CHARACTERIZATION AND PROPOSAL OF TECHNOLOGIES FOR THE TREATMENT OF DOMESTIC SEWAGE IN ILHA GRANDE BAY - RJ

Objective: To characterize the situation of sanitary wastewater discharge in the hydrographic basins draining into the Baía da Ilha Grande (BIG) and to propose wastewater treatment alternatives based on the literature on decentralized solutions. Theoretical framework: The BIG has been experiencing negative environmental impacts due to the urbanization process in the region, mainly due to the irregular discharge of domestic wastewater into the environment. Method: The methodology was developed in two stages, with stage 1 involving data collection from available data in the 2017 Wastewater Atlas, and stage 2 focusing on identifying the most appropriate treatment technologies for this study from the fifteen options evaluated. Results and conclusion: The characterization revealed that municipalities within the BIG are already using decentralized solutions for domestic wastewater treatment, albeit below the national average coverage rates (18-54%). The five most promising technologies identified were Septic Tanks, Compact UASB, Biodigesters, Compartmentalized Anaerobic Reactors, and Integrated Biosystems. It is concluded that the communities have a sanitation deficit and show potential for implementing decentralized solutions. Implications of the research: The study helped develop strategies for decision-makers to select the most appropriate wastewater treatment technologies to meet local needs. It also served as a model for scientific studies in other locations. Originality


INTRODUCTION
Ilha Grande Bay (BIG), Hydrographic Region I (RH-I), in the state of Rio de Janeiro has suffered negative environmental impacts in recent years due to the region's urbanization process, through the irregular dumping of domestic effluents, destruction of vegetation due to disordered occupation, occupation of river banks, among other factors determining the continued degradation of this ecosystem (CBH-BIG, 2020).
The release of sewage without adequate treatment, in addition to compromising water quality, has caused impacts on human and environmental health.Furthermore, it has made it difficult to meet the multiple uses of water resources, such as supply, bathing, irrigation, recreation, leisure, among others (ANA, 2017).According to ANA (2020), Brazil presented unsatisfactory rates in relation to sanitary sewage services, with 46.5% of the population served centrally with collection and treatment of domestic sewage, while 53.5% is not served satisfactorily. .In relation to individual systems (single or multifamily), the data presents the following situation: 12.3% with a septic tank and sink, 20.1% with a rudimentary septic tank and 7.8% of the population without treatment.
In order to minimize the consequences of the lack of access to basic sanitation, decentralized solutions for the treatment of domestic sewage, single or multifamily, are one of the paths to the universalization of the sanitary sewage service (RABELLO et al., 2019;HONORATO et al., 2021).
The design of the decentralized sewage treatment unit project is the stage in which the technology that will be used is selected, taking into account the characteristics of each region (PRYSTHON et al., 2023).The most common solution around the world for the decentralized treatment of domestic sewage is the septic tank, however, there is no standard technology that solves the health deficit in developing countries, as there are countless combinations and they all need to have a different approach.accessible (MASSOUD et al., 2009).
Therefore, the objective of the work was to characterize the sewage situation in the hydrographic region I (RH -I) of the Baía da Ilha Grande (BIG) hydrographic basin, and to propose alternatives for treating domestic sewage based on decentralized solutions.

