Wastewater reuse for irrigation of produce: A review of research, regulations, and risks

Capsid Integrity Detection of Enteric Viruses in Reclaimed Waters

Climate change, unpredictable weather patterns, and droughts are depleting water resources in some parts of the globe, where recycling and reusing wastewater is a strategy for different purposes. To counteract this, the EU regulation for water reuse sets minimum requirements for the use of reclaimed water for agricultural irrigation, including a reduction in human enteric viruses. In the present study, the occurrence of several human enteric viruses, including the human norovirus genogroup I (HuNoV GI), HuNoV GII, and rotavirus (RV), along with viral fecal contamination indicator crAssphage was monitored by using (RT)-qPCR methods on influent wastewater and reclaimed water samples. Moreover, the level of somatic coliphages was also determined as a culturable viral indicator. To assess the potential viral infectivity, an optimization of a capsid integrity PMAxx-RT-qPCR method was performed on sewage samples. Somatic coliphages were present in 60% of the reclaimed water samples, indicating inefficient virus inactivation. Following PMAxx-RT-qPCR optimization, 66% of the samples tested positive for at least one of the analyzed enteric viruses, with concentrations ranging from 2.79 to 7.30 Log10 genome copies (gc)/L. Overall, most of the analyzed reclaimed water samples did not comply with current EU legislation and contained potential infectious viral particles.

Screening Disinfection Byproducts in Arid-Coastal Wastewater: A Workflow Using GC×GC-TOFMS, Passive Sampling, and NMF Deconvolution Algorithm

Disinfection during tertiary municipal wastewater treatment is a necessary step to control the spread of pathogens; unfortunately, it also gives rise to numerous disinfection byproducts (DBPs), only a few of which are regulated because of the analytical challenges associated with the vast number of potential DBPs. This study utilized polydimethylsiloxane (PDMS) passive samplers, comprehensive two-dimensional gas chromatography (GC×GC) coupled with time-of-flight mass spectrometry (TOFMS), and non-negative matrix factorization (NMF) spectral deconvolution for suspect screening of DBPs in treated wastewater. PDMS samplers were deployed upstream and downstream of the chlorination unit in a municipal wastewater treatment plant located in Abu Dhabi, and their extracts were analyzed using GC×GC-TOFMS. A workflow incorporating a multi-tiered, eight-filter screening process was developed, which successfully enabled the reliable isolation of 22 candidate DBPs from thousands of peaks. The NMF spectral deconvolution improved the match factor score of unknown mass spectra to the reference mass spectra available in the NIST library by 17% and facilitated the identification of seven additional DBPs. The close match of the first-dimension retention index data and the GC×GC elution patterns of DBPs, both predicted using the Abraham solvation model, with their respective experimental counterparts-with the measured data available in the NIST WebBook and the GC×GC elution patterns being those observed for the candidate peaks-significantly enhanced the accuracy of peak assignment. Isotopic pattern analysis revealed a close correspondence for 11 DBPs with clearly visible isotopologues in reference spectra, thereby further strengthening the confidence in the peak assignment of these DBPs. Brominated analogues were prevalent among the detected DBPs, possibly due to seawater intrusion. The fate, behavior, persistence, and toxicity of tentatively identified DBPs were assessed using EPI Suite™ and the CompTox Chemicals Dashboard. This revealed their significant toxicity to aquatic organisms, including developmental, mutagenic, and endocrine-disrupting effects in certain DBPs. Some DBPs also showed activity in various CompTox bioassays, implicating them in adverse molecular pathways. Additionally, 11 DBPs demonstrated high environmental persistence and resistance to biodegradation. This combined approach offers a powerful tool for future research and environmental monitoring, enabling accurate identification and assessment of DBPs and their potential risks.

