The issue of food security as a multifaceted problem is still of great concern in the semi-arid region and countries in Africa, with poor infrastructure to bring new water resources, because high and unevenly distributed population growth is still expected in the first half of the 21st century. In this context, increased efforts are needed to exploit existing water resources and recover new ones.
Through wastewater treatment, they can be reused in irrigation or watering, provided that their components meet international standards. This article is dedicated to letting consumers know the risks of reuse and what strategies to put in place to predict the health and safety of people with whom they may come into contact.
Risk Evaluation and Control for Treated Wastewater Reuse in Green Spaces1. Introduction: Understanding the Importance of Reusing
Treated Wastewater
Traditionally ,wastewater reuse on agricultural
land is widely acknowledged and the most desirable alternative as it requires
little advanced treatment.
Only 10–15% of wastewater currently receives some kind
of treatment; the other proportion ,especially greywater –,s only discharged
directly to the environment. Thus, reclaiming wastewater for non-agricultural
purposes (mainly irrigation of fodder, ornamental plants, and urban green
areas) is the second best since, despite additional barriers, it represents a
market and value to society.
Understanding the importance of reusing treated
wastewater for non-potable applications on a global scale is helping to reduce
the reliance on increasingly scarce freshwater resources (Gatica & Cytryn, 2013).
The utilization of reclaimed water in green spaces
is one of the successful practices for integrating water management planning in
a bid to alleviate water-stressed conditions ma,inly in areas with intermittent
water supply (H. Sadek et al., 2021).
However, the potential exposure and associated health risks of chemicals and microbial contaminants due to the resumed human activities are largely unknown in the outside environment (Guergachi, 2000).
Also, it is essential to properly manage these small-scale water supply systems at a local level to cope with intermittent supply conditions and emthe erging risk of water crisis.
2. Potential Risks Associated with Reuse of Treated
Wastewater
When assessing whether treated domestic wastewater is suitable for reuse, the primary health risks can be divided into waterborne contamination and human contact with sewage (Mara & Hamilton, 2014). There are some concerns regarding the potential human health impacts of water reuse, especially from microbiological pollution.
The presence of human enteric pathogens and microorganisms has been detected in raw or treated wastewater, as well as differences between removal rates for various elements or organisms, such as Giardia duodenalis cysts or Cryptosporidium oocysts (Gomes et al., 2019).
There is also evidence that shows the chemical and biological risks in water reuse, potentially exposing humans – as end users – via micro-sprinklers or breathing in biological and virological pollution (Sidhu et al., 2019). However, it is already known that safely managed, treated, and monitored wastewater reuse in agricultural irrigation systems can reduce exposure risks for the general population and contaminants.
This principle has been demonstrated in a small number of cases, with recent scientific studies on agriculture and aquaculture in the urban and peri-urban environment leading the way.
The combination of population growth, pollution, and climate change has exacerbated water scarcity problems. Treated wastewater reuse represents a sustainable water resource alternative for urban areas (Warsinger et al., 2019a).
The expansion of urban areas, municipal water consumption, and pollution pplacesheightened pressure on at-risk ecosystems (Tilley et al., 2014; Kusumawardhana et al., 2021).
Wastewater treatment plants release considerable amounts of treated water to surface water; this treated effluent has the potential to replenish water ecosystems and restore environmental function through integrated water management (Sheer & Lundie, 2018) (E. Schoen et al., 2018).
2.1. Microbial Contamination
In the case of irrigated wastewater, the microbial quality also needs to be taken care of in terms of coliforms, Escherichia coli, and Salmonella, total microbial content in the form of Bacteria (TVCC-Total Viable Cell Count) at least on a regular time interval or at least annually for Escherichia coli and Salmonella.
Microbial count over 100 cfu/100 ml of
Escherichia coli and 1000 cfu/100 ml of TVC at the point of
compliance is bonsidered ahe permissible limit according to the
relevant standard. According to the recommendation of the WHO, (004, effluent
for unrestricted irrigation should have no more than 1 E. coli per 100 mL in at
least 80% of the samples collected over the previous 4-6 weeks, and no sample
should have more than 10 E. coli per 100 mL.
