Improving Wastewater Quality Using Ultrafiltration Technology for Sustainable Irrigation Reuse

Abstract

This study evaluates the physical, chemical, and biological properties of wastewater—comprising domestic sewage and agricultural drainage water—both before and after treatment to assess the efficiency of the applied processes. The physical properties, including total suspended solids (TSS) and color, demonstrated significant improvements post-treatment, with TSS reduction reaching 91.4% and color removal at 99.5%, indicating the effectiveness of ultrafiltration and coagulation techniques. Chemically, the total dissolved solids (TDS) concentration decreased from 838.2 to 375.5 mg·L⁻¹, aligning with environmental standards and ensuring suitability for irrigation. Additional reductions were observed in biochemical oxygen demand (BOD) and chemical oxygen demand (COD), with removal efficiencies of 86.5% and 83.7%, respectively, highlighting the system’s capability in reducing organic pollutants. Biologically, the treatment process achieved 99.9% removal efficiencies for both Total Coliform and E. coli, meeting world health organization (WHO) guidelines for microbial safety. The water quality index (WQI) analysis classified the treated water in the “Excellent” category, demonstrating an overall enhancement in water quality. Beyond these performance evaluations, this study introduces a novel approach by employing conventional treatment techniques on a blended wastewater—comprising domestic sewage and agricultural drainage water—operated under real operational conditions to achieve safe and sustainable irrigation reuse. This study hypothesizes that the synergistic integration of ultrafiltration with sodium hypochlorite disinfection—without relying on biological treatment—can significantly enhance water quality for sustainable irrigation.

1. Introduction

The sustainable management of water resources is a pressing global challenge, particularly in arid and semi-arid regions where water scarcity is becoming increasingly critical due to population growth, urbanization, and climate change. Wastewater treatment and its reuse for irrigation have gained prominence as effective strategies to mitigate water shortages while enhancing environmental sustainability [1]. Among the advanced water treatment technologies, ultrafiltration (UF) stands out for its efficiency in improving wastewater quality by removing contaminants, pathogens, and suspended solids. Ultrafiltration technology offers a modern and sustainable approach to wastewater treatment, aligning with broader environmental goals of resource conservation and circular water economy. Unlike conventional treatment methods, ultrafiltration employs semi-permeable membranes capable of removing particles as small as 0.01 microns, delivering superior water quality [2]. In recent years, significant advancements have been made in UF technology, enhancing its design, operational efficiency, and overall sustainability. Modern UF systems are now engineered to effectively remove larger particulate matter from diverse water sources—ranging from rivers to lakes—, thereby expanding their applications to drinking water purification, industrial processes, and water recycling initiatives. Furthermore, these systems can be tailored to meet specific operational requirements, such as portable, solar-powered units that are ideal for remote or resource-limited areas [3]. Additionally, the development of hybrid UF systems that combine complementary technologies like forward osmosis (FO) and membrane distillation (MD) has enabled improved resource recovery from wastewater, thereby enhancing treatment efficiency while reducing environmental impacts [4]. The wastewater in this study is a mixture of domestic sewage from residential units and agricultural drainage water from landscaped areas irrigated with river water. This mixture contributes to a diluted wastewater composition, impacting the treatment process and the resulting water quality. Alresheedi et al. [5] emphasized that low-cost and decentralized wastewater treatment systems effectively address water scarcity while improving the resilience of communities in arid environments. The introduction of advanced technologies like ultrafiltration is essential for achieving long-term water sustainability and reducing reliance on freshwater sources. The use of ultrafiltration in wastewater treatment extends its impact to agricultural irrigation, one of the most water-intensive sectors globally [6]. Treated wastewater provides a viable alternative for irrigation, reducing the stress on freshwater resources while mitigating environmental risks associated with untreated effluent discharge, such as eutrophication and groundwater contamination.

To assess the suitability of treated wastewater for irrigating windbreak trees, dry cereals, cooked vegetables, and processed vegetables, the Water Quality Index (WQI) serves as a standardized numerical tool that evaluates water quality based on multiple parameters. WQI provides a simplified yet comprehensive assessment, classifying water into different categories based on its suitability for irrigation. The classification system indicates the level of treatment required before use: WQI < 50 represents excellent quality (suitable for irrigation), WQI 50–100 indicates good quality (requiring minor treatment), WQI 100–200 corresponds to poor quality (requiring significant treatment), and WQI > 200 is considered unsuitable for irrigation [7]. This classification aids in determining whether treated wastewater meets the necessary quality standards for safe agricultural reuse. Alresheedi et al. [8] highlighted that decentralized treatment systems have demonstrated remarkable success in improving water quality and gaining community acceptance, thus facilitating the implementation of wastewater reuse practices. Recent studies have further substantiated the advantages of ultrafiltration in water treatment. Khanzada et al. [9] demonstrated the effectiveness of ultrafiltration in removing harmful micro pollutants, ensuring the safety of treated water for agricultural reuse. Bhowmick et al. [10] highlighted the energy efficiency of ultrafiltration systems, emphasizing their compatibility with environmental sustainability goals by reducing greenhouse gas emissions associated with conventional treatment processes. Yang et al. [11] and Chew et al. [12] noted the economic viability and operational reliability of ultrafiltration systems, making them suitable for application in resource-limited settings. These findings underscore the role of ultrafiltration as a critical tool for achieving water and environmental sustainability. Alresheedi et al. [5] highlighted the importance of adapting treatment systems to local conditions, ensuring their effectiveness and acceptance. Tailoring ultrafiltration technology to specific contexts is critical for maximizing its benefits, particularly in areas with water scarcity and limited resources. Ultrafiltration systems are recognized for their minimal chemical usage, energy efficiency, and environmental compatibility, making them an integral part of modern wastewater treatment practices. Thus, the objective of this research is to evaluate the effectiveness of an ultrafiltration system in treating wastewater—comprising domestic sewage mixed with agricultural drainage water—under real operational conditions, without relying on biological treatment, to meet the required microbial and physicochemical quality standards for safe and sustainable irrigation reuse.

2. Materials and Methods

This study was conducted during the summer seasons of 2023 and 2024 at a residential resort in the New Administrative Capital, Cairo, Egypt. The research focuses on evaluating the effectiveness of wastewater treatment technologies in a real-world setting. The compound’s infrastructure allowed for the observation of treatment processes under varied environmental conditions.

2.1. Storage Tank

The storage tank has a capacity of 500 m³ and receives wastewater from the compound. The wastewater is a mixture of domestic sewage from residential units and drainage water from landscaped areas irrigated with river water. The presence of irrigation runoff results in a diluted wastewater composition with relatively lower organic content compared to typical municipal wastewater. It is expected that the BOD and COD values are lower due to the mixture between domestic wastewater and agricultural drainage water, while nitrogen and phosphorus concentrations remain within expected ranges due to contributions from both domestic wastewaters. The tank also serves as a primary filtration system, allowing solid impurities to settle, effectively acting as a preliminary filtration step. Given the low organic load, the treatment scheme was designed to rely primarily on physicochemical processes, eliminating the need for conventional biological treatment.

2.2. Filtration System Design

2.2.1. Design Considerations for the Filtration and Treatment System

Key considerations were made to address operational, environmental, and maintenance needs.

