Research & Reviews: Journal of Ecology and Environmental Sciences
MenuISSN: 2347-7830
ISSN: 2347-7830
+44-7723-59-8358 Abdul-Wahab Tahiru*, Ebenezer John Atsugah and Samuel Jerry Cobbina
Department of Environmental Sciences and Sustainability Sciences, University for Development Studies, Tamale, Ghana
Received: 24-May-2023, Manuscript No. JEAES-23-103724; Editor assigned: 26-May-2023, PreQC No. JEAES-23-103724 (PQ); Reviewed: 10-Jun-2023, QC No. JEAES-23-103724; Revised: 17-Jun-2023, Manuscript No. JEAES-23-103724 (R); Published: 24-Jun-2023, DOI: 10.4172/ 2347-7830.2023.11.001
Citation: Tahiru AW, et al. Emerging Contaminants and Public Health: Environmental Risk and Innovative Controls. RRJ Ecol Environ Sci.2023;11: 001
Copyright: © 2023 Tahiru AW, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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An estimated 12.6 million people died as a result of living or working in an unhealthy environment in 2012 – nearly 1 in 4 of total global deaths, according to new estimates from WHO. Environmental risk factors, such as air, water and soil pollution, chemical exposures, climate change, and ultraviolet radiation, contribute to more than 100 diseases and injuries. The growing challenges and negative impacts of emerging contaminates posing risk in human health and the environmental ecosystem in recent decades especially in groundwater, surface water, municipal wastewater, drinking water, and food sources has raised an alarming concern globally. Regardless of the numerous risks identified and associated with emerging contaminates, it is believed that not much work is done in terms of research, policies and strategies. The efficient and cost-effective solutions are yet to be deployed at scale.
This review has made recommendations base on literature review that can be adopted, improved on to help develop a more adoptive innovative treatment technology to manage emerging contaminates.
Contaminants; Environment; Water; Ecosystem
An estimated 12.6 million people died as a result of living or working in an unhealthy environment in 2012 nearly 1 in 4 of total global deaths, according to new estimates from WHO. Environmental risk factors, such as air, water and soil pollution, chemical exposures, climate change, and ultraviolet radiation, contribute to more than 100 diseases and injuries. The growing challenges and negative impacts of emerging contaminates posing risk in human health and the environmental ecosystem in recent decades especially in groundwater, surface water, municipal wastewater, drinking water, and food sources has raised an alarming concern globally. Paul E. Rosenfeld, described Emerging Contaminants (ECs) as synthetic or naturally occurring chemicals or any microorganisms that are not commonly monitored in the environment but have the potential to enter the environment and cause known or suspected adverse ecological and/or human health effects.
According to him ECs consist of pharmaceuticals, pesticides, industrial chemicals, surfactants, and personal care products that are consistently being found in groundwater, surface water, and municipal wastewater, drinking water, and food sources. They also include endocrine-disrupting compounds, analgesics, antibiotics, hormones, and a whole range of other pharmaceutical compounds including anti-inflammatory, antidiabetic, and antiepileptic drugs [1-3].
Addressing the challenge of emerging pollutants is necessary in order to achieve the SDG Target 12.4 to “reduce the release of chemicals to air, water and soil in order to minimise their adverse impacts on human health and the environment”, and other related SDGs on water (Target 6.3), human health (target 3.3), ecosystem protection, poverty alleviation, sustainable consumption and production, and sustainable agriculture, amongst others.
It is imperative for professional practitioners, stakeholders, researchers in the environmental sector to discuss, assess, analyse, and develop scientific and policy approaches to better understand and manage emerging contaminates and also device a smarter and innovative ways of treating these contaminants. Identifying the technological trends and knowledge gaps in relation to the removal of emerging contaminants in water is a priority that must be addressed to inform the scientific community towards the adoption of best practices to ensure the use of safe drinking water for all. Accordingly, the primary focus of this paper is to understand and review the innovative treatment technology of emerging contaminants helping to reduce or eliminate potential human or ecosystem health risks and the identification of current knowledge gaps and to determine future research directions. The review focuses on the impact of emerging contaminants on health and the environment, and as well their control. The method adopted for the study was a purposive literature search [4].
