Rapid population growth intensifies water scarcity, highlighting the importance of treatment technologies such as reverse osmosis and membrane filtration to ensure safe drinking water and preserve resources. The use of polystyrene as a filter for polluted water is valuable due to its porous surface, efficiently retaining impurities. The system, a tubular reactor with a mixed polystyrene bed, underwent evaluations with varying particle sizes, flow rates and times, operating in dead-end mode and series system without recirculation with theoretical residence times between 180 and 360 min. The study, divided into two phases, optimized the system in the first phase, characterizing the filter bed and carrying out maintenance for 360 min at 0.5 L/min. Phase two evaluated the performance of the reactor in treating wastewater with flow rates of 0.5 and 1 L/min for 180 min. Under the best conditions of Phase I, 55% of Escherichia coli and turbidity were deactivated, not meeting potability standards. In Phase II, there was efficiency in the removal of several parameters, such as chemical oxygen demand (78.26%), total phosphorus (75%), nitrate (73.42%), ammonia (73.13%), nitrite (69.33%), potassium (70.83%), and sodium (68.75%). In addition, 98.32% of E. coli was deactivated, meeting CONAMA Class 2 and 3 irrigation standards.

  • The reuse of wastewater is essential to address water scarcity, and the use of polystyrene as an alternative in wastewater treatment is valuable due to its porous surface, which efficiently retains impurities.

  • The system, a tubular reactor with a mixed polystyrene bed, underwent evaluations varying particle sizes, flow rates, and times, operating in dead-end mode and series system without recirculation.

  • In Phase I, 55% of E. coli and turbidity were deactivated, not meeting potability standards. In Phase II, the system treated wastewater, removing COD (78.26%), total phosphorus (75%), nitrate (73.42%), ammonia (73.13%), nitrite (69.33%), potassium (70.83%), and sodium (68.75%), as well as deactivating 98.32% of E. coli, meeting the irrigation standards of CONAMA Classes 2 and 3, making this the most successful analysis.

According to a study released in 2023 by the National Water Agency (ANA 2019), a 24% increase in water consumption and usage in Brazil is projected by 2030. The agency responsible for water resource management reports that the current average consumption is 283,000 million liters of water per second, expected to surpass 2.5 million liters per second by 2030. According to the ANA, the main uses of water in the country include human supply (urban and rural), animal supply, transitional industries, mining, thermoelectricity, irrigation, and evaporation from artificial reservoirs.

With population development increasingly evident, and in national terms, the Brazilian population in 2022 consisted of more than 215.3 million in habitants, thus bringing a notoriety of greater water demand. Given the scenario of such latent population development, it is necessary to have water reservoirs in their widest extension, such as dams and lakes, both in urban and rural areas, thus guaranteeing viability and greater security in terms of water resources.

However, the unavailability of water, through its contamination, causes a reduction in spaces conducive to life, generating costs that are not always measured, such as increased hospital costs, loss of productivity in agriculture and livestock, reduced fishing, the loss of biodiversity and the loss of tourist, cultural, and scenic values as well as a general loss of human and social productivity. Water thus becomes an important part of socioenvironmental and basic sanitation issues, and according to the United Nations, around 80% of wastewater from developing countries is eliminated into the environment without any prior treatment (UN-WATER 2018).

In the Brazilian context, about 75% of the country's water is in the rivers of the Amazon Basin, inhabited by less than 5% of the population. This creates regions of medium and high risk of scarcity in coastal areas, where most of the population resides. In addition, Brazil faces high wastage in distribution networks, with up to 60% of treated water lost, especially due to leaks in pipelines (CASTRO 2022).

The global demand for water is estimated to increase by 55%, but approximately 25% of large cities currently suffer from some degree of water stress. Climate change, severe droughts, population growth, increased demand, and mismanagement in recent decades have placed further pressure on the world's scarce freshwater resources, resulting in the loss of approximately 4 billion people. People face severe water shortages (Procházka et al. 2018; Khatibi & Arjjumend 2019; Orimoloye et al. 2020).

Approximately 2.2 billion people around the world do not have access to a safe drinking water supply. The literature on water scarcity focuses mainly on the quantity of this resource. However, if adequate safety measures are not taken, the quality of water supplied to consumers during periods of water scarcity may be compromised.