Human health risk assessment framework for new water resource recovery-based bio-composite materials

A new type of bio-composite material is being produced from water-recovered resources such as cellulose fibres from wastewater, calcite from the drinking water softening process, and grass and reed from waterboard sites. These raw materials may be contaminated with pathogens and chemicals such as Escherichia coli, heavy metals, and resin compounds. A novel risk assessment framework is proposed here, addressing human health risks during the production of new bio-composite materials. The developed framework consists of a combination of existing risk assessment methods and is based on three main steps: hazard identification, qualitative risk mapping, and quantitative risk assessment. The HAZOP and Event Tree Analysis methodologies were used for hazard identification and risk mapping stages. Then, human health risks were quantitatively assessed using quantitative chemical risk assessment, evaluating cancer and non-cancer risk, and quantitative microbial risk assessment. The deterministic and the stochastic approaches were performed for this purpose. The contamination of raw materials may pose human health concerns, resulting in cancer risk above the threshold. Microbial risk is also above the safety threshold. Additional analysis would be significant as future research to better assess the microbial risk in biocomposite production. The framework has been effectively used for chemical and microbial risk assessment.

Utilization of treated municipal effluent for irrigating agricultural land in Palestine: The driving factors and existing practices

This article investigates the motivations and practices of using treated wastewater (TWW) to irrigate crop fields in Jenin, Palestine. Around 40 farmers were surveyed for data collection. The results showed that 66% of the farmers grew alfalfa crops while 30% grew fruit trees. The main obstacles the farmers faced before starting to use TWW were disgust (68.2%), worries about the quality of TWW (68.2%), health concerns (63.6%), and concerns about adverse effects on the soil (63.6%). All interviewed farmers considered the establishing and funding of an irrigation project to be the cornerstone for any reuse project. The second most important driving factor was the price of TWW that is 10-25% of the fresh water prices. After reusing TWW for irrigation, 59% of the farmers did not use any fertilizer, but they were not sufficiently aware of the crops' water needs, nor the nutrients in the TWW. All the fodder-growing farmers abstained from selling their crops before drying. The farmers used the TWW for five to nine months annually. After the TWW was reused, the main positive impacts of the TWW reuse were increased crop yields (77.3%), crops quality (50.0%), and crops marketing (47.7%). On the other hand, the main negative impacts were blocking of the irrigation systems (77.3%) and release of odors (54.5%). After practicing TWW use in crops irrigation, the key factors contributed to the "no difference" index were the effects on human health (100%), soil quality (56.8%), and insects spread (54.5%). Therefore, the results of the study support the decision makers to implement TWW reuse policies for crop irrigation in arid regions with scarce water resources. Monitoring TWW reuse and training farmers and helping them overcome obstacles is essential.

Pharmacokinetics of the Recalcitrant Drug Lamotrigine: Identification and Distribution of Metabolites in Cucumber Plants

Treated wastewater is an important source of water for irrigation. As a result, irrigated crops are chronically exposed to wastewater-derived pharmaceuticals, such as the anticonvulsant drug lamotrigine. Lamotrigine is known to be taken up by plants, but its plant-derived metabolites and their distribution in different plant organs are unknown. This study aimed to detect and identify metabolites of lamotrigine in cucumber plants grown for 35 days in a hydroponic solution by using LC-MS/MS (Orbitrap) analysis. Our data showed that 96% of the lamotrigine taken up was metabolized. Sixteen metabolites possessing a lamotrigine core structure were detected. Reference standards confirmed two; five were tentatively identified, and nine molecular formulas were assigned. The data suggest that lamotrigine is metabolized via N-carbamylation, N-glucosidation, N-alkylation, N-formylation, N-oxidation, and amidine hydrolysis. The metabolites LTG-N2-oxide, M284, M312, and M370 were most likely produced in the roots and were translocated to the leaves. Metabolites M272, M312, M314, M354, M368, M370, and M418 were dominant in leaves. Only a few metabolites were detected in the fruits. With an increasing exposure time, lamotrigine leaf concentrations decreased because of continuous metabolism. Our data showed that the metabolism of lamotrigine in a plant is fast and that a majority of metabolites are concentrated in the roots and leaves.

