EVALUATION OF TREATED WASTEWATER QUALITY FOR REUSE IN THE NORTHERN REGION OF MINAS GERAIS

Objective: This study aims to analyze the quality of effluents treated at three Wastewater Treatment Plants (WWTPs) in the northern region of Minas Gerais, evaluating reuse potential and proposals. Theoretical framework: The practice of reusing sanitary effluents holds significant economic and environmental importance. It conserves water resources allocated for higher priority uses. When assessed and compliant with regulations, effluents become potential water sources for agriculture and urban squares. The trend towards reusing treated effluents presents an alternative to meet water demands that could be satisfied with lower-quality water. Method: The study conducted laboratory analyses of three COPASA MG sewage treatment plants, referred to as WWTPs I, II, and III, between January 2021 and September 2022. Parameters crucial for effluent reuse, including Biochemical Oxygen Demand (BOD), Electrical Conductivity (EC), Hydrogen Potential (pH), Escherichia coli , Sodium Adsorption Ratio (SAR), and viable helminth eggs, were monitored and evaluated. The feasibility of proposed water reuse methods was assessed by analyzing the quality of treated effluents from the three WWTPs, considering that the treatments adhered to the conditions and effluent discharge standards outlined in Joint Normative Decision COPAM and CERH-MG No. 01 of May 5, 2008 (Minas Gerais, 2008), as well as the reuse parameters defined in Normative Decision CERH-MG No. 65/2020 of June 18, 2020 (CERH-MG, 2020). Results and Conclusion: The findings indicate that the effluents treated in the studied WWTPs are suitable for reuse, with potential corrective measures for non-compliant parameters. This allows for irrigation of urban squares, subject to approval by local authorities, and internal irrigation within interested businesses. Research Implications: This approach is highly relevant for fostering discussions on expanding reuse practices and shaping regulations through legislation, norms, and deliberations. Originality: This study stands out due to its in-depth investigation, ensuring a viable water reuse source for localities facing water scarcity, particularly in the northern region of Minas Gerais. This innovative topic, though less explored in literature, is gaining momentum in environmental discourse, thanks to the potential of effluents for agricultural purposes.


INTRODUCTION
In the semi-arid region of the North of Minas Gerais, the reduction of rainfall and the poor distribution of water resources generate impacts on water availability, going so far as to cause a shortage of water in several localities.
Faced with this scenario, the search for alternatives for facing up to the water crisis has led to debate the need for adopting measures for the reuse and reuse of water, so that it is destined for less noble purposes -urban reuse, agricultural and forestry, environmental, industrial and aquaculture -waters of inferior qualities such as the effluents of the Sanitary Exhaustion System (SES).
The replacement of water sources by reuse to meet the great population, industrial and agricultural demand becomes an alternative for the lack of water in the arid and semi-arid regions that suffer from the irregularity and lack of rain.Lower quality water, such as treated effluent, can be considered as an option for less restricted uses, which reduces the intense consumption of better quality water, which can be destined for more noble uses such as domestic supply (Spanish, 2002).Dantas and Sales (2009) consider that the recovery of the polluted waters like the effluents from the Effluent Treatment Plants (ETP) is an option for reverting the scenario of scarcity with the practice of reuse.However, they emphasize that a social, legal and environmental commitment is needed in the approach to the theme, so that the properties of each water used and the specific purpose of each reuse are taken into account, in order to save waters of superior quality for more noble uses.
ETP is responsible for minimizing the impact of effluent discharges on watercourses.However, even following the standard of release of the current legislations, these systems do not completely remove the polluting substances, but it should be stressed that the release of treated effluent in the rivers is responsible, in many cases, for the maintenance of the flow and the supply of water in the regions that suffer from drought.
Authors such as Florencio, Bastos and Aisse (2006) and Asano (2002) state that the reuse of effluent implies the relief of demand and supply of water for multiple uses; economy in the use of inputs and fertilizers when destined for agriculture; besides the reduction of the flow destined for the release into receiving bodies.
By using the treated effluent for irrigation, the number of open wells can be reduced to meet the water demand in agriculture, because, according to ANA (2021), irrigation is responsible for capturing about 50% of the water volume from Brazil's water sources.
The use of treated effluent also avoids the need to use agricultural inputs mainly in a context where there is an increase of more than 50% in fertilizer prices in Brazil, due to the war between Russia and Ukraine (Duarte, 2022).Whereas the agronomic potential of effluents for plant growth lies in the quantities of nutrients present in their chemical composition, such as the macronutrients potassium, phosphorus and nitrogen (Nichelle, 2009).
Depending on the characteristics of the region and the research being developed, aiming to provide nutrients and supply the water need for the crops, by means of irrigation with the treated effluent, the present study aims to evaluate the potential of the effluents of the studied TEEs and present alternatives for reuse, when reused in a safe and effective manner.