Goal 6 of the United Nations 2030 Agenda for Sustainable Development Goals sets the goal of ensuring universal and equal access to safe drinking water for all (United Nations 2021). Related objectives include widespread access to basic sanitation, improving water quality by reducing pollution, halving the proportion of untreated wastewater, and significantly increasing efficiency in water use.

Classifying water is a common practice for evaluating water quality and determining suitability for different uses. In many countries, including Brazil, water classification follows standards established by regulatory bodies. In Brazil, for example, the National Environmental Council (CONAMA) defines water classes according to CONAMA Resolution 357/2005.

Expanded polystyrene (EPS), like other plastics, is derived from petroleum. After oil extraction, this raw material passes through refineries to remove impurities through fractional distillation, resulting in naphtha. This naphtha fraction is then directed to the Petrochemical Industry, where it is used to break the chemical bonds between molecules and obtain monomers, with styrene being the monomer used in the case of EPS. The chemical industry acquires this monomer in the form of tiny spheres and subjects it to the pre-expansion process. At this stage, high temperature water is added to allow the vapor to penetrate the spheres more quickly than pentane, which leaks out. The result of this styrene polymerization process is EPS.

After a rest period of approximately 6 h in the silos, the EPS is injected into their respective molds using compressed air. Finally, the pieces are exposed to steam again to fuse and acquire the desired finish before being made available to the end consumer. It is worth noting that this is not the end of the EPS cycle, as it can be recycled after use, contributing to sustainability, since its decomposition time is indeterminate.

ABIQUIM (2020) highlights the benefits of EPS, such as excellent cost/volume ratio, good resistance/mass and adaptability in civil construction, in addition to being 100% recyclable. Its use as a filter element is linked to the particle adsorption capacity and the biological processes resulting from the formation of biofilms in the filter bed. Sorbents can be synthetic (polyurethane, PS) or natural (extracted from nature). Studies on the development of sorbents emphasize characteristics such as ease of application and high sorption rate. Polymers such as polypropylene and PS are investigated as synthetic sorbents, especially for removing oil spills. Adsorption and filtration for the removal of heavy metals and organic compounds are studied due to environmental concerns.

Polymers such as polypropylene, polyurethane foams, and PS are being studied as synthetic sorbents due to their hydrophobic and oleophilic properties. The surface area of the sorbent material is crucial for sorption affinity, and fibrous adsorbents with submicrometer to nanometer diameters are considered promising for removing oil spills (ALNAQBI et al. 2016). Adsorption and filtration methods are being studied to remove heavy metals and organic compounds from water, with emphasis on PS spheres due to their high adsorption and filtration capacity. However, improper disposal of PS, which takes more than 150 years to decompose and can cause environmental damage, is a concern. Despite this, the material can be recycled and reused in construction, offering a sustainable alternative.

The use of this material presents notable benefits in the short and long term, highlighting the preservation of its properties over time, low rot potential, and positive impact on the economy and accessibility. Furthermore, its sustainable nature promotes the effective reuse of water, thanks to its power to adsorb particles in sewage and the biological process generated by the formation of biofilm. Its non-hygroscopicity maintains its thermal characteristics even in humid environments, contributing to its applicability in different contexts, while its odorlessness makes it suitable for reuse in soil, water and air, highlighting the importance of promoting this practice.

The study was carried out at the Desalination Reference Laboratory (LABDES) of the Federal University of Campina Grande (UFCG), where the optimization of a tubular reactor system in series was carried out using varied granulometry of PS spheres. Its configuration was studied to provide filtration of contaminated water, and the flowchart in Figure 1 shows the developed methodology.
Figure 1

Flowchart of the phases that make up the system.

Figure 1

Flowchart of the phases that make up the system.

Close modal

Characteristics of the filtration system

Figure 2 shows a schematic representation of the tubular system, as follows:
  • 1. A tubular polyvinyl chloride (PVC) reactor with a height of 1.5 m and a diameter of 20.0 cm, each closed with a 20.0 cm PVC cover at both ends, to prevent water leakage, at the end of its lower end featuring a tap for collecting water samples; it has a volume of 40.0 L without filter media and a volume of 2.8 L with filter media.

  • 2. 250 L reservoir to supply reused water received during the process.