Short-term effect of reclaimed wastewater quality gradient on soil microbiome during irrigation

To investigate the effect of wastewater (WW) treatment on soil bacterial communities, water of different quality was used to irrigate eight lettuces per tank: raw municipal wastewater (RWW), WW treated with an aerated constructed wetland (CWW) and WW treated with a membrane bioreactor (MBW), and tap water (TW). The physicochemical and microbiological characteristics (quality indicators) of these water types were characterized, and the water and soil bacterial communities were monitored by quantitative PCR (qPCR) and 16S rRNA gene sequencing. Despite marked differences in microbial load and diversity of waters, soil communities remained remarkably stable after irrigation. Microbial biomass was increased only in soils irrigated with RWW. At the end of the irrigation period (day 84), soil and water shared a large fraction of their bacterial communities, from 43 % to 70 %, depending on the water quality, indicating a transfer of bacterial communities from water to soil. Overall, the relative abundance of Proteobacteria and Acidobacteria was increased and that of Actinobacteria was decreased in soils irrigated with MBW, CWW and even more with RWW. Multivariate ordination clearly separated soils in three groups: soils irrigated with the cleanest water (TW), with treated WW (MBW and CWW), and with untreated WW (RWW). Nitrifying, denitrifying, and nitrogen-fixing bacteria were quantified by qPCR targeting amoA, narG, and nifH, respectively. Nitrifying bacteria were the most affected by the water quality, as indicated by amoA copy number increase in RWW-irrigated soil and decrease in CWW-irrigated soil. Overall, the abundance of all three genes was positively influenced by RWW treatment. In conclusion, the 84 days of irrigation influenced the soil microbial communities, and the impact depended on the quality of the used water.

Enhanced Adsorption of Textile Dyes by a Novel Sulfonated Activated Carbon Derived from Pomegranate Peel Waste: Isotherm, Kinetic and Thermodynamic Study

The rapid growth of the dye and textile industry has raised significant public concerns regarding the pollution caused by dye wastewater, which poses potential risks to human health. In this study, we successfully improved the adsorption efficiency of activated carbon derived from pomegranate peel waste (PPAC) through a single-step and surface modification approach using 5-sulfonate-salicylaldehyde sodium salt. This innovative and effective sulfonation approach to produce sulfonated activated carbon (S-PPAC) proved to be highly effective in removing crystal violet dye (CV) from polluted water. The prepared PPAC and S-PPAC were characterized via FESEM, EDS, FTIR and BET surface area. Characterization studies confirmed the highly porous structure of the PPAC and its successful surface modification, with surface areas reaching 1180.63 m2/g and 740.75 m2/g for the PPAC and S-PPAC, respectively. The maximum adsorption capacity was achieved at 785.53 mg/g with the S-PPAC, an increase of 22.76% compared to the PPAC at 45 °C. The isothermic adsorption and kinetic studies demonstrated that the adsorption process aligned well with the Freundlich isotherm model and followed the Elovich kinetic model, respectively. The thermodynamic study confirmed that the adsorption of CV dye was endothermic, spontaneous and thermodynamically favorable onto PPAC and S-PPAC.

