water treatment technologies based on total risk indicators to human health in Penza has not been conducted. This fragmented approach prevents us from fully determining which combination of purification methods is optimal for reducing the total number of diseases associated with water consumption from a specific source. The current research aims to address this gap by systematically analyzing and comparing alternative water treatment scenarios for Penza city conditions.

One of the natural sources of water for the central water supply in Penza is the Surskoye reservoir. According to the data from sanitary and hygienic monitoring, and classification of natural waters based on physical-chemical indicators of water quality, the Surskoye reservoir is classified as a first-class surface source [16]. The current method of water treatment for this source involves mechanical purification, followed by coagulation and flocculation, and disinfection through chlorination. Under this system, natural water from the source is filtered through a series of filtration grids and settled in special clarifying tanks to remove suspended particles. Coagulants are then added, which help to aggregate fine and colloidal particles into larger flocs, which can be filtered out. Finally, the water is chlorinated to ensure its safety from bacteria when it enters the central water supply systems.

The disadvantages of this process of water treatment before it enters the central water supply systems include:

• the formation of large amounts of sludge that must be disposed of, which can have a negative impact on the environment during storage;
• the potential risk to public health from residual aluminum content in the water if there is a possible dosage error, which can harm human health;
• the risk to public health from incomplete elimination of pathogenic viruses and bacteria, which also contributes to the deterioration of public health.

Modern water treatment technologies rely on an integrated approach implemented through a multi-step process where different purification methods work together to compensate for the limitations of each individual technique. One such technology involves pre-treatment designed to prepare water for further purification. The basic treatment step removes fine particles and dissolved contaminants. Disinfection ensures the microbial safety of water entering the central network. Pretreatment consists of mechanical filtration of surface water through drum screens, aggregation of the smallest particles into large flakes, followed by precipitation and physical removal of these agglomerates from the treated water. This step reduces turbidity and color, as well as removes up to 90% of suspended solids and colloidal impurities.

The main cleaning is carried out using ultrafiltration and sorption methods to remove pathogenic microorganisms, organic compounds, disinfection by-products, and substances that cause unpleasant taste and odor.

At the disinfection stage, water first passes through chambers with ultraviolet radiation to destroy the DNA and RNA of microorganisms. After that, a small amount of chloramine is added to ensure complete disinfection. The effect of this treatment lasts throughout the distribution network, ensuring that the water is safe from a microbiological and chemical point of view, has excellent organoleptic properties, and reaches the system with minimal risk to consumer health.

Figure 1 shows algorithms for purification methods for water supplied to the central water supply systems from the Surskoye reservoir.

To compare the cleaning efficiency of the presented methods, we conducted an assessment of the overall risk to public health and the degree of effectiveness in accordance with MR 2.1.4.0289-22⁵. We selected the controlled parameters that had a negative impact on human health, and in the analyzed water body they were in excess of maximum permissible values (MPV), according to GOST⁶ and SanPiN⁷. We examined water samples before and after purification using two methods.

The primary aim of this study was a comparative assessment of the effectiveness of drinking water treatment technologies of centralized water supply systems in terms of the overall risk to human health.

To achieve this goal, the following tasks were expected to be solved:

• to analyze physical-chemical and biological composition of water from natural water supply sources in Penza in order to identify the most significant pollutants;
• to calculate the cumulative risk of disease burden for different scenarios of water treatment;
• to assess the effectiveness of water treatment provided to centralized water supply systems.

The novelty of this work lies in the application of an integrated approach, which allows you not only to determine compliance or non-compliance with standards, but also to quantify and compare the final effects of introducing various technologies in terms of preventing potential harm to public health.

Materials and Methods. During the research, we analyzed scientific publications, patents, and regulatory documents containing information on the composition, indicators and methods of water treatment. Mathematical modeling was used with subsequent statistical processing of its results. We studied the influence of the composition of drinking water on human health and environmental quality.

The assessment of the drinking water composition was carried out based on the following groups of indicators, which were regulated by Russian and international regulatory documents: organoleptic, generalized, sanitary-microbiological, parasitological, and sanitary-chemical parameters.