REUSE OF WASTE WATER
Internationally, the first law for reusing water in agricultural areas came into being in 1918 in California and currently the United States has regulations throughout its territory known as the USEPA -Guidelines for Water Reuse, which depending on the States have their own regulations on the subject (Obraczka et al., 2019).
The U.S. is considered one of the largest users of reclaimed water in the world, about 6 billion m³/year of water in 2018, the country alone is not the largest user, because China utilized more than 7 billion m³/year in 2017 (CEBDS, 2022).
Still on the international side, Israel is considered a reference in the treatment and reuse of treated waters, since even with the reality of the country, built on the concept of water scarcity, almost 100% of its sewage is treated and 90% of this sewage is reused, almost half of it being destined to the demand for necessary water of the agricultural sector (Santos et al., 2021).The country has a reclaimed water pipeline network that irrigates more than half of agriculture in the Negev Desert, for example (Digital Water, 2020).
Brazil does not have federal legislation that regulates the use of residual water.What you have is normative deliberations and state resolutions.The first publication on the reuse of effluents from treatment plants was in the Brazilian standard NBR 13.969 of October 30, 1997 named "Septic tanks -Complementary treatment units and final disposition of liquid effluents -Design, construction and operation" (ABNT, 1997).This Brazilian Standard was important for inserting the discussion about reuse.
In 2005, the National Council of Water Resources published Resolution CNRH No. 54 of November 28, 2005, which regulates and stimulates the practice of direct non-drinkable reuse of water, but does not define quality standards (Brazil, 2005).Years later, in 2011, the effluent release standard was published by the National Council for the Environment (CONAMA) in Resolution n°430 of May 13, 2011(Brazil, 2011).
Few states have state laws that consider wastewater reuse practices in their activities, among them: Bahia, São Paulo, Ceará, Rio Grande do Sul and Minas Gerais, which rely on regulatory documents that establish standards and criteria for reuse according to the destination and the necessary demand (Santos et al., 2020).
With the publication, in Minas Gerais, of the CERH-MG Normative Resolution No. 65/2020 (CERH-MG, 2020), which establishes guidelines, modalities and procedures for the direct reuse of non-drinking water from WWTP effluents, reuse can become an important option for fertilization, with an proper management capable of meeting the nutritional and water needs of the plant species, in regions with water scarcity.
On October 20, 2022, a Resolution Minute of the National Water6 Resources Council was in public consultation, which establishes general modalities, guidelines and criteria for the practice of non-drinking direct reuse of water, and provides other measures.Among the information in the document, it includes that the modalities of water reuse can be carried out simultaneously in the same area, that is, one modality does not exclude the other in its applications, provided that human health and the environment are preserved.
According to information released by the University of São Paulo, in studies carried out by the Research Nucleus, the reuse of treated sewage in agriculture increased the productivity of the plantations by 6 tons per hectare a year, on average, compared with the areas irrigated in a common manner.In addition, there were savings of almost 80% of nitrogen fertilizers (Reis, 2015).
For Santos and Cândido (2013), agriculture is responsible for feeding the world and is dependent on natural resources to meet the demands of the population.With this, the authors point out that agricultural activities exert great pressure on the environment, mainly by making inappropriate use of natural resources, such as water resources, which can intensify environmental degradation.

