Under European Economic Area Agreement, Romania and Norway have developed a project for monitoring the quality of raw and potable water (from production technology until distribution) supplied by two Romanian water companies. In the present study was investigated the microbiological quality of water, which was compared with organic matter loads. Resulting free chlorine and trihalomethane compounds after disinfection processes were also analysed. The raw water collected from Danube hydrographical basin showed significant pollution with potential pathogenic microorganisms with faecal origin such as Salmonella sp., Escherichia coli, Enterobacter sp., Klebsiella pneumoniae, Proteus mirabilis, Citrobacter braakii, Providencia stuartii, and Enterococcus sp. Also other bacteria such as Pseudomonas aeruginosa, Acinetobacter, total number of bacteria at 22 and 37 °C were detected, being related to high water oxidability. The microbial load was reduced considerably after the disinfection process. However, the total number of bacteria at 22 or 37 °C was constantly higher than the imposed limit and Clostridium perfringens was identified occasionally. The tap water presented a sporadic microbial loading with Enterococcus sp., Pseudomonas aeruginosa and E. coli and constantly with total number of bacteria due to an improper water distribution network.

INTRODUCTION

Drinking water quality represents a priority area of all European Union countries for human health, safety and life quality improvement. It is unanimously recognized that water resources are limited and do not fulfil the proper quality conditions required by regulations. In Romania, the water intended for human consumption is obtained 63% from surface waters and 36.8% from groundwater and it is estimated that only 55% of the population have access to a public water supply system.

Danube River is one of the main sources of drinking water for many surrounding cities/villages and for some areas it is the only drinking water source (for example: Danube Delta area). Crucially, the Romanian and also Ukrainian Danube is the end carrier of all pollutant discharges from 10 countries into the Black Sea (ICDPR 2006; Nichersu et al. 2010).

Due to the shipping activities, agriculture production, tourism activities and climate change, the levels of organic matter, nutrients, pesticides and metal concentrations in aquatic ecosystems are usually high (Stoica et al. 2012; Vosniakos et al. 2012). These changes may chronically disturb the community functions of aquatic ecosystems. The bacteria are the most important components of trophic chains attributed to aquatic ecosystems as they break down organic matter, entail nutrients in biogeochemical cycle and are involved in pollutant degradation pathways. For these reasons faecal coliforms, intestinal enterococci and heterotrophic bacteria are analysed frequently in the surface water quality control. Their presence in the aquatic environment indicates the natural state of rivers and shows also the impact of anthropic activities through faecal pollution (Velimirov et al. 2011). Moreover, total coliforms are widely used as a general measure of faecal contamination and enteric pathogen frequency (Stevens et al. 2003; Martins et al. 2014).

A realistic knowledge about microbial pollution in the aquatic environment is important for water management activities in order to maintain the potable water safety (Kolarević et al. 2011). The bacterial pollution is recognized as the major source of humans' epidemiological diseases (WHO 2004). There is a positive relationship between microbial and chemical indicators (such as organic and inorganic pollutants, pH, temperature, oxygen and salinity), later playing an important role in the survival and transmission of microorganisms in the aquatic ecosystems (Ajeagah et al. 2012). In this context a regular biological water quality monitoring of rivers like Danube Basin is necessary.

The microbiological control of the surface water intended for use in drinking water technologies is regulated through Directive 75/440/EC similarly with Romanian Governmental Decision (G.D.) no. 100/2002 modified by G.D. no. 662/2005. According to the above mentioned Directive, the surface water sources are classified into three quality classes: A1, A2 and A3, depending on imposed limits for several physical, chemical and microbiological indicators (total coliforms: 50/100 cm3, 5,000/100 cm3, 50,000/100 cm3; faecal coliforms: 20/100 cm3, 2,000/100 cm3, 20,000/100 cm3; Enterococcus: 20/100 cm3, 1,000/100 cm3, 10,000/100 cm3 and Salmonella sp.: absent/5,000 cm3, absent/1,000 cm3, respectively). Several international norms of Environmental Protection Agency (EPA) have recommended the control of some parasites, such as Giardia sp. or Cryptosporidium sp., which can affect human and animal health. Moreover, microbiological safety of water intended for human use is required through Directive 98/83/EC amended by Regulation 1882/2003/EC and 596/2009/EC, which are similar to Romanian Law no. 458/2002 (r1/15.12.2011). According to this Directive, Escherichia coli, enterococci bacteria, total coliforms and Clostridium perfringens should be absent and the colony count at 22 and 37 °C may be present in the limits of 100 CFU/cm3, respectively 10 CFU/cm3 in tap water, where CFU means colony forming unit.

Under European Economic Area (EEA) Agreement, Romania and Norway have developed a project for monitoring the quality of Danube River water used as drinking water source by two Romanian companies responsible for potable water production and distribution in Calarasi and Braila counties. Therefore the present work was focused on the evaluation of water microbial quality compliance during drinking water production technology and distribution. The recorded results were compared with the current regulations for drinking water quality. Another goal of the study was to highlight the treatment process efficiency in microbial and organic pollution removal in the period of 2009–2010. Also, the trihalomethane (THM) precursors occurring after water disinfection were investigated taking into account their potential health threat.

MATERIALS AND METHODS

Sampling and investigated indicators

The case study involved investigations in two Regional Water Companies from the South-East of Romania (Public Utilities Company ‘Danube’ SA Braila and ECOAQUA SA Calarasi). There are operating 13 Drinking Water Treatment Plants (DWTPs) that provide services of potable water production and distribution for more than 200,000 inhabitants. Seven DWTPs use as raw water source Danube River from different catchment points presented in Table 1. The water treatment processes applied by all monitored plants ensure compliance with quality norms for almost all chemical and microbiological indicators.

Table 1

Technological and operational characteristics of investigated DWTPs

DWTPsExploitation capacityWater treatment processesDistribution network length
SC ECOAQUA SA Calarasi 
Chiciu–Calarasi 1,400–1,800 m3/h from 2,880 m3/h Two treatment steps: – coagulation–flocculation, decantation, prechlorination – sand filtration, chlorination/disinfection (max. 2.1 mg Cl2/L) 186 Km 
Oltenita 600 m3/h from 1,600 m3/h Desanding, coagulation–flocculation, sand filtration, chlorination/disinfection (max. 2.1 mg Cl2/L) 85 Km 
Public Utilities Company ‘Danube’ SA Braila 
Braila 2,990 m3/h Micro sieving, coagulation–flocculation, decantation, sand filtration, chlorination/disinfection (≈ 3.5 mg Cl2/L) 972.5 Km 
Chiscani 
Gropeni 80 m3/h Coagulation–flocculation, decantation, sand filtration. chlorination (2 mg Cl2/L) 85.9 Km 
Ianca 648 m3/h 267.47 Km 
Movila Miresii 80 m3/h 146.73 Km 
DWTPsExploitation capacityWater treatment processesDistribution network length
SC ECOAQUA SA Calarasi 
Chiciu–Calarasi 1,400–1,800 m3/h from 2,880 m3/h Two treatment steps: – coagulation–flocculation, decantation, prechlorination – sand filtration, chlorination/disinfection (max. 2.1 mg Cl2/L) 186 Km 
Oltenita 600 m3/h from 1,600 m3/h Desanding, coagulation–flocculation, sand filtration, chlorination/disinfection (max. 2.1 mg Cl2/L) 85 Km 
Public Utilities Company ‘Danube’ SA Braila 
Braila 2,990 m3/h Micro sieving, coagulation–flocculation, decantation, sand filtration, chlorination/disinfection (≈ 3.5 mg Cl2/L) 972.5 Km 
Chiscani 
Gropeni 80 m3/h Coagulation–flocculation, decantation, sand filtration. chlorination (2 mg Cl2/L) 85.9 Km 
Ianca 648 m3/h 267.47 Km 
Movila Miresii 80 m3/h 146.73 Km 

During a period of 1 year 2009 (October) – 2010 (September), more than 1,250 samples were collected from the following sampling points of investigated DWTPs: catching, along the technological flow of water treatment (after decantation, filtration and chlorination), stock reservoirs and from different consumers such as: schools, hospitals, train stations, local public buildings, magazines, markets, particular residence, etc.

The sampling was performed monthly, according to national and international standards concerning surface water and drinking water sampling (SR EN ISO 19458:2007 and SR ISO 5667/1-6). The samples were collected in specific volumes, in sterilized glass bottles for microbiological indicators (Table 2), transported to the laboratory at 4 °C and immediately tested. The investigated indicators are presented in Table 2.

Table 2

Monitored indicators, methods and techniques applied for their measurement and number of samples collected from different sampling points on water treatment flow of investigated DWTPs

Raw waterAfter decantationAfter filtrationAfter chlorinationOutflow of DWTPs/tap water
MonitoredNumber of samples/month/DWTP
indicatorMethod *TechniqueSample volume (mL)/replicate730461680
Total number of bacteria at 22 °C SR EN ISO 6222:2004 Multiple dilutions 10 − − − − 
Total number of bacteria at 37 °C 10 
Total coliforms SR EN ISO 9308-1:2004/AC/2009 ISO9308/2:1990 Membrane filtration and Multiple-tube method 250 
Faecal coliforms ISO9308/2:1990 Multiple-tube method 250 − 
Enterococcus SR EN ISO 7899/2:2002 Membrane filtration 250 
E. coli SR EN ISO 9308-1:2004/AC/2009 ISO9308/2:1990 Membrane filtration and Multiple-tube method 250 − − − − 
Clostridium perfringens ASTM D 5916:1996 Membrane filtration 250 − − − − 
Salmonella sp. SR ISO 6340:2000 ISO 19250:2010 Growing on selective culture media Microscopic examination Exoenzymatic tests 1,000 − − − − 
Giardia ISO 15553:2006 EPA 1623:2005 Membrane filtration Filtration of 100 L − − − − 
COD SRISO 6060-96 SR EN ISO 8467-01 Volumetric 10 
BOD SR EN 1899/1-2003/2-2002 Electrochemical 500 − − − − 
Cl2 SR EN ISO 7393-2002 Volumetric 100 
THMs SR EN ISO 10301-2003 Gas chromatography – Electron capture detector 10,000 − − − 
Raw waterAfter decantationAfter filtrationAfter chlorinationOutflow of DWTPs/tap water
MonitoredNumber of samples/month/DWTP
indicatorMethod *TechniqueSample volume (mL)/replicate730461680
Total number of bacteria at 22 °C SR EN ISO 6222:2004 Multiple dilutions 10 − − − − 
Total number of bacteria at 37 °C 10 
Total coliforms SR EN ISO 9308-1:2004/AC/2009 ISO9308/2:1990 Membrane filtration and Multiple-tube method 250 
Faecal coliforms ISO9308/2:1990 Multiple-tube method 250 − 
Enterococcus SR EN ISO 7899/2:2002 Membrane filtration 250 
E. coli SR EN ISO 9308-1:2004/AC/2009 ISO9308/2:1990 Membrane filtration and Multiple-tube method 250 − − − − 
Clostridium perfringens ASTM D 5916:1996 Membrane filtration 250 − − − − 
Salmonella sp. SR ISO 6340:2000 ISO 19250:2010 Growing on selective culture media Microscopic examination Exoenzymatic tests 1,000 − − − − 
Giardia ISO 15553:2006 EPA 1623:2005 Membrane filtration Filtration of 100 L − − − − 
COD SRISO 6060-96 SR EN ISO 8467-01 Volumetric 10 
BOD SR EN 1899/1-2003/2-2002 Electrochemical 500 − − − − 
Cl2 SR EN ISO 7393-2002 Volumetric 100 
THMs SR EN ISO 10301-2003 Gas chromatography – Electron capture detector 10,000 − − − 

‘ + ’ sampled; ‘–’ not sampled; * standard methods used in period of 2009–2010.

Several additional biochemical investigations were performed in order to identify Salmonella, Klebsiella, Pseudomonas, Proteus, Enterobacter and Citrobacter species from all water samples suspected of this contamination. In the raw water Giardia sp. was monitored as a preventive measure of human contamination. Related to biological indicators, some chemical parameters were monitored, such as organic load: chemical oxygen demand (COD), biochemical oxygen demand (BOD), free chlorine (Cl2) and THMs.

Microbiological results were interpreted according to SR EN ISO 8199:2008 and the quality evaluation of raw water sources and drinking treated water was carried out in accordance with national and EU legislation related to the surface water used for potabilization processes (Law no. 100/2002 updated by Law no. 567/2006; Directive 75/440/EC) and also, potable water quality (Law no. 458/2002(r1); Directive 98/83/EC).

Statistical analyses

All analyses were performed in three replicates for each sample. The mean values of microbiological indicators transformed into logarithmic values and the standard deviations were graphically represented. The differences between results and admissible values normed by the Directives described above were carried out using Student's t-test (probability value, P) and the significance level was set at 0.05 (5%) statistically significant.

RESULTS AND DISCUSSION

During the monitoring program, more than 10,000 microbiological analyses were performed in order to ensure an efficient control of water quality from catching to final consumers.

SC ECOAQUA SA Calarasi

The microbiological control and monitoring performed for Chiciu–Calarasi and Oltenita DWTPs showed that raw water presented significant values of total number of bacteria at 37 °C (591–9·103/cm3 at Calarasi Chiciu and 159–18·103/cm3 at Oltenita) (Figures 1(a) and 1(b)), total and faecal coliforms (102–103/100 cm3, P < 0.001 related to A1 limits of Directive 75/440/EC) (Figures 1(c) and 1(d)), E. coli (10–7·102/100 cm3) and Enterococcus (13–14·102/100 cm3). There have been also identified several pathogenic bacteria, such as Salmonella inganda, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus mirabilis, Enterobacter cloacae, Enterobacter amnigenus and Citrobacter asburiae. Moreover, Giardia parasites were identified occasionally. The presence of these parasites (30 cysts/L of Giardia and 65 oocysts/L of Cryptosporidium) was also recorded by Gideon et al. (2013) in the Romanian sector in Galati zone in August 2010. Another study revealed the presence of 135–300 Giardia cysts/100 L and 5–40 Cryptosporidium oocysts/100 L in the Danube River in the Hungarian sector (Plutzer et al. 2007).

Figure 1

Total number of bacteria at 37 °C on technological flow from Chiciu–Calarasi DWTP (a) and Oltenita DWTP (b), number of total coliforms (c) and number of faecal coliforms (d) from raw water from Chiciu–Calarasi and Oltenita DWTPs.

Figure 1

Total number of bacteria at 37 °C on technological flow from Chiciu–Calarasi DWTP (a) and Oltenita DWTP (b), number of total coliforms (c) and number of faecal coliforms (d) from raw water from Chiciu–Calarasi and Oltenita DWTPs.

In DWTPs outflow bacteria were recorded at 22 and 37 °C (May and July – September 2010) and sporadic occurrence of Clostridium perfringens (January, March, August and September 2010) that could be attributed to a poor sand filtration.

The microbiological loads have a considerable decrease after chlorination process, but, sporadically, bacteria at 37 and 22 °C, Enterococcus spp. and Pseudomonas aeruginosa were still recorded in the potable water outflows and in the tap water of consumers, especially during July and September. Pseudomonas aeruginosa, an opportunistically pathogenic bacterium which can be a threat for human health, has raised problems in its detection because of viable or non-cultivable state.

Public utilities company ‘Danube’ Sa Braila

The microbiological control and monitoring were performed within five DWTPs from Braila. The raw water samples presented the following microbiological characteristics: total number of bacteria at 37 °C (91–33·103/cm3) (Figures 2(a) and 2(b)), total and faecal coliforms (2–13·102/100 cm3, P < 0.05 related to A1 limits of Directive 75/440/EC), Enterococcus spp. (2–49/100 cm3). The presence of the following bacterial species was also identified: E. coli, Proteus mirabilis, Acinetobacter spp., Alcaligenes sp., Enterobacter cloacae, Enterobacter amnigenus, Enterobacter agglomerans, Salmonella enterica, Salmonella typhimurium, Klebsiella pneumoniae, Pseudomonas aeruginosa, Providencia stuartii and Citrobacter freundii. Klebsiella spp., Citrobacter spp., Enterobacter spp., E. coli and frequently clostridia, Bacillus spp., Pseudomonas aeruginosa were also identified in catchment areas of the Danube River in the Romanian sector by Kolarević et al. (2011).

Figure 2

Total number of bacteria at 37 °C on technological flow at Braila DWTP (a) and Chiscani DWTP (b), total number of bacteria at 22 °C (c) and 37 °C (d) at Braila – Ianca DWTP consumers (November 2009–July 2010).

Figure 2

Total number of bacteria at 37 °C on technological flow at Braila DWTP (a) and Chiscani DWTP (b), total number of bacteria at 22 °C (c) and 37 °C (d) at Braila – Ianca DWTP consumers (November 2009–July 2010).

The pathogenic bacteria were especially identified at Gropeni DWTP. After the chlorination/disinfection step the water quality was improved. However, in summer time, total number of bacteria at 22 and 37 °C were found. Moreover, Clostridium perfringens was occasionally noticed in the outflow of Movila Miresii DWTP.

The bacterial reactivation was constantly found at 70% of consumers (40% with P < 0.001 and 30% with P < 0.05 related to admissible limits of Directive 98/83/EC) compared with the DWTPs' effluents (Figures 2(c) and 2(d)). This result could be attributed to the promotion of bacterial biofilm development (Gatel et al. 2000) due to the presence of easily biodegradable organic compounds, sediment accumulation and improper water distribution network (especially corrosion of pipes). Other factors that favoured the reaffirmation of microorganisms' community could be the water temperature, water volume ratio, stationary time in the distribution system and the pipe materials in relation to water (van der Kooij & van der Wielen 2013).

A high number of bacteria at 22 and 37 °C could correspond to organic matter contamination (Basemer et al. 2005). In the USA the relationship was established between organic matter load and the frequency of coliform bacteria, as also of certain opportunistic pathogens (van der Kooij & van der Wielen 2013).

Monitoring data of organic loading have highlighted exceeding values for oxidability in the Danube water catchment areas, the average of COD in the raw water samples being 5–16 mgO2/L (Figures 3(a) and 3(b)) and BOD 3–8 mgO2/L. It was concluded that the organic matter from Danube water was mainly biodegradable (BOD5/COD ≥0.35). After technological processes COD is reduced to values <5 mg/L. Moreover, the concentrations of anionic detergents (≤0.7 mg/L), dissolved hydrocarbons (0.8–1.5 mg/L), total organic carbon (TOC) (3.5–4.2 mg C/L) and organic nitrogen (3.9–4.2 mg/L) have exceeded the maximum imposed limits of the regulations (Lucaciu et al. 2010; Vasile 2010).

Figure 3

COD of water on technological flow: Chiscani DWTP (April-September 2010) (a), Braila DWTP in 2010 (b); THMs in raw water and effluent of Braila DWTP (c) and at consumers supplied by Braila DWTP in 2010 (d); free chlorine on technological flow: Chiscani DWTP (e) and at consumers supplied by Braila DWTP in 2010 (f).

Figure 3

COD of water on technological flow: Chiscani DWTP (April-September 2010) (a), Braila DWTP in 2010 (b); THMs in raw water and effluent of Braila DWTP (c) and at consumers supplied by Braila DWTP in 2010 (d); free chlorine on technological flow: Chiscani DWTP (e) and at consumers supplied by Braila DWTP in 2010 (f).

Many water users can be found in Braila and Calarasi counties (municipal services, industrial activities, livestock farms and householders) that discharge poor quality effluents into the surface water. Most of the municipal treatment plants were built years ago and have currently become inadequate as a result of long exploitation and improper technological infrastructure. The domestic wastewaters of Braila and Calarasi cities are insufficiently treated, being discharged directly into the Danube River, WWTPs being currently in upgrading operations. As a result, concentrations of total suspensions, BOD5, COD, extractable substances and pH values frequently exceed the imposed limits, thus explaining the occurrence of high organic load in the receiving surface waters. In 2009, the quality of Danube River water in these sectors corresponded to Class II (Good quality) and the lake water was oligotrophic (for example Movila Miresii) (Territorial Planning of Braila County 2008). Considering the abovementioned results, the treatment processes applied for surface water assured the compliance of water within the A2 quality class.

Other factors responsible for increase of microorganisms in the raw water, also in the tap water, could be the high temperature in the summer months. In the monitored period, temperatures over 30 °C were frequently registered, often 37–40 °C, and also poor rainfall that influenced bacterial proliferation and reduced pollution dilution.

Besides the low efficiency of microbiological load removal from raw water, there was also noticed a high production of THMs after the disinfection process. As a result of the organic pollution from natural and anthropogenic origin and chlorination, THMs and free chlorine were frequently detected in the outflow water (Figure 3(c)) and on the distribution network (Figure 3(d)) (especially at the consumers located near the DWTPs), mainly in summer time.

Chlorination is the most common disinfection method in Romania and the maximum Cl2 concentration allowed in drinking water is 0.5 mg/L in the outflows of DWTP and 0.1–0.25 mg/L at consumers. More than 50% results obtained for this indicator in treated and potable water samples revealed that limits were exceeded about three times in the DWTP effluents (Figure 3(e)) and also, tap water (Figure 3(f)). A negative effect of chlorination is THM precursors production (chloroform was the major detected compound) that indicate a low efficiency of coagulation–flocculation processes and also the presence of dissolved organic matter with high reactivity towards chlorine. Also, the presence of THMs is correlated with the organic matter concentration from the raw water, concentration of residual chlorine in water and contact time, pH and temperature (EPA 2011).

At Chiscani, Braila, Ianca, Movila Miresii and Gropeni DWTPs the removal efficiency of COD using potassium dichromate (COD-Cr) was 31–40% (with an oxidation efficiency of 20%). At Chiciu–Calarasi and Oltenita DWTPs removal efficiency was 40–50% (with an oxidation efficiency of 15–18%). Both recorded values indicated a low removal efficiency of organic load from raw water and consequently, the risk of THM occurrence and bacterial biofilm development. As a result, the THMs exceeded (P < 0.05) the maximum imposed norm (100 μg/L) in 25% of samples collected from Braila–Chiscani, 33% at Gropeni, 83–100% at Oltenita and Calarasi. Long time exposure to THM compounds through drinking water can lead to cancer disease or reproductive problems in humans and animals.

Based on the obtained results, the treatment processes' efficiencies were evaluated for each monitored DWTP. The possible technical causes which could negatively influence the drinking water quality were estimated and solutions for optimization were recommended to improve the quality of drinking water. Thus, it was recommended to separate the coagulation–flocculation processes and to establish the optimal treatment parameters (pH, reaction time, coagulant/flocculant doses) to increase the efficiency of organic matter removal. It is also necessary to take measures to increase the efficiency of the filtration process, through optimization of filtration rate and filtration/washing cycles. In order to remove the organic and microbiological load of raw water sources several suitable advanced treatment operations are also required, such as the following: pre-oxidation (ClO2, Cl2, O3), membrane processes (membrane filtration or ultra-filtration), coupling of oxidative and biological processes (bio-filters). The bacterial biofilms developed in the water system can be limited by a periodic cleaning of pipes or by replacement of the entire distribution system. Further studies regarding the dynamics of THM concentration in different water treatment steps were also recommended in order to assure the population health.

Currently, Calarasi and Braila municipalities have a solid development strategy for potable water services. European projects in progress are mainly aimed at ensuring a continuous water distribution to all consumers connected to the system, a good water quality whatever the source of raw water by optimizing treatment processes and developing the water distribution network, maintenance of existing operating systems, reduction of energy consumption, ensuring water pressure in the distribution system and reduction of water loss.

CONCLUSIONS

Water is an important component of ecological balance and its pollution is a considerable global problem with current environmental impacts and negative effects on human health. Danube River is the main source of drinking water for South-East Romanian inhabitants and in some areas it is even the only source of water. The raw water used for drinking water production was found bacteriologically polluted (classified in A2 category), but generally after technological treatment (physical, chemical and disinfection steps) its quality was improved. The investigation performed on microbiological quality of treated water/drinking water supplied to consumers by seven DWTPs operating within regional water companies in Calarasi and Braila has shown a constant non-compliance of microbial increases at 22 and 37 °C in summer. Clostridium perfringens, Enterococcus spp., Pseudomonas aeruginosa and E. coli were sporadically detected in the tap water, indicating an inefficient drinking water treatment process and an improper water distribution network. High concentrations of free chlorine and THMs were recorded in drinking water as a result of low removal efficiency of organic pollution.

The study had a great impact on public awareness and it provided important information that highlights the necessity to improve the management practices and drinking water treatment technologies performed in the period October 2009 – September 2010, by investigated DWTPs.

ACKNOWLEDGEMENTS

The authors would like to thank the European EEA and national authorities for the financial support needed for this study. Also, many thanks to the leadership and representatives of two regional water companies, which have facilitated monitoring program implementation.

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