  • 3. Rotameter with a scale of 0.4–4.0 L is placed at the system inlet to control the flow rate inside the reactor.

  • 4. Pump (centrifugal) 1/4 HP motor to dispense water into the system and carry out backwashing.

  • 5. It has a set of ball valves (1/2 inch) and taps, both made of PVC, installed at the inlet and outlet of each reactor to control the flow and flow of water.

  • 6. The system has a bypass: used to control the flow of water entering the system, returning the water to the supply tank.

Figure 2

Model of the treatment system used in the research.

Figure 2

Model of the treatment system used in the research.

Close modal

Characterization and treatment of PS spheres

Understanding the wide use of PS, the research proposed the use of different spherical particle sizes of PS, as shown in Table 1, as a means of treating the reuse effluent under study. We know that expandable PS is the raw material for the production of ‘styrofoam’, widely used commercially for packaging fragile and thermal insulating materials, so different spheres in different sizes were chosen because they exhibited granulometric properties similar to sand. The advantages of using this treatment medium are the following: It is not a heavy, inert, non-pigmented medium and is commercially available (SCHÖNTAG 2015). Table 1 shows the particle size and properties of the PS used in the treatment process.

Table 1

Properties of PS spheres

Characteristics of the PS spheres used
Granulometry 1 mm 20% 
Granulometry 2 mm 45.79% 
Granulometry 5 mm 34.21% 
Quantity used 605 g 
Characteristics of the PS spheres used
Granulometry 1 mm 20% 
Granulometry 2 mm 45.79% 
Granulometry 5 mm 34.21% 
Quantity used 605 g 

The characterization of the PS spheres was carried out before and after the filtration process depending on particle size and weight. Due to its low density (0.95 g/cm3), the filter medium was confined in a geotextile filter to prevent backflow during the process, as shown in Figure 3.
Figure 3

PS shape.

It is worth noting that before the filter bed was placed inside the reactor, it was weighed dry and with the material wet, as shown in Table 2, following the assumption in the literature that classifies PS as a sorbent.

Table 2

Mass of PS contained in the reactor before and after effluent treatment

PS putty
Dry 605 g 
Wet 1,174 g 
PS putty
Dry 605 g 
Wet 1,174 g 

To determine the characteristics of PS in terms of adsorption capacity in relation to mass, the following experiment was carried out: in a glass tube containing volumes of 150, 180 and 250 mL, the following masses were added: 2.028, 3.0497, and 4.000 g, respectively, after a period of 1,440 min as shown in Table 3, with mixed PS of 1.00, 2.00 and 5 mm, the methods used to measure PS, as well as other physicochemical and bacteriological parameters, included weighing the PS with a precision scale. pH was measured with a pH meter, turbidity was assessed with a turbidimeter, and color was determined with a colorimeter. Electrical conductivity (EC) was measured with a conductivity meter. Chemical oxygen demand (COD) was determined using a COD analyzer or through titration methods. Ammonia levels were measured using a spectrophotometer or an ammonia selective electrode, while nitrite and nitrate concentrations were measured using a spectrophotometer or ion chromatography. Finally, Escherichia coli was detected and quantified using membrane filtration followed by incubation in selective medium, or using molecular methods such as polymerase chain reaction, as shown in Figures 4 and 5.
Table 3

Characteristics of PS before and after 1,440 min

Characteristics of PS after 1,440 min
Initial volume (mL)Final volume (mL)Initial mass (g)Final mass (g)
150 75 2,028 12 
180 100 30,497 10 
250 250 4,000 20 
Characteristics of PS after 1,440 min
Initial volume (mL)Final volume (mL)Initial mass (g)Final mass (g)
150 75 2,028 12 
180 100 30,497 10 
250 250 4,000 20 
Figure 4

Spheres with effluent.

Figure 4

Spheres with effluent.

Close modal
Figure 5

Spheres with effluent after 1,440 min.

Figure 5

Spheres with effluent after 1,440 min.

Close modal

We can observe what was evidenced in the literature (Sikhwivhilu et al. 2011). PS has been recognized for its ability to adsorb a wide range of substances, including volatile organic compounds, inorganic contaminants, and air and water pollutants.

