Life cycle assessment of variants of water treatment technological processes in Pilsen (Czech Republic) Open Access

High-quality drinking water is an essential and most important commodity for human life and the functionality of ecosystems. Produced drinking water supplied to the sampling facility by the public water supply must meet the prescribed drinking water quality parameters according to the relevant national legislation. The composition of the technological treatment steps and the material and energy intensity of the drinking water treatment plant (DWTP) are directly related to the nature of the water source, the quality of the incoming raw water, the location of the DWTP facility, and the extent of the supplied region.

In the last two decades, the issue of sustainable operation and life cycle assessment (LCA) of specific water processes has begun to permeate the field of water management. LCA has been used increasingly as an instrument for environmental performance evaluation in the water sector. The standardized LCA method provides an analysis of water treatment processes through an input–output approach and subsequent identification and quantification of associated environmental impacts (Lemos et al. 2013; Barjoveanu et al. 2019). In the water sector, LCA has been used for applications in the whole water use cycle (Barjoveanu et al. 2014; Loubet et al. 2014), for environmental performance assessment of drinking water treatment processes (Bonton et al. 2012), and for wastewater treatment processes (Pintilie et al. 2016). So far, more studies have been published focusing on the environmental assessment using LCA of wastewater treatment plants (WWTPs) (Byrne et al. 2017).

In the field focused on the production and distribution of drinking water, the application of LCA is a widely used approach to assess the environmental impacts of water treatment processes (Mohapatra et al. 2002; Bonton et al. 2012), compare advanced and conventional technologies (Barrios et al. 2008), development scenarios (Mery et al. 2014; Ribera et al. 2014; Hofs et al. 2022), and optimize drinking water production and costs (Capitanescu et al. 2016). Most often, LCA studies consider the quantification of the environmental impacts of drinking water production plants and supply in relation to the volume of drinking water produced. The LCA study (Barjoveanu et al. 2019) defines two additional functional units related to removing contaminants besides the traditional 1 m³ of treated water. In most cases, published LCA studies assessing the actual DWTPs have dealt with the operational phase of water production, and only a few have dealt with the construction phase (Biswas & Yek 2016; Barjoveanu et al. 2019). Published LCA studies related to drinking water production and distribution vary in scope and system boundaries. Some expert studies aim to assess the environmental impacts of drinking water production (Barrios et al. 2008; Bonton et al. 2012), while other studies assess the environmental impacts of drinking water distribution and the water supply system (Venkatesh & Brattebø 2012). Large-scale LCA studies approach entire water service systems. In these cases, the analysis focuses on assessing the impacts of drinking water production and distribution, wastewater disposal, and wastewater treatment (Lundie et al. 2004; Friedrich et al. 2012; Qi & Chang 2012; Lemos et al. 2013).

A significant number of LCA studies have found that electricity consumption and process chemicals consumption are the most significant impacts generators in the drinking water production and distribution sector (Amores et al. 2013; Barjoveanu et al. 2014; Saad et al. 2019). There are other LCA studies that, unlike the previously mentioned studies, also include the construction of the plant along with the environmental impact of various phases of drinking water production, technological processes, and distribution of drinking water in the water supply network in CO₂ equivalents, as the so-called carbon footprint (Qi & Chang 2012; Beeftink et al. 2021; Hofs et al. 2022).

In the Czech Republic, 95.6% of the total population is currently supplied with drinking water from the public water supply (Czech Statistical Office 2023). The quality of the produced water supplied to the point of use by the public water supply must comply with the drinking water quality parameters according to the National Regulation 252/2004 Sb. Water management infrastructure operators in the Czech Republic are starting to include environmental aspects in their plans for the modernization and reconstruction of waterworks. In order to select technologies, equipment, or materials with a lower environmental impact, an environmental assessment of real operations or components must first be carried out. The objective of this study is to evaluate the environmental performance of the Pilsen DWTP using LCA. The DWTP treats water from the river into high-quality drinking water for 200,000 inhabitants of a metropolis in the west of the Czech Republic.

The aim of our study is to comprehensively assess the environmental impacts of the life cycle of the real drinking water production process. Also, the aim is to compare the current technological process and the process before its modernization. The reconstruction of the DWTP was not carried out to reduce environmental impacts but to improve the quality of drinking water output. With surface water treatment, a well-functioning and optimized water coagulation and flocculation process is essential for subsequent water treatment processes. Therefore, this study also focused on the evaluation through LCA and the comparison of the environmental impacts of drinking water production at the DWTP with the aluminum-based coagulant and the model variant with the iron-based coagulant alternative. Most LCA analyses identified electricity consumption as the most significant impact generator in the water production sector. In view of this fact, another objective is to evaluate the process of drinking water production with electricity from the energy grid mix and electricity produced from alternative sources using LCA.