MATERIAL AND METHODS
Because of the water scarcity of the northern region of Minas Gerais, the intermittences of the rivers and the need for adequate use of the treated effluent from Sewage Treatment Plants, the study was conducted in three stages:

Step One -Bibliographic Survey
The advances achieved in the discussion of the theme with regard to normatives and legislation and the potential of effluent reuse in the world context and in Brazil were verified, looking for information in the literature, in scientific articles and complementary materials.This stage was of fundamental importance in the evaluation of the proposals for reuse implanted in the TEEs.

3.2
Step Two -Analysis of effluent data treated in three WWTPs for reuse viability.
To perform this work, data from the results of effluent analysis at the outlets of the treatment of the WWTPs of three cities in the north of Minas Gerais, in the period from January 2021 to September 2022, were used, in compliance with the conditions and the effluent release standard established by Joint Normative Decision COPAM and CERH-MG No. 01 of May 05, 2008(Minas Gerais, 2008), besides meeting the specific parameters for reuse, considering the DN CERH No. 65 of June 120 10.

Units of study
The study was developed in Effluent Treatment Stations -ETS of three cities in the north of Minas, which use different biological treatment processes.
WWTP I (Figure 1) has a capacity of 750 L s -1 , an annual average flow in 2021 of 432.25 L s -1 , has preliminary treatment (grating, sieving and de-sanding); secondary treatment with 12 upstream anaerobic reactors (UASB), 6 percolator biological filters and 6 secondary decanters.The unit has sludge dehydration systems with 7 drying beds, centrifuges, thermal dryer and 2 sanitary landfill ditches.The gases from the UASB are stored in the gas meter and used in the heat dryer.WWTP II (Figure 2) has a nominal flow rate of 49.3 L s -1 and an average annual flow rate in 2021 of 22.73 L s -1 .The effluent receives preliminary treatment (grating and de-sanding); secondary treatment, with two UASB reactors, an optional pond and two maturing ponds; and final disposal of the effluent in the soil, by means of infiltration into capineiras.The system has a biogas burner and eight drying beds.WWTP III (Figure 3) operates with preliminary treatment (grating and de-sanding); secondary treatment with two UASB reactors, an optional pond and two maturation ponds, with a nominal flow of 35 L s -1 and an average annual flow in 2021 of 10.97 L s -1 .For the evaluation of reuse, the parameters E. coli, pH and Electrical Conductivity were analyzed.The evaluated parameters of Sodium Adsorption Ratio (RAS) and viable helminth eggs were performed in a third-party laboratory.

Step Three -Proposal Evaluation for Reuse
The proposals for reuse were implanted and evaluated according to the quality of the treated effluent, the location of the unit, the area available, the market demand, the nutritional requirements and the characteristics of the plants and the soil.

RESULTS ACHIEVED
The effluents, treated by appropriate technologies, showed average efficiencies in BOD in the period from January 2021 to September 2022 for WWTPs I, II and III of 84,99, 86,98 and 77,70% respectively.The monthly and annual BOD results were higher than 60% and 70%, respectively, and the other parameters established by DN No. 01/2008 were met, showing that reuse of this treated effluent is possible.

Quality of treated effluents
Effluent quality was assessed according to the parameters DBO, Total Phosphorus, Nitrate, Ammoniacal Nitrogen, E. coli, pH and Electrical Conductivity; Sodium Adsorption Ratio (RAS) and viable helminth eggs.

Oxygen Biochemical Demand (BOD)
Considering the effluent discharge conditions of DN N° 01/2008, the DBO of the influents and effluents and the monthly DBO reduction efficiencies of the WWTP studied are shown in Figures 4, 5 and 6.WWTPs I and II showed DBO reduction efficiency results above the minimum monthly limit of 60% established by DN No 01/2008 throughout the period analyzed.In the case of TEE III, only January/2022 obtained a BOD reduction efficiency result below the monthly limit, since the raw sewage at the beginning of the treatment process is diluted by rain, compromising the effluent's physico-chemical characteristics.Even though this result was out of the standard, the annual average was higher than 70%, and was not jeopardized by this single nonconforming result.
It is noted that there is overload in the treatment process when conducting rainwater to SES.Siqueira, Correa and Araújo (2017) stated that this circumstance brings low efficiency in sewage treatment, in addition to raising the costs of the process.
In WWTP II and III, the frequency of collection and analysis of the results occurs bimonthly, so there were no results of the samples in every month as occurred in WWTP I.The pH results of treated effluent I and II ranged from 6.42 to 7.75 in the period evaluated, within the range of 6.0 to 9.0.The pH value of the effluent from WWTP III, on the other hand, showed results higher than 9.0 during the rainy period, when the conditions of the sewage arriving at the treatment station are different, due to the dilution of the sewage with rainwater that impacts on the physico-chemical characteristics of the treated effluent.
It is important to consider that in periods of rain there is not so much need to irrigate the plants.Then there will be no impairment of the alkalinity of the soil, since the effluent showed pH outside the limit range for reuse in the rainy period, when irrigation can be suspended or occur less frequently.