Wastewater reuse in agriculture: Prospects and challenges

Sustainable water recycling and wastewater reuse are urgent nowadays considering water scarcity and increased water consumption through human activities. In 2015, United Nations Sustainable Development Goal 6 (UN SDG6) highlighted the necessity of recycling wastewater to guarantee water availability for individuals. Currently, wastewater irrigation (WWI) of crops and agricultural land appears essential. The present work overviews the quality of treated wastewater in terms of soil microbial activities, and discusses challenges and benefits of WWI in line with wastewater reuse in agriculture and aquaculture irrigation. Combined conventional-advanced wastewater treatment processes are specifically deliberated, considering the harmful impacts on human health arising from WWI originating from reuse of contaminated water (salts, organic pollutants, toxic metals, and microbial pathogens i.e., viruses and bacteria). The comprehensive literature survey revealed that, in addition to the increased levels of pathogen and microbial threats to human wellbeing, poorly-treated wastewater results in plant and soil contamination with toxic organic/inorganic chemicals, and microbial pathogens. The impact of long-term emerging pollutants like plastic nanoparticles should also be established in further studies, with the development of standardized analytical techniques for such hazardous chemicals. Likewise, the reliable, long-term and extensive judgment on heavy metals threat to human beings's health should be explored in future investigations.

Current challenges and future perspectives for the full circular economy of water in European countries

This paper reviews the current problems and prospects to overcome circular water economy management challenges in European countries. The geopolitical paradigm of water, the water economy, water innovation, water management and regulation in Europe, environmental and safety concerns at water reuse, and technological solutions for water recovery are all covered in this review, which has been prepared in the frame of the COST ACTION (CA, 20133) FULLRECO4US, Working Group (WG) 4. With a Circular Economy approach to water recycling and recovery based on this COST Action, this review paper aims to develop novel, futuristic solutions to overcome the difficulties that the European Union (EU) is currently facing. The detailed review of the current environmental barriers and upcoming difficulties for water reuse in Europe with a Circular Economy vision is another distinctive aspect of this study. It is observed that the biggest challenge in using and recycling water from wastewater treatment plants is dealing with technical, social, political, and economic issues. For instance, geographical differences significantly affect technological problems, and it is effective in terms of social acceptance of the reuse of treated water. Local governmental organizations should support and encourage initiatives to expand water reuse, particularly for agricultural and industrial uses across all of Europe. It should not also be disregarded that the latest hydro politics approach to water management will actively contribute to addressing the issues associated with water scarcity.

Microplastics in agriculture - a potential novel mechanism for the delivery of human pathogens onto crops

Mulching with plastic sheeting, the use of plastic carriers in seed coatings, and irrigation with wastewater or contaminated surface water have resulted in plastics, and microplastics, becoming ubiquitous in agricultural soils. Once in the environment, plastic surfaces quickly become colonised by microbial biofilm comprised of a diverse microbial community. This so-called 'plastisphere' community can also include human pathogens, particularly if the plastic has been exposed to faecal contamination (e.g., from wastewater or organic manures and livestock faeces). The plastisphere is hypothesised to facilitate the survival and dissemination of pathogens, and therefore plastics in agricultural systems could play a significant role in transferring human pathogens to crops, particularly as microplastics adhering to ready to eat crops are difficult to remove by washing. In this paper we critically discuss the pathways for human pathogens associated with microplastics to interact with crop leaves and roots, and the potential for the transfer, adherence, and uptake of human pathogens from the plastisphere to plants. Globally, the concentration of plastics in agricultural soils are increasing, therefore, quantifying the potential for the plastisphere to transfer human pathogens into the food chain needs to be treated as a priority.

Challenges for Circular Economy under the EU 2020/741 Wastewater Reuse Regulation

Wastewater reuse is seen as an opportunity to support a circular economy and optimize water resources. However, the use of wastewater is limited by the need for the proper protection of health and the environment and demands a certain minimum quality of treated reclaimed water. The objective of this work is to evaluate the opportunities both for the agents in the water treatment chain (from municipalities to farmers) and for technology providers under the recently approved Regulation EU-2020/741. The new market and opportunities require new value chains, technology development, governance, risk assurance, and adapted local regulation. Bottlenecks also pose technological, environmental, institutional, economic, and social challenges. The identified needs and barriers must be properly addressed in order to accelerate the transformation of the water sector toward the circular economy. As a conclusion, Reg EU 2020/741 introduces minimum requirements for urban wastewater reuse and requires the definition of risk management and transparency. The real impact of regulation on circular-economy objectives is limited by water scarcity and crop profitability. Social acceptance is critical for success.