The main reason for the reconstruction of the DWTP Pilsen was the presence of undesirable pesticide substances in the water source and insufficient technology for their removal. A significant shortcoming of the DWTP before the reconstruction was the absence of filtration through granular-activated carbon. The reconstruction of the DWTP started in August 2013 and was completed in September 2015 and was carried out without the interruption of drinking water production. A description of the DWTP technology without GAC filtration is provided in Section S2 and Figure S1, SD. The complete refurbishment involved the filtration and ozonation technology part. By replacing the original ozone generators with more efficient ones and by changing the way ozone is introduced into the treated water, the annual electricity consumption of the ozone process was reduced. The ozonation process before the reconstruction consumed approximately three times more electricity than the ozonation process after the refurbishment. Detailed information on the DWTP reconstruction is provided in Section S3, SD. The electricity consumption of the ozonation process before the reconstruction (in 2012) and after the reconstruction (in 2019) is presented in Table 1 (see ‘Inventory Analysis’ section). The electricity consumption in the ozonation process in both years was calculated by approximation from the actual measured values of the sub-facilities.

LCA is a well-established methodology that is applied to evaluate the used resources and environmental impacts, from the cradle to the grave, throughout a product's life cycle. LCA can also be used to calculate the resources utilized and the emissions produced in specific stages of a life cycle, as we have done in this study. The LCA was performed according to the ISO framework and complies with the requirement (ISO 14040 2006a; ISO 14044 2006b). The components of an LCA that follows the ISO guideline are as follows: goal and scope, life cycle inventory, life cycle impact assessment (LCIA) and interpretation.

The main objective of the study was to assess the existing drinking water treatment process in DWTP Pilsen using the LCA method. Due to the nature of the raw water source, the key variable in the year-on-year comparison of the drinking water production process is the consumption of chemicals, especially coagulants.

The water treatment process cannot work without electricity. The electricity for the production of drinking water comes from the energy grid. The composition of the average electricity grid mix in the Czech Republic is 50.8% from fossil sources (lignite and black coal, natural gas, and oil), 42.8% from nuclear sources, and 6.4% from renewable sources (biomass, solar, water, and wind).

The functional unit, i.e. a quantified expression of the magnitude of the function considered by the DWTP, and also the reference flow, was chosen to be 1 m³ of produced drinking water of a quality corresponding to the national decree in force.

Due to the unavailability of relevant data, the following processes were placed outside the boundaries of the constructed model of the system under consideration: buildings and building materials, production and refurbishment of process equipment, production of water pipelines, GAC reactivation process and production and maintenance of transport vehicles and human labour.

The inventory analysis phase of the LCA study quantifies all material and energy flows throughout the product lifecycle. The material and energy inventory was developed for this study based on process-specific operational data obtained from internal documentation, personal consultation with the expert colleague, system manuals, technical literature, and general data from databases contained in specialized LCA for Experts (formerly GaBi) software (GaBi 2021). For the assessment of the current operation and the creation of model variants of the current DWTP, operational data from the DWTP Pilsen from 2019 and 2023 were used. For the assessment of the operation of the DWTP Pilsen before reconstruction, operational data from 2012 were selected.

The output data from the inventory analysis are used to assess and quantify results for specific impact categories. In the LCIA, characterization models such as CML 2001 (Heijungs et al. 1992), Recipe (Goedkoop et al. 2013), USEtox (Rosenbaum et al. 2008), and product environmental footprint (PEF) can be used to compare different impact categories.

The life cycle model of drinking water production in the treatment process in DWTP Pilsen was created using the specialized software LCA for Experts (former GaBi), version 10, and using current versions of databases and inventory sets Sphera Databases and Ecoinvent version 3.8 (Ecoinvent v3.8 2021). The EF 3.0 methodology (as recommended by the European Commission) was used to quantify potential environmental impacts. The PEF is an LCA-based method to assess the environmental performance of products (EC 2021). For the introduction of PEF, the environmental footprint (EF) method included recommendations for LCIA models that address 16 midpoint impact categories, three of which relate to toxicity (Sala et al. 2022).

The EF 3.0 methodology includes 16 impact categories and their subcategories: climatic change (total, fossil, biogenic, and land use and land use change), stratospheric ozone depletion, human toxicity cancer (total, inorganics, metals, and organics), human toxicity non-cancer (total, inorganics, metals, and organics), particulate matter, ionizing radiation, photochemical ozone formation, acidification, eutrophication (terrestrial, aquatic freshwater, and aquatic marine), land use, water use, resource use (fossil, mineral, and metals), and ecotoxicity (total, inorganics, metals, and organics). This study presents the impact results obtained by the EF 3.0 method.

