Wastewater Management in Swimming Pools: A Circular Economy Approach

Abstract

Water is a vital resource for sustaining life; however, it is increasingly at risk due to escalating demand and heightened pollution levels. Swimming pool facilities generate diverse wastewater streams whose management offers opportunities for water recovery within a circular economy framework. The quantitative and qualitative analysis of research identifies five primary categories of wastewater: swimming pool basin outflow, filter washings, rainwater and meltwater, sanitary wastewater, and technological sludge, at a public swimming pool complex in Poland. Annual volumes were determined through direct measurements and calculations: pool basin outflow—2829.7 m³/year; filter washings—7179.2 m³/year; rainwater and meltwater—1172.6 m³/year; sanitary wastewater—5849.3 m³/year; and technological sludge—90.1 m³/year. Laboratory testing included physicochemical parameters (pH, redox potential, conductivity, COD, BOD, nutrients, heavy metals) and microbiological parameters (Escherichia coli, Pseudomonas aeruginosa, Legionella spp., Salmonella spp., Ascaris sp., Trichuris sp., Toxocara sp., Coagulase-positive Staphylococcus). The results showed that the filter washings, despite exceeding the limits for total suspended solids and combined chlorine, exhibited stable quality and significant volume, making them the most promising candidate for reuse after treatment. Rainwater quality was compromised by elevated heavy metal concentrations (Zn: 244.67 mg/L, Pb: 92.33 mg/L), while technological sludge exceeded the legal pollutant thresholds, classifying it as hazardous waste. The experimental conditions included year-round monitoring of operational flows, standardised backwash cycles every three days, and sampling under routine operational load. The findings support the development of targeted treatment systems that allow the recirculation of up to 7000 m³/year of water, thus reducing the demand for potable water and operational costs in swimming pool facilities.

1. Introduction

Water, essential for all life, is increasingly scarce due to pollution and increasing demand. Much of the water used in economic activities becomes wastewater, which, if not treated, contaminates the soil and water bodies, accelerating resource degradation. Effective wastewater treatment and sustainable management are crucial for socioeconomic growth and environmental protection [1,2,3,4,5]. Swimming pools generate large amounts of wastewater; with proper technologies, this water can be treated and reused within facilities, including for sanitation or irrigation [6,7,8,9].

Similar approaches to sustainable water management, including stormwater reuse, have been studied in various European and non-European contexts, demonstrating both technical feasibility and regulatory and social acceptability [10]. These studies provide valuable information on how reclaimed water, including stormwater, can be integrated into urban systems while ensuring compliance with environmental and sanitary standards, as well as contributing to reducing the water crisis in urban centers. Initiatives focused on water reuse in Europe and globally consider technical, regulatory, environmental, and public health factors. The EU Directive (EU) 2024/3019, Recast Urban Wastewater Treatment Directive, strengthens wastewater treatment requirements by introducing binding targets for energy efficiency and sanitary monitoring while promoting circular economy measures [11]. This aligns with the Water Framework Directive 2000/60/EC [5]. Globally, the WHO/UNEP Guidelines for the Safe Use of Wastewater, Excreta, and Greywater establish health-based targets and recommend multibarrier risk management strategies for various applications, including recreational waters [12]. Frameworks such as the US National Pollutant Discharge Elimination System (NPDES) [13] and the Australian Guidelines for Onsite Wastewater Management [14] serve as important references for aligning national practices with internationally recognised benchmarks for safe and sustainable water reuse.

The wastewater streams have been categorised according to their origin and physicochemical composition with corresponding water reuse possibilities, as illustrated in Figure 1. The analysis identifies five primary types of wastewater:

• Outflow from the pool basin—this category encompasses wastewater that is discharged during the comprehensive drainage of the pool, which typically occurs once or several times annually, depending on the specific category of the pool; this category also includes the water that users splash onto, which subsequently enters the wastewater system through inlets that are placed on the pool deck.
• Filter washings—this type of wastewater is produced by the cleaning processes applied to the filter beds utilised in the swimming pool water treatment systems.
• Rainwater and meltwater—this category refers to water derived from the drainage of rooftops and impervious surfaces associated with the facility.
• Sanitary wastewater—generated from the usage of sanitary facilities, showers, changing rooms, staff quarters, and technical rooms.
• Technological sludge—produced through the sedimentation process and collected in designated sludge tanks.

This paper presents a detailed analysis of the primary wastewater streams generated within the facility and classifies the streams’ quantity and quality. The evaluation covers management strategies for each stream, including discharge into the municipal system and alternative disposal methods, such as release into water bodies and ground infiltration. Analysing physicochemical parameters assesses the potential for reusing specific streams and informs recommendations for required treatment technologies. The analysis also considers the economic feasibility of water treatment investments, anticipated quality of treated wastewater, and operational costs.

A significant finding is the wastewater stream from the filter backwashing processes, notable for its substantial and consistent volume throughout the year [15,16,17]. These characteristics enable the design of purification systems for direct recirculation into the technological cycle, reducing the need for large retention tanks and minimising risks of stagnation, putrefaction, and secondary microbial contamination.

The paper addresses rainwater contamination, particularly by heavy metals, underscoring the need to reassess roof water collection systems and explore source-level filtration [18]. More comparative studies are essential to assess the quality of water collected directly from atmospheric precipitation against that which has interacted with roof surfaces. Moreover, technological sludge produced during purification processes has been classified as problematic waste due to high pollutant load, biological instability, and limited reuse potential under current conditions [19,20,21,22].

Overall, the analyses define major wastewater sources, highlight optimisation opportunities, and provide guidance for sustainable water and wastewater management in line with technical, economic, and regulatory considerations [8,23,24].

2. Characteristics of the Facility

The facility analysed is a three-story building, including an underground level, designed as a single free-standing structure located in the western part of the investment site. The main entrance is located on the northern façade, and the building is located in the Lower Silesian Voivodeship, Poland.

The functional and utility program of the facility includes the following:

• A main lobby that serves as the representative entrance area.
• A swimming hall featuring four reinforced concrete pool basins:
  • SP—a sports pool measuring 25.00 × 14.25 m, equipped with seven swimming lanes.
  • RP—a training pool for swimming lessons with a water surface area of 75.00 m² and dimensions of 10.00 × 7.50 m, and a children’s wading pool with water attractions, covering a surface area of 21.21 m².
  • WT—a whirlpool tube, accommodating up to 12 persons.

In addition, an outdoor seasonal pool (OP) is located outside the building, intended for use during the summer months, and is accompanied by a large recreational area. The first floor has a fitness and gym zone, complete with associated changing rooms and sanitary facilities. A sauna area has also been designated, featuring its own sanitary facilities. The underground level houses the technical zone, which contains all technical installations and sanitary facilities for the service personnel. The boiler room is located on the rooftop of the building.

