Cleaning Wastewater for Agricultural Use

Freshwater scarcity is an issue faced by many areas in the world today. Freshwater sources are diminishing due to over use and many sources have become polluted by either municipal or agricultural waste (Huibers & Van Lir, 2005). Several methods must be used to combat this growing issue but one of the most important is reducing the use of potable fresh water in crop irrigation. One possible replacement for this potable water is wastewater coming from municipal and industrial sources (i.e., it has been partially treated). Despite the fact that it will have undergone some treatment, the waste water still contains several contaminants such as hormones and heavy metals (Yildiz, Kemik, & Hazer, 2010). When crops are grown with wastewater, these contaminants tend to concentrate in the plant. The contaminants are then consumed and build up in the body over time. Once the contaminant reaches a certain concentration they can have adverse health effects (Yildiz et al., 2010). To minimize any potential health risks, it would be beneficial for wastewater to undergo another phase of treatment to remove as much of the contaminants as possible. One possible treatment includes the use of hydrogels.

Hydrogels are polymeric networks that can store and release large quantities of water in response to environmental stimuli such as temperature and pH. Superabsorbent polymer hydrogels (SAP) are a type of hydrogel that can swell up to a thousand times their initial weight with water (Shi, Dumont, & Ly, 2014).  Their polymer networks can be synthetic (petroleum based) or bio-based in nature. Synthetic SAPs are known for their rapid swelling rate, however they have a high toxicity which limits their applications (Al-kawaz, 2016). Bio-based hydrogels are synthesized from chemicals derived from biomass such as starches and proteins. Bio-based hydrogels are advantageous due to their low toxicity (Shi et al., 2014).

Credit: https://pixabay.com/en/hydrogel-irrigation-saving-water-2922171/

Synthetic hydrogels are traditionally used in products ranging from baby diapers to feminine hygiene products. However, due to their polymeric network structure they are also powerful ion chelators (they can bind to ions and remove them from solution) (Yildiz et al., 2010). This means that they would be very effective at removing heavy metal ions from wastewater therefore allowing it to be used to irrigate crops.

Despite its promising laboratory test results, there are issues with the method. Ion chelating ability is highly dependant on the base of the hydrogel, the pH of the solution and the size and charge of the ion (Yildiz et al., 2010). The pH of the solution has a pivotal role in ion chelation, as changing the pH changes the charge of the hydrogel. As a general rule, hydrogels are most effective at ion chelation at pHs around 8. Additionally, hydrogels tend to be more effective at removing copper and nickle ions than other heavy metal ions (due to the ion’s size and charge) (Yildiz et al., 2010). Lastly hydrogels tend to break down during use, causing some chemical leaching and leading to toxic synthetic polymers entering the wastewater.

Bio-based SAPs offer an innovative solution to one of these issues. While they cannot change the conditional nature of ion chelation, they can address the issue of toxic polymer leaching. Bio-based SAPs are made from naturally occurring polymers such as proteins and starches (Duquette & Dumont, 2018). Therefore, if they break down they are only releasing starches and proteins into the environment rather than toxic synthetic chemicals.

These SAPs are most effective when used to remove heavy metals from industrial wastewater. One of the most heavily researched SAPs is made from corn starch. One such SAP is able to bind up to 1.36 mmol of Cu2+/g (Duquette & Dumont, 2018). This is a very reasonable binding rate when compared to synthetic SAPs and concentrations of ions generally found in wastewater. SAPs can also be made from wastes such as proteins resulting from the vegetable oil making process. For this reason, bio-based SAPs are an important new innovation in the fight against pollution and for a healthier environment.

 

References

Al-kawaz, D. A. (2016). Synthetic Petroleum-Based Polymers. Petrochemical Industry.

Duquette, D., & Dumont, M.-J. (2018). Influence of Chain Structures of Starch on Water Absorption and Copper Binding of Starch‐Graft‐Itaconic Acid Hydrogels. Starch, 70(7-8). doi:https://doi.org/10.1002/star.201700271

Huibers, F. P., & Van Lir, J. B. (2005). Use of wastewater in agriculture: the water chain approach. Irrigation and Drainage, 54(S1), S3-S9. doi:https://doi.org/10.1002/ird.181

Shi, W., Dumont, M.-J., & Ly, E. B. (2014). Synthesis and properties of canola protein-based superabsorbent hydrogels. European Polymer Journal, 54, 172-180. Retrieved from http://www.sciencedirect.com/science/article/pii/S0014305714000871. doi:https://doi.org/10.1016/j.eurpolymj.2014.03.007

Yildiz, U., Kemik, Ö. F., & Hazer, B. (2010). The removal of heavy metal ions from aqueous solutions by novel pH-sensitive hydrogels. Journal of Hazardous Materials, 183(1–3), 521-532. Retrieved from http://www.sciencedirect.com/science/article/pii/S0304389410009404. doi:https://doi.org/10.1016/j.jhazmat.2010.07.055

2 responses to “Cleaning Wastewater for Agricultural Use”

  1. pierrelucmorin says:

    1. Title: Informative but confusing
    2. The take-home message of the text is the great potential that hydrogel has on decreasing water scarcity by its ability to clean wastewater.
    3. The strongest aspect of this post is the explication of a scientific topic (hydrogel) into a fairly understandable language for readers that never heard of it.
    4. The most compelling argument was when the author used a scientific source to show that the capacity of Superabsorbent polymer hydrogels (SAP) can bind up to 1.36 mmol of Cu2+/g.
    5. A suggestion for improvement could be to specify what kind of wastewater is meant to be cleaned by SAP (industrial or municipal) and enumerate the most common contaminant (heavy metal) that need to be extracted. That way, the readers could see more easily the potential of hydrogel on decontaminating wastewater.

  2. thomasgiguere says:

    1-Intrigant, détaillé

    2-Les polymères super absorbants d’origine biologique pourraient s’avérer être une solution efficace et écoresponsable pour le traitement des eaux usées destinées à être utiliser pour l’irrigation en agriculture.

    3-L’introduction de cet article constitue une excellente mise en situation, efficace et concise. Elle permet au lecteur de bien saisir l’enjeu que représente l’usage des eaux usées en agriculture, en plus de piquer sa curiosité en ce qui concerne l’utilisation d’hydrogels comme solution potentielle. Elle donne envie de lire la suite de l’article.
    4-L’argument le plus saisissant de cet article est le fait les contaminants qui se retrouvent dans l’eau usée utilisée en agriculture peuvent avoir des effets négatifs sur notre santé.

    Puisque cela a un impact direct et néfaste sur nous, il est d’autant plus pressant que l’on trouve une solution à cette problématique.

    5-Le choix de vocabulaire est parfois un peu trop complexe et technique. De ce fait, il pourrait être difficile pour un lecteur qui n’a pas les connaissances scientifiques de base de comprendre l’intégralité de l’article. Par exemple, aucune définition n’est donnée pour les termes « biocompatibilité » ou « chélation d’ions », qui ne sont pourtant pas des concepts auxquels les gens sont généralement familiers. Un travail de vulgarisation pourrait être de mise.

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