Normalization is the step whereby the results of an LCIA are multiplied by normalization factors to calculate and compare the magnitude of their contributions in relation to a reference unit of a given impact category. In the context of normalization, the results of impact category indicators (EF 3.0) are converted into dimensionless quantities in a well-defined manner. This is done by expressing the number of emissions in a given impact category as a proportion of the total impacts in a particular region. For our study, the results for each impact category were normalized in relation to the sum of total emissions from the 28 countries of the European Union.

Weighting is a step in the PEF methodology and supports the interpretation of the analysis results. In this step, the normalized results are multiplied by a set of weighting factors that reflect the perceived relative importance of the impact categories under consideration. The weighted results can also be combined across life cycle impact categories to produce an overall score (European Commission. Joint Research Centre 2019).

The LCIA of the Pilsen DWTP was conducted using the EF 3.0 method, which enabled the development of the comprehensive environmental profiles presented and discussed in this section. The EF methodology was chosen because it contains both midpoint and endpoint categories, and these are, in several cases, further specified in subcategories, which brings complex insight into the environmental impacts of studied technology. Using the EF 3.0 methodology, the results from the inventory were classified into all available EF 3.0 impact categories and characterized in terms of the equivalent indicators of each impact category. The resulting values of the indicators of impact categories are broken down into the functionally related parts of the water process (electricity, natural gas, chemicals, transportation, and disposal) in Table 2. Table 2 shows the percentage contribution of each part of the drinking water production process to the total impact. The results presented in Table 2 show that a significant proportion of the production and consumption of electricity or production and consumption of chemicals used is reflected in all impact categories except water consumption. The value of the total impact category of the water use output generally follows from the inherent nature of the DWTP function. The EF 3.0 impact categories that have the most significant impact on the overall impacts of the water treatment process include: resource use fossil, land use, ecotoxicity freshwater, climate change, ionizing radiation – human health, ozone depletion, and acidification. Direct projection of the energy and material intensity of the drinking water production process on the environmental impacts of the entire water supply process has also been found by LCA studies (Barrios et al. 2008; Bonton et al. 2012). The LCA study (Lemos et al. 2013) identified electricity and chemicals consumed in the water treatment process as critical environmental aspects. Also, the study Igos et al. (2014) found that electricity consumption in the production and distribution of drinking water significantly affects the impact categories: climate change, human carcinogenic and non-carcinogenic toxicity, terrestrial and freshwater ecotoxicity and particulate matter formation. The current state of DWTP uses energy from the Czech grid mix, which is based largely on fossil fuels. During this energy production, a significant amount of greenhouse gases and toxic substances is produced, which is reflected in the mentioned categories.

All chemicals in the water production process have more than half of the impact in the following categories: ozone depletion, freshwater eutrophication, resource use of minerals and metals, carcinogenic and non-carcinogenic human toxicity, and freshwater ecotoxicity.

The contribution of transport to the total impacts is not significant for any of the impact categories, except for the specified category – climate change, land use, and land use change (12.4%). The contributions of the part involving disposal to the total impacts of the drinking water production process are negligible.

As part of the DWTP reconstruction, the input parameters of the ozonization process were reduced. More efficient and energy-saving ozone generators were installed, and the ozone production process and its input to the treated water were streamlined. Although the DWTP technology has been extended with one more separation stage and the energy-intensive UV disinfection process has been added during the refurbishment, it shows lower total environmental impacts compared to the DWTP operation before the reconstruction. Significant savings in the overall electricity consumption of the ozonation process were realized in all impact categories. Similar results were achieved by the authors of the study (Saad et al. 2019), where the replacement of the original low-efficiency pumps with 90% efficiency pumps as part of the water plant refurbishment resulted in reduced impacts in all impact categories related to energy flows.

The coagulation process is a key and irreplaceable technological process, especially in a surface water treatment. The coagulation process is described in more detail in Section S4, SD. In the DWTP Pilsen process, the aluminum coagulant, aluminum sulfate, is dosed on a long-term basis. The alternative iron coagulant was selected based on the literature and laboratory tests. The presented results in Table 3 document the different values of the impact category indicators according to the EF 3.0 methodology of the drinking water production process with dosed aluminum coagulant and the DWTP model with an iron coagulant. Higher values for all indicators of impact categories, except for the categories of freshwater ecotoxicity and inorganics, are represented by the current water treatment process with dosing of aluminum sulfate. The collective of authors of the study (Ortíz Rodriguez et al. 2016) identified the dosed aluminum coagulant in the assessed DWTP as a significant contributor mainly to the impact categories: ozone depletion, eutrophication, resource use – minerals and metals, ecotoxicity, and the human toxicity.