The list of swimming pools, their surface area, and volume is shown in

Table 1. List of surface area, volume of swimming pool basins, and deck area.

Parameter (Unit)	I (SP)	II (RP)	III (WT)	IV (OP)
Basin area (m2)	362.5	96.21	3.3	500.0
Basin volume (m3)	580.0	73.5	2.6	575.0
Pool deck area (m2)	571.75			1098.3

.

Table 2. Technical parameters of pool filtration systems.

Parameter (Unit)	I (SP)	II (RP)	III (WT)	IV (OP)
Filter dimensions (mm)	Ø2000	Ø2000	Ø1600	Ø2600
Number of filters (pcs)	2	1	1	2
Filtration area * (m2)	3.14	3.14	2.00	5.31
Total filtration area (m2)	6.28	3.14	2.00	10.61

* Assumed for one filter.

presents the technical parameters of the filters used in the swimming pool facility analysed in this investigation.

The subject building is designed with a flat roof that incorporates the Geberit Pluvia^® vacuum water collection system. This advanced system effectively collects precipitation from the roof surface and directs it to a rainwater tank located in the basement. From this tank, the collected water is subsequently pumped to either a water recovery station or an external retention tank. In addition, the building is equipped with an emergency discharge system that manages excess water during periods of heavy rainfall, directing it outside the boundaries of the building. The characteristics of the roof, including its surface area and rainwater drainage methods, are presented in

Table 3. Characteristic parameters of the roof.

Parameter (Unit)	Value
Roof surface (m2)	1675.2
Number of rainwater inlets (pcs)	10
Number of emergency rainwater inlets (pcs)	10
Roof waterproofing material	EPDM roofing membrane

.

The water used for the filter backwashing, along with the rainwater collected in the sludge tank, is directed to the water recovery station. This water is retained within the sedimentation tank, where, through the decantation process, the supernatant liquid above the settled sediment is transferred to the water recovery station. The sludge accumulated in the sludge tank is removed twice a year by a specialised septic tanker. The characteristics of the sludge tanks are shown in

Table 4. The amount of water discharged into the wastewater system from the pool basin.

Parameter (Unit)	Flushing Tank 1	Flushing Tank 2
Dimensions (m)	7.49 × 6.34	7.49 × 6.32
Area (m2)	47.49	47.35
Active volume—max (m3)	75.98	75.76

.

3. Materials and Methods

The presented study investigates the quantitative and qualitative characteristics of wastewater discharged/released from a swimming pool facility. The scope of this research encompasses both quantitative analyses, which facilitate the determination of the volume of each wastewater stream, and qualitative analyses, which involve the assessment of physicochemical parameters and the testing for pathogenic microorganisms and parasite eggs. Comprehensive results will be provided in subsequent sections of the study.

3.1. Quantitative Analysis of Wastewater Streams

The quantitative analysis of wastewater streams was designed to determine the volume of various types of wastewater generated by the facility. The scope of the analysis included both theoretical calculations and empirical data obtained from water meters installed in the building, which record water consumption.

3.1.1. Outflow from the Swimming Pool Basin

In this study, a quantitative analysis was conducted to assess the volume of wastewater discharged from the swimming pool basin, using the methodology outlined by Mika-Shalyha et al. [25]. This approach establishes that the volume of wastewater routed to the sanitary wastewater system is determined by the volume of the product of the swimming pool basin and the frequency of water exchange, as stipulated by the relevant operating guidelines. The sport pool (SP) is expected to be drained once a year, while the recreational pool (RP) will be drained twice a year. The whirlpool tube (WT) will be drained monthly and the outdoor pool (OP) will also be drained annually. The volume of wastewater discharged through the inlets located on the deck of the swimming pool is generated by the splashing of water from the users. This estimate was derived from expression (6) provided in the aforementioned publication [25].

3.1.2. Filter Washings

To ensure optimal water quality, it is imperative to rinse the filters on a regular basis. This procedure mitigates excessive contamination and helps preserve the integrity of pool water. The frequency of filter backwashing should be determined by the level of contamination in the filter bed. However, it is recommended to perform this task a minimum of two times a week, according to the German DIN 19643 standard [26]. This allows for an accurate estimation of the volume of water used for filter rinsing, which may either be directed to the wastewater system or be repurposed. The volume of wastewater discharged into the wastewater system in the form of filter washings was estimated based on Formula (1), which was analysed in detail by Mika-Shalyha et al. [25].

3.1.3. Rainwater and Meltwater

The maximum value Qr_max (Formula (1) for this system was calculated using a probabilistic model based on maximum rainfall data for Wrocław, with observations spanning from 1960 to 2009. For a rainfall duration of 15 min, with a recurrence frequency of five years, the model estimates a rainfall intensity of 181.7 L/s∙ha, consistent with the guidelines established by the Municipal Water and Sewage Company in Wrocław [27].

Qr_max = q_max∙ψ_s∙F_r

(1)

where

• q_max—maximum unit rainfall intensity for a duration equal to the flow time in the channel, with a frequency of occurrence “C”, L/s·ha (frequency assumed C = 5 years)
• ψ_s—peak maximum coefficient of rainwater runoff (from the roof surface assumed ψ_s = 1.0)
• F_r—rainwater catchment area, ha

The average number of rainy days per year and the average rainfall in the city of Wrocław were assumed to estimate the annual volume of rainfall collected from the roof surface into the capturing tank. These data were obtained from meteorological records provided by the Institute of Meteorology and Water Management (IMGW) [28].

3.1.4. Sanitary Wastewater

The volume of domestic and utility wastewater was measured using the water meter that serves the facility, with the data recorded by the Building Management System (BMS) through the MBUS communication interface. Furthermore, according to normative requirements, the amount of wastewater for the facility was tracked to assess any discrepancies between the calculated values and the actual measurements obtained for the analysed facility.

The flow rate of wastewater (Q_ww) within the domestic and utility wastewater system was determined using the following Formula (2):

Q_ww = K √(∑DU)

(2)

where

• K—characteristic runoff, depending on the purpose of the building, K = 0.7 (-)
• DU—drainage unit (L/s)

Table 5. List of sanitary facility equipment.

Sanitary Equipment	Quantity (pcs)	DU (L/s)	∑DU (L/s)
Washbasin	25	0.5	12.5
Urinal	4	0.5	2
Sink	6	0.8	4.8
Toilet	15	2	30
Shower	35	0.8	28
External shower	16	0.8	12.8
Eyewash	1	2	2
Floor gully DN50	24	0.8	19.2
Floor gully DN100	2	2	4

presents the assumptions for the sanitary wastewater system, calculated in accordance with [29].