On the other hand, if the public is not allowed in the irrigation area, up to 5 E. coli per 100 mL are recommended, and not every sample has more than 10 E. coli per 100 mL in effluent for unrestricted irrigation (O'Dwyer et al., 2020). The risk associated with direct oral ingestion of untreated primary effluent and secondary effluent is calculated to be 100 to 1000 times more than that of treated effluent per year in the scenario evaluated in this study. Streams receiving untreated sewage are found to be disproportionately contaminated.
Given the occurrence of multiple drought periods and the water shortage in Oman, the application of treated wastewater in the soil-plant system has received much attention (Gatica & Cytryn, 2013). However, such reuse concerns related to human health and environmental risks need to be appraised for minimizing the potential threats.
Among others, microbial quality, the presence of heavy metals, organic micro-pollutants, and antibiotic resistance,emerge as potential issues that need to be addressed. According to the standard guidelines, a microbial quality assessment of E. coli has always been the preferred bacterium for the assessment of microbial load in treated wastewater and reclaimed water (E. Schoen et al., 2018).
2.2. Chemical Contaminant
Assessment of risks to prevent WW from reaching natural water systems is fundamental for public health and ecosystem preservation. Authors should consider pthe roteomic CPU for multipurpose use and convey its significance regarding WW management.
Wastewater treatment processes do not always completely remove chemical pollutants such as heavy metals, pharmaceuticals, pesticides, and industrial chemicals. The presence of elements like lead, mercury, cadmium, and arsenic in irrigation water can have long-term effects on soil health and plant growth.
Many of these contaminants enter the water supply through domestic and industrial discharge, and their accumulation in the environment can pose significant health risks. For instance, exposure to certain endocrine-disrupting chemicals (EDCs) in treated wastewater has been linked to reproductive and developmental disorders in both humans and wildlife.
2.3. Nutrient Imbalance
Nutrient imbalances, represented by factors such as tank depletion and drying periods, are observed in treated wastewater (TWW) usage across different geographical and climatic conditions.
These imbalances affect green spaces, leading to changes in vegetation patterns and crop productivity. The supplementation of potable water with TWW for irrigation purposes has shown mixed results, impacting both vegetable production and plant growth characteristics.
Concerns about urban environmental management, including water scarcity and agricultural risks, have prompted a shift towards reducing water-intensive horticulture, particularly in urban areas where greywater is commonly used. However, reliance on effluent-derived channels for irrigation exacerbates water scarcity issues.
Nutrient imbalances, exacerbated by chemical fertilizers in TWW, have become characteristic of urbanization, particularly in low-income countries. The role of nutrient dispersal and floc development in urban agroecosystems has been discussed, highlighting the need for balanced nutrient loops. TWW usage in green spaces often results in theoretical deficiencies of nitrogen, carbon, and sulfur, due to the absence of local soluble nutrients, necessitating careful management to address these shortcomings.
3. Strategies to Mitigate Risks
To ensure the safe reuse of treated wastewater in green spaces, proactive risk management strategies must be implemented. These strategies involve improving wastewater treatment technologies, establishing rigorous monitoring systems, and adopting best irrigation practices.
3.1. Water Treatment Technologies
Advancements in wastewater treatment processes have made it possible to produce high-quality reclaimed water suitable for irrigation. Key treatment methods include:
- Coagulation and Sedimentation: Removes suspended solids and reduces turbidity.
- Filtration (Sand or Membrane): Eliminates fine particles and microbial contaminants.
- Disinfection (Chlorination, UV, Ozonation): Inactivates harmful microorganisms to ensure public safety.
- Advanced Oxidation Processes (AOPs): BBreakdown complex organic pollutants and pharmaceuticals.
Implementing multi-barrier treatment approaches can significantly reduce microbial and chemical risks, ensuring compliance with national and international reuse standards.
3.2. Monitoring and Testing Protocols
Regular testing of treated wastewater is crucial for ensuring its safety before reuse. Comprehensive monitoring programs should assess:
- Microbiological Quality: Pathogen levels, including coliform bacteria and viruses.