The lower overall impacts can be partly explained by the lower need for iron sulfate than aluminum sulfate for the same treated water contamination. A comparison of the use of the two chemicals in the coagulation process for each impact category revealed interesting differences. Aluminum sulfate production is associated with emissions of ozone-depleting substances, which is connected with the most significant impact on the impact category ozone depletion, with the most significant difference in values being five orders of magnitude (1.40 × 10⁵). Smaller differences can be observed for the following impact categories: the ecotoxicity of freshwater – total, the ecotoxicity of freshwater – metals, the eutrophication – freshwater, the human toxicity of cancer, and the resource use – minerals and metals.

In contrast, for iron coagulants, the values for the following impact categories are significantly higher: the freshwater ecotoxicity – inorganics, the human toxicity cancer – inorganics, and the human toxicity non-cancer total than the values for aluminum coagulant. For the other impact categories listed in Table 3, the differences in the output values for the two coagulants are negligible.

In the energy grid mix of the Czech Republic, electricity generated from fossil fuels accounts for the majority, followed by electricity generated from nuclear power plants and only 13% from renewable energy sources (see section ‘Goal and scope’). Unsurprisingly, the process of producing drinking water using electricity from the grid is the second largest in terms of overall environmental impact, just behind the modeled option of electricity from coal. The lowest overall impact of producing 1 m³ of drinking water is shown by the DWTP operation with electricity generated solely from hydropower. This hypothesis may be realistic in the future given the geographic location of the DWTP and the existing small hydroelectric power plant on the Úhlava River. From the presented results of the impacts of the current DWTP with electricity from the energy mix of the Czech Republic and the modeled energy source options for each impact category in the EF 3.0 methodology, an analogy with the results of the study (Saad et al. 2019) can be drawn. The results of this study show that electricity generated from solar and wind power for the operation of the considered DWTP implies a reduction in impacts in almost all impact categories. Also, in the LCA study (Biswas & Yek 2016), a model-based approach to electricity source variations was used to assess the impacts of real water treatment plants. The results of this study indicate that the use of more renewable sources for electricity generation helps to reduce the overall impacts of the DWTPs evaluated.

The DWTP process with electricity from photovoltaics is the most significant in the ozone depletion impact category among electricity source options (Figure 10). The largest share of the DWTP operation variant with electricity from solar energy seems to be related to the production of photovoltaic panels and their disposal at the end of life.

The aim of this study was to evaluate the real process of treating water from a surface source in the Water Treatment Plant Pilsen from an environmental perspective. The EF 3.0 characterization methodology was used to classify and evaluate the midpoint and endpoint impacts of DWTP. The obtained results of environmental impacts according to the mentioned methodology were divided into logically related areas and phases that participate in the process of treating surface water to drinking water quality.

From the results, it was found that the production and consumption of electrical energy and dosed chemicals, especially coagulants, have the largest share of the overall environmental impacts of the production process of 1 m³ of drinking water. The highest energy consumption in the technology has pumping of water into and out of the DWTP plant, ozonation, and UV disinfection.

The largest share of emissions from the water treatment process in most of the categories concerned is the generation of electricity consumed from the energy grid mix. Electricity generation in the Czech Republic is mostly linked to the impact categories: fossil resource use, climate change, acidification, carcinogenic human toxicity, freshwater ecotoxicity, eutrophication, and ionizing radiation. Considering the largest contribution of electricity to the total impacts of DWTP, model variants of energy scenarios of the water treatment process were assessed. The evaluation of the normalized results showed that the variant of DWTP with electricity generated in hydroelectric or wind power plants has the lowest environmental impacts. Using a higher proportion of electricity generated from renewable sources, the environmental impacts of the entire water treatment plant will be reduced.

An important function of the DWTP is the treatment of raw water to drinking water quality. In general, DWTPs do not have many options for energy self-sufficiency compared to WWTPs, and therefore, they focus on reducing environmental impacts in other ways.

A comparison of the normalized results of the existing technology with aluminum coagulant and the developed DWTP model with dosed iron coagulant showed more favorable results in all impact categories for the model variant. By replacing the aluminum coagulant with the iron coagulant, the environmental impacts of the whole DWTP process will be reduced in the production of drinking water.

The installation of new and efficient equipment as part of the DWTP refurbishment resulted in a reduction in overall environmental impacts.

It should be mentioned that nowadays DWTP operators are slowly starting to use environmental criteria when considering the modernization or optimization of their facilities. However, in the decision-making processes before upgrading existing plants or building new DWTPs in the Czech Republic, the emphasis is mainly on the output quality of treated water regarding legislative requirements.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.