METHODOLOGY
For the purposes of planning, water management and the environment as a whole, the state of Rio de Janeiro was divided into nine Hydrographic Regions ( RHs ), according to CERHI-RJ Resolution nº 107/2013 (RIO DE JANEIRO, 2013).The location of this study was the Ilha Grande Bay Hydrographic Region (RH-I), formed by coastal basins, covering the continental part and the islands of the municipalities of Paraty and Angra dos Reis, in full, and the municipality of Mangaratiba, partially covering the district of Conceição de Jacareí, with a total area of 1,758 km 2 (INEA, 2015) (Figure 1).The methodology applied in the present work was divided into two stages.In Stage 1 , a diagnosis of the sanitary sewage situation of RH-I was carried out, using the database of the National Water and Basic Sanitation Agency, the Sewage Atlas (ANA, 2017) and data from the Ilha Baía Hydrographic Basin Committee Big (CBH-BIG).The data collected from the byproducts of the ANA diagnosis were obtained from the "Municipal Sanitary Sewage Report", from each of the 3 municipalities covered by RH-I.
In Stage 2, the selection criteria for the most recommended technologies for this study were defined, through 2 steps: Step 1 -The support flowchart was applied when choosing sewage treatment technologies, according to the methodology described by Tonetti (2018).This preliminarily presents the most suitable technologies through questions whose answers can be "yes" or "no".
They are based on variables that relate the use of water in flushing, the composition of the sewage (gray water, black water, etc. ) and the intention to use the by-products; Step 2 -Selection criteria were created based on the summary table of the main characteristics of the fifteen technologies selected for the treatment of sewage from isolated communities prepared by Tonetti (2018).Table 1 below presents the exclusion criteria adopted in this work.The inclusion criteria were: i) Low implementation and operation costs; ii ) Constructive and operational simplicity; iii ) Single-family system; iv ) Domestic sewage; v) Compliance with the NOP-INEA-45 legislation, which establishes criteria and standards for the discharge of treated sewage into receiving bodies, reducing the organic load by 60% (RIO DE JANEIRO, 2021).Furthermore, in this study it was considered that all benefited homes would have up to 5 inhabitants, would use water in the toilet and there would be a mixture of the types of effluents generated (domestic sewage).In this way, the technologies were classified into three categories as: " Complies ", " Partially complies " and " Does not comply " according to established criteria.

Table 1
Exclusion criteria for choosing technologies for domestic sewage treatment in RH-I.

Exclusion Criteria Justification
High cost of implementation, operation and/or maintenance In general, residents and municipal managers of isolated areas do not have the financial resources to afford large investments in the implementation of these technologies.
Constructive or operational complexity Solutions that depend on specialized technicians or highly qualified labor have high operation and maintenance costs, in addition to making the autonomy of beneficiaries unfeasible.

Dependent on electrical energy
Technologies that use electrical energy to operate require greater maintenance and increase the cost of operating the system.

Direct disposal technologies on the soil surface
They present greater risks of contamination to the environment aand human health.
Semi-collective systems Due to the high cost of the sewage collection network.
Source: Prepared by the authors (2023).Of the 3 municipalities covered by the region, only Angra dos Reis has sewage collection and treatment, with 9% of service, a much lower rate compared to the state of Rio de Janeiro, which has an average of service for the urban population with systems collective sewage collection and treatment around 40.4% (ANA, 2020).This reveals how deficient the supply of these services has been in RH-I, causing health and environmental problems in the region.
The municipality of Mangaratiba has the highest rate of service for individual solutions for sanitary sewage treatment, with around 54.2%, having a greater reach than at national level for this modality (ANA, 2020).However, there is no data on the types of technologies that are used, their operation and frequency of maintenance to be able to measure the efficiency of the treatment.Furthermore, Angra dos Reis has services provided by an autonomous company, while Paraty and Mangaratiba have public services.
According to preliminary studies developed by Atlas Esgotos (ANA, 2017), the technical alternatives suggested for the 3 RH-I municipalities foresee investments of 10% in individual solutions (decentralized solutions) and 90% in sewage treatment plants (centralized solutions ) with a planned investment for collection and treatment (centralized type) of R$329,664,079.45.It is clear that even in municipalities where the service provider is a private company, progress in sewage treatment remained low, revealing that this deficit is independent of the type of company.
Step 2 -To propose the technologies, the two steps previously described in the methodology were carried out.In Step 1 there is the result regarding the flowchart (yes or no answers) ( Figure 3 ).