The maximum permissible values (MPV), which were established by Russian regulatory documents, were used as criteria for assessing the quality of drinking water. The study was conducted on the basis of Penza State University.

According to MR 2.1.4.0289–22⁸, in order to assess the effectiveness of measures to improve the quality of water treatment, it was necessary to calculate the average values for all sets of actual values of the controlled parameters before () and after () water treatment:

(1)

(2)

where P_i,before, P_i,after — actual values of the controlled parameters before and after water treatment; n — number of samples taken.

Having obtained the average values for all sets of actual values of the controlled parameters before and after water treatment, the multiplicity of exceeding the maximum permissible concentration was determined by the formula:

(3)

Dividing the range of changes in values in accordance with Table 1 for each of the values calculated by formula (3), the membership function to the range μ(x) was determined:

(4)

After that, an assessment of the risk to public health was conducted for all controlled parameters, which were grouped into categories (sanitary and chemical). Based on the estimates obtained, a weighting factor was calculated for each controlled parameter, which established the relationship between the parameter and the class of diseases caused by pollutants present in the water. At the next stage of the research, we used the Fishburne principle to determine how common each class of disease was when assessing the magnitude of risk to public health using weight coefficients (W). At the same time, health risk rank (k) and disease class rank by degree (l) were taken into account:

(5)

where k — health risk rank (Table 1); l — disease class rank by severity (Appendix 2 to MR 2.1.4.0289-22 Table P2)⁹).

Next, weighting coefficients (G_i) were determined for each i-th controlled parameter in each group:

(6)

where m — number of all considered parameters in the group: for organoleptic parameters — 3, for generalized parameters — 5, for sanitary-microbiological and parasitological parameters — 6, for sanitary-chemical parameters — 9.

This was followed by the calculation of the cumulative contribution of each of the five groups of the controlled parameters (w_k) to the total amount of risk to public health:

(7)

We used the formula to determine the risk to public health from exposure to each group of the controlled parameters:

(8)

where R_g — public health from exposure to each group of the controlled parameters;  — average value of the variation range of risk value to public health resulting from exposure to the k-th group of the controlled parameters.

Overall risk was calculated for all controlled parameters for two situations — before and after water treatment:

(9)

where R — overall risk to public health; R_g — value of risk to public health for each group of the controlled parameters; V_g — total weighting factor of the k-th group of the controlled parameters in determining the overall risk to public health;  — average weighting coefficient of the k-th group of the controlled parameters in determining the overall risk to public health (Fig. 2).

When calculating the effectiveness of reducing the risk to public health by means of water treatment (Э) the value of cumulative risks before () and after () water treatment was taken into account:

(10)

Based on the obtained value of Э (%) qualitative value of the degree of effectiveness of the measures taken was determined (Fig. 3).

A comprehensive assessment of the effectiveness of measures to improve the quality of drinking water in centralized water supply systems was conducted using the program implementing MR 2.1.4.0289–22¹⁰. Table 2 provides the initial data.

Results. Table 3 provides the results of calculating the parameters for evaluating the effectiveness of water treatment. Three options were considered: before treatment, after treatment by treatment No. 1, after treatment by method No. 2.

According to Table 1, it can be seen that in the source water (before treatment), almost all controlled parameters exceeded the maximum permissible concentration. The greatest cumulative risk in this case was formed by organoleptic (0.42) and generalized indicators (0.31), which was due to a significant excess of standards for turbidity, color, hardness and dry residue. Sanitary and chemical indicators also made a significant contribution (0.09) due to increased concentrations of copper, nitrates, nitrites, and ammonia.

The results obtained demonstrated a different level of treatment of the two methods under consideration. Based on the calculations, we determined the degree of treatment efficiency for each method (Table 4).

It was found that the use of water purification method No. 1 showed average purification efficiency, since the risk to public health was reduced from 0.36 to 0.16. At the same time, physical fine impurities, chemical pollutants (nitrates, nitrites), ions of certain metals (for example, aluminum), and disinfection byproducts (chlorine compounds) remained in the water. Method No. 2 reduced the overall risk to 0.007, which indicated a high efficiency of water treatment.

Figure 4 demonstrates the dynamics of public health risk for each group of the controlled parameters. The histogram shows the exclusion of the risk to public health in terms of organoleptic and sanitary-chemical indicators of water quality as a result of the application of treatment method No. 2.