To ensure precise control of the flow rates of 0.5 and 1.0 L/min in the reactor, a bypass system was implemented at the inlet, regulated by a valve that adjusts the water flow in the system. It is essential to highlight that, as the effluent passes through the filtration process, there is a resistance provided by PS, resulting in a reduction in flow. This mechanism is of crucial importance, since the amount of water that flows through the reactor must comply with its characteristics, such as size and volume occupied by the filter bed. It should be noted that a high flow rate can compromise the effectiveness of adsorption of impurities on PS.

The practice of washing the PS at the end of the day was essential to analyze changes in the physicochemical and microbiological properties of the feed water from one day to the next. To do this, 150 L of tap water was supplied for 30 min, thus demonstrating the complete washing of the PS to be used the following day. Thus, the water used to feed the system on subsequent days has different characteristics compared to the water used on the previous day, simulating a periodic renewal of this liquid in the feed tank. This procedure contributes to the consistency of experimental results over time, allowing a more precise analysis of the variables involved in the treatment of water in the reactor.

Feeding and evaluation of system water quality parameters

To conduct the experiments, 10 L were transported daily, initially, and, subsequently, a final volume of 20 L of water from the lagoon to the Desalination Reference Laboratory (LABDES), where the treatment system is implemented. The experiments were carried out following a sequential methodology that covered the entry time and the volume used in the system. Three different sizes of PS particles – 1.0, 2.0, and 5.0 mm – were used to evaluate the adsorption of impurities present in water. These particle sizes were selected because they represent the most prevalent on the market. The specific choice of filter medium particle size was based on data obtained by Andrade et al. (2021), who conducted fixed bed analyses, highlighting the influence of adsorption capacity. Given this scenario, we opted for the mixed bed composed of the mentioned particles.

  • 1. System supply with time of 180 min and flow of 0.5 and 1.0 L/min.

  • 2. System supply with a time of 360 min and a flow rate of 0.5 L/min;

To evaluate the efficiency of wastewater treatments, the parameters ‘Color’ (colorimetric method) and ‘Turbidity’ (nephelometric method) were analyzed in triplicate before and after the treatments. The analyses of NH4, NO2, NH3, PO4, K, At, COD, and bacteriological E. coli were analyzed according to the procedures of the ‘Standard Methods for the Examination of Water and Wastewater’ (APHA, AWWA, WEF 2023).

The water collection schedule consisted of operating the reactor for 6 h daily, configured in series. Initially, water collection occurred every 30 min of operation at a flow rate of 0.5 L/min, considering the operation of a single reactor with mixed particle size (1.0, 2.0, and 5.0 mm). Subsequently, experiments were conducted at 15-min intervals over 3 h, maintaining the same flow rate. The results of the physicochemical and microbiological analyzes of water were used to calculate the initial and final removal rates, providing the basis for constructing the graphs.

Through the statistical analysis method, it was possible to observe significant differences in the removal of parameters: color, turbidity, COD, and E. coli, in addition to the total phosphorus, sodium, and potassium parameters when the reactor was filled with mixed PS, varying the flow rate from 0.5 to 1.0 L/min, with collection every 15 and 10 minutes. This step was crucial to determine the average time needed to treat the wastewater supplied to the reactor and assess the need for cleaning the system. It is important to mention that, at the end of each experiment, tap water was added to the reactor to wash the PS spheres and, when necessary, NaOH was added to adjust the amount of organic matter, while observing the culture medium and checking if it was not possible to count and control the pH, which was obtained with drastic variations from 6.5 to 8.0, not being constant or with a minimal difference. In the end, 18 experiments were carried out.

The evaluation of the efficiency in removing or reducing specific parameters, such as E. coli, is extremely important in this research. Such indicators play a fundamental role in certifying the suitability of the proposed system in relation to the quality required for reuse in the agricultural context.

In the first stage, the experiment was carried out to characterize the PS spheres according to granulometry in function of the time and volume of operation. For this, the removal rate of the physicochemical and bacteriological parameters was verified. As shown in Figure 6, turbidity removal rates exceeded 80% in all volumes (150, 180, and 250 mL). However, when analyzing nitrate and color, we only obtained values above 50% in volumes of 180 and 250 mL. For EC, only volumes of 250 mL were able to remove color, and EC and nitrate exceed values above 50%.
Figure 6

Removal rate under volumes of 150, 180, and 250 mL.