Figure 3
Flowchart answers to define the most suitable technologies for applying the study exclusion criteria .
The results of this flowchart pointed to 9 domestic sewage treatment solutions as the most suitable, namely: Built Flooded Systems (SAC), Upflow Anaerobic Reactor (RAFA), Septic Tank (TS), Anaerobic Filter (FA), Water Filter Sand ( FAr ), Vermifilter (VF), Biodigestor (BIO), Compartmented Anaerobic Reactor (RAC) and Integrated Biosystem (BI). In Step 2 , the selection criteria were applied and as a final result the systems were classified into three categories ( Table 2 ): " Do not meet " the Built Wetland Systems, Anaerobic Filter, Vermifilter and Sand Filter; " Partially serve " the Upflow Anaerobic Reactor, Biodigestor, Compartmented Anaerobic Reactor, integrated Biosystem and the Septic Tank.
None of the technologies were classified as "Complies" according to the justifications presented.As a result of the inclusion and exclusion criteria, five technologies were considered to be of greater viability (partially met), namely: Septic Tank, Upflow Anaerobic Reactor, Compartmented Anaerobic Reactor, Biodigestor and Integrated Biosystem to be applied in the three municipalities of RH-I.
The Septic Tank (TS) is the most implemented decentralized sewage treatment technology worldwide (MASSOUD et al., 2009) and partially met the requirements critériosof this study, as its operation alone would not reach the minimum limits established by the legislation of the state of Rio de Janeiro, NOP-INEA-45/2021 requiring additional treatment.
Anaerobic Filters are widely used in combination with this technology, with the aim of posttreatment of effluent from these units, before final disposal, which can be done in a Sinkhole, Infiltration Trenches or Bodies Hídricos(SANTOS, 2019).
The Upflow Anaerobic Reactor (RAFA), also known as oUASB ( Upflow Anaerobic Sludge Blanket ) and its other configuration, the Compartmented Anaerobic Reactor (RAC) were classified with partial compliance due to their higher cost.However, the degree of efficiency of the treatment allows it to be installed without the need for additional treatment, and can be arranged in the same way as that presented in Septic Tanks (SANTOS, 2019).When you need better efficiency in reducing organic load and removing nutrients, the system can be followed by other technologies, such as: Anaerobic Filter, Sand Filter, Built Wetland Systems (COSTA et al., 2015).
There are several types of Biodigesters (Chinese, Canadian, pre-molded models) and they have been widely disseminated in rural areas due to the possibility of using the biogas generated (ADLER et al., 2017).In this study, this technology partially met the criteria, due to the cost and the need for more frequent maintenance than the other technologies presented.
After the treatment carried out in the biodigester, the effluent still requires additional treatment before its final disposal, commonly using empregadosAnaerobic Filters, Built Wetland Systems and Integrated Biosystems (TONETTI, 2018).
The Integrated Biosystem baseia-sein the combination of conventional and ecological technology, commonly consisting of a biodigester, anaerobic filter and constructed flooded systems (RODRIGUES et al., 2006, JACOB et al., 2021) and can be disposed of directly in Infiltration Trenches, Circles of Banana Trees, Bodies Hídricoor non-potable Reuse .This system partially met the criteria, with cost and maintenance as limitations.
The stage of final disposal of the treated effluent must be evaluated according to the quality required to respect the limits established by current municipal environmental legislation.
These will guide the level of efficiency of the necessary treatment, and it may be necessary to include a complementary treatment unit to ensure a greater reduction in organic load, for example (KADIM & ABD, 2022).Therefore, it is recommended that combined units be installed to increase the quality of the final effluent.
Regarding the removal of nutrients from sewage, the proposed treatment alternatives do not guarantee this efficiency (TONETTI, 2018).To this end, tertiary treatment is recommended, however, it requires greater complexity in operation, maintenance and costs (SALOMÃO et al., 2012).
The choice of the appropriate technology needs to be done with great caution to avoid possible problems in the treatment due to lack of adherence by the population served, maintenance, costs and other factors (SILVA JUNIOR et al., 2022).Therefore, it is necessary to analyze the accessibility and suitability of technologies so that the chosen one is "economically accessible, environmentally sustainable and socially acceptable".Furthermore, an assessment of the cost, life cycle, design, construction, operation, maintenance, management, repairs and replacement of the designed system must be carried out (MASSOUD et al., 2009).
Additionally, this project did not foresee the stage of final disposal of the sludge accumulated in the treatment units, leaving these for future studies.It should be noted that both for reuse and final disposal, both must comply with the criteria established by current regulations.