• Contaminant removal efficiency: A multi-stage process includes a lamella clarifier, advanced membranes, and activated carbon and crushed glass media for enhanced filtration.
• Flow management and stability: Tanks and pumps ensure stable flow, with a 30 m³·h⁻¹ feed pump, a 60 m³·h⁻¹ backwash pump, and an air blower for media regeneration.
• Automation and monitoring: A PLC control system automates operations, minimizes errors, and provides real-time maintenance alerts.
• Durability and system longevity: Corrosion-resistant materials ensure long-term reliability in wastewater environments.
• Sustainability and environmental impact: Recycled crushed glass media promote sustainability, and the system supports water reuse.
• Scalability and adaptability: A modular design allows system expansion to meet future demands.
• Ease of performing maintenance operations.

2.2.2. Filtration and Treatment System Components

The filtration and treatment system, illustrated in Figure 1, was meticulously designed to ensure optimal removal of contaminants and to enhance the performance and longevity of drip irrigation systems. This system integrates multiple components to achieve effective filtration, precise monitoring, and efficient operation.

• Clarifier unit

The lamella clarifier is the first stage of the filtration system, designed to remove large, suspended solids from wastewater. It uses inclined plates to enhance sedimentation efficiency by increasing the settling surface area. Water enters through a controlled feed inlet, while settled sludge is discharged via a sludge outlet. The clarified water is then transferred to the next treatment stage.

The clarifier’s design is based on key calculations, ensuring optimal performance. For a flow rate of 20 m³·h⁻¹ and a settling velocity of 1.5 mm·s⁻¹, the required surface area is ~13.3 m², resulting in a diameter of ~4.1 m. The total height is 3.5–4 m, including a sedimentation zone (1.5–2 m), bottom flow zone (1 m), and freeboard (0.5 m). With a surface loading rate of ~1.5 m³·m⁻²·h⁻¹, these parameters ensure efficient sedimentation and smooth operation of the treatment process.

2.

Break tank and feed water tanks

After the clarification process, the water flows into the break and feed water tanks, which serve critical roles in the treatment system. The break tank has a capacity of 15 m³ and acts as an intermediate storage unit, providing a passive buffer to accommodate variations in flow rates, ensuring smooth operation. The feed water tank, with a larger capacity of 30 m³, ensures a continuous and pumped supply of pretreated water to the filtration units. The tank capacities were calculated based on the system’s flow rate and operational requirements, with the break tank sized to handle short-term flow fluctuations and the feed tank designed to maintain a steady supply to downstream units. For a system flow rate of 30 m³·h⁻¹, the break tank’s volume was set to accommodate half an hour of flow, while the feed tank’s volume allows for one hour of flow, ensuring sufficient storage capacity for uninterrupted operation.

Both tanks are constructed from high-density polyethylene (HDPE), a material chosen for its excellent chemical resistance, lightweight structure, and durability. HDPE ensures the tanks can withstand prolonged exposure to wastewater and the environmental conditions of the treatment facility, providing long-term reliability and structural integrity in the treatment process.

3.

Filter vessels

The filtration system comprises three specialized filter vessels, each designed for efficient water treatment. The activated glass filter uses recycled crushed glass with angular grains to capture fine particles, supported by a 2250 kg gravel bed for uniform water distribution and clog prevention. The glass filter media have a particle size range of 0.5–1.0 mm, while the gravel bed consists of particles ranging from 2 to 4 mm. The term “activated” refers to the specialized surface modification process that enhances the glass media’s negative charge, improving its ability to capture fine particles, organic matter, and microorganisms. Compared to traditional sand filters, activated glass filters offer higher filtration efficiency, reduced biofouling, and a longer lifespan. The activated carbon filter, filled with Jacobi Aquasorb carbon, effectively removes organic pollutants, odors, and contaminants, enhancing water quality. Both filters are deep-bed types, constructed from mild steel (MOC) for durability, with a diameter of 1.62 m, height of 2.1 m, and an operating weight of 3.5–4.5 tons. They feature flanged tripond connections and operate under a PLC-based pressure control system. A robust backwashing mechanism removes debris, with a manual valve as a backup. Additionally, six polypropylene disc filters (3″, 130 microns) further improve efficiency. Pressure gauges placed before and after the filters monitor performance, ensuring real-time detection of blockages or reduced filtration efficiency.

4.

Ultrafiltration Membranes

After filtration, water undergoes advanced treatment through EMA-02 series membranes from DOW, ensuring the removal of fine contaminants and enhancing water quality. With a nominal pore size of 0.03 microns, these membranes capture microscopic particles and dissolved impurities, ensuring the permeate meets stringent standards. Housed in durable UPVC material, the system includes six reliable membrane units designed for efficiency under varying conditions. The treated water, or permeate, is directed to a storage tank for subsequent use or reuse in diverse applications. This membrane stage plays a vital role in the treatment process, targeting impurities left by conventional methods and supporting sustainable practices. By integrating EMA-02 membranes, the system delivers superior purification, optimal water clarity, and safety, meeting the demands of industries requiring advanced water treatment. Moreover, the operational cycle of these membranes is meticulously managed to ensure long-term performance and efficiency. Initially, the membranes are subjected to rigorous monitoring of critical parameters such as flow rate and operating pressure to detect early signs of fouling. Over time, regular cleaning cycles—employing both mechanical and chemical techniques—are implemented to remove accumulated contaminants and restore membrane functionality. When the membranes reach a threshold beyond which their efficiency cannot be recovered despite repeated maintenance, they are replaced in accordance with the manufacturer’s guidelines. This proactive approach not only maintains the high quality of the treated water but also extends the overall lifespan of the treatment system, ensuring continuous optimal performance under dynamic operational conditions.

5.

Pumps and blowers

To maintain a consistent flow of water throughout the system, various pumps and a blower are employed, each serving a specific purpose in the filtration process. The feed pump, operating at a flow rate of 30 m³·h⁻¹, ensures a controlled delivery of water from the feed tank to the filter vessels. The system includes two fed pumps, each equipped with a pressure vessel, to provide redundancy and maintain steady and efficient filtration. For cleaning the filter media, a backwash pump is utilized, offering a robust capacity of up to 60 m³·h⁻¹ to effectively remove accumulated debris and restore the media’s performance. Additionally, an air blower is integrated into the system to enhance the backwashing process. This side-channel blower (1 pc) introduces pressurized air into the media layers, dislodging trapped particles and ensuring thorough cleaning.

6.

Auxiliary components

The system is supported by a range of auxiliary components that enhance its functionality and efficiency. The permeate and backwash tanks are designed as a shared unit with a capacity of 20 m³, serving a dual purpose: storing treated water for subsequent use and holding water required for the backwashing process. This design ensures seamless operation by maintaining readily available resources for filtration and cleaning cycles, optimizing space and operational efficiency.