Figures 5 and 6 show a graphical representation of the calculation results.

Discussion. The conducted research clearly demonstrated significant differences in the effectiveness of the two considered approaches to water treatment of the Surskoye reservoir. The data analysis presented in Table 2 and Figure 4 showed that the source water did not meet sanitary standards in many key parameters (odor, color, turbidity, hardness, ammonia, nitrates, etc.), which confirmed high initial overall risk to public health (Table 3).

The existing technology No. 1, based on coagulation and chlorination, really brought most of the parameters within the limits of the maximum permissible values. However, its effectiveness could be described as insufficient. For a number of critically important indicators, such as nitrites (3.0 mg/l with a MPV of 3 mg/l) and iron (0.3 mg/l with a MPV of 0.3 mg/l), water treatment was only up to the upper limit of the standard. This did not create the necessary "safety margin" and left the system vulnerable to seasonal deterioration in the water source quality. As a result, after the application of technology No. 1, a significant residual risk remained for the groups of generalized (0.21) and sanitary-chemical (0.03) parameters (Fig. 5), which was associated with incomplete removal of fine impurities, dissolved chemicals and the formation of chlorination by-products.

In turn, the proposed multi-stage method No. 2 demonstrated a radically higher level of water treatment. It not only adjusted the parameters to the maximum permissible concentration, but also significantly reduced their concentration. For example, turbidity decreased to 0.5 FTU (at the rate of 2.6), sulfate concentration decreased to 250 mg/l (at the rate of 500 mg/l), and ammonium ion decreased to 1.1 mg/l (at the rate of 2 mg/l). Such deep cleaning was a direct consequence of technological features of this approach: ultrafiltration and sorption effectively removed both suspended particles and dissolved organic and chemical compounds. Two-stage disinfection (UV radiation + chloramine) ensured complete microbiological safety while minimizing by-products.

The key result was the reduction in overall risk, as shown in Figure 5. Method No. 2 eliminated the risks associated with organoleptic, sanitary-microbiological, and sanitary-chemical parameters completely (to zero). The total overall risk was reduced to a negligible value of 0.007, indicating that this technology enabled the production of not only formally safe drinking water, but also water with excellent organoleptic qualities, thereby increasing the reliability and safety of the centralized water supply system.

Conclusion. Within the framework of this research, we successfully achieved our goal. We conducted a comparative assessment of the effectiveness of two drinking water treatment technologies based on the indicator of the overall risk to human health.

During the work, we performed the following tasks:

• the analysis of the water composition from the Surskoye reservoir revealed an excess of maximum permissible concentrations in several organoleptic, generalized, and sanitary-chemical parameters. This caused high initial cumulative risk to public health at the level of 0.36;
• we calculated the cumulative risk for three scenarios: before water treatment, after applying the existing technology No. 1, and after applying the proposed technology No. 2;
• the assessment of the effectiveness was conducted, which revealed that the current technology No. 1 had an average level of effectiveness (55%), whereas the proposed technology No. 2 had a very high level (82%).

The research showed that the existing water treatment technology, which was based on coagulation and chlorination, was not effective enough. This technology reduced the overall risk by only 0.16, leaving residual risks for general and sanitary-chemical indicators, and did not provide the necessary margin of safety, as the concentrations of certain pollutants remained at the upper limits of the standards.

At the same time, it was clearly demonstrated that the proposed multi-stage method No. 2, including ultrafiltration, sorption and two-stage disinfection, allowed for a radically higher level of water treatment. This technology reduced the overall risk to a negligible value of 0.007, completely eliminating the risks of organoleptic, sanitary-microbiological and sanitary-chemical indicators.

Thus, the work shows that the use of modern multi-stage water treatment technologies makes it possible not only to formally comply with regulations, but also to obtain drinking water of significantly higher quality. This ensures the creation of a "safety margin" for the water supply system in case of seasonal and emergency deterioration of the source water quality. The results obtained can be used as a scientific justification for making decisions on the modernization of existing water treatment plants and the introduction of the best available technologies to provide the population with high-quality and safe drinking water.