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Article

Feasibility of Using Reclaimed Water from the Alegria Wastewater Treatment Plant in Concrete Mixing Plants in Rio de Janeiro, Brazil

by
Luis Carlos Soares da Silva Junior
1,* and
Marcelo Obraczka
2
1
Civil, Environmental, and Construction Engineering Department, Texas Tech University, Lubbock, TX 79409, USA
2
Sanitary and Environmental Engineering Department, State University of Rio de Janeiro, Rio de Janeiro 20950, Brazil
*
Author to whom correspondence should be addressed.
Appl. Sci. 2024, 14(12), 5293; https://0-doi-org.brum.beds.ac.uk/10.3390/app14125293
Submission received: 8 May 2024 / Revised: 31 May 2024 / Accepted: 6 June 2024 / Published: 19 June 2024
(This article belongs to the Special Issue New Approaches to Water Treatment: Challenges and Trends)
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Abstract

:
Due to the rising costs of transportation and the more advanced treatment needed to meet the water demands of the urban population, the costs of potable water tend to increase as cities expand. For some water uses, potable water is not required, such as concrete mixing industries. Previous studies have proven the viability of using reused water in concrete production. In Caju, Rio de Janeiro, four large concrete mixing plants (CMPs) are located close to the Alegria Wastewater Treatment Plant. This study focused on assessing the technical and financial feasibility of reusing these effluents as an alternative source of water for the four CMPs. The alternatives were potable and reused water via two supply methods, water tank trucks and pipelines. All costs were analyzed and projected into the future with the market cost of capital. After comparing the costs, the use of reclaimed water proved to be highly feasible, especially when a using pipeline to supply the CMPs. The present costs for the reclaimed water supply were calculated to be USD 0.99 per m3 for the pipeline alternative and the other alternatives varied in being 5 to 7 times more costly. This water reuse project using pipelines to transport reclaimed water to concrete mixing plants provides a feasible, sustainable alternative water supply in water stressed regions such as Rio de Janeiro.

1. Introduction

The Guandu Water System supplies 70% of the Metropolitan Region of Rio de Janeiro (MRRJ) potable water demands and is structured mainly from a diversion of 120 m3/s from the Paraíba do Sul River basin to the Guandu River basin, of which 45 m3/s are captured for treatment and distribution [1]. This complex system involves high costs due to the stages of diversion, treatment, pumping, and distribution, and this complexity is reflected in the tariff paid by the consumer, one of the highest in Brazil [2]. Recently, this system has been facing several difficulties, aggravated by the pollution of its main water sources, as demonstrated by the severe water shortage crisis that occurred in 2019/2020, generating supply problems for much of the Rio de Janeiro population [3,4].
In this context, the search for alternative and more sustainable and economically advantageous sources of water has become a high priority. Among the available options, the reuse of effluents from wastewater treatment plants (WTP) is configured as a strategic tool for water resource management and supply [5,6]. Wastewater reuse can reduce industrial production costs and benefit the environment by providing a more rational use of water resources, as well as reducing the discharge of pollutants into water bodies [7,8]. In addition to optimizing the rational use of water, reuse provides an increase in the water security of the watershed [9,10].
Several authors identify urban and industrial water demands fulfilled with reclaimed water from larger WTPs as the typology that presents greater technical and economic feasibility, especially in more urbanized areas [2,5,11,12]. Some of the most impactful aspects pointed out in these studies were: distance between potential producers and consumers; flow rate of reclaimed water demanded by the consumers; requirement/guarantee of minimum flow rate and quality of reclaimed water production; and potable water tariffs from the conventional water supply system.
However, the reuse of wastewater from WTPs in MRRJ is still incipient and basically supplies the internal demands of the sanitation companies that operate them, such as equipment cleaning and clearance of sewer pipes. There are isolated initiatives as well aimed at specific demands in which reclaimed water transported by water tank trucks from Penha WTP are used by COMLURB to wash and clean streets and public fairs [1,13,14].
There are many examples of market niches and companies whose water demands can be partially or fully met with reclaimed water, generating new sources of revenue for the sanitation companies as well [15]. In Brazil, however, there are only a few successful “cases”, such as the AQUAPOLO system, which uses almost 1 m3/s of reclaimed water from the ABC WTP and its wastewater reclamation plant (WRP) pumped through a 17 km long 900 mm diameter pipeline to supply the water demands of a cluster of 13 industries in Sao Paulo [16].
According to [17], the reclaimed water from distinct WRP/WTPs in the MRRJ has high-quality characteristics which fulfill the standards and requirements for its use even in more restricted purposes such as the water supply for cooling towers.
Several authors indicate that the concrete production industry can use the reuse water produced by a WWTP as a raw material, in some cases even increasing concrete performance parameters [18,19,20]. According to [21,22,23], the use of treated sewage does not cause deleterious effects on concrete, and the criteria used to determine the water quality for concrete production are entirely different from the parameters required for potable purposes [24].
Although reuse is a practice already known, institutionalized, and widely used in several countries, in Brazil it still faces several challenges, including lack of regulation, and technical and practical knowledge about the subject as well [25].
Based on evidence that the absence of financial feasibility analysis is a barrier to the effective implementation of the reuse practice [14,26], this study sought to assess the use of reclaimed water as an alternative to the conventional supply system, analyzing as a case study the case of four concrete mixing plants (CMPs) located in the neighborhood of Caju, RJ. First identified in the work of [27], this cluster is composed of CMPs with similar rates of water consumption for industrial purposes (e.g., concrete production), all of them located within a radius of 2 km from the Alegria WRP/WTP, which is currently inoperative [10,11].
In the present work, a water supply system was analyzed using a pipeline as was designed for the use of reclaimed water from the Alegria WTP/WRP to supply the demands of the cluster above mentioned. In addition, the alternative of transporting the reclaimed water by tanker trucks was also analyzed, and both options were compared to two other available water supply alternatives, both using potable water: via the conventional distribution network or tanker trucks [20].