To regulate water flow and facilitate precise adjustments, a variety of valves are strategically integrated throughout the system. These include automated solenoid and actuator valves (5 pcs) for dynamic control and manual UPVC valves (6 pcs) for straightforward operational flexibility. Together, these valves provide robust control mechanisms to adapt to varying system demands, enhancing operational reliability and responsiveness. Central to the system’s automation is the PLC control panel, which ensures streamlined and efficient operation. Equipped with an inline multi-parameter probe for real-time monitoring of critical metrics such as temperature, pH, and turbidity, the control panel provides operators with actionable insights into the system’s performance. Additionally, it features advanced alarms and notifications to alert operators to maintenance needs or potential issues, enabling timely interventions and minimizing downtime.

7.

Chemical treatment components

The hypochlorite injection system at point 15 consists of several key components to ensure an efficient and controlled dosing process. The chemical storage tank is made of high-density polyethylene (HDPE) for chemical resistance, with a capacity of 400 L and is equipped with a level indicator to monitor hypochlorite levels. The dosing pump, point 14, provides accurate metering with an adjustable flow rate between 0.5 and 5 L·h⁻¹ to match treatment needs, operating based on flow sensor feedback to maintain proper hypochlorite concentration. At the injection point, sodium hypochlorite is directly injected into the pipeline leading to the disc filters, with a static mixer included to enhance uniform distribution. The flowmeter and control panel continuously monitors the water flow rate and adjusts dosing, accordingly, utilizing a PLC-based system for automated control and real-time adjustments. To ensure system integrity, a Backflow valve is installed to prevent contamination of the hypochlorite storage tank by backflow from the main water stream.

2.3. Field Experiment

The field experiment involved operating the filtration and treatment system with a pump discharge rate of 30 m³·h⁻¹. First, a preliminary experiment was conducted in February 2023 to determine the best concentration of sodium hypochlorite (NaOCl) using four levels: 5, 10, 15, and 20 mg·L⁻¹, which were selected according to ECP 501 [13]. During this phase, Total Coliform and E. coli levels were measured before and after treatment to assess the disinfection efficiency.

Following the preliminary experiment, the main experiment was carried out by injecting the optimal concentration of sodium hypochlorite into the filtration unit at point 14. The system was then operated, and comprehensive water quality assessments were performed, including the evaluation of physical, chemical, and biological parameters before and after filtration.

2.4. Laboratory Measurements

2.4.1. Physical Parameters

Physical parameters like total suspended solids (TSS) and color (Hazen Units) are essential for assessing water quality, especially for irrigating windbreak trees, dry cereals, cooked vegetables, and processed vegetables. TSS, determined by gravimetric filtration (APHA Method 2540D), measures particulate matter that can affect irrigation systems. pH is measured with a pH meter (APHA Method 4500-H+) to assess water’s acidity or alkalinity, crucial for plant health. Water color, expressed in Hazen Units and measured using a spectrophotometer APHA Method 2120C), indicates dissolved organic compounds that can impact water clarity and quality.

2.4.2. Chemical Parameters

Oil and grease concentrations, measured by liquid–liquid extraction and gravimetric analysis (APHA Method 5520B), assess hydrocarbon levels that can affect plant absorption. Biochemical oxygen demand (BOD), measured using the 5-day test (APHA Method 5210B), evaluates microbial oxygen demand for organic matter degradation. TDS, measured with a digital meter (APHA Method 2540C), indicates dissolved salts for irrigation suitability. Chemical oxygen demand (COD), analyzed by the closed reflux method (APHA Method 5220D), quantifies oxygen demand for oxidation of organic/inorganic compounds. Nitrite (NO₂) levels, assessed by ion chromatography (APHA Method 4500-NO2 B), reflect nitrogen concentrations, while total nitrogen (N Total), measured by TKN analysis (APHA Method 4500-N), indicates overall nitrogen content. Total Phosphorus (P Total), determined by colorimetric analysis (APHA Method 4500-P), identifies phosphorus that may cause eutrophication. Free Chlorine (Free Cl) is measured by the DPD colorimetric method (APHA Method 4500-Cl G), ensuring safe chlorine levels. Copper (Cu Total), detected by AAS or ICP-MS (APHA Method 3120B), reveals heavy metals affecting soil and plants.

2.4.3. Biological Parameters

Microbiological parameters, such as Total Coliform and E. coli, are crucial for evaluating water quality and safety, particularly for irrigation purposes, including windbreak trees, dry cereals, cooked vegetables, and processed vegetables. Total coliform, measured using the membrane filtration technique with selective growth media (APHA Method 9222B), serves as an indicator of fecal contamination in water, providing a general assessment of microbial presence. E. coli, detected through the Most Probable Number (MPN) method or membrane filtration with selective media (APHA Method 9221F), confirms the presence of fecal contamination and ensures microbial safety, helping determine the suitability of water for agricultural use.

2.5. Evaluating Criteria

2.5.1. Removal Efficiency (η)

Removal efficiency of each parameter was assessed by analyzing the removal of contaminants, including turbidity and microbial loads. The η was calculated using Equation (1):

$$\mu ={\displaystyle \frac{C_i-C_o}{C_i}}\times 100,$$

(1)

where C_i is the contaminant concentration at the inlet; C_o is the contaminant concentration at the outlet.

2.5.2. Water Quality Index (WQI)

The first step in determining the water quality index (WQI) involved measuring the concentration of each parameter in the treated water and comparing it to the standard values from the EMCR 2006 Sixth Schedule. The concentrations observed before and after treatment were recorded for 2023 and 2024.

The second step focused on determining the water quality parameters for irrigation based on the EMCR 2006 Sixth Schedule. These standards are crucial to ensure the water used for irrigation is suitable for crops and does not harm plant growth or soil health. Key parameters include Total Dissolved Solids (TDS), which should not exceed 1200 mg·L⁻¹, as high levels can lead to soil salinization. The pH range of 6.5 to 8.5 ensures water is neither too acidic nor too alkaline, allowing for proper nutrient uptake by plants. Total Suspended Solids (TSS) should be below 30 mg·L⁻¹, as high TSS can clog irrigation systems. BOD and COD levels, capped at 30 and 50 mg·L⁻¹, respectively, indicate organic matter presence, which can deplete oxygen levels in the soil. Nitrite and Nitrate (NO₂ and NO₃) levels should also be monitored to prevent nutrient imbalances, and the presence of pathogens, such as coliforms and E. coli, is closely regulated for safe irrigation. These standards, outlined in the EMCR 2006 Sixth Schedule, are essential for maintaining water quality, promoting sustainable agriculture, and protecting plant health and the environment.

In the third step, the WQI was calculated using the equation described by Meireles et al. [7]:

$$WQI={\sum }_{i=1}^n\left({\displaystyle \frac{Q_i\times W_i}{\sum W_i}}\right),$$

(2)

where Q_i is the sub-index for the ith parameter (based on its concentration and standard); W_i is the weighting factor based on the parameter’s significance.

The quality rating (Q_i) for each parameter was calculated using Equation (3):

$$Q_i={\displaystyle \frac{C_m}{C_s}}\times 100,$$

(3)

where C_m is the measured concentration (Treated water); C_s is the regulatory standard.

While pH was calculated using Equation (4):

$$Q_{pH}={\displaystyle \frac{C_{m-C_s}}{C_s}}\times 100$$

(4)

The weighting factor (W_i) for each parameter has a different significance in water quality evaluation. Higher weights are given to more critical parameters like BOD, COD, Total Coliform, and E. coli, which directly impact irrigation safety. A suggested weight (

Table 1. Weighting factors for water quality parameters.

Parameter	Weight (Wi)
TDS	0.10
pH	0.10
Oil and Grease	0.05
BOD	0.15
COD	0.15
NO2	0.07
N Total	0.07
P Total	0.05
Total Coliform	0.13
E. coli	0.13

) distribution is as follows.

Parameters that have a direct and significant impact on plant health, soil structure, and microbial activity were given higher weights. Total dissolved solids (TDS) and pH were assigned higher weights because they directly influence soil salinity and nutrient availability, which are vital for crop growth, particularly in the context of Egyptian soil conditions. According to ECP 501 [13], these parameters are crucial for ensuring sustainable irrigation practices, particularly in regions where soil salinity is a common concern. Biological oxygen demand (BOD) and chemical oxygen demand (COD) are also weighted significantly due to their role in indicating organic pollution levels, which can affect both plant roots and soil microorganisms. According to ECP 501 [13], where agricultural practices face challenges related to water quality and organic pollutants, these parameters are essential for determining irrigation water safety. On the other hand, parameters like total phosphorus (P Total) and total nitrogen (N Total) were assigned moderate weights, as their excess can lead to nutrient imbalances, but they are less immediately toxic compared to parameters like E. coli and Total Coliform. This is particularly important in Egypt, where waterborne diseases can pose a significant threat to human health through contaminated irrigation water. Trace elements, such as copper (Cu) and free chlorine (Cl), were given lower weights unless present at toxic levels, as their impact is often less pronounced at typical environmental concentrations. This approach is in line with ECP 501 [13], which prioritizes the evaluation of parameters based on their immediate and long-term effects on irrigation safety and crop production.

2.5.3. Interpret the WQI

The Water Quality Index (WQI) is a numerical representation used to assess the suitability of water for irrigation purposes. It provides a simplified yet comprehensive evaluation based on various water quality parameters. The following classification outlines the interpretation of WQI values, indicating the level of treatment required before use [7]:

• WQI < 50: Excellent quality (suitable for irrigation);
• WQI 50–100: Good quality (minor treatment needed);
• WQI 100–200: Poor quality (requires significant treatment);
• WQI > 200: Unsuitable for irrigation.

2.6. Statistical Analysis

The data were analyzed using ANOVA to determine the significance of differences among treatments. Means were compared using the Least Significant Difference (LSD) test at a 0.05 significance level.

3. Results

3.1. Preliminary Experiment

The results presented in Figure 2 demonstrate the effectiveness of sodium hypochlorite in reducing microbial contamination in treated effluent intended for agricultural irrigation. The concentration of 0 mg·L⁻¹ represents untreated wastewater before the addition of sodium hypochlorite. The initial concentrations of Total Coliform (TC) and E. coli were 218,532 CFU/100 mL and 200,845 CFU/100 mL, respectively, indicating severe microbial contamination. With the gradual increase in sodium hypochlorite doses from 5 to 20 mg·L⁻¹, a significant reduction in bacterial counts was observed. At 5 mg·L⁻¹, TC and E. coli were reduced to 21,853 CFU/100 mL and 15,943 CFU/100 mL, respectively, corresponding to removal efficiencies of 90.0% and 92.1%. Increasing the dose to 10 mg·L⁻¹ further decreased microbial loads to 1092 CFU/100 mL for TC and 980 CFU/100 mL for E. coli, achieving a removal efficiency of 99.5% for both indicators. Complete elimination of TC was achieved at 15 and 20 mg·L⁻¹ (100% removal), while E. coli showed near-complete removal at 15 mg·L⁻¹ (29.7 CFU/100 mL) and 100% removal at 20 mg·L⁻¹.

Based on the EMCR 2006 SIXTH SCHEDULE, the permissible limits for treated wastewater reuse in irrigation are 1000 CFU/100 mL for TC and 100 CFU/100 mL for E. coli. The results indicate that a sodium hypochlorite dose of 15 mg·L⁻¹ is the optimal concentration to meet these regulatory limits. At this dose, TC was reduced to 33 CFU/100 mL, and E. coli was nearly eliminated at 29.7 CFU/100 mL, making the water suitable for agricultural use. Increasing the dose to 20 mg·L⁻¹ achieved complete disinfection but may be unnecessary given the acceptable microbial thresholds at 15 mg·L⁻¹. Statistical analysis using one-way ANOVA confirmed a significant reduction in microbial loads (p < 0.05) across increasing doses, with the highest efficacy at 15 mg·L⁻¹. A post hoc Tukey test further revealed that the microbial reductions at 15 mg·L⁻¹ and 20 mg·L⁻¹ were not significantly different (p > 0.05), indicating that increasing the dose beyond 15 mg·L⁻¹ does not provide additional benefits. These results highlight the importance of optimizing disinfectant dosing to achieve effective microbial control while minimizing chemical usage.

Furthermore, the decision to forego biological treatment processes was based on the intrinsic characteristics of wastewater. The mixing of domestic sewage with agricultural drainage water results in a diluted wastewater composition with a low organic load. Under these conditions, conventional biological treatment would likely offer minimal additional benefit while increasing operational complexity and cost. Instead, the targeted physicochemical disinfection using sodium hypochlorite was deemed sufficient to meet the required microbial and physicochemical quality standards for safe and sustainable irrigation reuse. These results, aligned with previous studies, demonstrate the efficacy of sodium hypochlorite for microbial inactivation in wastewater treatment. Kesar and Bhatti [14] reported similar removal efficiencies of coliform bacteria with sodium hypochlorite disinfection in municipal wastewater. More recently, Boni et al. [15] confirmed that a dose range of 10–15 mg·L⁻¹ effectively reduces bacterial contaminants to permissible levels, supporting the findings of this study.

3.2. Properties of Wastewater

3.2.1. Physical Properties of Wastewater

Figure 3 shows the physical properties of wastewater, focusing on TSS and color, before and after treatment. Figure 3a shows the reduction in TSS, which represents undissolved particles in wastewater. The results show a significant decrease in TSS after treatment, demonstrating the ultrafiltration system’s efficiency. Post-treatment TSS levels were within acceptable ranges, aligning with studies like Al-Salmi et al. [16], they observed a 90% reduction in TSS using similar filtration methods. The reduction is attributed to the ultrafiltration membranes’ advanced pore structure. However, some studies, such as the one by Cooper [17], warn that ultrafiltration may face fouling issues with excessive organic matter or oil residues, but this was not observed here, suggesting effective pre-treatment. Reducing TSS not only meets regulatory standards but also minimizes environmental risks like eutrophication, while maintaining the necessary nutrients for soil fertility, as suggested by Sun et al. [18].

Figure 3b presents the results for the color of wastewater. The results show a marked improvement in water clarity after treatment, with the color intensity significantly reduced. Pre-treatment samples exhibited a dark hue, indicative of high concentrations of organic compounds, dyes, and other contaminants. Post-treatment samples, in contrast, showed a much lighter color, suggesting effective removal of color-causing substances. This reduction aligns with findings from [19], they reported similar results using ultrafiltration systems combined with coagulation pre-treatment. However, some studies, such as [20], argue that ultrafiltration alone may not eliminate color, especially if wastewater contains high concentrations of persistent organic dyes. These substances often require advanced oxidation processes or activated carbon adsorption to achieve full removal. Moreover, as noted by Nagial et al. [21], the presence of color in irrigation water can affect soil aeration and plant growth by altering light penetration and microbial activity. The results in Figure 3b, therefore, highlight the potential for ultrafiltration technology to address these concerns effectively.

3.2.2. Chemical Properties of Wastewater

The total dissolved solids (TDS) in wastewater showed a significant reduction after treatment, as seen in

Table 2. Chemical properties of wastewater before and after treatment.

Property	EMCR 2006 SIXTH SCHEDULE	2023		2024		Average
		Before Treatment	Treated Water	Before Treatment	Treated Water	Before Treatment	Treated Water
TDS, mg·L−1	1200	863.3	368.7	813.0	382.3	838.2	375.5
pH	7.5	7.4	7.3	7.2	7.0	7.3	7.2
Oil and grease		1.2	0.3	0.6	0.2	0.9	0.3
BOD, mg·L−1	30	116.7	18.9	215.6	26.1	166.2	22.5
COD, mg·L−1	50	249	45	235.0	34.1	242.0	39.6
NO2, NO3, and NH4, mg·L−1	100	92.3	83.6	75.7	49.9	84.0	66.7
N Total, mg·L−1	30	67.1	20.6	54.2	11.9	60.7	16.3
P Total, mg·L−1	10	9.9	5.3	8.4	5.7	9.1	5.5
Free Cl, mg·L−1	0.1	<0.02	<0.02	<0.02	<0.02	<0.02	<0.02
Cu Total, mg·L−1	1	<0.04	<0.04	<0.04	<0.04	<0.04	<0.04

. The average pre-treatment TDS level was 838.2 mg·L⁻¹, which decreased to 375.5 mg·L⁻¹ post-treatment, well below the EMCR 2006 Sixth Schedule limit of 1200 mg·L⁻¹. This reduction underscores the treatment system’s efficiency in removing dissolved salts and minerals, ensuring the treated wastewater is suitable for irrigation. Elevated TDS levels in untreated water can harm soil and crops, leading to salinization, reduced yields, and toxicity to sensitive plants. Loganathan et al. [22], confirm the effectiveness of technologies like ultrafiltration in reducing TDS by over 50%, consistent with the results in Table 2. The slight variation in pre-treatment TDS levels between 2023 (863.3 mg·L⁻¹) and 2024 (813.0 mg·L⁻¹) likely reflects seasonal or industrial changes in wastewater composition. Despite these variations, the treatment process reliably reduced TDS to less than half of the initial concentrations, demonstrating its robustness and suitability for sustainable agricultural reuse.

The pH levels of wastewater before and after treatment, as shown in Table 2, exhibited minor changes, remaining within the EMCR 2006 Sixth Schedule limit of 7.5. The average pre-treatment pH was 7.3, slightly alkaline, while the post-treatment average was 7.2. These values indicate that the treatment process maintained near-neutral conditions, ensuring the treated water’s suitability for irrigation. Ahmad et al. [23] confirmed that biological treatments and ultrafiltration technologies effectively maintain near-neutral pH levels in treated wastewater. The slight pH reduction post-treatment likely results from the removal of organic matter and pH -altering compounds.

The concentrations of oil and grease in wastewater decreased significantly after treatment, as shown in Table 2. Before treatment, the average oil and grease concentration was 0.9 mg·L⁻¹, while post-treatment levels reduced to 0.3 mg·L⁻¹. These treated levels fall well below the acceptable limits outlined in the EMCR 2006 Sixth Schedule, ensuring safe reuse in irrigation. High oil and grease levels in wastewater can form a hydrophobic layer on the soil surface, impairing water infiltration and oxygen exchange. This can negatively affect soil microorganisms and crop health. The treatment system’s ability to reduce oil and grease concentrations by approximately 66% underscores its effectiveness in mitigating these risks.

The significant reduction is likely attributed to the use of physical and chemical separation techniques, such as sedimentation, filtration, and coalescence, during the treatment process. Studies by Abuhasel et al. [24] highlight the efficacy of such methods, with removal efficiencies often exceeding 70%. These findings align with Table 2, highlighting the practical benefits of integrated treatment technologies. Pre-treatment values varied slightly (1.2 mg·L⁻¹ in 2023 vs. 0.6 mg·L⁻¹ in 2024), likely due to fluctuations in industrial discharge composition. Despite this, the treatment consistently reduced concentrations to safe levels, confirming its robustness.

The biological oxygen demand (BOD) levels in wastewater showed a dramatic reduction after treatment, as highlighted in Table 2. Before treatment, the average BOD was 166.2 mg·L⁻¹, while post-treatment levels decreased to 22.5 mg·L⁻¹. This reduction aligns with the permissible limit of 30 mg·L⁻¹ specified in the EMCR 2006 Sixth Schedule, ensuring that the treated water is safe for irrigation. BOD is a critical parameter that indicates the amount of organic matter present in wastewater. Elevated BOD levels before treatment suggest a high concentration of biodegradable organic pollutants, which can deplete dissolved oxygen in water bodies, adversely affecting aquatic life and soil health. The treatment system reduced BOD by approximately 86%, demonstrating its efficiency in removing organic matter. The treatment’s success can be attributed to the use of biological processes, such as activated sludge systems, and advanced filtration technologies. These methods are widely recognized for their ability to degrade organic pollutants effectively. Sharma et al. [25] supports these findings, highlighting that biological treatment systems can achieve BOD removal rates exceeding 85%.

The year-to-year variation in pre-treatment BOD values (116.7 mg·L⁻¹ in 2023 versus 215.6 mg·L⁻¹ in 2024) could reflect differences in the source and composition of the wastewater. However, the post-treatment values remained consistent, underscoring the reliability of the treatment system in achieving regulatory compliance.

The chemical oxygen demand (COD) levels in the wastewater, as shown in Table 2, demonstrated a substantial reduction after treatment. The average COD before treatment was 242.0 mg·L⁻¹, while post-treatment levels decreased to 39.6 mg·L⁻¹. These post-treatment levels comply with the EMCR 2006 Sixth Schedule limit of 50 mg·L⁻¹, indicating that the treated water is safe for reuse in irrigation. COD represents the total amount of oxygen required to oxidize both biodegradable and non-biodegradable organic matter in the water. High COD levels in untreated wastewater indicate a significant presence of organic and chemical pollutants, which can cause environmental harm if released untreated. Elevated COD levels can reduce dissolved oxygen in water bodies, leading to anaerobic conditions harmful to aquatic life and soil health. The treatment process achieved approximately an 84% reduction in COD, showcasing its efficiency in removing organic pollutants and improving water quality. This reduction can be attributed to the combined effects of biological and physical treatment processes, including oxidation and advanced filtration. Al-Salmi et al. [16] demonstrated similar results, with COD removal rates exceeding 80% in wastewater treated with biological and ultrafiltration systems. The study emphasized that such reductions are crucial for meeting environmental and agricultural reuse standards. The year-to-year variation in COD levels before treatment (249 mg·L⁻¹ in 2023 versus 235 mg·L⁻¹ in 2024) may be due to fluctuations in the wastewater’s chemical composition. Thus, the inherent dilution from mixing domestic wastewater with agricultural drainage water—which typically has a lower organic load—likely contributed to the lower pre-treatment levels of both BOD and COD, thereby enhancing the treatment system’s efficiency in meeting regulatory standards

Nitrite (NO₂⁻) levels moderately decreased after treatment, from 84.0 to 66.7 mg·L⁻¹, remaining within EMCR 2006 limits for irrigation. While nitrite can be toxic to plants and humans, the reduction confirms the system’s ability to manage nitrogenous compounds. The modest decrease is likely due to biological nitrification, where ammonium converts to nitrate. Sharma et al. [25] supports this, highlighting filtration’s role in nitrite removal. Despite yearly variations, the treatment consistently ensured compliance with safety standards.

The wastewater treatment system significantly reduced total nitrogen (N Total) levels from 60.7 to 16. mg·L⁻¹, achieving a 73% reduction and complying with the EMCR 2006 limit of 30 mg·L⁻¹. Although high nitrogen levels can cause eutrophication and groundwater contamination, biological processes like nitrification and denitrification effectively removed nitrogen compounds. Patel [26] confirms that advanced treatment systems achieve similar removal rates. Despite annual variations (67.1 mg·L⁻¹ in 2023 vs. 54.2 mg·L⁻¹ in 2024), the system-maintained nitrogen levels well below regulatory limits. Total phosphorus (P Total) also decreased from 9.1 mg·L⁻¹ to 5.5 mg·L⁻¹, a 40% reduction, complying with the EMCR 2006 limit of 10 mg·L⁻¹. While phosphorus supports plant growth, excess levels contribute to eutrophication. The reduction was likely due to chemical precipitation and biological removal processes, as supported by Bunce et al. [27]. Annual fluctuations (9.9 mg·L⁻¹ in 2023 vs. 8.4 mg·L⁻¹ in 2024) did not affect the system’s ability to achieve consistent phosphorus removal.

Free chlorine levels remained below the detection limit (<0.02 mg·L⁻¹), well within the EMCR 2006 limit of 0.1 mg·L⁻¹, ensuring safe agricultural reuse. Excessive chlorine can harm plants, but efficient dechlorination using activated carbon or chemical neutralizers prevented residual chlorine buildup. Bunce et al. [25] highlight controlled disinfection methods that maintain low chlorine levels. Consistency in results across 2023 and 2024 demonstrates the robustness of the disinfection process. Total copper (Cu Total) remained undetectable (<0.04 mg·L⁻¹) before and after treatment, far below the EMCR 2006 limit of 1 mg·L⁻¹. While copper is essential for plants, excessive amounts can be toxic and accumulate in soil. Minimal industrial discharge and effective adsorption or filtration steps likely contributed to these low levels. Raza et al. [28] emphasize that advanced filtration methods, such as ultrafiltration and reverse osmosis, help maintain low metal concentrations. Stability in copper levels across both years underscores the system’s reliability in handling trace contaminants

3.2.3. Biological Parameters

Figure 4 illustrates the biological parameters of water quality, where Figure 4a represents Total Coliform levels, and Figure 4b depicts E. coli concentrations. The results for Total Coliform indicate significant contamination, with values ranging between 193,487.0 and 203,126.0 CFU/100 mL before treatment, far exceeding the permissible limit of 1000 CFU/100 mL, as specified by the EMCR 2006 SIXTH SCHEDULE. After treatment with a sodium hypochlorite dose of 15 mg·L⁻¹, as recommended by the preliminary experiment in this study, the levels dropped significantly to 35.0 CFU/100 mL in 2023 and 31.0 CFU/100 mL in 2024, with an average of 33.0 CFU/100 mL. The substantial reduction highlights the effectiveness of the applied disinfectant. LeChevallier and Au [29] highlight that excessive coliform presence in water is often linked to poor sanitation infrastructure and inefficient wastewater treatment. Payment et al. [30] confirm that exposure to coliform-contaminated water correlates with an increased incidence of gastrointestinal illnesses, reinforcing the urgency of controlling microbial contamination. Implementing stringent monitoring and advanced filtration methods can significantly reduce coliform presence, ensuring safe water for irrigation.

For E. coli, the results reveal bacterial contamination well beyond the acceptable limit of 100 CFU/100 mL before treatment, with recorded values of 201,854.0 CFU/100 mL in 2023 and 185,349.0 CFU/100 mL in 2024, exceeding the permissible limit of 100 CFU/100 mL set by the EMCR 2006 SIXTH SCHEDULE. After treatment with the 15 mg·L⁻¹ sodium hypochlorite dose, E. coli levels were reduced to 32.1 CFU/100 mL and 29.7 CFU/100 mL, respectively, with an average of 30.9 CFU/100 mL. The presence of E. coli in water is a direct indicator of fecal contamination, posing severe health risks, including diarrheal diseases and infections [31]. Ashbolt [32] highlights that insufficient water treatment and deteriorating infrastructure contribute to bacterial contamination, particularly in regions with poor sanitation systems. Tsaridou et al. [33] emphasize that advanced treatment techniques, such as ultraviolet (UV) disinfection and membrane filtration, are effective in eliminating E. coli and reducing waterborne disease outbreaks. Strict enforcement of water quality regulations, along with routine monitoring, is essential in preventing public health hazards associated with microbial contamination.

3.3. Removal Efficiency

3.3.1. Removal Efficiency of Physical Properties

Figure 5 illustrates the removal efficiency of physical parameters in the treatment process. The Total Suspended Solids (TSS) removal reached 91.4%, indicating an effective sedimentation and filtration process. This aligns with studies by Haile [34], which reported that well-optimized treatment systems could achieve TSS removal above 90%. Similarly, color removal was 99.5%, highlighting the effectiveness of coagulation and flocculation in eliminating organic and colored contaminants.

Conversely, the Total Dissolved Solids (TDS) removal was 55.2%, suggesting that the treatment was only moderately effective in eliminating dissolved minerals. Research by Anis et al. [35] confirms that TDS is difficult to remove using conventional treatment, often requiring advanced techniques like reverse osmosis. Additionally, pH removal was only 1.8%, indicating minimal impact on acidity levels, which is expected if the raw water was already within a neutral range.

3.3.2. Chemical Properties of Wastewater

Figure 5 also demonstrates the varying chemical removal efficiencies. The oil and grease removal was 72.2%, which is acceptable but may require enhancement in cases of high concentrations. According to Pintor et al. [36], combining physical separation with biological treatment can improve oil and grease removal to over 85%.

The biochemical oxygen demand (BOD) and chemical oxygen demand (COD) removal efficiencies were 86.5% and 83.7%, respectively, reflecting a significant reduction in organic matter. These findings align with Patel [26], they observed that activated sludge systems could achieve similar BOD and COD reductions when aeration rates are optimized. However, nitrogenous compounds (NO₂, NO₃, NH₄) showed relatively low removal at 20.6%, indicating incomplete nitrification and denitrification. Research by Abuhasel et al. [24] suggests that nitrogen removal requires specialized biological treatment to enhance efficiency.

The Total Nitrogen (N Total) removal was 73.2%, indicating moderate effectiveness, whereas Total Phosphorus (P Total) removal was 39.6%, suggesting that additional chemical precipitation is necessary for higher efficiency.

The Free Chlorine (Free Cl) and total copper (Cu Total) removal efficiencies were not determined because their values before and after treatment remained below 0.4 mg·L⁻¹, as shown in Figure 5. This suggests that they were already at trace levels or that the treatment process had little impact.

3.3.3. Removal Efficiency of Biological Parameters

Figure 5 shows the high efficiency of microbial removal in the treatment process. Total Coliform removal reached 99.9%, while E. coli removal was 99.9%. These values comply with WHO [31] guidelines, which recommend removal rates exceeding 85% for effective microbial control. The treatment process utilized a sodium hypochlorite dose of 15 mg·L⁻¹, achieving removal efficiencies that align with the recommended standards of the EMCR 2006 SIXTH SCHEDULE. This highlights the effectiveness of the disinfection process in significantly reducing microbial contamination, ensuring safe water for irrigation and other applications. Kesar and Bhatti [14] reported similar removal efficiencies of coliform bacteria with sodium hypochlorite disinfection in municipal wastewater.

It should be noted that pH has not been included in Figure 5 because pH is not a substance that is removed, but rather a property of water that changes because of the removal or addition of other chemical components. In other words, “pH removal” cannot be measured in the same way as the removal of pollutants such as nitrate or ammonium, since the change in pH occurs due to alterations in the water’s chemical composition rather than the removal of pH itself.

3.4. Water Quality Index (WQi)

The Water Quality Index (WQI) offers a comprehensive evaluation of water quality by incorporating various physicochemical and biological parameters into a single value. This index is useful for assessing the suitability of treated water for irrigation.

Table 3. Water quality index (WQI) parameter values.

Parameter	Cm	Cs	Qi	Wi	Qi × Wi
TDS, mg·L−1	375.5	1200	31.3	0.1	3.13
pH	7.2	7.5	4.6	0.1	0.46
Oil and Grease	0.3	1	25.0	0.05	1.25
BOD, mg·L−1	22.5	30	75.0	0.15	11.25
COD, mg·L−1	39.6	50	79.1	0.15	11.87
NO2, mg·L−1	66.7	100	66.7	0.07	4.67
N Total, mg·L−1	16.3	30	54.2	0.07	3.79
P Total, mg·L−1	5.5	10	55.0	0.05	2.75
Total Coliform, CFU/100 mL	33.0	1000	3.3	0.13	0.43
E. coli, CFU/100 mL	30.9	100	30.9	0.13	4.02
WQI	43.61

presents the average WQI values for the treated water samples, calculated based on the observed concentrations of key parameters and their corresponding standard values.

The assessment of water quality was conducted using the Water Quality Index (WQI), which integrates multiple physicochemical and biological parameters. Table 3 presents the calculated values for each parameter, including the measured concentration (Cm), the regulatory standard (Cs), the sub-index (Qi), the weighting factor (Wi), and the product of the sub-index and weight (Qi × Wi). The computed WQI value for the treated water is 43.61, indicating that the water falls within the “Excellent quality” category (WQI < 50), making it suitable for irrigation. The total dissolved solids concentration of 375.5 mg·L⁻¹ is well within the permissible standard of 1200 mg·L⁻¹, resulting in a sub-index value of 31.3. Given its weight factor of 0.1, the contribution to WQI is 3.13. TDS levels below the regulatory limit suggest minimal salinity concerns, making the water suitable for agricultural use. The recorded pH value of 7.2 is close to the standard of 7.5, yielding a sub-index value of 4.6. With a weight of 0.1, the overall impact on WQI is 0.46, confirming a neutral pH that aligns with optimal irrigation conditions. The concentration of oil and grease was found to be 0.3 mg·L⁻¹, with a standard limit of 1 mg·L⁻¹. The sub-index score of 25.0 and weight factor of 0.05 result in a contribution of 1.25 to WQI, indicating that contamination from petroleum-based pollutants is minimal. The biochemical oxygen demand value of 22.5 mg·L⁻¹ and chemical oxygen demand value of 39.6 mg·L⁻¹ indicate moderate organic pollution levels. The respective sub-indices of 75.0 and 79.1 contribute 11.25 and 11.87 to WQI. Although these values are significant, they remain within acceptable limits for irrigation. The nitrite concentration of 66.7 mg·L⁻¹ and total nitrogen concentration of 16.3 mg·L⁻¹ produced sub-index values of 66.7 and 54.2, respectively. With weight factors of 0.07, their combined contribution to WQI is 8.46, highlighting moderate nutrient levels that support plant growth without excessive eutrophication concerns. The phosphorus level was measured at 5.5 mg·L⁻¹, generating a sub-index of 55.0 and contributing 2.75 to WQI. Controlled phosphorus levels prevent algal blooms while supporting plant nutrient requirements. Total coliform at 33.0 mg·L⁻¹ and E. coli at 30.9 mg·L⁻¹ exhibited sub-index values of 3.3 and 30.9, respectively. Their collective impact on WQI was 4.45, indicating effective microbial control in the treated water. Proper disinfection ensures minimal risk of pathogen-related health hazards. Figure 6 illustrates the proportional contributions of physical, chemical, and biological parameters to the overall WQI. Chemical properties dominate the index, accounting for 65.3%, followed by physical properties at 17.8% and biological parameters at 16.9%.

4. Discussion

The objective of this research is to evaluate the performance of an ultrafiltration unit in improving wastewater quality for sustainable irrigation reuse. The findings demonstrate the efficacy of sodium hypochlorite in significantly reducing microbial contamination in treated effluent, highlighting its role in ensuring compliance with regulatory standards for agricultural irrigation. The observed trend of microbial reduction, with increasing sodium hypochlorite doses, aligns with previous studies. Kesar and Bhatti [14] reported similar removal efficiencies of coliform bacteria with sodium hypochlorite disinfection in municipal wastewater, further supporting these findings. Additionally, Boni et al. [15] confirmed that a dose range of 10–15 mg·L⁻¹ effectively reduces bacterial contaminants to permissible levels. The study confirms that a 15 mg·L⁻¹ dose achieves the required microbial quality standards without unnecessary excess use of chemicals, as further increasing the dose to 20 mg·L⁻¹ provided no statistically significant additional benefit. This optimization is crucial in balancing microbial safety with chemical usage, as excessive disinfectant application can result in unintended environmental and health impacts, such as the formation of disinfection byproducts (DBPs) [29].

The effectiveness of the ultrafiltration system in reducing total suspended solids (TSS) was also evident, as post-treatment TSS levels were well within acceptable ranges. This aligns with the findings of Al-Salmi et al. [16], who reported a 90% reduction in TSS using similar filtration technologies. The significant decrease in TSS suggests the system’s advanced membrane structure effectively removes particulates, which is crucial in preventing clogging in irrigation systems. However, Cooper [17] cautions that ultrafiltration membranes may be prone to fouling, particularly in wastewater with high organic matter content, potentially impacting long-term efficiency. The absence of fouling in this study suggests that adequate pre-treatment measures were in place to mitigate this issue, supporting the robustness of the applied filtration system.