Data collection and analysis
The sources of the information were Science Direct and Emerald. The Web libraries also provide advanced search filters with keywords, type, research, and year fields by publications. The keywords related to the title were then searched. Search keywords were also formulated using Boolean OR/AND operators to confirm the search quality and fuse these search terms to upgrade the importance of the search process. Many papers showed up, but only papers of interest were selected, read, and analysed. Thus, the papers focusing on the title were eligible for inclusion.
Further description of the emerging contaminates (ECs) specific to water quality as the chemical compounds that are commonly present in water but are only recently being recognized as significant water pollutants. Emerging contaminants are natural or synthetically occurring substances not commonly monitored in the environment and having known or suspected undesirable effects on humans and the ecosystem. This group include compounds such as Pharmaceutical and Personal Care Products (PPCPs), pesticides, and hormones that have adverse effects on human and wildlife endocrine systems. There have been several research on innovative ways to manage emerging containment across the globe, this review will critically mention two typical innovations across Europe and Indian, where these technologies have been deployed [5].
In Europe, efforts to address emerging pollutants in drinking and wastewater are already in progress. Using applied research and demonstration sites across Europe, the DEMEAU project (Demonstration of promising technologies to address emerging pollutants in water and waste water) is demonstrating new, collaborative approaches for advancing the uptake of knowledge, prototypes, practices, and technologies that enable the water sector to tackle emerging pollutants more effectively. The project consists of a network of partners from research, water utilities and SMEs that are exploring five promising water treatment technologies: Managed Aquifer Recharge (MAR), Hybrid Ceramic Membrane Filtration (HCMF), Automated Neural Net Control Systems (ANCS), Advanced Oxidation Techniques (AOT), and Bioassays. The DEMEAU project is using new collaborative approaches to provide new, improved approaches for developing and testing relevant water treatment technologies as a way to innovatively and effectively address the gaps and opportunities for tackling emerging containments. Bridging the gap between research and industry, DEMEAU facilitates close collaboration and feedback among the research community, SMEs and water utilities by lowering the economic and shared risks associated with innovation and trial of such new, promising technologies.
To fuel innovation and knowledge exchange, the project actively explores synergies among drinking and wastewater treatment technologies. This integrated approach has been critical to the overall success and uptake of the five technologies explored in the project. On the one hand, researchers have been able to receive inspiration and critical feedback from SMEs, while SMEs and utilities have been able to broaden their markets by pioneering the water sector.
Technologies for emerging contaminants
Managed Aquifer Recharge (MAR): Managed Aquifer Recharge (MAR) is a versatile technology that provides drinking water supply, process water for industry, for irrigation and for sustaining groundwater dependent ecosystems. MAR uses natural aquifer treatment processes, such as mechanical filtration, sorption, and biodegradation, at the subsurface level. These natural treatment processes do not require additional chemicals, offering a more sustainable alternative to traditional treatment processes.
MAR has been shown to provide a variety of benefits, including water storage and improved water quality. However, the implementation of MAR is often hampered by uncertainty relating to economic and environmental profiles. To address this, Life Cycle Assessments (LCA) and Life Cycle Costing (LCC) tools, based on a set of indicators selected for environmental impacts and costs, are being applied to MAR sites for comparison against other competitive water treatment technologies. From the assessments, it has been found that natural, infiltration pond systems are a low- cost and low-energy option for groundwater recharge, provided that a suitable long-term strategy to prevent clogging is implemented. Such ponds can be upgraded or combined with advanced oxidation processes to enhance their capacity for removal of organic micro pollutants [6-12].