Challenges and Solutions for Global Water Scarcity

Climate change, global population growth, and rising standards of living have put immense strain on natural resources, resulting in the unsecured availability of water as an existential resource. Access to high-quality drinking water is crucial for daily life, food production, industry, and nature. However, the demand for freshwater resources exceeds the available supply, making it essential to utilize all alternative water resources such as the desalination of brackish water, seawater, and wastewater. Reverse osmosis desalination is a highly efficient method to increase water supplies and make clean, affordable water accessible to millions of people. However, to ensure universal access to water, various measures need to be implemented, including centralized governance, educational campaigns, improvements in water catchment and harvesting technologies, infrastructure development, irrigation and agricultural practices, pollution control, investments in novel water technologies, and transboundary water cooperation. This paper provides a comprehensive overview of measures for utilizing alternative water sources, with particular emphasis on seawater desalination and wastewater reclamation techniques. In particular, membrane-based technologies are critically reviewed, with a focus on their energy consumption, costs, and environmental impacts.

Leveraging green infrastructure for efficient treatment of reclaimed water

Global water scarcity necessitates creative, yet practical, solutions to meet ever-growing demand. Green infrastructure is increasingly used in this context to provide water in environmentally friendly and sustainable ways. In this study, we focused on reclaimed wastewater from a joint gray and green infrastructure system employed by the Loxahatchee River District in Florida. The water system consists of a series of treatment stages for which we assessed 12 years of monitoring data. We measured water quality after secondary (gray) treatment, then in onsite lakes, offsite lakes, landscape irrigation (via sprinklers), and ultimately in downstream canals. Our findings show gray infrastructure designed for secondary treatment, integrated with green infrastructure, achieved nutrient concentrations nearly equivalent to advanced wastewater treatment systems. For example, we observed a dramatic decline in mean nitrogen concentration from 19.42 mg L^-1 after secondary treatment to 5.26 mg L^-1 after spending an average of 30 days in the onsite lakes. Nitrogen concentration continued to decline as reclaimed water moved from onsite lakes to offsite lakes (3.87 mg L^-1) and irrigation sprinklers (3.27 mg L^-1). Phosphorus concentrations exhibited a similar pattern. These decreasing nutrient concentrations led to relatively low nutrient loading rates and occurred while consuming substantially less energy and producing fewer greenhouse gas emissions than traditional gray infrastructure-at lower cost and higher efficiency. There was no evidence of eutrophication in canals downstream of the residential landscape whose sole source of irrigation water was reclaimed water. This study provides a long-term example of how circularity in water use can be used to work toward sustainable development goals.

Coliphages as viral indicators in municipal wastewater: A comparison between the ISO and the USEPA methods based on a systematic literature review

The use of traditional faecal indicator bacteria as surrogate organisms for pathogenic viruses in domestic wastewater has been noted as a problematic as concentrations and removal rates of bacteria and viruses do not seem to correlate. In this sense, bacteriophages (phages) emerge as potential viral indicators, as they are commonly found in wastewater in high levels, and can be quantified using simple, fast, low-cost methods. Somatic and F-specific coliphages comprise groups of phages commonly used as indicators of water quality. There are two internationally recognised methods to detect and enumerate coliphages in water samples, the International Standardization Organization (ISO) and the US Environmental Protection Agency (USEPA) methods. Both methods are based on the lysis of specific bacterial host strains infected by phages. Within this context, this systematic literature review aimed at gathering concentrations in raw and treated domestic wastewater (secondary, biological treatment systems and post-treatment systems), and removal efficiencies of somatic and F-specific coliphages obtained by ISO and USEPA methods, and then compare both methods. A total of 33 research papers were considered in this study. Results showed that the ISO method is more commonly applied than the USEPA method. Some discrepancies in terms of concentrations and removal efficiencies were observed between both methods. Higher removal rates were observed for both somatic and F-specific coliphages in activated sludge systems when using the USEPA method compared to the ISO method; in other secondary (biological) treatment systems, this was observed only for F-specific coliphages. The use of different standardised methods available might lead to difficulties in obtaining and comparing phage data in different conditions and locations. Future research comparing both ISO and USEPA methods as well as viral and bacterial pathogens and indicators in WWTP is recommended.