CONCLUSIONS
In view of this mapping, it is concluded that the municipalities of RH-I (Angra dos Reis, Paraty and Mangaratiba) were below average regional and national sewage service rates, causing social, environmental and economic losses for the region.
The decentralized domestic sewage treatment technologies proposed in this study, which partially met the criteria of low implementation and operation cost, constructive and operational simplicity, single-family system and organic load removal compliance of the NOP-INEA-45/2021 legislation, were the Upflow Anaerobic Reactor, Biodigester, Compartmented Anaerobic Reactor, Integrated Biosystem and the Septic Tank.All of these would require a complementary treatment unit to reach the limits for releasing the treated effluent into receiving bodies estabelecidosunder current legislation.
After the data presented, it can be observed that there are different decentralized technologies for treating domestic sewage, single or multi-family, to be applied in urban, periurban and rural regions.Therefore, this study mainly contributed to the development of strategies for decision makers (public managers, private institutions, etc. ) in choosing the most appropriate treatment technologies, which best meet local needs and which could be implemented in these areas.In addition to serving as a basis or model for scientific studies in other locations with similar characteristics .
One of the challenges of this study was access to data on domestic sewage treatment services in the municipalities of RH-I, as there are no periodic publications by the municipal bodies responsible for service indices, which hinders the development of more proactive actions to improve the sector.
It is recommended that more in-depth technical-scientific studies be carried out, with technical visits, to define and implement sewage treatment systems, considering the final disposal of all by-products, appropriate to the particularities of each location.
Finally, the three municipalities of RH-I have a vocation for decentralized solutions, being a promising path to the universalization of domestic sewage treatment, in order to meet the goals of the Sustainable Development Goals (SDGs) of the United Nations (UN).), in particular, SDG 6.

Figure 1
Figure 1 Location of Ilha Grande Bay, Hydrographic Region I (RH-I) of the state of Rio de Janeiro and its municipalities: Paraty, Angra dos Reis and Mangaratiba.
Characterization and Proposal of Technologies for The Treatment of Domestic Sewage in Ilha Grande Bay -RJ ___________________________________________________________________________ Rev. Gest.Soc.Ambient.| Miami | v.18.n.3 | p.1-14 | e05240 | 2024.6 3 RESULTS AND DISCUSSION Stage 1 -The characterization of the sanitary sewage situation in RH-I indicated that the composition of the majority of sewage treatment systems existing in the 3 municipalities was based on individual solutions (single or multi-family ), with 36.4% of the service being donethrough this modality, similar to the situation in the rest of Brazil (ANA, 2020).However, there is no guarantee of treatment efficiency, as these are generally rudimentary septic tanks and the biggest challenge of these systems has been adequate operation and maintenance(MORAES et al. 2020).Furthermore, only 3% of the population has centralized collection and treatment, 30.3% has collection without treatment and 30.3% has neither collection nor treatment (Figure2).

Figure 2
Figure 2 Characterization of domestic sewage treatment services by municipality located in Hydrographic Region I -Angra dos Reis, Paraty and Mangaratiba.

Table 2
Synthesis and comparison of the 9 domestic sewage treatment technologies with application of the selection criteria.The technologies were classified as compliant , partially compliant and non-compliant , according to the comparison of the results presented in each of the evaluated parameters.