3.1.5. Technological Sludge

The quantitative analysis of technological sludge encompassed actual measurements collected over a designated period, beginning with the initiation of the facility’s operations in 2022 and concluding at the end of 2024, during its exploitation phase. These measurements were averaged annually, allowing the identification of representative values that accurately reflect the long-term operational cycle of the facility.

3.2. Qualitative Analysis of Wastewater Samples—Laboratory Testing

The qualitative analysis of the specified wastewater streams encompassed comprehensive laboratory evaluations of selected physicochemical and microbiological parameters. The tests provided a foundation for the evaluation of the environmental status of wastewater and allowed a comparison with the applicable legal standards and requirements established by regulatory authorities.

Table 6. Methodology for analytical determination of selected indicators of biological and physicochemical contamination of wastewater.

Parameter	Unit	Method	Measurement Uncertainty	Detection Limit (LOD)
Bacteriological parameters
Escherichia coli	CFU/100 mL	PN-EN ISO 9308-1:2014-12 [30]	±30% (10–200 CFU/100 mL) or ±1–5 CFU for low counts	1 CFU/100 mL
Pseudomonas aeruginosa	CFU/100 mL	PN-EN ISO 16266:2009 [31]	±30% (10–200 CFU/100 mL) or ±1–5 CFU for low counts	1 CFU/100 mL
Total number of microorganisms at 36 ± 2 °C after 48 h	CFU/1 mL	PN-EN ISO 6222:2004 [32]	±0.1 log (≈±25%)	1 CFU/mL
Coagulase-positive Staphylococcus	CFU/100 mL	PB/BB/11/A:04.07.2011 [33]	±30% (10–200 CFU/100 mL) or ±1–5 CFU for low counts	1 CFU/100 mL
Legionella sp.	CFU/100 mL	PN-EN ISO 11731:2017-08 [34]	±0.2 log (≈±50%) for low counts	1 CFU/100 mL
Salmonella spp.	CFU/100 g w.m.s *	PN-EN ISO 6579-1:2017-04 [35]	qualitative (presence/absence)	1 CFU/1000 mL
Number of live eggs of intestinal parasites: Ascaris sp., Trichuris sp., Toxocara sp.	pcs/1 kg d.m.s **	PB/BB/8/C:23.06.2014 [36]	±1 egg	1 egg/100 mL
Physicochemical parameters
Redox potential (oxidation–reduction) at electrode Ag/AgCl 3.5 m KCl	mV	PB-13, Edition 1, dated 07 May 2018 [37]	±5 mV	1 mV
Hydrogen ion concentration (pH)	-	PN-EN ISO 10523:2012 [38]	±0.1	0.01
Conductivity	μS/cm	PN-EN 27888:1999 [39]	±2%	1 μS/cm
Chlorides	mg Cl−/L	PN-ISO 10304-1:2009 [40]	±5%	0.5 mg/L
Free chlorine	mg Cl2/L	PN-EN ISO 7393-2:2018-08 [41]	±0.02 mg/L	0.01 mg/L
Combined chlorine	mg Cl2/L	PN-EN ISO 7393-2:2018-08 [41]	±0.02 mg/L	0.01 mg/L
Chemical oxygen demand (COD)	mg O2/L	PN-ISO 6060:2006 [42]	±5%	3 mg/L
Biological oxygen demand (BOD)	mg O2/L	PN-EN 1899-1:2002 [43]	±5%	2 mg/L
Nitrate nitrogen	mg N-NO3/L	PN-EN ISO 13395:2001 [44]	±5%	0.1 mg/L
Ammonium nitrogen	mg N-NH4/L	PN-ISO 7150-1:2002 [45]	±5%	0.02 mg/L
Total nitrogen	mg Ntot./L	PN-EN 12260:2003 [46]	±5%	0.5 mg/L
Total phosphorus	mg Ptot./L	PN-EN ISO 6878:2006 [47]	±5%	0.01 mg/L
Total organic carbon (TOC)	mg C/L	PN-EN 1484:1998 [48]	±5%	0.5 mg/L
Inorganic carbon (IC)	mg C/L	PN-EN 1484:1998 [48]	±5%	0.5 mg/L
Total carbon (TC)	mg C/L	PN-EN 1484:1998 [48]	±5%	0.5 mg/L
Turbidity	NTU	PN-EN ISO 7027-1:2016-09 [49]	±0.1 NTU	0.01 NTU
Total suspended solids (TSS)	mg/L	PN-EN 872:2007 [50]	±5%	2 mg/L
Sulphureous	mg SO4−2/L	PN-EN ISO 10304-1:2009 [51]	±5%	0.5 mg/L
Sulphides	mg S/L	PN-82/C-04566.02 [52]	±5%	0.05 mg/L
Aluminum	mg Al/L	PN-EN ISO 11885:2009 [53]	±0.01 mg/L	0.005 mg/L
Color, wavelength 436 nm	-	PN-ISO 7887:2013 [54]	±5%	1 mg Pt/L
Ammonium ion	mg NH+/L	PN-EN ISO 11732:2007 [55]	±5%	0.02 mg/L
Iron	mg Fe/L	PN-ISO 6332:2001 [56]	±0.02 mg/L	0.005 mg/L
Copper	mg Cu/L	PN-EN ISO 11885:2009 [53]	±0.01 mg/L	0.005 mg/L
Zinc	mg Zn/L	PN-EN ISO 11885:2009 [53]	±0.01 mg/L	0.005 mg/L
Lead	mg Pb/L	PN-EN ISO 11885:2009 [53]	±0.005 mg/L	0.001 mg/L
Nickel	mg Ni/L	PN-EN ISO 11885:2009 [53]	±0.005 mg/L	0.001 mg/L
Phenol (phenol index)	mg C6H5OH/L	PN-EN ISO 11885:2009 [53]	±0.01 mg/L	0.002 mg/L
Oxidisability	mg O2/L	PN-EN 25813:2004 [57]	±5%	0.5 mg/L

* w.m.s—wet mass of the sample; ** d.m.s—dry matter substance.

presents the methodology for the analytical determination of selected indicators of biological and physicochemical contamination of wastewater. Microbiological analyses were performed under accredited laboratory conditions, following the ISO and PN-EN standards [30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57] listed in Table 6. The water samples were collected in sterile polypropylene containers, transported at 4 ± 2 °C, and analysed within 24 h. The membrane filtration method was used to detect Escherichia coli, Pseudomonas aeruginosa, Legionella spp., and coagulase-positive Staphylococci. A specified volume of the sample was filtered through sterile 0.45 µm membrane filters. The membranes were aseptically transferred to selective agar media: m-Endo agar for E. coli, Cetrimide agar for P. aeruginosa, GVPC agar for Legionella spp., and Baird–Parker agar supplemented with egg yolk tellurite for Staphylococcus spp. Incubation was carried out according to standards (e.g., 36 ± 2 °C for 24–48 h for E. coli and P. aeruginosa, up to 10 days for Legionella spp.). Colony-forming units (CFUs) were counted and expressed as CFU per 100 mL of sample. To determine total microbial count at 36 ± 2 °C after 48 h and detect Salmonella spp. and intestinal parasite eggs (Ascaris sp., Trichuris sp., Toxocara sp.), direct inoculation onto solid media was employed in accordance with ISO standards and PB methods. Physicochemical analyses, including pH, redox potential, electrical conductivity, nutrients, heavy metals, chemical oxygen demand (COD), biochemical oxygen demand (BOD), total organic carbon (TOC), and turbidity, were performed in triplicate, utilising reference standards and control samples to ensure accuracy.