Socio-economic impact assessment of large-scale recycling of treated municipal wastewater for indirect groundwater recharge

Reusing treated wastewater is an emerging solution to address freshwater scarcity, and surface water contamination faced worldwide. A unique large-scale wastewater recycling project was implemented to replenish groundwater by filling secondary treated wastewater (STW) into existing irrigation tanks in severely drought-hit areas of the Kolar districts of Southern India. This study quantifies the socio-economic impacts of this large-scale indirect groundwater recharge scheme. The changes in areas receiving STW i.e., impacted areas and those areas which did not receive STW i.e., non-impacted areas was studied. Also, pre and post recycling changes were quantified in the Kolar district. The results show that surface water quality meets India's most stringent treated wastewater discharge standards prescribed by the Hon'ble National Green Tribunal. Due to these recycling efforts, significant improvements in groundwater level and quality were found. It was observed that there was a noticeable difference in agricultural cropping areas, seasons, patterns, and production between impacted and non-impacted areas. Post-recycling, farmers tended to cultivate cash and water-intensive crops over less water-intensive crops. During the post-recycling period, livestock and milk production also increased, and in impacted areas, it was significantly higher. Post-recycling, fish production increased and land prices per hectare increased by 118 % in impacted areas. The farmer's net income under flowers and vegetable farming increased by 202 % and 150 % respectively in impacted areas compared to non-impacted areas. Furthermore, this project contributes to a circular economy transition in the water sector, which has economic, environmental, social, and cultural benefits. A key recommendation from the outcomes of the study is to draft and implement a policy that encourages the reuse of recycled water for groundwater recharge which in turn will improve the agro-economic system and food security.

New insights on simultaneous nitrate and phosphorus removal in pyrite-involved mixotrophic denitrification biofilter for a long-term operation: Performance change and its underlying mechanism

Simultaneous nitrate and phosphorus removal can be completed by pyrite- and influent organics-involved mixotrophic denitrification and chemical phosphorus removal via iron precipitation. However, so far, how their removal performances change with iron precipitation accumulation remains unclear. In this study, the differences in nitrate and phosphorus removal from municipal tailwater between volcanic and pyrite supported biofilters (V-BF, P-BF) for a long-term operation were investigated, as well as the underlying mechanism for these differences. The nitrate removal efficiencies (NREs) in P-BF were greater than those in V-BF due to the synergistic effect of influent organic and pyrite, as evidenced by comparable TOC consumption and Fe²⁺/SO₄^2- production. The NREs in P-BF were gradually lower than in V-BF as a result of bacterial cell-iron encrustation observed in TEM images, which would deteriorate microbial activity. However, the phosphorus removal efficiencies (PREs) in P-BF remained consistently higher than in V-BF, resulting from chemical phosphorus removal which was confirmed that P, Fe and O elements dominated on the pyrite surface after use by SEM-EDS. The dominant denitrifying bacteria differed significantly, autotrophic and heterotrophic denitrifying microorganisms coexisted in P-BF. The relative abundances of the narG coding gene in P-BF were higher than that in V-BF, which was consistent with the total relative abundances of identified denitrifying bacteria. Besides, the mechanism of simultaneous nitrogen and phosphorus removal in the pyrite-involved mixotrophic denitrification process has been deduced. This work has significant implications for the practical application of a pyrite-involved mixotrophic denitrification process for low C/N wastewater treatment.