Figure 6

Removal rate under volumes of 150, 180, and 250 mL.

Close modal
A relevant fact is that the decrease in E. coli in the volumes studied only occurred in the volume of 250 mL, which managed to reduce by 30%, a value that should be disregarded given that it does not meet the standards required by CONAMA. Influence evidenced by the amount of PS mass, due to the greater aggregation and proximity between them, as they have a number of spheres of mixed diameter, the greater their compaction, resulting in greater percolation of water between the PS pearls. In the first phase, four experiments were carried out for 360 minutes at a flow rate of 0.5 L/min, with collection carried out every 30 minutes to study the removal rate of physical and chemical parameters and the elimination rate of contaminants present in the aqueous medium. Figures 712 show the values of turbidity, nitrate, nitrite, ammonia, DQO, and E. coli for each experiment.
Figure 7

Variation of feed water turbidity, permeate, and removal rate for four experiments carried out over 360 min containing 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Figure 7

Variation of feed water turbidity, permeate, and removal rate for four experiments carried out over 360 min containing 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Close modal
Figure 8

Variation of ammonia in feed water, permeate, and removal rate for four experiments carried out for 360 min containing 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Figure 8

Variation of ammonia in feed water, permeate, and removal rate for four experiments carried out for 360 min containing 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Close modal
Figure 9

Variation of feed water nitrite, permeate, and removal rate for four experiments carried out for 360 min containing 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Figure 9

Variation of feed water nitrite, permeate, and removal rate for four experiments carried out for 360 min containing 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Close modal
Figure 10

Variation of feed water nitrate, permeate, and removal rate for four experiments carried out for 360 min containing 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Figure 10

Variation of feed water nitrate, permeate, and removal rate for four experiments carried out for 360 min containing 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Close modal
Figure 11

Variation in DQO of feed water, permeate, and removal rate for four experiments carried out for 360 min containing 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Figure 11

Variation in DQO of feed water, permeate, and removal rate for four experiments carried out for 360 min containing 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Close modal
Figure 12

Variation of E. coli in feed water, permeate, and removal rate for four experiments carried out for 360 min containing 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Figure 12

Variation of E. coli in feed water, permeate, and removal rate for four experiments carried out for 360 min containing 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Close modal
Under the aforementioned operating conditions, the effectiveness of the treatment process in reducing parameters such as E. coli, turbidity, ammonia, nitrate, nitrite, and DQO was evident, with consistent removals of approximately 50–56%. These results indicate an improvement in water transparency and a reduction in the load of organic and nitrogenous compounds, essential for human health and aquatic ecosystems. However, the increased residence time in the PS mixed bed had a negative impact on treatment performance, resulting in less organic matter removal. This was due to the tendency for the size of PS particles to increase, leading to saturation of the filter bed, decreased porosity, and filtration effectiveness, in addition to particle wear and obstruction by biofilms, compromising the efficiency of the process. The variation in pH and EC in relation to the time of 360 min with a flow rate of 0.5 L/min was observed in Figure 13, highlighting the importance of monitoring these parameters during the treatment process.
Figure 13

Variation in pH and EC removal rate for four experiments carried out for 360 min with tap water contaminated with 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Figure 13

Variation in pH and EC removal rate for four experiments carried out for 360 min with tap water contaminated with 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Close modal
Treatment processes, whether chemical or biological, have a direct impact on the chemical composition of the water, as indicated by the maximum removal percentages of 35% for EC and 45% for pH. Chemical reactions such as ion precipitation and acid neutralization play a significant role, affecting both conductivity and ionic balance. Variations in temperature not only influence the solubility of compounds but can also modulate microbial activity in biological processes. The graph in Figure 14 illustrates the removal rate over time, highlighting the initial, intermediate, and final moments of the treatment process.
Figure 14

Color variation in removal rate for four experiments carried out for 360 min with tap water contaminated with 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Figure 14

Color variation in removal rate for four experiments carried out for 360 min with tap water contaminated with 10 L of wastewater for a volume of 250 L under a flow rate of 0.5 L/min.