Escherichia coli and helminth eggs
The results of the E. coli analyzes for the WWTP studied and the reuse limits according to DN No. 65/2020, are shown in Figures 10, 11     12 The E.coli values of WWTP I and II were above the limits set by CERH-MG ND No 65/2020.The limit is 10³ NPM 100 mL -1 , for urban use in the broad category and 10 6 NPM 100 mL-12 for agrosylvipastoril, limited category, as shown in Figures 10, 11 and 12. On the other hand, the results of the E.coli analyzes of WWTP III met the limits of the deliberation for reuse.
WWTP I helminth egg results are in accordance with DN N°65/2020 with the limit of less than or equal to 1 egg L -1 .
Thus, when assessing the feasibility of water reuse based on the E.coli parameter, the effluent from WWTP III is the most indicated, as it does not need additional treatment, which brings savings in the final destination process, since the other WWTP need disinfection processes, depending on their mode of reuse.However, the effluent analysis of this WWTP and also of WWTP II for viable helminth eggs should be carried out in order to ensure greater reliability and microbiological safety in the disposal of these effluents, following the minimum monitoring frequency of DN CERH-MG n° 65/2020.

Electrical Conductivity and Sodium Adsorption Ratio (RAS)
The limits for the effluent electrical conductivity parameter based on DN No 65/2020 shall be greater than 500 µS cm -1 .Figures 13, 14 and 15 show the results of this parameter for the WWTP studied.In all WWTP studied, the results of electrical conductivity are in accordance with DN No. 65/2020, that is, higher than 500 µS.cm -1 .For WWTP I, the results of RAS were higher than the limit established by the legislation, of less than or equal to 3, and there is no restriction of use, and it can be used in almost all soils.According to Ayers et al. (1985) by the guidelines for interpretation of irrigation water quality, there is no restriction on use in irrigation considering the infiltration capacity for RAS sodium adsorption ratio values of 3 to 6 and electrical conductivity of Ceai irrigation water ≥ 1200 µS cm -1 .
For the other WWTP, the analyzes of the RAS should be carried out according to the minimum frequency required in the resolution for reuse.

Restructuring of WWTPs for the implementation of effluent reuse
With the results of the parameters evaluated, the actions were carried out in the WWTPs, so as to be implanted the reuse in native seedlings and in the gardening of the units evaluated.

WWTP I
In 2022, the system for collecting reuse water was installed in one of the treatment lines with an operational capacity of 125 L s -1 (Figure 16), at the exit of the secondary decanter, with delimitation of the area of application of reuse (Figure 17), to dispose of the treated effluent in the irrigation of the green area of the garden of the WWTP and to cuttings of native species of the region.Figure 18 shows the development of the garden in the month of October 2022, with the beginning of irrigation with the treated effluent, where one notices the conditions of the grasses that received the reuse water in comparison with a part of the area that did not receive this treatment.In May 2022, seedlings of native species of the region were planted in WWTP I and received effluent treated with the drip irrigation system.The growth of the species is evidenced in Figure 19.An agreement is under way with the local government for the modality of urban reuse, according to DN CERH-MG N°65/2020.The town squares will receive the treated effluent from WWTP I as an alternative source of water for irrigating the gardens.
An industry close to the WWTP is assessing the viability of the reuse of water to irrigate the internal green area of the enterprise.

WWTP II and WWTP III
Part of the flow of the treated effluent was destined for the project of fertilization in the planting of native species in an area of WWTP II (Figure 21) and for the irrigation of trees in WWTP III (Figure 22).The construction of new capineiras is under study, as an alternative for reuse in WWTP II.The implantation of capineiras in unit III is under consideration.