Hybrid Ceramic Membrane Filtration (HCMF): Polymeric membranes are widely used in water treatment to remove pathogens, particles and organics from surface, ground, and process and filter backwash water. However, ceramic membranes are much more resilient, outperforming polymeric membranes even under extreme conditions (e.g. temperature, pH and chemicals). LCC assessments based on case studies also show that HCMF have lower operational costs than polymeric membranes, though implementation costs were higher for HCMF. In order to improve cost effectiveness, several alterations to the ceramic membrane modules have already been tested and successfully applied within the DEMEAU project. For example, by combining several membranes into one vessel, fewer valves, and therefore steel, are needed. In addition, an improved bottom plate has helped to enhance its durability, making the technology more resilient during backwashing, particularly in the long-term.
Automated Neural Net Control Systems (ANCS): Automated Neural Net Control Systems (ANCS) are computer-based, process optimization systems that use tailored mathematical algorithms, with applications in drinking water processing and supply, urban drainage systems, and activated sludge reactors in wastewater treatment plants. In the drinking water industry, ANCS technology is usually applied as an add-on to optimize membrane filtration, and thus is widely applicable. Within DEMEAU, marked improvements in filtration and enhancements in process productivity (of about 4% to 15%) has made ANCS particularly lucrative as an add-on for existing membrane filtration plants in Europe to increase their increasing environmental and economic sustainability [13].
However, several barriers to widespread uptake still exist for ANCS. Life cycle assessments have revealed that a certain degree of complexity is necessary in order for ANCS to be cost-effective. Consequently, larger plants are more cost-effective than smaller plants. Similarly, as maintenance is a necessary aspect of the technology, ANCS is more cost-effective at larger scales. As a result, understanding the extent and costs of maintenance required for the plant is an important aspect to account for prior to implementation.
Advanced Oxidation Techniques (AOT): Oxidation techniques have a long tradition for use in disinfecting drinking and wastewater, however, its benefits for use in removing emerging pollutants have only recently come to light. Results from pilot plants and the first full-scale application using post-ozonation produced removal rates greater than 80% for many emerging pollutants. Within DEMEAU, researchers, utilities and SMEs are testing a combination of various oxidation processes (including O3, O3/ H2O2, UV/H2O2) as well as different post- treatment applications, such as sand filtration or biological activated carbon filtration.
Due to the collaborative character of DEMEAU, the project is actively facilitating a safe environment for utilities and SMEs to experiment and apply this innovative technology in a full-scale drinking water plant. The results have been promising: one oxidation reactor developed by a Dutch SME projects significant energy reductions. In fact, the SME estimates 30%-40% less energy consumption with its oxidation reactor as compared to conventional reactors using UV/H2O2 processes.
Bioassays: Current mainstream water monitoring strategies rely exclusively on chemical analysis. However, chemical analysis only identifies specific, targeted compounds with no information on the biological effects of the pollutants. Bioassays address this gap in monitoring strategies, and hold the potential to serve as an additional, complementary technology to chemical analysis. Because bioassays measure the biological effects of single compounds present in water samples, they are particularly useful for application in assessing the harmful effects of complex mixtures of unknown pollutants. As a result, bioassays have the potential to widen the scope of water quality monitoring and can be tailored to and adjusted for testing a range of water sources, from general toxicity tests to very specific biological activities [14-18].
Though some scientists and end-users view bioassays as a potential replacement of more costly techniques, currently, regulatory acceptance of bioassays is slow. Demonstration and validation studies are being carried out in an effort to bring bioassays toward regulatory acceptance. The studies found that in order to facilitate the operational use of these tools for decision-makers, knowledge dissemination is essential.
In India other innovative treatment technology developed in India, also use the Light- Driving Processes. Light-driven processes involve two main reactions: Direct photolysis and Generation of highly reactive oxidative substrates, such as hydroxyl (OH), chlorine (Cl), sulphate (SO4−), and hydroperoxyl radicals (HO2), by catalytically converting water or oxidants for the degradation of wastewater.