3.2.1. Range of Analytical Determinations for the Outflow from the Swimming Pool Basin

The Decree issued by the Health Minister on 10 May 2022 [58], establishes the requirements that swimming pool water must meet, necessitating a thorough analysis of water samples with respect to both microbiological and physicochemical parameters.

Within the scope of the microbiological assessment, the analysis focused on the detection of specific indicator organisms, including Escherichia coli, Pseudomonas aeruginosa, and bacteria belonging to the Legionella genus. Additionally, the total number of microorganisms cultivated at a temperature of 36 ± 2 °C and coagulase-positive Staphylococcus was determined.

The physicochemical analysis consisted of measurements of various parameters, including oxidation–reduction potential (redox), pH value, concentrations of free and total chlorine, nitrate concentration, and turbidity. In addition, assessments were conducted to determine the concentration of total organic carbon (TOC), inorganic carbon (IC), and total carbon (TC).

3.2.2. Range of Analytical Determinations for the Filter Washings

At the end of the backwashing process of the pressure filter operating in the feed water circuit of the recreational pool, samples of the washings were taken from the overflow trough. The purpose of the analysis of the collected washing samples was to determine their degree of contamination and to compare them with the regulations defining wastewater conditions for the discharge into the collective sewerage system [59] and into surface water or the soil [60,61].

The analysis focused on several parameters that, according to the researchers’ hypothesis, may be present in the washings resulting from the operation of filtration systems within the technological circuits of the swimming pool. The parameters assessed included oxidation–reduction potential (redox potential), pH, electrolytic conductivity, concentration of chloride ions, free and total chlorine, chemical oxygen demand (COD), biochemical oxygen demand (BOD), total nitrogen and phosphorus, total organic carbon (TOC), inorganic carbon (IC), total carbon (TC), turbidity (measured before and after the coagulation process), concentration of total suspended solids (TSS), sulphates, aluminium, ammonium ions, as well as colour measured at a wavelength of 436 nm and oxidisability.

3.2.3. Range of Analytical Determinations for the Rainwater and Meltwater

Rainwater collected from roof surfaces can contain various contaminants, including heavy metals, which can originate from atmospheric deposition and roofing materials. Samples were collected from a surge tank utilised for the storage of rainwater for subsequent analysis.

This study involved the examination of several physicochemical parameters, including oxidation–reduction potential (redox potential), pH, specific electrolytic conductivity, free and total chlorine concentrations, chemical oxygen demand (COD), biochemical oxygen demand (BOD), total nitrogen and phosphorus content, as well as total organic carbon (TOC), inorganic carbon (IC), and total carbon (TC).

Furthermore, measurements were conducted to assess turbidity (both before and following the application of a coagulant), the concentration of total suspended solids (TSS), the presence of sulphur compounds, and the levels of aluminium, ammonium ions, and heavy metals, namely iron (Fe), copper (Cu), zinc (Zn), and lead (Pb). The colour of the water was measured at a wavelength of 436 nm, in addition to assessing its oxidation potential.

3.2.4. Range of Analytical Determinations for the Sanitary Wastewater

Microbiological and physicochemical analyses were performed on municipal sanitary wastewater samples collected from the pump station. The bacteriological evaluation identified Salmonella spp. and live eggs of intestinal parasites, including Ascaris sp., Trichuris sp., and Toxocara sp.

The physicochemical evaluations included measurements of the oxidation–reduction potential, pH, specific electrolytic conductivity, chloride ion concentration, and free and total chlorine levels. Additionally, chemical oxygen demand (COD), biochemical oxygen demand (BOD), total nitrogen and phosphorus, total organic carbon (TOC), inorganic carbon (IC), and total carbon (TC) were measured.

Turbidity was assessed before and after coagulant treatment, along with total suspended solids (TSS), sulphur compounds, and concentrations of aluminium, ammonium ions, and lead (Pb). The colour of wastewater was evaluated at 436 nm, and the oxidation–reduction potential was also determined.

3.2.5. Range of Analytical Determinations for the Technological Sludge

The technological sludge generated from the sedimentation process is removed twice a year. The primary objective of the tests was to evaluate the level of sediment contamination and to analyse the feasibility of discharge of this material into the wastewater system, surface waters, or the ground, according to the relevant regulations [59,60,61].

Microbiological analysis focused on detecting indicator microorganisms found in backwash water from swimming pool filters, including Escherichia coli, Pseudomonas aeruginosa, Legionella spp., coagulase-positive strains of Staphylococcus spp., and the total number of microorganisms cultivated at 36 ± 2 °C.

Physicochemical analysis included measuring oxidation–reduction potential (redox potential), pH, specific electrolytic conductivity, as well as concentrations of chloride ions, free chlorine, and total chlorine. Chemical oxygen demand (COD) and biochemical oxygen demand (BOD) were assessed in both the mixed sediment and supernatant water.

Further evaluations included concentrations of nitrate nitrogen, ammonium nitrogen, total nitrogen, and total phosphorus. Additionally, total organic carbon (TOC), inorganic carbon (IC), and total carbon (TC) were measured. The study also addressed turbidity before and after coagulant application, total suspended solids (TSS), sulphur compounds, sulphides, and the presence of metals such as aluminium, lead (Pb), and nickel (Ni).

4. Results

4.1. Quantitative Analysis of Wastewater Streams

4.1.1. Outflow from the Swimming Pool Basin

The volume of water generated during the process of emptying the basin and the resulting splashes is presented in

Table 7. The amount of water discharged into the wastewater system from the swimming pool basin.

Parameter (Unit)	I (SP)	II (RP)	III (WT)	IV (OP)
Water splashing (m3/d)	1.4	0.8	0.4	1.8
Water splashing (m3/year)	511.0	182.5	146.0	657.0
Volume of water in a basin (m3)	580.0	73.5	2.6	575.0
Total (m3/year)	1091.0	329.5	177.2	1232.0

.

4.1.2. Filter Washings

The filter backwashing is carried out according to a schedule every three days, which is 120 times a year. The volume of water used for this purpose is presented in

Table 8. The amount of water discharged into the wastewater system from the filter washing.

Parameter (Unit)	I (SP)	II (RP)	III (WT)	IV (OP)
Backwash water (m3) *	25.12	12.56	8.00	42.44
Backwash water (m3/year)	3014.4	1507.2	960.0	1697.6

* Backwash water for single rinse.

.

4.1.3. Rainwater and Meltwater

Table 9. The quantity of rainwater and meltwater collected from the roof surface.

Roof Surface	Runoff Coefficient	Reduced Surface	Quantity of Rainwater	Quantity of Rainwater
(m2)	(-)	(m2)	(L/s)	(m3/year)
1675.2	1.0	1675.2	30.4	1172.6

presents the annual volume of rainwater theoretically collectable from the roof surface. The calculation was carried out based on the specific design parameters of the rainfall in the city of Wrocław.

4.1.4. Sanitary Wastewater

Design flow for wastewater, calculated according to Formula (2), amounts to the following:

Q_ww = 0.7∙√116.5 = 7.5 (L/s),

Assuming about 8 h of use, this gives a value of 216.0 m³/d, 78,840 m³/year.

The value obtained from the water meter data, however, was 5849.28 m³/year. Figure 2 shows the monthly water consumption for domestic and commercial purposes for the facility.

4.1.5. Technological Sludge

The volume of sludge was estimated based on the geometry of the sedimentation tanks, taking into account their surface area and the measured height of the accumulated sludge layer. Tank emptying is performed twice a year as part of routine maintenance operations.

Table 10. The amount of technological sludge collected during the year.

Parameter (Unit)	Flushing Tank 1	Flushing Tank 2
Measured sludge height (m)	0.5	0.45
Sludge volume (m3) *	23.75	21.31
Sludge volume (m3/year)	47.50	42.62

* The amount of sludge per visit of the wastewater truck.

shows a summary of the technological sludge collected during the year.

4.2. Qualitative Analysis of Wastewater Samples—Laboratory Tests

Table 11. Physicochemical and microbiological characteristics of wastewater streams and compliance with regulatory limits.

Parameter	Unit	Water from the Pool Basin (RP)	Limit Value Journal of Laws 2022, Item 1230 [58]	Filter Washings	Rainwater	Sanitary Wastewater	Technological Sludge	Limit Value Journal of Laws 2016, Item 1757 [59]	Limit Value Journal of Laws 2014 Item 1800 [60]	Limit Value Journal of Laws 2019, Item 1311 [61]
Bacteriological parameters
Escherichia coli	CFU/100 mL	0	0	x	x	x	0	x	x	x
Pseudomonas aeruginosa	CFU/100 mL	0	0	x	x	x	0	x	x	x
Total number of microorganisms at 36 ± 2 °C after 48 h	CFU/1 mL	absence	20—in circulation 100—in the basin	x	x	x	>300	x	x	x
Coagulase positive	CFU/100 mL	0	0	x	x	x	0	x	x	x
Legionella sp.	CFU/100 mL	0	0	x	x	x	0	x	x	x
The presence of Salmonella spp.	CFU/100 g w.m.s **	x	x	x	x	not detected	x	x	x	x
Number of live eggs of intestinal parasites: Ascaris sp., Trichuris sp., Toxocara sp.	pcs/1 kg d.m.s ***	x	x	x	x	0	x	x	x	x
Physicochemical parameters
Redox potential (oxidation–reduction) at electrode Ag/AgCl 3.5 m KCl	mV	774.31	720–770	303.33	313	261.67	0.35	x	x	x
Hydrogen ion concentration (pH)	-	7.13	6.5–7.6	7.14	7.19	6.98	7.14	6.5–9.5	6.5–9	6.5–12.5
Conductivity	μS/cm	2280	x	1771	8297.6	1826.5	1427.5	x	x	x
Chlorides	mg Cl−/L	450	x	361	x	794	367	1000	1000	1000
Free chlorine	mg Cl2/L	0.38	0.3–2.0	0.07	0.01	0.01	absent	1	0.2	0.2
Combined chlorine	mg Cl2/L	0.18	0.2—in circulation 0.3—in the basin	0.52	0.02	0.02	0.33	x	0.4	0.4
Chemical oxygen demand (COD)	mg O2/L	x	x	25.42	4.42	44.8	10,800 (supernatant water 3115)	2000	125	125
Biological oxygen demand (BOD)	mg O2/L	x	x	23.5	1	5.65	1400 (supernatant water 100)	700	25	25
Nitrate nitrogen	mgN-NO3/L	8.9	20	x	x	x	0.61	x	x	x
Ammonium nitrogen	mgN-NH4/L	x	x	x	x	x	16.75	x	x	x
Total nitrogen	mg Ntot./L	x	x	6.8	1.66	15.36	17.45	x	30	30
Total phosphorus	mg Ptot./L	x	x	0.33	0.17	5.68	0.81	15	3	3
Total organic carbon (TOC)	mg C/L	0.477	x	2.1	0.21	3.98	42.71	x	30	30
Inorganic carbon (IC)	mg C/L	2.08	x	3.78	1	14.98	37.44	x	x	x
Total carbon (TC)	mg C/L	2.557	x	5.87	1.21	18.96	80.15	x	x	x
Turbidity	NTU	0.18	0.3—in circulation 0.5—in the basin	11.87 (after coagulation 6.77)	1.15	6.64 (after coagulation 4.34)	179.55 (after 2 h sedimentation 40.15)	x	x	x
Total suspended solids	mg/L	x	x	62 (after coagulation 5.3)	x	17.5 (after coagulation 4.0)	1206.5 (44.00 *)	400	35	35
Sulphureous	mg SO4−2/L	x	x	303	58.8	262.33	165	x	x	x
Sulphides	mg S/L	x	x	x	x	x	absent	x	x	x
Aluminum	mg Al/L	x	0.2	0.07	0.01	0.09	0.09	x	x	x
Color, wavelength 436 nm	mgSO4−2/L	x	x	3.61	0.28	2.17	x	x	x	x
Ammonium ion	mg S/L	0.051	x	0.12	0.58	1.45	x	x	x	x
Iron	mg Fe/L	x	0.2	x	11.33	x	x	4	x	x
Copper	mg Cu/L	x	x	x	<20	x	x	1	0.5	0.5
Zinc	mg Zn/L	x	x	x	244.67	x	x	5	2	2
Lead	mg Pb/L	x	x	x	92.33	0.5	0.79	1	0.5	0.5
Nickel	mg Ni/L	x	x	x	x	x	0.6	x	x	x
Phenol (phenol index)	mgC6H5OH /L	x	x	x	x	x	1.08	x	x	x
Oxidisation	mg O2/L	x	4	1.79	3.6	5.89	x	x	x	x

* Total suspended solids from supernatant water after 2 h; ** w.m.s—wet mass of the sample; *** d.m.s—dry mass of sediment.

provides a summary of the key physicochemical and microbiological parameters characterizing the analyzed wastewater streams. Both the average values obtained in the study and their compliance with regulatory limits are presented. This comparison enables the assessment of wastewater quality in terms of potential reuse or the need for treatment prior to discharge into the environment.