2. Materials and Methods

To analyze the feasibility of the option of using a reclaimed water supply system through a pipeline to supply the potential industrial water demands of the cluster with four CMPs, this approach (D) was compared to three other water supply options (A, B, and C). The four options are briefly described below:
  • Alternative A: potable water supply using the conventional system (the existing potable water distribution network);
  • Alternative B: potable water supply using water tank trucks from the Cicada Nova water supply terminal (CEDAE);
  • Alternative C: reclaimed water supply from the Alegria WRP/WTP using water tank trucks;
  • Alternative D: reclaimed water supply from the Alegria WRP/WTP using a pipeline designed to supply the four CMPs.
Based on previous research [11,20], several pieces of information were collected to support the present study, including the installed supply capacity of reclaimed water from the Alegria WRP/WTP; information regarding the water demand flows for concrete mixing and the current sources of water supply in the listed CMPs; and the costs of the conventional potable water supply system, transported both by the public network and by water tank truck. Through the development of the study, it was possible to calculate and analyze indexes that relate concrete production to water consumption and the respective unit costs (BRL/m3 of concrete) for the four identified CMPs.
The costs of potable water from the public network system were obtained based on the tariff structure of the local water supply company [17]. Given the consumption characteristics and the location of the industries (CMPs), tariffs 2 and 3 were adopted for industrial consumption in Area A, in which Caju neighborhood is located.
The costs of potable water supplied by water tank trucks were obtained through market quotations with local transportation companies. Regarding the supply/distribution alternatives using reclaimed water, the cost established by CEDAE [28] was adopted. For comparison purposes, the cost suggested by [29] was used as well.
The transportation cost was taken from the National Research System of Costs and Indexes of Civil Construction (SINAPI) [30], based on the methodology proposed by [2]. The costs were calculated based on the sum of the productive hours (when the truck effectively transports the water) and the non-productive hours (when the truck is not working, such as during the loading and unloading of water).
The route of the water tank trucks was estimated based on the shortest road distance between each of the listed CMPs and the two options of supply sites: the CEDAE’s Cidade Nova water tank truck supply terminal (for potable water—Alternative B) and the Alegria WRP/WTP (for reclaimed water—Alternative C).
To estimate the cost of the alternative using reclaimed water with a pipeline connecting the Alegria WRP/WTP and the four PODs (Alternative D), a supply system was designed and its cost of installation and operation determined.
Costs in Brazilian reals (BRL) picked from the different sources which subsidized the present study were brought forward to the present year [31] and, finally, the total achieved costs for all the alternatives were converted from Brazilian money (BRL) to US dollars, according to the rate of April, 2024 [32].