Close modal

The initial color reduction by 30% followed by a decrease to 40% within 160 min and finally reaching 100% after wastewater treatment using PS as a filter bed can be attributed to several operational mechanisms and characteristics of the material used. The adsorption of chromophoric substances stands out as a primordial process, where PS acts as an adsorbent, efficiently retaining components responsible for the color in the water. In addition, physical filtration processes remove particles and suspended organic matter that contribute to water color. The chemical interaction between PS and organic compounds in water leads to the removal or transformation of these substances, contributing to the decrease in color. Treatment efficiency, subject to variations over time due to saturation of the filter bed and changes in operating conditions, directly influences color reduction. The selective adsorption of PS by specific dyes or organic substances explains the initial 30% decrease, while the gradual wear of the material increases its adsorption capacity over time, contributing to a more pronounced reduction in color during treatment. These combined mechanisms illustrate the effectiveness of PS as a filter bed in removing color from wastewater, highlighting the complexity of the processes involved.

In the second phase, seven experiments were carried out with a flow rate of 0.5 L/min for 180 min, evaluating the removal of organic matter and the reduction of physicochemical parameters, including total phosphorus. E. coli inactivation and turbidity reduction achieved a maximum removal rate of 75% in 180 min. PS acts as an adsorbent and filter bed, contributing to the efficient removal of particles and microorganisms, in addition to chemically interacting with contaminants. The maximum removal rate of 70% for ammonia, nitrate, nitrite, DQO, and total phosphorus highlights the effectiveness of PS. Color removal was 41% initially, reaching 100% in 90 min, demonstrating the effectiveness of PS with optimized residence time.

With a flow rate of 1.0 L/min, E. coli inactivation reached 98.32% in 180 minutes, highlighting the efficiency of PS in a shorter time. Potassium and sodium removal reached 70%, demonstrating the viability of the system for wastewater treatment. Conductivity and pH removal reached significant rates of 66 and 30%, respectively, suggesting a remarkable ability to reduce conductivity and adjust pH. Color removal reached 100% in 90 minutes, showing sensitivity to operating conditions and the need to adjust the flow rate. These results highlight the effectiveness of PS in the treatment of wastewater, highlighting the importance of continuous monitoring of the system.

For all experiments carried out and described above, the values are shown in Figures 1519.
Figure 15

Nephelometric turbidity unit (NTU) and pH removal rate for all analyzes.

Figure 15

Nephelometric turbidity unit (NTU) and pH removal rate for all analyzes.

Close modal
Figure 16

mgPt/L and pH removal rate for all analyzes.

Figure 16

mgPt/L and pH removal rate for all analyzes.

Close modal
Figure 17

NH4, NO2, and NO3 removal rate for all analyzes.

Figure 17

NH4, NO2, and NO3 removal rate for all analyzes.

Close modal
Figure 18

DQO, PO4, K, and NA+ removal rate for all analyzes.

Figure 18

DQO, PO4, K, and NA+ removal rate for all analyzes.

Close modal
Figure 19

UFC/mL removal rate for all analyzes.

Figure 19

UFC/mL removal rate for all analyzes.

Close modal

The spherical geometry of PS plays a crucial role in the effectiveness of the backwashing process. As noted by Schöntag (2015), light particles such as PS require lower speeds during backwashing. Furthermore, it is highlighted that PS has the ability to recover more quickly after cleaning compared to sand filters. This contrasts with sand, which requires more time for the development of the microbial consortium, thus limiting the efficiency of the system. These attributes highlight the advantage of spherical PS in optimizing the cleaning process and more effectively restoring the filtering medium, contributing to the overall efficiency of the filtration system. The backwash water is sent to a storage tank to be treated before being discarded into the environment.

Adsorption technologies, based on the accumulation of phosphorus at the interface between two phases (contaminated water and solid adsorbent), are a possibility for removal of this parameter (Ali et al. 2012). This adsorption can occur from the interactions of universal Van der Waals or by the chemical bonds between the adsorbent molecule and the adsorbed pollutant (Dabrowski 2001).

The conclusions of this work were as follows:

The use of a mixture of PS spheres of different diameters showed quite acceptable impurity removal.

The synergy of size and properties of mixed spheres, which encompass a wider distribution of sizes and physical characteristics, facilitates the capture of varied particles, resulting in improved overall efficiency. Furthermore, complementarity in filtration, chemical and physical interactions between spheres of different compositions, more effective clogging resistance, the ability to adapt to variations in water characteristics, and optimization in dynamic filtration processes contribute to the superior effectiveness of mixed PS spheres.

