NMR spectroscopy of wastewater: A review, case study, and future potential

https://doi.org/10.1016/j.pnmrs.2021.08.001Get rights and content

Highlights

  • Wastewater composition has implications for environmental and human health.

  • NMR is incredibly powerful for studying molecular structure and interactions.

  • Relevant NMR techniques and applications are reviewed and discussed.

  • A case study combining targeted/non-targeted NMR and in-vivo toxicity is provided.

  • NMR has huge potential for both monitoring wastewater and treatment processes.

Abstract

NMR spectroscopy is arguably the most powerful tool for the study of molecular structures and interactions, and is increasingly being applied to environmental research, such as the study of wastewater. With over 97% of the planet’s water being saltwater, and two thirds of freshwater being frozen in the ice caps and glaciers, there is a significant need to maintain and reuse the remaining 1%, which is a precious resource, critical to the sustainability of most life on Earth. Sanitation and reutilization of wastewater is an important method of water conservation, especially in arid regions, making the understanding of wastewater itself, and of its treatment processes, a highly relevant area of environmental research. Here, the benefits, challenges and subtleties of using NMR spectroscopy for the analysis of wastewater are considered. First, the techniques available to overcome the specific challenges arising from the nature of wastewater (which is a complex and dilute matrix), including an examination of sample preparation and NMR techniques (such as solvent suppression), in both the solid and solution states, are discussed. Then, the arsenal of available NMR techniques for both structure elucidation (e.g., heteronuclear, multidimensional NMR, homonuclear scalar coupling-based experiments) and the study of intermolecular interactions (e.g., diffusion, nuclear Overhauser and saturation transfer-based techniques) in wastewater are examined. Examples of wastewater NMR studies from the literature are reviewed and potential areas for future research are identified. Organized by nucleus, this review includes the common heteronuclei (13C, 15N, 19F, 31P, 29Si) as well as other environmentally relevant nuclei and metals such as 27Al, 51V, 207Pb and 113Cd, among others. Further, the potential of additional NMR methods such as comprehensive multiphase NMR, NMR microscopy and hyphenated techniques (for example, LC-SPE-NMR-MS) for advancing the current understanding of wastewater are discussed. In addition, a case study that combines natural abundance (i.e. non-concentrated), targeted and non-targeted NMR to characterize wastewater, along with in vivo based NMR to understand its toxicity, is included. The study demonstrates that, when applied comprehensively, NMR can provide unique insights into not just the structure, but also potential impacts, of wastewater and wastewater treatment processes. Finally, low-field NMR, which holds considerable future potential for on-site wastewater monitoring, is briefly discussed. In summary, NMR spectroscopy is one of the most versatile tools in modern science, with abilities to study all phases (gases, liquids, gels and solids), chemical structures, interactions, interfaces, toxicity and much more. The authors hope this review will inspire more scientists to embrace NMR, given its huge potential for both wastewater analysis in particular and environmental research in general.

Introduction

Water is a precious and limited resource, needed for everything from industry and agriculture to sustaining life as a whole. However, with over 97% of the Earth’s water being saltwater, and two thirds of freshwater being frozen in the ice caps and glaciers [1], there is a significant need to maintain and reuse this precious resource. Hence, modern society applies a number of techniques, collectively known as wastewater treatment, to prevent waterway pollution and even to recover water that has been previously utilized. This idea is not new, and, in fact, mankind has been employing wastewater treatment techniques since as early as 2500 BCE [2].Water treatment has (quite obviously) improved since then, and as our technology has improved, questions such as “how effective is this treatment technique?”, “what gets left behind?” and “what treatment technique would best fit wastewater from a specific source?” have begun to arise. Scientific understanding of wastewater treatment processes and their effects is necessary for the development of effective water treatment policies to help maintain our precious water supply.

Wastewater can span storm water runoff, as well as water comprised of industrial, domestic or commercial sewage [3]. This is quite a broad definition and exemplifies the considerable heterogeneity of wastewater. Depending on the source, wastewater varies in composition, which in turn determines its potential for pollution and subsequent environmental and human health risks [4]. As an example, the tannery industry, which is often considered a major source of pollution in general, employs a number of chromium salts to create high quality leather [5], [6]. Around 90% of the water used in the tanning process is released as wastewater [7], a total of around 300 million tons per year [8]. Prior to treatment, the wastewater may have concentrations of chromium hundreds to thousands of times greater than the recommended drinking water standards set by the United States Environmental Protection Agency [5], [6], [7], [9], [10]. On the other hand, storm water runoff, which picks up pollutants from buildings, roads and other sources as it flows into storm drains, is much more dilute, and commonly less biologically harmful than examples such as tannery effluent or raw sewage [4]. However, even storm water runoff may be harmful, and has been shown to have higher biological toxicity than properly treated wastewater [4]. In some instances, storm water can overwhelm treatment works, carrying raw sewage into watercourses or into the ocean. Clearly, if left untreated, all forms of wastewater can have a potentially detrimental impact on the environment.

Understanding the chemistry of wastewater is especially important if the wastewater is to be reused, for example in agricultural irrigation [11], [12], [13]. Inevitably, as environmental regulations shift, so too do the structures of chemical compounds being manufactured and used, many of which can end up in wastewater. Emerging contaminants are constantly being discovered [14], and, importantly, it is unclear if current wastewater treatments are effective in dealing with new compounds. As an example, there has been an increase in the concentrations of various antibiotics in waterways into which wastewater effluent flows, as many wastewater treatment plants are ill-equipped to handle pharmaceuticals [15], [16], [17], [18]. It is crucial to understand how these new (and old) contaminants are affected by wastewater treatment, as well as how they interact with the environment as a whole, in order to make effective decisions to protect our environment - an area in which NMR is an invaluable tool.

There have been a number of reviews published on the techniques used in wastewater treatment in general [19], [20], [21], [22], [23], [24], [25], [26], as well as reviews of treatment practices in specific industries [13], [27], [28], [29], [30], [31], [32]. Here, we aim to briefly mention the three basic phases of water treatment and their properties, in order to help demonstrate the applications of NMR in understanding these processes.

Modern wastewater treatment is typically divided into three phases: primary, secondary and tertiary treatments [33], [34]. A general schematic of wastewater treatment can be found in Fig. 1. Conventional primary treatment is made up of physical methods, involving screens and sedimentation chambers (often called clarifiers) that rely on gravity to settle large components [34]. This is used to remove large components such as sand, twigs, stones and some primary biosolids. However, removal of suspended particles smaller than 50 μm is typically inefficient, and chemical flocculants are often added to help settle smaller particles [35]. This is known as chemically enhanced primary treatment (CEPT), and typically involves the addition of metal salts such as FeCl3, Al(SO4)3 and FeSO4 and/or organic polyelectrolytes to aid in flocculation [35], [36]. Though the efficiencies of various flocculants vary with factors such as pH, CEPT has been shown to be effective in removing up to 90% of total suspended solids, and significant proportions of total phosphorus [34], [35], [37].

Following primary treatment, secondary treatment, which involves biological processes, is applied. In this case, the wastewater is added to one or more bioreactors, which have a controlled population of bacteria in the form of activated sludge [34]. This can be done under aerobic, anaerobic or hybrid conditions [38], [39], with the main goal of degrading organic matter. Following this, an additional sedimentation step is employed to remove any biosolids formed, often with the aid of flocculants [33]. At this point, the water is sufficiently treated to be released into the environment, and is commonly used in crop irrigation, especially in arid regions [11], [12].

For household and industrial use, however, additional treatment is required. This is known as tertiary treatment and is meant to reduce or remove components that were not effectively removed in the first two phases. These include excessive phosphorus and nitrogen (which can lead to eutrophication) [40], leftover heavy metals [41], and pathogenic viruses or bacteria [42]. Tertiary treatment employs a separation technique such as sand beds [43], active charcoal [22], ultrafiltration [44] or reverse osmosis [45] to help remove heavy metals and any additional flocculated components. Further, the water is disinfected to allow safe consumption. This is commonly done through chlorination [34], [46], [47], though due to the formation of potentially hazardous chlorinated by-products [48], [49], [50], [51], there has been a shift towards other disinfection techniques such as UV irradiation [42], ozonation [52] and oxidation processes based on radical reactions [53]. A general schematic of wastewater treatment can be found in Fig. 1.

Like many environmental samples, wastewater can contain various phases (solids, liquids, gels) and chemical categories including carbohydrates, lipids, proteins and xenobiotics [33], [34], [40]. Heterogeneous complex sample analysis is an area in which NMR excels in comparison to other commonly used techniques such as mass spectrometry [54]. NMR has the potential for analysis of solids, solutions and gels, even using a single NMR probe [54], [55], [56], non-destructively and in their native, unconcentrated state [54], [57], preventing any of the biases or losses associated with sample preparation or cleanup. Further, NMR is a versatile technique that is able to analyze any analyte with a spin active nucleus such as 1H or 13C, along with many heteronuclei (e.g. 19F, 15N, 31P) [54] – a constraint that is met by virtually all environmentally relevant compounds. Using multidimensional NMR techniques, NMR has been reported to have considerable resolving power [58], making it applicable to even the most complex matrices and samples. Not only is NMR useful for structure determination and compound identification, it can also be used to examine non-covalent interactions [59], [60], [61], [62] between the components of wastewater, such as pollutant-protein or pollutant-humic substance binding - which is very difficult to do using other techniques.

In this review, we aim to examine the use of and potential applications of NMR as a tool for understanding wastewater and the processes and effects of wastewater treatment. While there have been many studies involving the use of NMR for the study of wastewater, to the authors’ knowledge there has only been one published review [33] directly linking NMR with wastewater. A deeper exploration of NMR techniques that have been and can be applied to wastewater is therefore warranted. Though this review will focus primarily on wastewater and wastewater treatment, where key NMR studies from related fields (e.g. natural waters, soils, sediments, agriculture) afford important examples, they will be included to demonstrate the breadth of NMR and its application to environmental research. In addition, we aim not only to provide a review of the literature, but also a short case study showing that when various NMR characterization approaches are combined with NMR based toxicity evaluation, the result is a comprehensive understanding of both wastewater and its impacts, that cannot be matched by any other modern analytical approach.

Section snippets

Sample preparation

Though one of the advantages of NMR is the possibility of little/no sample preparation [55], whether or not sample preparation is necessary is dependent on the goal of the research, the available NMR hardware, the experiments employed, and the concentrations of the analytes of interest. Indeed, the Achilles’ heel of NMR – sensitivity – may make sample preparation preferable, or even unavoidable, for the analysis of trace components. It is important to note that the following sections focus

Water suppression

In the case that unaltered samples are directly analyzed by NMR, water, which is the largest constituent of wastewater samples, contributes a very large and broad signal to the 1H NMR spectrum. Not only can this overlap with and mask signals of interest, it can also prevent optimization of receiver settings, leading to a lower signal-to-noise ratio, along with baseline roll and other distortions [132], [133]. Consequently, water suppression techniques are commonly employed in such studies to

Applications of wastewater NMR organized by nucleus of study

1D analysis, specifically 1H NMR, is by far the most commonly used NMR technique. However, the field of NMR is vast and there are many different nuclei and techniques that can be used in the study of wastewater and its treatment. The use of these techniques, especially in combination, has excellent potential for structure elucidation and mixture deconvolution, as well as the study of non-covalent interactions. In this section we will discuss a number of NMR techniques, and follow up with

Non-targeted analysis

One of the major benefits of 1H NMR is that it is a completely non-selective detector. While techniques like MS need to be optimized for individual compounds, and other techniques such as fluorescence detect only fluorescent compounds, 1H NMR can, to an equal degree, analyze any compound that contains protons. Non-targeted analysis refers to the study of a mixture without the goal of studying a certain compound or group of compounds [268]. Commonly 1H NMR is applied along with statistical

Integrating NMR approaches into a cohesive framework

Thus far, the use of NMR in the context of wastewater has been introduced and applications to date have been reviewed. However, what makes NMR stand out amongst all other analytical approaches for environmental analysis is its great versatility [54].