2.1. Characterization of the Study Area

The region surrounding the Alegria WTP has several potential demands for industrial water to be supplied with reclaimed water [11,12,25,33]. More specifically, the water demands of several concrete production plants stand out [6,25], there being at least four CMPs located very close to the Alegria WTP: SUPERMIX CONCRETO, TOPMIX, POLIMIX CONCRETO, and CONCREVIT (Figure 1).
WTP Alegria is the biggest wastewater treatment plant in the state of RJ and treats about 1.5 m3/s of raw sewage at the secondary level, through the activated sludge process with extended aeration, which gives the system greater reliability, achieving, on average a biochemical oxygen demand concentration of 25 mg/L and a total suspended solids concentration of 44 mg/L [34].
The WRP of the Alegria WTP (Figure 2a) is fed by part of the effluent flow from the secondary treatment, and basically consists of an in-line filtration stage, followed by disinfection using sodium hypochlorite. The entire system is inserted in a container (Figure 2b), and the reclaimed water is then pumped for loading water tanker trucks (Figure 2c) [1]. The WRP has an installed capacity to supply 720 m3/day of reclaimed water, i.e., less than 1% of the sewage flow treated at the WTP [12]. The system was built to provide reclaimed water for the Porto Maravilha construction works, which was one of the major projects in the city’s preparation program to host the 2016 Olympic Games in Rio de Janeiro [2], but it is currently inoperative [10]. Thus, all treated effluent from the Alegria WTP is currently being discharged into the Cunha Channel, which flows into Guanabara Bay (Figure 2d).

2.2. Project to Supply the Four CMPs through a Reclaimed Water Pipeline

For the design of Alternative D, in which reclaimed water is transported by pipeline, the topographical base available on the Google Earth tool was used. The proposed route for the pipeline starts at the Alegria WRP/WTP and branches out to the entrances of the four CMPs, following the shortest and most feasible route through the roads and streets of the neighborhood (Caju).
The designed system supplies these companies by gravity, from a reservoir to an upper water tank positioned next to the Alegria WRP to ensure a minimum dynamic pressure of 10 m of water column at the entrances/water connections of the concrete plants [35]. The diameters of the branched type of network were predefined according to the flows, based on the economic velocity criterion in each section. Both the pumping system for the reservoir and the distribution pipeline network were calculated based on the distributed head losses by Darcy’s universal formula, disregarding local head losses [36]. The pumping system adopted two centrifugal pumps, in parallel, working alternately, estimating an 8-h daily operation regime, throughout 22 days per month.
The implementation costs include the acquisition of materials and equipment such as the pipes, pumps, reservoirs, and labor necessary for the installation of the system and were based on SINAPI [30] and on market quotations when necessary.
Since the main component of the operating costs were largely the expenses of electricity consumption for pumping reclaimed water to the upper water tank, others cost such as equipment maintenance were not considered. Based on the BHP (brake horsepower) and the estimated period of the pumping operation over the project horizon (10 years), the total operating cost was calculated by applying the average electricity tariff for the year 2019 of BRL 1.48/kWh or USD 0.38/kWh [37].
It was also considered that operational costs to produce the reclaimed water (the filtration and disinfection of the secondary treated wastewater) are already included in the reclaimed water tariff defined by CEDAE [28].

2.3. Financial Feasibility Analysis and Comparison between Water Supply Alternatives

To evaluate the financial feasibility and compare the listed four alternatives, both demands and costs were annualized and projected for a project horizon of 10 years of operation of the reclaimed water supply and distribution system. This period was adopted considering the aspects of useful life and amortization of investments that are usual in similar projects. Finally, the study compared the alternatives according to (a) discounted cash flows; (b) the internal rates of return (IRR); (c) the payback period; and (d) the unit cost of the cubic meter of water, calculated from the net present value (NPV).
Due to the difficulties of prognosis, the study did not consider the possible variations of aspects such as: (a) energy and potable water tariffs; (b) demand flows; (c) costs that influence the composition of road transport costs as well as potential economic impacts and indirect (or intangible) costs of externalities, such as increased consumption of fossil fuels and atmospheric pollution, in addition to traffic and the deterioration of the roads, in the alternatives using water tank trucks [38].
For being considered negligible, the maintenance costs of the distribution pipeline networks for both potable water and reclaimed water were also disregarded.
To financially analyze the alternatives, a survey was conducted to define an adequate discount rate (DR), and a considerable variation was found among the rates found, from 5% to 18% [39,40,41]. Thus, the weighted average cost of capital (WAAC) of 10.81% was used, referring to the water and sanitation sector in 2019, covering water supply and sanitation companies listed on the stock market (the listed companies of the water and sanitation sector in brazil that generated the data for the weighted average cost of capital were: Águas e Saneamento (CASAN), Companhia de Saneamento Básico do Estado de São Paulo (SABESP), Companhia de Saneamento de Minas Gerais (COPASA), and Companhia de Saneamento do Paraná (SANEPAR)) [42]. The rate is compatible with the proposed social discount rate for infrastructure projects in Brazil. Sensitivity analysis was performed to analyze the project’s feasibility in extreme scenarios.

3. Results

Three of the four alternatives to supply the cluster of CMPs listed by the study are represented in Figure 3. The fourth alternative—based on the supply by conventional potable water distribution pipeline network (Alternative A)—was not represented since the public water supply network is infrastructure that has already been established in all the streets of the Caju neighborhood.
Table 1 compiles general information and data concerning the CMPs, such as water consumption water consumption for concrete production rates, and the respective road distances from these CMPs to the Alegria WRP/WTP.
The potable water consumption of the CMPs obtained based on information from CEDAE was considered unreliable, especially when compared to the information from the field data survey conducted with the companies [20]. Thus, the values obtained by this author were adopted, inferring that the data from CEDAE refer only to potable water consumption, thus they did not reflect the real total water demands for the entire industrial process of concrete production by the CMPs.
The index of water consumption per m3 of concrete observed is quite homogeneous, ranging from 0.19 to 0.22 m3, therefore showing the existence of a degree of uniformity among the production processes of the different CMPs, despite the differences in terms of each concrete production volumes. In addition to the aspect of location and geographical proximity of these industries and the Alegria WRP/WTP, such uniformity reinforces their adoption as a cluster of potential consumers to analyze the feasibility of alternatives to supply their industrial water demands.
Based on the current installed capacity of the Alegria WRP/WTP, 720 m3/day [1], it would be possible to supply about 16,000 m3 of reclaimed water monthly, operating the system (WRP) only 22 days per month. Considering the total water consumption for concrete production of 6110 m3 per month observed, it is possible to estimate that the Alegria WRP/WTP would be able to supply about 2.5 times the total estimated industrial demand for water of the four CMPs cluster, without improvements and/or expansions of the existing facilities, demonstrating the great potential already observed in previous researches [5,6,25].
The survey found that the average cost of water for the three CMPs supplied by water tank trucks was BRL 31.11/m3 (USD 6.32/m3). On the other hand, BRL 40.41 (USD 8.21/m3), is the average cost of potable water for CONCREVIT, the sole industry of the CMP’s cluster supplied with water from the conventional distribution network [20], representing a cost difference of almost 25%.
The other three CMPs had their water supply water made by water tanks trucks, due to the reduction of operational costs, since water is one of the main raw materials in concrete production. According to Faria [25], in industries with high water consumption, the water tariff represents a strong impact on their operational costs. Thus, reducing the cost of water in the production process directly impacts the costs of concrete, as can also be seen in Table 1.
The three CMPs that use water tank trucks had an average water cost of BRL 11.44 per m3 (USD 2.32/m3) of concrete produced, while CONCREVIT, supplied by the conventional public water pipeline network, had a water cost of BRL 15.82 per m3 (USD 3.22/m3) of concrete produced, representing a difference in production costs of almost 30%. Thus, the option of water supply by road (water tank trucks) is much more advantageous than the alternative using distribution via the conventional public water pipeline network.
Paradoxical as it may be, this finding demonstrates that water supply companies do not consider providing punctual large demands of water—such as those for industries—through their conventional distribution pipeline network. Consequently, these potential customers need to find other supply options, such as water tank trucks, from wells, or from other water sources, even though these may have restrictions: as is the case for water of inferior quality that needs to be treated before it can be used in the production process.
Additionally, providing those industrial demands using reclaimed water would not compete with the conventional water supply. In fact, this demonstrates the potential of reclaimed water as an alternative to increase water company revenues.
From the perspective of the location of the CMPs’ water demands in relation to the Alegria WRP/WTP, it can be observed that about 40% of them are located at a 0.6 km distance (2500 m3/month from SUPERMIX only) and almost 50% at a 0.8 km distance (3150 m3/month from SUPERMIX and TOPMIX combined). The remaining 50% (2960 m3/month), referring to the water demands of CONCREMIX and POLIMIX, are located less than 2 km from the Alegria WRP/WTP.
It should be noted that all these distances involved are much shorter and fully compatible with the feasibility radius from the Alegria WRP/WTP for the use of its reclaimed water proposed [2,11].