- Chemical Composition: Presence of heavy metals, pesticides, and pharmaceutical residues.
- Nutrient Levels: Balance of nitrogen, phosphorus, and potassium to prevent soil damage.
Governments and regulatory bodies should enforce strict quality control measures to prevent public health hazards and environmental degradation.
3.3. Proper Irrigation Practices
Effective irrigation management minimizes health and environmental risks associated with treated wastewater reuse. Best practices include:
- Drip Irrigation: Reduces human contact with wastewater and prevents aerosol formation.
- Time-Controlled Irrigation: Conducting irrigation during off-peak hours to limit public exposure.
- Buffer Zones: Establishing restricted areas around irrigated landscapes to minimize direct contact.
- Soil Testing: Regularly assessing soil conditions to detect potential contamination.
Adopting these practices ensures the safe integration of reclaimed water into urban landscapes while protecting human and environmental health.
Treated wastewater reuse network
Treated wastewater reuse can provide a sustainable and low-energy solution to water scarcity in urban green spaces (UGS). This work includes five processes, including coagulation, precipitation, sedimentation, filtration, and chlorination, for treating secondary effluents.
3.4 The elements contained in reused water
If there are more Nickel, Calcium, Chromium, Iron, Magnesium, Manganese, Selenium, Sodium, Lithium, Cadmium, Copper, Lead, and Zinc in the Wastewaters that are required to be used for irrigation, it might be risky to carve minerals upon absorption and corrupts the soil structure for some situations on those subject (Taheri, 2021).
4. Quality Standards for Water Intended for Reuse
Inappropriate irrigation practices and reclaimed water
with high quality pose risks. The standards for treated wastewater reuse in
irrigation were observed to lack these. ater quality standards for urban green
spaces (TWW-I-UGS) defining irrigation with treated wastewater.
The proposed
TWW-I-UGS was found to be more conservative than other standards. The findings
of the study will improve the guidelines and quality standards for treated
wastewater reuse in urban green spaces (Al-Sa’ed,
2007).
Water quality standards are rules that make sure water
is safe for people and the environment. They focus on two things: chemicals and
living things in the water. The World Health Organization sets these standards.
The California standards did not contain pathogen-related criteria in itstheirandard. The microbial quality of treated wastewater
substantially meets WHO guidelines. The treated wastewater does not comply with
the other standards (Chen & Franklin, 2023).
Documents related to treated wastewater reuse for the
green spaces were considered for the comparison analysis. The California state
regulations and WHO guidelines were observed to be inadequate for treated
wastewater reuse in urban green spaces.
The reuse of treated wastewater for irrigation in urban green spaces is an integral part of a sustainable urban water cycle (UWC) due to the rapidly expanding urbanization and water scarcity (Gatica & Cytryn, 2013). Risk assessment and management (RAM) of wastewater reuse for irrigation substantially depends on the regulations that define the water quality standards.
The safe and reliable reuse in urban green spaces depends on the quality and degree of treatment and methods of safe application. The review critically assesses the guidelines and quality standards for irrigation water reuse.
Comparison of various regulations across the world for
different standards necessitates ca omprehensive discussion. Furthermore, the
present knowledge of the quality of treated wastewater reuse is pbasedto
reclaim as considered against the recommended standards. Reclaimed wastewater
has been used for irrigation without considering the health hazards associated
with contaminated food and soil.
4.1. Environmental Considerations for Water Reuse
The underlying values of water reuse technologies
are critical for grasping the public significance and environmental and
infrastructural challenges. They include securing the quality of water and
security; protecting the dignity of fresh water; and the integration and
cultivation of green and sustainable techniques for water in structural
innovations.
Given the harsh climate conditions and water
scarcity, the adoption of water reuse techniques has been the highest in
Kuwait, United Arab Emirates, Israel, Singapore, and Bahrain. They are regularly
strapped with limited resources, so it has often required money, operating
funding,g and inputs.
This process is competitive across
all countries, but consumers primarily use wastewater for irrigation,
particularly in the Mediterranean and western Asia ,but are not incentivized to use
wastewater on a larger scale. Water reuse is, indeed, predicted to rise by 50
percent globally (Kulionis et al., 2024).