Direct photolysis occurs when the light energy used (E λ) is more than the associated bond energy of the contaminants. The energy supplied by the light processes could be approximated to a specific wavelength, whereas radicals react directly with CECs and degrade them. The generation of reactive species is dependent on the process and will be further elaborated below. The key reaction mechanisms and graphical illustration of the mechanisms are summarised in Figures 1a-1d [19].
Critical factors that affect light-driven processes
Figure 1: Graphical illustration of the reaction mechanisms for various light-driven processes Note: (a) UV/oxidant; (b) UV/ozone photo-Fenton (homogenous); (c) Photo-Fenton (heterogeneous); (d) Photo catalyst.
Generally, light-driven processes are affected by UV absorbance, pH, water matrix, reagent dosages, and UV sources. The organic and inorganic composition of water affects the performance of light drive processes either by inhibition of chemical processes or inhibition of light penetration. The presence of turbid water or NOM reduces the photocatalytic effect due to charge carrier generation and UV absorbance. The pH affects the process due to the inhibition effect from the stability of the oxidant or catalyst. Too low a pH would affect the stability of metal-based catalyst in Fenton-based and photo catalyst systems. Oxidant dosage and catalyst dosage affect the performance of CEC degradation since they affect the generation of oxidative species needed for CEC degradation. In excess, it might have scavenging effects or even change the physical characteristic of the water (i.e., light penetration), which affects the overall CEC degradation performance. Lastly, the irradiation source also affects the CEC degradation performance of light-based systems. Generally, light waves with shorter wavelengths carry more energy and hence better performance. However, a shorter wavelength of light is more energy-intensive and ongoing research is being done to have systems that use a longer wavelength of light or even natural sources of light for irradiation.
UV/oxidant: Due to the ease of operations, UV/oxidant processes have been widely applied in synthetic and spiked wastewater effluent. UV/oxidant processes use a variety of different oxidative species (chlorine, peroxide, nitrates, sulphate, and its derivatives) for the generation of oxidative radicals. Generally, the reaction is operated in the neutral pH, with a Hydraulic Retention Time (HRT) between 20-180 min and a vast majority of the systems use high-energy UVC irradiation systems to activate the oxidants. Most of the investigations using UV/Oxidant processes have focused on the removal of target compounds spiked in synthetic matrices at laboratory and pilot scales with a good degree of degradation of between 80%–90% of the CECs.
It was also found that generally, UV/H2O2 processes were less effective in the degradation of CECs as compared to other oxidative species. Certain CECs are also more resilient to UV/H2O2 processes. Per Fluoro Octanoic Acid (PFOA), Per Fluoro Octane Sulfonate (PFOS), and Bisphenol A (BPA) were found to have low degradation performance of <30%, <30%, and <50% respectively. This is likely due to low values of H2O2 molar absorption coefficient at 254 nm (19.0 M−1 cm−1), resulting in higher hydrogen peroxide and UV dose for efficient removal.
UV/ozone: The majority of UV/O3 processes were operated at slightly alkaline pH (≥ 9), with low-pressure mercury lamps, bench-scale reactors, and an HRT of 20–180 min. UV/O3 showed better removal performance as compared to purely ozonation process with the same treatment condition. Jing et al. [15] reported a better removal of COD and NH3-N in the treatment of atrazine production wastewater (from 2% to 21% respectively in O3 to 55% and 65% respectively in UV/O3). Another study by Xu, et al., showed that UV/O3 had better degradation of synthetic wastewater containing sucralose as compared to UV and ozonation alone. Total organic carbon (TOC) removal of 89.8% for UV/O3 as compared to UV and O3 at <5% and 39.1% removal, respectively, was reported. This could be due to a large number of hydroxyl radicals that can be generated in a fast manner which is adequate for the mineralization of CECs. However, it was noted that the combination of ozone and UV process did not improve the degradation of gasoline compounds (benzene, toluene, and isomers of xylene) in comparison with ozone [16,20].