3.1. The Design of the Reclaimed Water Distribution System by Pipeline (Alternative D)

Based on the data of surveyed water demands and the locations of potential consumers (CMPs), the layout of the local road system and the distances and elevations of the points of interest, it was possible to design and dimensioned the of the supply system and its pipeline network, which has a total length of 2259 m (diagram in Figure 4).
To achieve the minimum pressure standards recommended in the pipeline network it was necessary to increase the upper water tank height by at least 10 m, basically to supply the demands of POLIMIX, which corresponds to about 20% of the total water demand of the cluster. In addition to being more distant from the Alegria WRP/WTP, POLIMIX is located at an elevation of +19 m, i.e., 10 m and 13 m higher than CONCREVIT and the other CMPs, respectively.
Therefore, an alternative to reduce the global cost of the system is reducing the demanded height required by the elevated water tank; however, this then requires the installation of a booster to supply POLIMIX. Despite the addition of the installation and operation costs of this second pump to the project, both the costs of the installation and construction of the upper water tank and the energy consumed in pumping would be lower. Since this alternative would also increase the complexity of the system and its operation, it was discarded.
As usually adopted in projects for building water reservation systems in Brazil, the total capacity of reservation (110 m3) was designed to provide at least one-third of the estimated daily demand for reclaimed water (278 m3). The total projected reservation capacity (110 m3) was divided into two reservoirs: one cistern, with a capacity of 90 m3 (around 80% of the total daily demand), and an upper water tank, with a capacity of 20 m3 (around 20% of the total daily demand).
A water level of 35 m at the upper water tank was established to guarantee the minimum dynamic pressure of 10 m of water column in the entire pipeline/distribution network.
To pump the reclaimed water from the cistern to the elevated water tank, two centrifugal pumps of 2 HP each, in parallel, were adopted. To connect both reservoirs a pipeline of 100 mm diameter with an extension of 50 m was adopted.
Based on the specifications of the pump manufacturer, the estimated operating point of the pump, and the estimated number of hours of equipment operation, it was possible to estimate a BHP of 5069 kW per year.