Water scarcity is a growing threat that endangers food
security and the growth of communities, primarily in the developing world.
Water reuse, also known as water recycling, reclaims water from sewage,
greywater, and blackwater for reuse (Yang et al.,
2020).
The aim is to mitigate the drinking water crisis by obtaining water that meets only quality requirements and improving environmental problems related to water, energy, and ecosystem conservation through urban and residential activities.
In some of the global scenarios for climate change, the form and quantity of available water resources will vary across the northern, sub-tropical, and tropical latitudes. Techniques for risk control include proper and effective handling of the wastewater before use, and regular evaluation of procedures for water quality (Alevizos et al., 2023).
4.2. Text of standards for water intended for Reuse
The standards that exist worldwide for treated
wastewater reuse for irrigation are agnostic concerning the proposed method of
irrigation, either drip, sprinkler irrigation, or spread ,but advise users when
the treated wastewater reuse risk presents a subcategory of potential public
exposure. The risk is calculated using the likelihood and the potential public
offset, not only the total amount of water that is reused, but also the
microbial water quality of the treated wastewater and the actual paths to the people
that are reusing it.
| Standard | E. coli Limit (per 100 mL) | Other Key Parameters |
|---|---|---|
| WHO Guidelines | ≤1 (unrestricted irrigation) | No heavy metals above safe limits |
| EU Directive | ≤1000 (restricted irrigation) | Pathogen-free, low turbidity |
| US EPA Regulations | ≤14 (for public landscapes) | Disinfection required |
| California Standards | Not specified for pathogens | Focus on nutrient content |
If irrigation presents no potential for aerosol
inhalation, not all fecal paths are planned for reuse in the irrigation
project, such as urinal flows, and the hydraulic loading is high, all the
fecal bacterial indicators may be at a low predefined concentration for the
potential public exposure, otherwise, the potential public exposure is much
higher than in this case. All these parameters could be incorporated into a
biological green project risk-adjusted microbiological standard (R. Srivastava & K. Singh, 2021).
Water reuse presents an innovative approach to
managing urban water and closing the urban water cycle (Reynaert
et al., 2021). Water intended for reuse could be either stormwater or
treated wastewater, as they all could be used for various reasons, such as, for
the irrigation of green spaces in the cities. Some countries have developed
standards based on the risk management of potentially pathogenic andtoxic substancess
to protect public health.
The risk management approach uses
microbiological standards microbiological standards as entry-level barriers for facial bacterial
indicators, but these results may not be sufficient to assess the public health
risk related to the other potential contaminants in the treated wastewater or
stormwater. There are currently no microbiological standards, specifically
designed for the water intended for reuse in a biological green project.
5. Conclusion
Treated wastewater reuse in green spaces is an effective solution to water scarcity, promoting environmental sustainability and urban resilience. However, potential risks, including microbial contamination, chemical pollutants, and nutrient imbalance,s must be carefully managed to protect public health and ecosystems.
By implementing advanced treatment technologies, rigorous monitoring protocols, and best irrigation practices, communities can maximize the benefits of wastewater reuse while minimizing risks. Adhering to established water quality standards and environmental guidelines ensures that reclaimed water can be safely and effectively integrated into urban landscapes, contributing to sustainable water management worldwide.
FAQs
1. Is treated wastewater safe for irrigation in public parks?
Yes, if it meets international safety standards and undergoes proper treatment and disinfection to remove harmful contaminants.
2. What are the main risks of using treated wastewater in green spaces?
Microbial contamination, chemical pollutants, and nutrient imbalances can affect soil health and human safety.
3. How can wastewater treatment reduce contamination risks?
By using multi-barrier approaches, including filtration, disinfection, and advanced oxidation, to remove pathogens and hazardous chemicals.
4. Are there global regulations for wastewater reuse?
Yes, organizations likethe WHO, Ethe PA, and the EU provide guidelines for water quality and safe reuse practices.
5. What is the best irrigation method for using treated wastewater?
Drip irrigation is the safest method as it minimizes direct contact and reduces the risk of airborne contamination.
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