• Vol 9, No 6 (2018)
  • Chemical Engineering

Solubilized Chitosan Biopolymers for Sequestration of Organic Acids in Aquatic Environments after Biodegradation in a Constructed Wetland Treatment System

Mohamed H Mohamed, Chukwuemeka Ajaero, Dena W McMartin, Kerry M Peru, Vanessa Friesen, Monique Simair, John V Headley, Lee Wilson

Cite this article as:
Mohamed, M.H., Ajaero, C., McMartin, D.W., Peru, K.M., Friesen, V., Simair, M., Headley, J.V., