Physical-chemical and microbiological quality of water used for public supply in the municipality of Alvorada D’Oeste, Rondônia, Brazil

The study analyzed the physical-chemical and microbiological parameters carried out by the Autonomous Water and Sewage Service (AWSS) of the Municipality of Alvorada D’Oeste, Rondônia, Brazil. The parameters analyzed were: pH, turbidity, free residual chlorine, total coliforms (TC), thermotolerant coliforms (TTC) and heterotrophic bacteria. The values of hydrogen potential (pH) were obtained with a digital pH meter. The analyzes were carried out the 2013 to 2019. The turbidity and free residual chlorine values were obtained according to the method of the Practical Manual of Water Analysis of the National Health Foundation (FUNASA). To determine the microbiological parameters, Petrifilm plates (3M do Brasil Ltda) were used, following the manufacturer's guidelines. The analyzed values were compared with reference values described in Consolidation Ordinance no. 5, of September 28, 2017, of the Ministry of Health (MS) which sets the standards for potability of water intended for human consumption. The results varied for all parameters evaluated: pH (3.11 to 8.24), turbidez (0.02 to 3,01), TC (0 to 100%), TTC (0 to 100%) and heterotrophic bacteria (85 to 100%). The values obtained for free residual chlorine were the only parameter to follow the reference values. The highest contamination for TC and heterotrophic bacteria were reported in 2019, higher the limits established in Brazilian legislation. Thus, the water was characterized as unfit for consumption and requires severe control for TC and heterotrophic bacteria.


Introduction
Water is a fundamental and indispensable component of human survival (Wolkmer, 2012). In Brazil, according to Law nº. 9,433 of 8 January 1997, it is right to have access to drinking water without any risk to consumers' health (Brasil, 1997). Consolidation Ordinance nº. 5 of September 28, 2017, also reports that water destined for human consumption by a water supply system must meet the potability standards following physical and biological prerequisites (Brasil, 2017). Thus, the water must be free of contaminants, colorless and odorless (Abbasnia et al., 2018;Silva, 2020).
The biological prerequisites can suffer interference by the process of occupation of hydrographic basins (Duarte et al., 2020), mainly those related to the urbanization process (domestic sewage, pits), agricultural management (pesticides), and livestock (animal feces) developed in a disorderly and irregular manner (Santos et al., 2018). The percolation of rainwater and runoff can alter the quality of surface and underground water by the procedure of leaching of microorganisms from the process of disordered occupation of hydrographic basins (Moura et al., 2010). Although water does not provide the necessary conditions for the multiplication of microorganisms, they can remain in the fluid long enough to guarantee their transmission (Reis et al., 2020). In addition, in water treatment plants (WTPs), microorganisms can become resistant to disinfectant actions when present for long periods (Tenório, 2016;Silva et al., 2019).
Coliforms is a group of microorganisms widely distributed in nature, including in water Rodrigues, et al. 2020). This group includes thermotolerant coliforms (TTC), microorganisms used as a standard to measure the quality of surface water intended for supply, recreation and agricultural activities (irrigation and fish farming) (Peres, 2011;Ceballos & Diniz, 2017). Escherichia coli is a TTC found naturally in the gut of homeotherms with particular importance.
Thus, the presence of TTC or Escherichia coli in the water indicates fecal contamination and can be used as an indicator of hygienic-sanitary quality (Braga, 2014). When ingested in large quantities, it can cause intestinal and urinary tract infections (Buzanello & Martinhago, 2008;Lacerda et al., 2019).
The present study aimed to evaluate the results of the physical-chemical and microbiological analyzes carried out by the water treatment plant (WTP) in the municipality of Alvorada D'Oeste, Rondônia, Brazil, between the years 2013 to 2019, comparing with the reference values described in Consolidation Ordinance nº. 5, of September 28, 2017, of the Ministry of Health (MS) which sets the standards for potability of water intended for human consumption.

Methodology
The data presented in this study were obtained from Autonomous Water and Sewage Service (AWSS) of the Municipality of Alvorada D'Oeste, Rondônia, Brazil. The information comprises the monitoring period between the years 2013 to 2019. AWSS conducts monthly analyzes at 7 sample points located in the urban area of the municipality (Table 1). Through the public supply of drinking water, AWSS serves 95% of the municipal population. The water is taken from the Ribeirão do Cacau River and pumped to the water treatment plant (WTP) where it is treated and distributed. The region presents tropical climatic conditions, it is characterized by a dry and a rainy season (Cavalcanti, et al. 2016;Nogueira, et al. 2020), with temperatures ranging between 19-33 ºC and annual precipitation around 2500 mm (Krusche et al., 2005). The rainy period occurs from October to April, and the period from June to August corresponds to the drought period, May and September are considered transition months (Krusche et al., 2005).
The analyzes performed by AWSS comprise the physical-chemical parameters, which are pH, turbidity, and free residual chlorine, and the microbiological parameters, comprising total coliforms (TC), thermotolerant coliforms (TTC), and heterotrophic bacteria. The values of hydrogen potential (pH) were obtained with a digital pH meter (ST 2100-F, Ohaus, Brazil). To obtain the values of turbidity and free residual chlorine, the method established in the Practical Water Analysis Manual of the National Health Foundation (FUNASA) was used, being the nephelometric and determination method, respectively (Brasil, 2006). To determine the microbiological parameters, Petrifilm TM plates (3M TM do Brasil Ltda) were used, following the manufacturer's guidelines.
For physical-chemical analyzes, the results are presented as the average of the duplicate analyzes and for microbiological analysis, the data are presented in percentage of contamination. Physical-chemical and microbiological analyzes were carried out at all points analyzed.