3.2. Comparison between Water Supply Alternatives for the CMPs

Based on the estimated total monthly demand of 6110 m3, a volume of 73,320 m3 of reclaimed water was considered to be consumed by the four CMPs, each year.
Based on the estimated consumption range and location of the CMPs, the local water company (CEDAE) tariff of BRL 35.76 (USD 7.38) per m3 was adopted (Alternative A), while the cost of potable water transported by water tank trucks adopted was BRL 33.25 (USD 6.76) per m3 (Alternative B), based on average cost of five market quotations made by companies providing these sorts of services in MRRJ.
On the other hand, for both alternatives which employ reclaimed water (Alternatives C and D), the cost adopted was BRL 7.85 (USD 1.60) per m3, disregarding transportation. The transportation cost per tank truck determined was BRL 24.92 (USD 5.07) per m3, resulting in a total of BRL 32.77 (USD 6.66) per m3 for Alternative C.
The estimated initial investment for the implementation obtained with the reclaimed water supply system using a pipeline was BRL 309,327.00 (USD 62,871.35). In the first year, the system operation cost was BRL 5760.40 (USD 1170.81), or BRL 0.016 (USD 0.003) per m3. Thus, the total estimated operational cost was BRL 5.79 (USD 1.18) per m3 for Alternative D.
Figure 5 presents the differences (savings) between the cash flows for the three alternatives (A, B, and C) compared to Alternative D (reclaimed water supply using a pipeline), discounted for a COC of 10.81%, with the 10-year project horizon adopted.
Based on the comparison between the cash flows, the savings provided increase over the years and the most significant difference corresponds to the comparison between Alternatives A (potable water from the conventional distribution pipeline network) and D (reclaimed water from the Alegria WRP/WTP using a pipeline network).
Overall, Alternative D—referring to a distribution system (pipeline) using reclaimed water—showed the highest financial feasibility, with the lowest average projected cost of BRL 4.85 (USD 0.99) per m3, while the supply cost of reclaimed water using water tank trucks was estimated at BRL 32.77 (USD 6.66) per m3. Regarding the use of potable water, as already mentioned, the costs are BRL 35.76 (USD 7.38) per m3 and BRL 33.25 (USD 6.76) per m3, using the conventional water distribution network and water tank trucks, respectively.
According to the results obtained, the investments made for Alternative D implementation were already amortized in the first year after the start of operation of the reclaimed water distribution system using a pipeline network. The sensitivity analysis using the ranges found presented the same conclusions and showed that this project would still be feasible under uncertainty.
Actually, the information gathered by this study has demonstrated that there are two distinct levels of water supply costs for the evaluated cluster of four CMPs: a higher level, corresponding to the alternatives using potable water, either through transportation by the conventional network distribution system or water tank trucks, and a lower level, corresponding to the supply alternatives using reclaimed water, either through a pipeline or water tank trucks. The considerable difference that can be observed between these two levels of costs provides greater certainty in relation to the research results obtained, demonstrating the potential and feasibility of using reclaimed water to supply the cluster of the listed CMPs in the Caju neighborhood.