For example, NMR can provide targeted and non-targeted analysis, including overall compositional profiling (fingerprinting) and individual chemical identification/quantification along with physico-chemical information (such as dynamics, molecular

Conclusions and future work

As demonstrated in this review and case study, NMR has considerable potential to provide an exceptional understanding of the structures, interactions, processes, and toxicity of compounds in wastewater. In this review, applications were organized based on the nucleus of study (1H, 13C, etc.) and at the end of each section, future directions were thoroughly discussed, therefore there is no need to revisit them here. As a field in general, NMR applications to wastewater will likely diverge along

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We would like to thank the Natural Sciences and Engineering Research Council of Canada (NSERC) (Strategic (STPGP 494273-16), Discovery (RGPIN-2019-04165) and Alliance (ALLRP 549399 and ALLRP 555452) programs), the Canada Foundation for Innovation (CFI), the Ontario Ministry of Research and Innovation (MRI), and the Krembil Foundation for providing funding. A. J. S. would like to thank the Government of Ontario for an Early Researcher Award. Flavio Kock would like to thank the Brazilian

Glossary

ADP
Adenosine diphosphate
AMP
Adenosine monophosphate
ATP
Adenosine triphosphate
CDFA
Chlorodifluoroacetic acid
CEPT
Chemically Enhanced Primary Treatment
CFC
Chlorofluorocarbon
CMP
Comprehensive Multiphase
COD
Chemical Oxygen Demand
COSY
COrrelated SpectroscopY
CPC
Cetylpyridinium chloride
CP-MAS
Cross-Polarization Magic Angle Spinning
CRAM
Carboxylic Rich Aliphatic Material
DEAE
(Diethylaminoethyl)
DEPT
Distortionless Enhancement by Polarization Transfer
DFA
Difluoroacetic acid
DMSO‑d6
Deuterated Dimethylsulfoxide
DOC

References (717)

  • P.R. Gogate et al.

    A review of imperative technologies for wastewater treatment II: hybrid methods

    Adv. Environ. Res.

    (2004)
  • C.S. Lee et al.

    A review on application of flocculants in wastewater treatment

    Process Saf. Environ. Prot.

    (2014)
  • M.R. Johns

    Developments in wastewater treatment in the meat processing industry: A review

    Bioresour. Technol.

    (1995)
  • Y. Satyawali et al.

    Wastewater treatment in molasses-based alcohol distilleries for COD and color removal: A review

    J. Environ. Manage.

    (2008)
  • M. Kamali et al.

    Review on recent developments on pulp and paper mill wastewater treatment

    Ecotoxicol. Environ. Saf.

    (2015)
  • A. Asghar et al.

    Advanced oxidation processes for in-situ production of hydrogen peroxide/hydroxyl radical for textile wastewater treatment: a review

    J. Clean. Prod.

    (2015)
  • G. Lofrano et al.

    Chemical and biological treatment technologies for leather tannery chemicals and wastewaters: A review

    Sci. Total Environ.

    (2013)
  • C.P. Gerba et al.

    Municipal Wastewater Treatment, in

    Environ. Microbiol., Elsevier

    (2015)
  • G.R. Xu et al.

    Recycle of Alum recovered from water treatment sludge in chemically enhanced primary treatment

    J. Hazard. Mater.

    (2009)
  • L. Semerjian et al.

    High-pH–magnesium coagulation–flocculation in wastewater treatment

    Adv. Environ. Res.

    (2003)
  • E. Sanchez et al.

    Effect of organic loading rate on the stability, operational parameters and performance of a secondary upflow anaerobic sludge bed reactor treating piggery waste

    Bioresour. Technol.

    (2005)
  • L. Guardabassi et al.

    The effects of tertiary wastewater treatment on the prevalence of antimicrobial resistant bacteria

    Water Res.

    (2002)
  • J. Koivunen et al.

    Inactivation of enteric microorganisms with chemical disinfectants, UV irradiation and combined chemical/UV treatments

    Water Res.

    (2005)
  • M. Hamoda et al.

    Sand filtration of wastewater for tertiary treatment and water reuse

    Desalination.

    (2004)
  • D.T. Williams et al.

    Disinfection by-products in Canadian drinking water

    Chemosphere.

    (1997)
  • K. Watson et al.

    Chlorine disinfection by-products in wastewater effluent: Bioassay-based assessment of toxicological impact

    Water Res.

    (2012)
  • G. Hua et al.

    Comparison of disinfection byproduct formation from chlorine and alternative disinfectants

    Water Res.

    (2007)
  • S.E. Hrudey

    Chlorination disinfection by-products, public health risk tradeoffs and me

    Water Res.

    (2009)
  • T.A. Ternes et al.

    Ozonation: a tool for removal of pharmaceuticals, contrast media and musk fragrances from wastewater?

    Water Res.

    (2003)
  • A.J. Simpson et al.

    NMR spectroscopy in environmental research: From molecular interactions to global processes

    Prog. Nucl. Magn. Reson. Spectrosc.

    (2011)
  • D. Courtier-Murias et al.

    Comprehensive multiphase NMR spectroscopy: Basic experimental approaches to differentiate phases in heterogeneous samples

    J. Magn. Reson.

    (2012)
  • A. Mele et al.

    Non-covalent associations of cyclomaltooligosaccharides (cyclodextrins) with trans-β-carotene in water: evidence for the formation of large aggregates by light scattering and NMR spectroscopy

    Carbohydr. Res.

    (1998)
  • H.H. Mantsch et al.

    Deuterium magnetic resonance, applications in chemistry, physics and biology

    Prog. Nucl. Magn. Reson. Spectrosc.

    (1977)
  • R. Kc et al.

    Susceptibility-matched plugs for microcoil NMR probes

    J. Magn. Reson.

    (2010)
  • G.E. Martin

    Small-volume and high-sensitivity NMR probes

    Annu. Reports NMR Spectrosc.

    (2005)
  • P. Styles et al.

    A high-resolution NMR probe in which the coil and preamplifier are cooled with liquid helium

    J. Magn. Reson.

    (2011)
  • Y. Zhang et al.

    Hemicellulose isolation, characterization, and the production of xylo-oligosaccharides from the wastewater of a viscose fiber mill

    Carbohydr. Polym.

    (2016)
  • G.M. Hautbergue et al.

    Increasing the sensitivity of cryoprobe protein NMR experiments by using the sole low-conductivity arginine glutamate salt

    J. Magn. Reson.

    (2008)
  • J.H. Lee et al.

    Sensitivity enhancement in solution NMR: Emerging ideas and new frontiers

    J. Magn. Reson.

    (2014)
  • U. Sternberg et al.

    1H line width dependence on MAS speed in solid state NMR – Comparison of experiment and simulation

    J. Magn. Reson.

    (2018)
  • L.M.A. Silva et al.

    DESI-MS imaging and NMR spectroscopy to investigate the influence of biodiesel in the structure of commercial rubbers

    Talanta.

    (2017)
  • L.M.A. Silva et al.

    Comprehensive multiphase NMR spectroscopy: A new analytical method to study the effect of biodiesel blends on the structure of commercial rubbers

    Fuel.

    (2016)
  • R. Ghosh Biswas et al.

    Ex vivo comprehensive multiphase NMR of whole organisms: A complementary tool to in vivo NMR

    Anal. Chim. Acta X.

    (2020)
  • J. Hong et al.

    Magic-angle spinning sideband elimination by temporary interruption of the chemical shift

    J. Magn. Reson. Ser. A.

    (1993)
  • W. Dixon et al.

    Total suppression of sidebands in CPMAS C-13 NMR

    J. Magn. Reson.

    (1982)
  • S.L. Postel et al.

    Human Appropriation of Renewable Fresh Water

    Science.

    (1996)
  • S. Naidoo et al.

    Treated Wastewater Effluent as a Source of Microbial Pollution of Surface Water Resources

    Int. J. Environ. Res. Public Health.

    (2013)
  • D.M.S. Goswami

    Treatment of Chrome Tannery Wastewater by Biological Process - A Mini Review

    Int. J. Environ. Ecol. Eng.

    (2013)
  • M. Chowdhury et al.

    Characterization of the Effluents from Leather Processing Industries

    Environ. Process.

    (2015)
  • C. Zhao et al.

    A review for tannery wastewater treatment: some thoughts under stricter discharge requirements

    Environ. Sci. Pollut. Res.

    (2019)
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