5. Discussion

Swimming pools contribute significantly to wastewater generation, thus exerting a notable influence on the management of water and wastewater systems in urban environments [2,11]. Given the volume of pollutants produced and the specific operational characteristics of swimming pool infrastructure, a thorough analysis of their impact on urban water and wastewater systems has been conducted, with findings compared to existing international studies. To comprehensively address this important issue, we organise the discussion into two primary sections, adhering to a consistent structural framework throughout all chapters of this work. The objective is to provide an in-depth examination of wastewater management in swimming pools, incorporating both quantitative and qualitative aspects of the generated pollutant streams.

5.1. Quantitative Analysis of Wastewater Streams

The water discharged into the wastewater system from the pool outflow comprises water splashed into floor drains as well as water resulting from the systematic emptying of the pool basins. Annually, this amounts to 2829.7 m³ of purified water that requires discharge into the municipal wastewater system. The cyclical discharge of water from each pool basin plays a critical role in the overall water balance of the facility. The sports pool represents the highest proportion of wastewater generated, accounting for 38.5% of annual water discharge, which varies depending on the year of basin emptying. In contrast, the outdoor pool, despite its seasonal operation, is responsible for 43.5% of the discharge mainly due to splashing and the seasonal emptying of its basin. Furthermore, although the whirlpool tube has a smaller capacity, its high intensity leads to a rapid decline in water quality, necessitating monthly replacements. Consequently, the WT generates almost half of the wastewater of the recreational pool. According to guidelines established by the Environmental Protection Agency (EPA) [62], public pools should undergo water replacement every 3 to 7 years, depending on various water quality parameters. The quality critically influences the frequency of water replacement, which is essential to ensure user safety of users [63], and to minimise the buildup of pollutants, including micropollutants [64,65,66]. Furthermore, user hygiene significantly affects water quality, potentially mitigating the need for frequent changes [67].

Water utilised for backwashing filters represents a considerable portion of the wastewater generated in swimming pool facilities. In the facility under discussion, the filters that are washed every three days yield approximately 7179.2 m³ of wastewater per year. This volume exceeds 2.5 times the total water exchanged in the swimming pool basins. Silva et al. reported a value of 4197.6 m³ in their research [68]; however, their facility consisted of only two basins, which corresponds to half the operational load of the analysed facility. The Spanish team performed an analysis of swimming pool facilities in the country, selecting installations with comparable attributes for their audit [15]. They found that the average pool volume was 260 m³. Based on this assessment, they estimated that the average annual water consumption associated with the filter backwash process for a single pool amounted to 2017 m³, which represents only 28% of the total water consumption recorded in their study. It is noteworthy that the facility under examination had a cumulative volume of all its pool basins totalling 1231.1 m³. For each of the four basins analysed, the average annual water consumption for filter backwash was recorded at 1749.8 m³, with the average volume of an individual basin of 307 m³. Therefore, this figure was lower than the value reported by the Spanish team. The volume of water required to rinse 1 m² of filter bed varies, ranging from 4 m³. This aligns with data presented by E. Łaskawiec [21], whose findings indicated an average value of 4.09–4.39 m³/m². These statistics underscore the significant influence of filtration processes on overall water consumption within swimming pool facilities and highlight the need to incorporate these factors into water balance assessments. These statistics underscore the significant influence of filtration processes on overall water consumption within swimming pool facilities and highlight the need to incorporate these factors into water balance assessments. Although the present study did not include a direct economic or energy assessment of the water recovery processes, such evaluations have been conducted in previous research. These studies included qualitative and quantitative analyses of operational costs, potential savings in water consumption, and environmental benefits associated with the reuse of filter backwash water and other wastewater streams in swimming pool facilities [7,69,70,71].

The total amount of water collected from the roof surface throughout the year is 1172.6 m³, which represents less than 7% of the wastewater generated by the facility. This collected rainwater is used in the facility’s water recovery system. Specifically, it is directed to a recovery tank from which it supplies the swimming pools and toilets. Additionally, during the summer months, prior to treatment, water is utilised for irrigating green areas. This method of using rainwater for swimming pool supply was developed through collaborative efforts between a Costa Brava research team in Catalonia [72] and a Polish–British team based in the Silesian Voivodeship [73]. Research conducted in various countries has investigated stormwater reuse within urban environments, focusing not only on the technical treatment processes, but also analytical-probabilistic methods, event forecasting, and diverse applications for rainwater utilisation [10]. These results indicate that, in addition to improving the quality of harvested rainwater, the effective implementation of recovery systems requires addressing management structures and community participation and building public awareness. Implementing such rainwater recovery systems facilitates a considerable reduction in drinking water, decreases the operational costs associated with pool facilities, and contributes to the sustainable management of water resources.

Upon conducting an analysis of the annual volumes of domestic wastewater produced, an estimated figure of 78,840 m³/year was determined according to applicable regulations [29], which define the design flow on the basis of normative maximum daily water demand. On the contrary, the actual volume of wastewater generated, as recorded by the facility’s water meters via the Building Management System (BMS) under regular operating conditions, was measured at 5849.28 m³/year. This difference indicates a substantial reduction of 92.6% from the estimated normative estimations, resulting from a combination of factors: more efficient water management practices, user behaviour patterns, the application of water-saving fixtures, and optimisation of operational schedules. The observed lower actual consumption is favourable, as it translates into reduced operational costs and a smaller environmental footprint, while still meeting all sanitary and functional requirements of the facility. A Portugal research team investigated a swimming pool facility that consists of two indoor pools designated for sports and educational purposes, along with sanitary facilities that include changing rooms for women, men, and staff, as well as showers, toilets, and a cafeteria [68]. The annual water consumption required for domestic and economic purposes was quantified at 8119.6 m³. This figure represents an increase of 38.8% compared to a larger facility located in Poland. The facility recorded an average annual user attendance exceeding 24,000, which is correlated to an average water consumption of 23.5 dm³ per user. According to the Polish regulation regarding standards for water consumption, the established daily water demand is 160 litres per user [74]. When factoring in the additional water demand for refreshing activities, quantified at 30 dm³ per person according to the German standard DIN [26], the total water consumption per user amounts to 53.5 dm³. This figure constitutes 66.6% of the value stipulated in national regulations. Furthermore, the research conducted by Liebersbach et al. estimated the average water consumption at 93.3 L per person, which exceeds the findings of this analysis by 42.7% [75].