Results and Discussion
For the physical-chemical parameters analyzed by AWSS, only residual free chlorine (1.99 mg/L to 1.33 mg/L) was in accordance with the values described in Consolidation Ordinance nº. 5, of September 28, 2017 (0.20 to 2.00 mg/L) for the evaluated period. The values for turbidity did not change above that established by the ordinance (<1.0 NTU) in 2014, but for the remaining years, at least one month showed values above the established. For pH, in all years evaluated at least in one month, the values were not in accordance with those established in legislation (Table 2).  and December, all samples analyzed were positive for heterotrophic bacteria, in July, 55.5% (Table 3).  Table 3. Bacteriological analysis of water from the municipality of Alvorada D'Oeste between the years 2013 to 2019.
According to the results, an increase in turbidity and a decrease in pH during the rainy season were observed. This process may be associated with the influence of rain that facilitates the entrance of alien material (solid materials, foliage, algae, debris, and organic sediments) into the WTP, making it difficult to control turbidity (Almeida et al., 2017;Buzelli et al., 2013). Due to the amount of particulate material, the filtration and coagulation process employed by WTP may not be effective and may be impaired (Mendes & Ferreira, 2014).
Changes in pH can also be associated with the addition of a coagulant agent, ferrous aluminum sulfate, a chemical applied to reduce water turbidity (Lemos et al., 2020). However, the use of alkalinized products reduces the pH of the water, resulting in incrustations in the pipes (Asghari et al., 2018), corrosion in the drains and algae growth in the water distribution systems, allowing the growth of microorganisms (total coliforms, heterotrophic bacteria, mesophiles) . Carvalho et al. (2020) relates the presence of heterotrophic bacteria and acidic pH with the increase of nitrite in the water in the rainy season. Mata and Campos (2020) associate the growth of TC and heterotrophic bacteria with the lack of maintenance in outdated reservoirs, old pipes or infiltrations in the distribution systems. Oliveira et al. (2018), attributes the growth of TC and heterotrophic bacteria to poor pipe conservation.
According to Freire and Lima (2012) the growth of bacteria occurs under conditions of deterioration of free residual chlorine in the water distribution networks. This degradation process may explain the high bacteriological incidence. Another fact that can influence this result is the natural evaporation process, which can interfere with biological, physical and chemical Heterotrophic bactéria 100% -0%* 0%* 100% 0%* 44.5%* 0%* 100% 100% 0%* 0%* characteristics, increasing the concentration of nutrients, salinity, and conductivity, contributing to the high turbidity values in the period with the lowest rainfall (Nagata et al., 2015;Shuangchen et al., 2016;Diniz, 2017). According to Mendonça et al. (2017), the temperature influences the residual loss and evaporation of free residual chlorine in the water present during the distribution process, increasing bacterial growth in WTPs. This increase also contributes to the formation of biofilms in plumbing.
The correlation between the parameters evaluated where it was evidenced a decrease in pH, an increase in turbidity and bacterial growth can be related to several factors. Especially those associated with the integrity of the filters used by AWSS, as well as the maintenance of the distribution systems, which may have contributed to the physical-chemical and microbiological deviations. In this way, it is demonstrated the need for reforms and maintenance (maintenance and replacement of sand, fine and medium gravel, medium and coarse gravel) of the AWSS system during the periods from January 2012 to November 2019. The lack of maintenance decreases performance and affects the integrity of the WTP, changing the quality of the water distributed in distribution networks (Hachem et al., 2020).

Conclusion
The only physical-chemical parameter following the values described in Consolidation Ordinance nº. 5, of September 28, 2017 of the water distributed by the WTP in the municipality of Alvorada D'Oeste was the residual free chlorine. The bacteriological analyzes carried out in 2015, 2016, 2017 and 2018 were within the parameters described in Consolidation Ordinance nº. 5, of September 28, 2017. In 2019, 100% of the samples showed contamination by heterotrophic bacteria and total coliforms, thus, water was characterized as unfit for consumption.