ANALYSIS OF RESULTS
The evaluated TEEs showed higher efficiencies than those required by the legislation, demonstrating the good performance and potential of the waste water reuse practice.
The results obtained showed that WWTP I and II will require the implementation of post-treatment, with chlorine disinfection process, in order to meet the limits established by DN CERH-MG n° 65/2020 for E. coli, for urban reuse, agrosylvipastoril and environmental modalities.However, for the actions to be carried out within the areas of these stations, with restricted access to the employees of the units and the use of personal protective equipment (PPEs), this treatment has not yet been implanted.
In WWTP III, the results of the E.coli analyzes were lower than the limits established by DN CERH-MG n° 65/2020, showing that it is feasible to use the effluent in the modalities considered, without the need to apply chlorination.
With regard to pH, the treated effluents evaluated showed values within the required limits, i.e. pH values between 6 and 9.
Electrical conductivity is one of the chemical quality parameters for reuse in agrosylvipastoril modality and in the three WWTPs are in accordance with what is established in DN n° 65/2020, greater or equal to 500 µS cm -1 .
Microbiological analyzes have shown that WWTP I results for helminth eggs are relevant with the Deliberation limit for reuse.

CONCLUSIONS
The effluents of the three WWTPs analyzed present great potential for reuse in the North of Minas Gerais, considering the quality of the treated effluents and what corrective actions can be taken, so as to correct the parameters that are outside the standard of CERH-MG ND No. 65/2020.One of the actions required will be the intensification of the monitoring of noncompliant parameters and the implementation of soil analyzes and monitoring.In addition, it is important in reuse practice that those involved are trained and use appropriate PPE to minimize potential health risks.
It is recommended to continue the work to obtain more information, taking into account that the proposals for reuse are under way, such as irrigation of town squares, irrigation of green area in local industry and of plants native to the region, and the project of fertirrigation of culture on the premises of the WWTP.These actions, besides reducing the demand for the use of water of better qualities, also minimize the impact of the launch on the receiving body.The study of the impact of reuse on soil characteristics and plant production is also recommended.
The practice of water reuse needs to be prioritized as a viable alternative, technically and environmentally, particularly in places with a water deficit and with serious problems of water scarcity.Stressing that this also involves raising awareness, awareness and mobilization for its application.

Figure 1
Figure 1 COPASA Sewage Treatment Plant in the North of Minas (WWTP I) Source: Copasa Archives, 2022.

Figure 2
Figure 2 COPASA Sewage Treatment Plant in the North of Minas (WWTP II) Source: Google Earth, 2022.

Figure 3
Figure 3 COPASA Sewage Treatment Plant in the North of Minas (WWTP-III) Source: Google Earth, 2022.

Figure 4
Figure 4 Effluent and effluent BOD results and efficiency of WWTP I. Source: Copasa, 2022.
4.1.2Hydrogenionic potential (pH) The pH is one of the parameters of DN n° 01/2008 for reuse in Minas Gerais for effluent quality control and the results of the pH values of the effluents of the WWTP under study are shown in Figures 7, 8 and 9.

Figure 16 .
Figure 16.System for collecting reuse water in WWTP I. Source: From authors, 2022.

Figure 17 .
Figure 17.Delimitation of the reuse area in the garden of WWTP I. Source: Adapted from Google Earth, 2022.

Figure 18 .
Figure 18.Irrigation of the green area of WWTP I using treated effluent.Source: From authors, 2022.

Figure 19 .
Figure 19.Irrigation of native seedlings in WWTP I using treated effluent.Source: From authors, 2022.

Figure 20
Figure20shows the taps duly marked with signs indicating the new gardening system with the effluent treated as a source of reuse water. 16

Figure 20 .
Figure 20.Adaptations to the gardening system at WWTP I with reuse water from the treated effluent.Source: From authors, 2022.

Figure 21 .
Figure 21.WWTP II drip system for irrigation of native seedlings with treated effluent.Source: From authors, 2022.

Figure 22 .
Figure 22.Fertirrigation of WWTP III trees by the treated effluent drip system.Source: From authors, 2022.