The measured sediment volume is 90.12 m³, representing approximately 1.3% of the total rinsing water volume. Research conducted by Łaskawiec [21] indicates that sediment volumes can vary between 2% and 7.5%, demonstrating significant discrepancies in sediment formation under different technological conditions. On the contrary, Kluczek [76] reported a wet sediment content of around 5%, which serves as an intermediate figure relative to the findings of other researchers. The observed differences in sediment proportions can be attributed to the distinct characteristics of the various technological processes examined, the types of chemicals employed, and the operating parameters of the water treatment systems. A comprehensive analysis of these physicochemical and bacteriolytic parameters is outlined in the following chapter.

5.2. Qualitative Analysis of Wastewater Samples—Laboratory Tests

Initially, an analysis was performed on the water sourced from the recreational pool, which is typically characterised by elevated levels of contamination due to a significant volume of users and the occurrence of daily swimming lessons for children during the school week. This water, resulting from splashing activities, is transferred to the inlets situated on the pool deck before being discharged into the wastewater system. The microbiological tests conducted revealed no presence of bacteria in the wastewater. Furthermore, the evaluation of physicochemical parameters indicated that the values obtained in laboratory analyses do not exceed the permissible standards established in the regulation set forth by the Minister of Health [58].

Subsequent studies were undertaken to evaluate the feasibility of discharging individual wastewater streams into the wastewater infrastructure [59], releasing them into surface waters, and infiltrating them into the ground [60]. Additionally, the studies aimed to identify the presence of compounds with potentially significant environmental toxicity [61]. In addition to Polish and general EU requirements, the regulatory framework for wastewater reuse is shaped by several key international associations. The Directive (EU) 2024/3019, Recast Urban Wastewater Treatment Directive (2024) [11] extends the scope of wastewater treatment, introduces binding targets for energy efficiency, sanitary monitoring, and promotes circular economy measures. The overarching Water Framework Directive 2000/60/EC [5] integrates these requirements within the EU’s water resource management strategy. At the global level, the WHO/UNEP Guidelines for Safe Use of Wastewater [12], Excreta and Greywater establish health-based targets, multibarrier risk management approaches, and recommended monitoring procedures for different reuse applications, including agricultural irrigation, urban landscaping, and recreational waters. Beyond Europe, relevant frameworks include the U.S. National Pollutant Discharge Elimination System (NPDES), which regulates permits for discharges into surface waters [13], and the Australian Guidelines for Onsite Wastewater Management (EPA Victoria: Melbourne, Australia, 2024) [14], which apply risk-based assessment for wastewater reuse. These international standards provide additional reference points to align national practices with globally recognised benchmarks for water reuse.

Analysis of a water sample extracted from the overflow gutter of the backwash from the vacuum filters of the recreational pool indicated a combined chlorine concentration of 0.52 mg Cl₂/L, which is above the regulatory limit of 0.4 mg Cl₂/L [60,61]. Residual chlorine in recovered water can result in disinfection by-products (DBPs) such as combined chlorine, total trihalomethanes (THMs), and chloroform [64,65,77]. High levels of DBP can limit the viability of water reuse, particularly in applications with stringent sanitary standards, such as swimming pool systems. Research indicates that DBP formation is influenced by factors such as the rate of water renewal, the duration of filtration, organic contaminants, and the load of pool usage. Therefore, monitoring DBP concentrations is essential for effective water recovery management to ensure compliance with sanitary guidelines and enhance safe water reuse opportunities [64,65,77].

The biochemical oxygen demand (BOD₅) was recorded at 23.5 mg O₂/L, approaching the permissible threshold of 25 mg O₂/L [60,61]. Furthermore, the total suspended solids measured 62 mg/L, which is almost double the acceptable limit [60,61]. Following the implementation of the coagulation process, a substantial reduction in suspended solids was achieved, bringing the level to 5.3 mg/L. E. Łaskawiec measured concentration values of 251 mg/L for sample 1 and 128 mg/L for sample 3. After 30 min of sedimentation, these concentrations decreased to 130.25 mg/L for sample 1 and 92.25 mg/L for sample 3. After 24 h of sedimentation, a further significant reduction was observed, with concentrations dropping to 4.9 mg/L for sample 1 and 4.1 mg/L for sample 3 [21]. Analysis of the remaining physicochemical parameters revealed that no values exceeded established permissible standards. In 2018, J. Wyczarska-Kokot and A. Lempart conducted a comprehensive analysis of water recovery after filter backwash, examining samples from 20 different swimming pool facilities [70]. They analysed the physicochemical parameters of these samples. The total nitrogen in 9 of the analysed facilities did not exceed 10 mg/L. The results varied, ranging from 3.6 mg/L at facility P6 to 23.07 mg/L at facility P11. The research found that the average total phosphorus content was 0.33 mg/L, while measurements from 20 individual facilities ranged from 0.01 mg/L to 1.41 mg/L. In 6 of the 19 analysed samples, the phosphorus concentration exceeded the allowed level. Similar discrepancies were observed for chemical oxygen demand (COD). In 8 of the 20 samples, the COD value exceeded the permissible limit of 125 mg/L.

During the analysis of the quality of rainwater collected from the roof surface, a notably elevated concentration of sulphureous (SO₄²⁻) was identified, amounting to 58.8 mg/L. This finding may suggest the possible presence of hydrogen sulphide (H₂S) in the water sample. The roof is constructed using an EPDM membrane, while the rainwater drainage system (Geberit Pluvia^®) incorporates plastic pipes that are not expected to react with rainwater. Identified potential sources of H₂S emissions may include metal components of the earthing protection system and support structures of photovoltaic systems, which are prone to corrosion. Additionally, atmospheric pollutants can be introduced into the retention system via precipitation as sulphur compounds. Organic pollutants, such as animal excrement and other biodegradable materials, may also significantly contribute to the generation of hydrogen sulphide. These substances undergo fermentation processes under anaerobic conditions, leading to the formation of sulphur compounds. Stagnation of water both on the roof surface and within retention tanks can further exacerbate these processes by restricting access to oxygen and increasing the activity of anaerobic bacteria. Furthermore, the analysis revealed a significantly increased concentration of total iron, recorded at 11.33 mg Fe/L. This may indicate ongoing corrosion processes that affect steel or cast iron elements present within the roof installation. The observed iron concentration exceeds the permitted limit for emissions into wastewater systems, established by law at 4.0 mg Fe/L [31], which poses a considerable environmental and operational risk. Zinc and lead were also found to be concerning, measuring 244.67 mg Zn/L and 92.33 mg Pb/L, respectively. These levels may be associated with corrosion of metal surfaces, including protective coatings, roof fittings, and fastening screws, leading to the leaching of these metals into retention tanks. Given that lead is a highly toxic element, its presence disqualifies water from any potential utility use, including food and agricultural applications. The regulatory limits for these substances are set at 5.0 mg/L for zinc (when discharged into wastewater systems) [59] and 2.0 mg/L for water and soil [60,61]; for lead, the permissible values are 1.0 mg/L (wastewater system) [59] and 0.5 mg/L (water/soil) [60,61]. The exceedance of these physicochemical parameters requires a thorough analysis of pollution sources and an assessment of the suitability of rainwater for potential reuse in water recovery systems. It is also recommended to consider the implementation of filtration systems, heavy metal separation technologies, and modifications to existing roof infrastructure. Rainwater quality assessments in Roztocze National Park, undertaken by a Polish research team led by T. Grabowski, have indicated significant bacteriological contamination in the analysed rainwater samples [78]. Although this aspect was not the primary focus of the study by the authors, it is advisable for future research to encompass comprehensive microbiological analyses. The turbidity values of the three samples examined ranged from 1.54 to 3.24 NTU, with a maximum recorded turbidity of 10.4 NTU. On the contrary, a sample from the Lower Silesian Voivodeship demonstrated a turbidity level of 1.15 NTU. In particular, the presence of chlorides was detected at a concentration of 3.93 mg/L in the samples analysed by Grabowski’s team; this finding was absent in the samples from the current study. The sole metal identified in the Roztocze National Park samples was iron, with concentrations that did not exceed 1 mg/L. In comparison, a Chilean team led by P. Vidal et al. reported the following concentration ranges: turbidity of 0.8 to 1.9 NTU, phosphates (expressed as phosphorus) ranging from 0.01 to 0.2 mg/L, chlorides from 2.8 to 5.0 mg/L, and nitrates from 0.3 to 0.9 mg/L [79].