4. Discussion

As observed by [20], the supply of CMPs through the conventional potable water distribution network (Alternative A) is quite unfeasible, given the high potable water tariff practiced by CEDAE [2], especially for larger industrial demands. In this case, the cost of water from the conventional network was at least 40% higher than the cost of water supplied by water tank trucks.
Among all four water supply alternatives analyzed for the listed CMPs, it was found that those based on the use of reclaimed water are the most feasible by a large margin. With a present cost of BRL 5.27 per m3, representing, therefore, 18% of the tariff charged by the water company for water supplied through the conventional distribution network system and 21% relating to the cost of water transported by water tank truck, Alternative (D), using reclaimed water supplied through pipeline network, was the most attractive alternative for potential consumers.
Alternative D presented an IRR of 164.8% and an IL of 13.87, which can be considered as an investment of excellent return, with a short payback period of approximately 3 months. In a way, these results contradict [26] who stated that wastewater reuse projects are not viable only in the short term. However, these authors referred to wastewater reuse for agricultural purposes, in areas where the “willingness to pay” is usually low [43] and budgets for water payments are negligible or non-existent, which leads to longer payback periods. As already mentioned, and supported by [1,21,29], the reuse of effluents from WTPs for urban and industrial water demands and applications presents the greatest feasibility in urban areas such as the Caju neighborhood and in most of the MRRJ as well.
In addition to the perspective of reduced production costs for industries such as CMPs due to the use of a cheaper industrial water, other aspects favored the alternative using reclaimed water, either by pipeline or by water tank trucks: (1) the availability of a secondary effluent of excellent quality at the Alegria WRP/WTP, indicated for some industrial purposes [18,44,45], if particularly evaluated according to the requirements of Brazilian concrete production requirements and standards [6]; (2) The Alegria WRP/WTP has a steady and fair performance history in the water supply of Porto Maravilha works in the last decade [11,12,25], indicating both quantity and quality security for the supply of reclaimed water to the CMPs; (3) a considerable part of the costs involved in the production of reclaimed water are already incorporated into the daily operation of the Alegria WTP, which aims to meet the high environmental restrictions and water quality requirements for effluent discharge into the local water body (Canal do Cunha) [10,11]; and (4) the reduced distances (less than 2 km) between the Alegria WRP/WTP and the cluster of potential industrial water consumers examined (the CMPs) [2,46].
The estimated production availability of reclaimed water at the Alegria WRP/WTP—2.5 times higher than the estimated water demands of the CMP cluster—demonstrates the great potential for reclaimed water supply due to the presence of several other companies and industries in the studied region/neighborhood [25]. Thus, the reclaimed water supply can be expanded, with a few investments in the existing facilities (WRP), therefore increasing its attractiveness due to the economy of scale factor [10].
Comparing, more specifically, the two supply options which use reclaimed water (transported by water tank trucks or pipeline), it can be highlighted that the pipeline alternative provides more security and reliability due to the greater automation of its operational requirements, in addition to a more optimized logistics of the reclaimed water supply [13].
The alternative using a reclaimed water pipeline could become even more feasible and economically attractive if the existing and non-operational concrete tanks of the Alegria WTP could be used as reclaimed water reservoirs. In addition to providing a larger storage capacity to supply other potential industrial water demands in the surrounding areas, the existing tanks should replace the 90 m3 underground reservoir planned by the project, thus considerably reducing the total cost of system installation and, therefore, the final cost of the reclaimed water.
Other less tangible aspects involved in the operation of water tank trucks that negatively impact the standard of living of the population in the region should also be mentioned. The intensification of water tank truck traffic would increase noise and air pollution levels, as well as contributing to the premature deterioration of road paving, and increasing the risks of accidents [38].
In addition to being more economically viable, the two alternatives using reclaimed water could provide several environmental benefits, such as reducing annually the discharge of more than 2 tons of organic matter and 1.5 tons of Nitrogen and Phosphorus, considering only in the case of the Alegria WRP/WTP system [34]. This reduction would be especially important since the receiving water body of these effluents is the Cunha Channel, considered to be the most polluted stretch of Guanabara Bay, an important estuarine system already under strong environmental stress [47,48].
From a water security perspective, implementing the use of reclaimed water would support the necessary shift from a conventional model based on already saturated conventional supply systems to a water supply matrix with more sustainable and resilient systems [13,15], therefore increasing water supply security, especially in water stressed regions [14,49].
Recurrent periods of water scarcity coupled with the prohibitive water costs of the conventional water supply systems justify the global growing trend in which major corporations are seeking alternative water supplies, among them the employment of reclaimed water [50]. In particular, in the last two decades, companies such as Coca-Cola, Ambev, Arcellor Mittal, Santista, and Fiat-Chrysler have been investing in changing their water supply matrix aiming at greater water security, by rationalizing the use of water in their production processes and prioritizing more sustainable water supply alternatives such as wastewater reuse systems [50].
According to [49], the use of reclaimed water has the potential to promote economic growth and improve urban health conditions and social welfare, therefore configuring a public policy of relevant interest to society. However, the comprehensive implementation of wastewater reuse in the MRRJ requires a review of the current water permit values, especially in areas usually not affected by water scarcity. The present value of the Public Unit Price (PUP) for industrial water supply in the studied watershed is BRL 0.055 (USD 0.011) per m3 [51]. It corresponds to less than 0.1% of the estimated cost of the most viable alternative presented by this research (BRL 5.27 or USD 1.07 per m3 for reclaimed water delivered by pipeline), therefore considerably reducing the attractiveness of reclaimed water supply for industries and other potential consumers. Although it was not in the scope of the present work, the need for risk assessment in wastewater reuse projects should be investigated [15,52]. This is particularly important because the project comprises = non-potable reuse and it should be tailored according to the purpose of water reuse.

5. Conclusions

The industrial cluster of four CMPs, with similar industrial processes and water demands, is strategically located in the same neighborhood as the Alegria WRP/WTP, in which the quality and quantity of reclaimed water are able to meet the required demands for water with quality standards compatible with their industrial demands. Thus, those were factors of great importance to the feasibility of the analyzed project (Alternative D).
The financial modeling indicated a projected cost of BRL 4.41 (USD 0.99) per m3 for the reclaimed water distributed through the projected system/pipeline, with payback already in the third month of operation and an IRR of 164.5%. Compared to the other alternatives evaluated, it presented greater financial viability, as well as a safer operation, avoiding traffic problems and air pollution.
From an environmental, planning, and water management perspective, the two alternatives using reclaimed water—either by water tank trucks or pipeline—have the potential to reduce the pollution caused by the discharge of treated effluent and to increase water security in the studied region. In the case of the pipeline alternative, besides demonstrating more financial viability, it does not generate more traffic and air pollution that would be caused by the increase in the intense traffic of water tank trucks transporting reclaimed water.
Due to the urgent need for viable, resilient, and more sustainable alternative sources of water for industries, other potential clusters of water consumers and reclaimed water suppliers such as WTPs should be considered and evaluated in future wastewater reuse feasibility studies in the MRRJ.