Similarly, wastewater color, an indicator of organic and dye contamination, exhibited a substantial improvement post-treatment. This aligns with the findings of Sandoval-Olvera et al. [19], who reported similar color reduction in ultrafiltration systems coupled with coagulation pre-treatment. However, some studies, such as the one by Tiwari et al. [20], suggest that ultrafiltration alone may not completely remove persistent organic dyes, often requiring advanced oxidation or activated carbon adsorption for further refinement. The observed improvements in water clarity in this study highlight the system’s capability in addressing organic load, though supplementary treatments may enhance color removal efficiency in cases of high industrial effluent content.

The chemical properties of treated wastewater further underscore the effectiveness of the ultrafiltration system. Total dissolved solids (TDS) were significantly reduced, maintaining values well below the EMCR 2006 Sixth Schedule limit, confirming the suitability of the treated water for irrigation. Loganathan et al. [22] also reported similar TDS reductions using ultrafiltration, highlighting its efficacy in removing dissolved salts. The observed seasonal variations in TDS concentrations before treatment suggest that fluctuations in industrial and domestic discharges may influence raw wastewater characteristics. Despite this variability, the treatment system consistently achieved substantial TDS reduction, demonstrating its adaptability to diverse wastewater compositions.

The pH stability observed post-treatment is another indicator of the system’s suitability for irrigation. Maintaining near-neutral pH conditions is essential for plant health, as extreme pH values can affect nutrient availability and soil structure. Ahmad et al. [23] confirmed that ultrafiltration and biological treatment methods effectively sustain stable pH conditions, consistent with the findings of this study. The minimal pH variation before and after treatment indicates that the system primarily targets contaminants without significantly altering the chemical equilibrium of the water.

The reduction in oil and grease concentrations further supports the effectiveness of the treatment process, as high levels can impede water infiltration in soil and negatively impact plant and microbial activity. The 66% reduction observed in this study is comparable to the findings of Abuhasel et al. [24], who documented removal efficiencies exceeding 70% using integrated filtration and separation techniques. These findings highlight the importance of combining physical and chemical separation processes to optimize wastewater treatment efficiency.

The study also demonstrated substantial reductions in biological oxygen demand (BOD) and chemical oxygen demand (COD), indicating effective removal of organic pollutants. The BOD reduction of approximately 86% aligns with Sharma et al. [25], who reported similar removal efficiencies using biological treatment and filtration systems. Likewise, the observed 84% COD reduction is consistent with Al-Salmi et al. [16], who emphasized the necessity of such reductions in meeting environmental and agricultural reuse standards. The consistency in post-treatment values across different sampling years underscores the reliability of the system in achieving regulatory compliance despite variations in wastewater composition. In addition to the observed reductions, it is important to note that the relatively low pre-treatment BOD and COD levels can be attributed to the inherent dilution resulting from the mixing of domestic wastewater with agricultural drainage water. This blending reduces the overall organic load, thereby diminishing the oxygen demand in the wastewater. As a result, the need for extensive biological treatment is minimized, allowing the treatment process to rely predominantly on advanced physicochemical methods and ultrafiltration. This streamlined approach not only achieves the desired pollutant removal efficiently but also reduces operational complexity and the risk of forming disinfection byproducts, ultimately supporting sustainable irrigation practices.

Nutrient removal efficiency was also a key aspect of the system’s performance. The total nitrogen (N Total) reduction of 73% and total phosphorus (P Total) reduction of 40% comply with regulatory standards, preventing potential eutrophication risks associated with nutrient-rich effluents. Patel [26] confirmed that biological nitrification and denitrification effectively reduce nitrogen levels, supporting the mechanisms observed in this study. Similarly, Bunce et al. [27] highlighted that phosphorus removal is primarily driven by chemical precipitation and biological uptake, both of which were likely contributing factors here. The minor fluctuations in nutrient concentrations between sampling years further emphasize the need for continued monitoring to account for variable wastewater compositions. The biological parameters confirmed the system’s effectiveness in microbial inactivation. The substantial reductions in Total Coliforms and E. coli levels validate the efficacy of sodium hypochlorite disinfection, aligning with the findings of LeChevallier and Au [29] and Payment et al. [30]. These reductions are crucial in mitigating health risks associated with microbial contamination in irrigation water, as emphasized by WHO [31]. The results further confirm that a 15 mg·L⁻¹ sodium hypochlorite dose is sufficient for achieving compliance with microbiological safety standards, reinforcing the importance of optimizing disinfectant use to balance effectiveness and sustainability. The Water Quality Index (WQI) was calculated to provide a comprehensive assessment of the treated water’s suitability for irrigation. The WQI values showed a substantial improvement after ultrafiltration, shifting from a category of poor to good quality water, making it more suitable for agricultural applications. This improvement aligns with regulatory guidelines for irrigation water quality.

Thus, this study demonstrates the effectiveness of ultrafiltration and sodium hypochlorite disinfection in improving wastewater quality for sustainable irrigation reuse. The treatment process successfully reduces microbial contamination, TSS, TDS, organic pollutants, and nutrients while maintaining pH stability and minimizing chemical usage. The findings align with previous research, confirming the reliability of the applied treatment technologies. Future research could explore long-term operational performance, potential fouling mitigation strategies, and additional treatment options for enhanced color removal and nutrient recovery.

5. Conclusions

This study evaluates the effectiveness of an ultrafiltration system in treating wastewater—comprising domestic sewage mixed with agricultural drainage water—under real operational conditions, without relying on biological treatment, to meet the required microbial and physicochemical quality standards for safe and sustainable irrigation reuse. The ultrafiltration process achieved over 90% removal of suspended solids and significantly reduced color intensity, thereby enhancing water clarity. Additionally, reductions in total dissolved solids (TDS) and oil and grease underscore the system’s capacity to mitigate potential environmental risks associated with untreated wastewater, as reflected by the water quality index (WQI), which rates the treated water as “Excellent.” The integration of ultrafiltration with optimized sodium hypochlorite disinfection resulted in a significant improvement in water quality for sustainable irrigation. Notably, while the use of wastewater treatment technology for diluted municipal wastewater is well established, this study offers a distinct perspective by exclusively employing physical treatment methods—namely clarification, activated carbon (AC) filtration, and membrane filtration—to treat a blended stream of municipal wastewater and agricultural runoff without the incorporation of biological processes. This innovative approach for crop irrigation not only simplifies the treatment process but also demonstrates that high-quality water can be achieved solely through physical means, thereby broadening the scope of conventional treatment technologies. Nonetheless, continuous monitoring and process optimization remain essential to ensure compliance with environmental standards and long-term sustainability.

Future research should explore the incorporation of more advanced treatment technologies while also evaluating the economic aspects and global impact of ultrafiltration. This broader approach will not only enhance wastewater quality further but also provide insights into the economic feasibility and worldwide applicability of this technology, ultimately supporting its adoption in diverse contexts and contributing to sustainable water management practices.