In the evaluation of sanitary wastewater, the assessment was conducted exclusively in accordance with the provisions set forth in the Announcement of the Minister of Infrastructure and Construction of 28 September 2016 on the publication of the consolidated text of the Regulation of the Minister of Construction on the manner of fulfilling the obligations of industrial wastewater suppliers and the conditions for discharging wastewater into wastewater systems (Journal of Laws of 2016, item 1757) [59]. It is imperative to note that this type of wastewater is prohibited from being released into surface waters or the ground. Laboratory analyses revealed that all parameters examined were within the permissible limits outlined in the specified legal framework. Furthermore, a microbiological examination was performed to detect the presence of Salmonella spp. bacteria. The results indicated that no such pathogens were present in the analysed sample, thus confirming the sanitary appropriateness of the wastewater.

The concluding phase of the investigation involved a comprehensive analysis of the technological sludge generated after the sedimentation process. The results obtained indicate substantial exceedances of the permissible pollution indicators, both in terms of physicochemical and microbiological parameters. The total microbial count in the sample exceeded 300 CFU/100 mL, signifying a high microbiological load within the sludge and presents a potential sanitary risk. Studziski et al. reported a value of 16,200 mL⁻¹ and also noted the presence of 38 CFU/100 mL Pseudomonas aeruginosa bacteria [80].

The chemical oxygen demand (COD) in the sludge was measured at 10,800 mg O₂/L, while the COD in the supernatant water was 3115 mg O₂/L. These levels indicate that the permissible values outlined in the regulations established by the Minister of Construction for wastewater discharged into municipal wastewater systems were exceeded by more than five times [59]. In relation to the standards for surface water and soil, COD levels exceeded permissible limits approximately 86 times [60,61]. Similar discrepancies were observed regarding the biochemical oxygen demand (BOD₅), which exceeded the permissible level for wastewater by more than two times [59] and exceeded the limits for discharge into the natural environment (including water and soil) by more than 56 times [60,61]. The total organic carbon (TOC) content was recorded at 42.71 mg C/L, which exceeds the established limit of 30 mg C/L, indicating a significant saturation of the sludge with organic substances. Studzinski et al. reported a value of 22 mg C/L [80]. Moreover, the concentration of total suspended solids (TSS) was notably elevated, reaching 1206.5 mg/L prior to sedimentation. Following a two-hour settling period, the concentration of suspended solids in the supernatant liquid decreased to 44 mg/L. The Polish team achieved a value of 96.9 NTU [80].

However, this value remains considerable in the context of subsequent management. The collected data clearly demonstrate that the resulting technological sludge does not conform to the physicochemical and microbiological standards required for discharge into municipal wastewater systems, nor is it suitable for discharge into water or soil. According to applicable regulations, this material should be classified as particularly harmful sludge, necessitating specialised neutralisation or disposal in designated waste treatment facilities.

6. Conclusions

Following a comprehensive analysis of various wastewater streams generated within the swimming pool facility, in terms of both quantity and quality, the following conclusions and recommendations have been established for future consideration:

• Outflow from the swimming pool basin

The predominant source of wastewater generated at the facility is attributed to pool water losses, notably due to splashing and the periodic emptying of pool basins. The annual volume of this wastewater is 2829.7 m³; note that the presence of this water has been purified and treated, aligning with the quality standards set forth by the Regulation of the Minister of Health governing the water of swimming pools. This finding suggests a potential avenue for reuse following a dichlorination process. It is recommended to explore the technological feasibility of returning this water to the interceptor tanks. However, the substantial volume of this wastewater presents challenges in terms of storage that need to be carefully considered.

• Filter washings

The annual volume of water used for filter backwash amounts to 7179.2 m³, representing the most significant single stream of wastewater. Subsequently, this water is directed to a recovery station where it undergoes treatment processes before being reused within the technological circulation of the pool. Although certain physicochemical parameters—such as total suspended solids, turbidity, chloride concentration, and reduced redox potential have been exceeded, this water remains suitable for reuse following appropriate treatment.

• Rainwater and meltwater

The estimated annual volume of rainwater collected from the roof is 172.6 m³. Due to elevated levels of heavy metals, the use of this rainwater for watering green areas or for secondary treatment is not recommended. A long-term assessment of the quality of this water is suggested to verify the stability of its parameters. Additionally, it would be prudent to collect rainwater samples immediately after precipitation events to evaluate the impact of roof equipment and secondary pollution sources on water quality.

• Sanitary wastewater

According to actual measurements, the annual volume of domestic and social wastewater is 5849.28 m³, which is considerably lower than the volume predicted according to design standards. This discrepancy may indicate an increased efficiency in the management of water and wastewater in this context.

• Technological Sludge

The annual generation of technological sludge is reported at 90.12 m³. In light of significant exceedances of permissible pollutant parameters in comparison to applicable regulations, this sludge must be classified as hazardous waste and disposed of according to the regulations governing particularly harmful waste.

Future research should focus on evaluating the feasibility of reusing the wastewater streams identified in this study, especially through advanced treatment methods for safe application in swimming pool systems or other secondary uses. The provided serve as a foundation, offering crucial quantitative and qualitative data to select purification technologies, assess economic viability, and ensure compliance with sanitary and environmental regulations.