Despite the benefit of the enhanced degradation rate, there has been less focus on the study of the UV/O3 process, due to the higher cost of treatment. Ozonation and UV processes are widely known to be energy-intensive and as such the upscaling UV/O3 might not be viable.
Photo-fenton: Photo-Fenton processes have been used in a wide variety of CECs degradation of various scales and modes of operations. The majority of the photo Fenton processes uses lower energy UV wavelengths and even solar-powered systems. Degradation time also varies from 10–180 min, depending on the compounds being degraded. Most of the investigations using photo-Fenton processes focus on the removal of target compounds spiked in synthetic matrices at laboratory scale and pilot scales with a good degree of degradation of between 80%–90% of CECs.
Notable publications describing the effects of chemical structures on the efficiency of photo/Fenton-based systems are summarized above. Recent innovation with magnetic carbon-based heterogeneous composites addresses the reusability and separation of conventional heterogeneous catalysts. Alani et al., [18] reported that the photocatalytic performance of the magnetic catalyst remains relatively high even after 5 consecutive uses.
The recent innovation of the use of solar-assisted Fenton, raceway pond reactors, shows promising results for the degradation of CECs. This reactor configuration requires less energy input due to the use of solar energy and also shows a high degree of degradation. The height of the race pond bed seems to contribute significantly to the degradation performance of CECs. More recently, alternative and cheaper ligands such as NTA are also being test bedded against conventional EDDS ligands. At present, the study of this reactor is still in its infancy stage and hence has the potential to be developed further.
Photo catalysis: Photo catalysis uses solar energy/UV lamps with a catalyst and has been used in a wide variety of CECs degradation of various scales and modes of operations. The majority of the photo catalysis processes utilize both lower energy UV wavelengths and even solar energy. Degradation time also varies from 10–180 min, depending on the compounds being degraded. Most of the investigations using photo catalysis processes have been focused on the removal of target compounds spiked in synthetic matrices at a laboratory scale with a good degree of degradation of between 80%-90% of CECs. Various types of photo catalysts such as Titanium Dioxide (TiO2), Zinc Oxide (ZnO), Tungsten Trioxide (WO3), and Graphitic Carbon Nitrides (g-C3N4) have been explored.
The degradation rate of CECs by photo catalysis is found to be closely related to their molecular structures. Eskandarian, et al. found that decomposition kinetics of CECs by TiO2 photocatalytic followed the order: sulfamethoxazole > diclofenac >ibuprofen>acetaminophen. Sulfamethoxazole is highly reactive due to the NH group in its chemical structure. Ibuprofen could be decomposed via rearrangement of the acidic group, followed by decarboxylation reaction and dehydrogenation. However, it is less flexible in degradation sites due to its molecular structure. Degradation of acetaminophen is the most difficult of the four compounds. The mechanism involved the removal of the amide group (CH3CONH), formation of phenoxy radical that will react with superoxide radical. In another study, [20]Alverez–Corena. et al, found the decreasing trend of UV/TiO2 degradation kinetics for 5 CECs: Gemfibrozil > 17β estradiol > N-nitrosodimethylamine (NDMA) > 1,4-dioxane > tris-2-chloroethyl phosphate (TCEP). The high degradation for gemfibrozil could be attributed to the presence of a deprotonated carboxyl group in its structure which can enhance its adsorption capacity on the photocatalyst surface. N-NO bond in NDMA could act as an electron donor to the TiO2 surfaces. C-O bonds in 1,4-dioxane could be served as hydrogen bond acceptors for dipolar attractions [21-23]. TCEP is without ionizable functional groups in its structure. In addition, a high pKa of 14.86 of its leaving group 2-chloroethanol and higher dipole moment makes it difficult to be removed. Hence, TCEP showed the slowest degradation rate.
Despite these challenges, the adoption of appropriate practices and technologies that effectively address and tackle emerging contaminates remains low. Improved knowledge transfer and better science communication among key stakeholders, including scientists, the private sector, and water utilities have been identified as central to addressing the low rate of uptake of appropriate technologies. In particular, Small and Medium-sized Enterprises (SMEs) have emerged as key go-betweens for increasing innovation in the water sector and encouraging knowledge dissemination and uptake of research.
UV/oxidant processes are generally more selective in the degradation of CECs. As found in the review, UV/H2O2 has low values of H2O2 molar absorption coefficient at 254 nm. Photo oxidant processes use persulfate and its derivatives were found to be better at CECs degradation. However, this process requires pH adjustment and the radicals generated to have a lower charge compared to other radicals formed. Thus, the lower oxidative power of the generated radicals leads to selective CEC degradation. UV/chlorine process has a higher reported degradation performance than UV/H2O2. UV/chlorine uses chemicals that are common for pipeline disinfection for wastewater treatment plant effluent, and hence little modification of the treatment process is needed for immediate application. However, studies noted the formation of undesirable DBPs, and more studies need to be done to limit the formation of such products.
Despite the benefit of the enhanced degradation rate, there has been less focus on the study of the UV/O3 process, due to the higher cost of treatment. Ozonation and UV processes are widely known to be energy-intensive and as such the upscaling UV/O3 might not be viable. Furthermore, ozonation requires pH restriction to perform optimally, which might not be suitable for CEC treatment. CECs are concentrated mostly in the effluent stream of wastewater treatment facilities which generally have a neutral pH. As such, pH adjustment needs to be done before and after the UV/O3 process for effluent discharge, increasing treatment costs.
Regardless of the numerous risks identified and associated with emerging contaminates, it is believed that not much work is done in terms of research, policies and strategies has been carried out. The efficient and cost-effective solutions are yet to be deployed at scale. From the review above it is notable that some effective treatment technologies have been identified and tested yet, the operational cost of these technologies does not make it adoptable especially for low-income beneficiaries.
It is therefore recommended that, the following suggestions can be adopted, improved to help develop a more adoptive innovative treatment technology for emerging contaminates.
There are several ongoing technology initiatives, especially, on a smaller scale that are at various stages of development including provisional license stage, siting permit stage, development/prototype permit stage. A policy framework can be developed to ensure all the Promising water treatment technologies to effectively tackle emerging pollutants, regulatory standards have to be defined for emerging contaminants at the global, national and also decentralized to the community levels, for example, laws that establish long-term target values for water quality of waste water treatment plant effluent, surface water, and drinking water. In addition, increasing regulatory pressures will motivate water utilities to implement innovative solutions-oriented technologies, while also providing an incentive for technology developers to generate innovations.
There are economic barriers and associated risks. As mentioned previously, SMEs and water utilities often cannot bear the burden posed by such economic barriers. Because innovation in the water sector is often fraught with uncertainty, it requires a very specific environment for actors to be willing to engage and also be successful.
Increase research in these areas, to identify more innovative approached and technology to treat emerging contaminants that posing high risk to human and the environment.
It is believed that the adoption of this recommendation will not only help identify solutions to emerging contaminates but also go a long way to reduce the risk to humans and the environment.
Acknowledgement
The authors thank everyone who has contributed to improving the quality of this study.
Funding
This research received no funding from any source.
Ethics approval
The authors declare that the submitted manuscript is original. The authors also acknowledge that the current research has been conducted ethically and the final shape of the research has been agreed upon by all authors. The authors declare that this manuscript does not involve researching humans or animals.
Conflicts of interest/Competing interests
The authors declare no conflicts of interests/competing interests.
Authors' contributions
Ebenezer John Atsugah: Conceptualization, Methodology, Investigation, Supervision, Writing- Original draft preparation, Validation, Writing- Reviewing and Editing. Samuel Jerry Cobbina: Data curation, Validation, Writing- Reviewing and Editing. Abdul-Wahab Tahiru: Methodology, Investigation, Writing- Reviewing and Editing.
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