The analysis of the experimental planning highlighted that the configuration with a flow rate of 0.1 L/min for a time of 180 min obtained an evident performance compared to 360 min, demonstrating a reduction of up to 98% in E. coli and 70% in the values of turbidity, color, COD, E. coli and ammonia, potassium, sodium, and total phosphorus.

The system backwashing process proved to be essential to maintain the quality of the permeate. The PS spheres, after tests and results, demonstrated to be effective as a filtering element for the treatment of effluents intended for agricultural reuse, presenting good resistance to aging, and the system met the standards established for Classes 2 and 3 of CONAMA in relation to pH, turbidity, nitrate, and E. coli, allowing reuse in various applications, from irrigating green areas to washing vehicles. In this way, the wastewater treatment system studied demonstrates the potential to transform environmental pollutants into economic resources, presenting itself as a sanitary safe, economically viable, and environmentally sustainable solution.

The water used to clean the PS spheres was stored in tanks to be treated before being released into the environment.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.

ABIQUIM (São Paulo)
2020
What is EPS?
Available from: http://www.epsbrasil.eco.br/eps/index.html (accessed 12 February 2024)
.
Ali
I.
,
Yeah
O.
&
Khan
T. A.
2012
Low cost adsorbents for the removal of organic pollutants from wastewater
.
Journal of Environmental Management
130
,
170
183
.
Alnaqbi
M. A.
,
Greish
Y. E.
,
Moshin
M. A.
,
Elumalai
E. J.
&
Blooshi
A. A.
2016
Morphological variations of micro-nanofibrous sorbents prepared by electrospinning and their effects on the sorption of crude oil
.
Journal of Environmental Chemical Engineering
4
(
2
),
1850
1861
.
American Public Health Association
, American Water Works Association, Water Environment Federation 2023 Standard Methods for the Examination of Water and Wastewater, 24th ed. APHA Press, Washington, D.C.
ANA – National Water Agency
2019
SDG 6 in Brazil: ANA's View of the Indicators
.
ANA
,
Brasília
.
Andrade
L. R. S.
,
Araújo
S. M. S.
&
France
K. B.
2021
Alternative Wastewater Treatment System Intended for Agricultural Reuse. 151f
.
Thesis (Doctorate in Natural Resources)
,
Postgraduate Program in Natural Resources, Center for Technology and Natural Resources, Federal University of Campina Grande
,
Paraíba, Brazil
.
Castro
C. N.
2022
Água, Problemas Complexos E O Plano Nacional de Segurança Hídrica
.
Ipea
,
Rio de Janeiro
.
Dabrowski
A.
2001
Adsorption – From theory to practice
.
Advances in Colloid and Interface Science
93
,
135
224
.
Khatibi
S.
&
Arjjumend
H.
2019
Water crisis in making in Iran
.
Grassroots Journal of Natural Resources
2
(
3
),
45
54
.
Reis
M. M.
2020
Impacts of Heavy Metals Present in Water and Treated Sewage Used for Irrigation of an Area Located in the Vieira River Basin and in a Millet (Pennisetum Glaucum) Cultivation System
.
Doctoral thesis
,
Faculty of Agricultural Engineering at the State University of Campinas
,
Campinas
.
Schöntag
J. M.
2015
Esferas de Poliestireno Como Elemento Filtrante em Filtração Rápida Descendente
.
Tese de Doutorado
,
Universidade Federal de Santa Catarina, Centro de Tecnológico, Programa de Pós-Graduação em Engenharia Ambiental
, p.
280
.
Sikhwivhilu
V. S.
et al
2011
Polystyrene functionalized with hexacyanoferrate(II) as a selective adsorbent for cesium ions
.
Journal of Hazardous Materials
186
(
2–3
),
1522
1529
.
UN
2021
Access to a healthy environment is declared a human right. UN News Perspective – Global Reportagens Humanas, [S. l.], p. 1. Available from: https://news.un.org/pt/story/2021/10/1766002 (accessed 8 September 2023)
.
UN-WATER
2018
The United Nations World Water Development Report 2018: Nature-Based Solutions for Water
.
UNESCO
,
Paris
.
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