Author Contributions

Conceptualization, L.C.S.d.S.J. and M.O.; methodology, L.C.S.d.S.J. and M.O.; writing—original draft preparation, M.O.; writing—review and editing, L.C.S.d.S.J. and M.O. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The raw data supporting the conclusions of this article will be made available by the authors on request.

Acknowledgments

The authors acknowledge their respective institutions.

Conflicts of Interest

The authors declare no conflicts of interest.

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Applsci 14 05293 g001
Figure 1. Location of the Alegria WTP/and potential consumers for reclaimed water, including the four CMPs in the study region (Caju and surroundings) listed by this research.
Figure 1. Location of the Alegria WTP/and potential consumers for reclaimed water, including the four CMPs in the study region (Caju and surroundings) listed by this research.
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Figure 2. Details of the reclaimed water production system of the Alegria WTP. (a) A container that houses the reclaimed water production system; (b) details of the filtration and disinfection system; (c) water tanker truck loading/supply system, and (d) the outflow channel for the discharge of treated effluent into the Cunha Channel.
Figure 2. Details of the reclaimed water production system of the Alegria WTP. (a) A container that houses the reclaimed water production system; (b) details of the filtration and disinfection system; (c) water tanker truck loading/supply system, and (d) the outflow channel for the discharge of treated effluent into the Cunha Channel.
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Figure 3. Water supply alternatives for the cluster of four CMPs located near the Alegria WRP/WTP, in Caju, except Alternative A.
Figure 3. Water supply alternatives for the cluster of four CMPs located near the Alegria WRP/WTP, in Caju, except Alternative A.
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Figure 4. Diagram of the projected distribution system to supply the four CMPs with reclaimed water from the Alegria WRP/WTP.
Figure 4. Diagram of the projected distribution system to supply the four CMPs with reclaimed water from the Alegria WRP/WTP.
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Figure 5. Difference between the discounted cash flows of water supply Alternatives A, B, and C and Alternative D.
Figure 5. Difference between the discounted cash flows of water supply Alternatives A, B, and C and Alternative D.
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Table 1. Data on the consumption and monthly production of drinking water and concrete production rates in the CMPs of the cluster identified around the Alegria WTP. Source: Zahner Filho [20].
Table 1. Data on the consumption and monthly production of drinking water and concrete production rates in the CMPs of the cluster identified around the Alegria WTP. Source: Zahner Filho [20].
CMPConcrete ProductionMonthly Water ConsumptionWater-to-Concrete Consumption RatioWater CostsCost of Water per m3 of Concrete
m3/monthm3/monthm3/m3BRL/m3 of WaterUSD/m3 of Water (*)BRL/m3 of ConcreteUSD/m3 of Concrete (*)
SUPERMIX11,50025000.2230.266.1511.712.38
TOPMIX35006500.1935.337.1811.682.37
POLIMIX600012000.2030.266.1510.772.19
CONCREVIT800017600.2240.418.2115.823.22
Average725015270.2133.686.8511.442.32
Total29,0006110-- --
* 1 USD = BRL 4.92 in April, 2024 [32].
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Silva Junior, L.C.S.d.; Obraczka, M. Feasibility of Using Reclaimed Water from the Alegria Wastewater Treatment Plant in Concrete Mixing Plants in Rio de Janeiro, Brazil. Appl. Sci. 2024, 14, 5293. https://0-doi-org.brum.beds.ac.uk/10.3390/app14125293

AMA Style

Silva Junior LCSd, Obraczka M. Feasibility of Using Reclaimed Water from the Alegria Wastewater Treatment Plant in Concrete Mixing Plants in Rio de Janeiro, Brazil. Applied Sciences. 2024; 14(12):5293. https://0-doi-org.brum.beds.ac.uk/10.3390/app14125293

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Silva Junior, Luis Carlos Soares da, and Marcelo Obraczka. 2024. "Feasibility of Using Reclaimed Water from the Alegria Wastewater Treatment Plant in Concrete Mixing Plants in Rio de Janeiro, Brazil" Applied Sciences 14, no. 12: 5293. https://0-doi-org.brum.beds.ac.uk/10.3390/app14125293

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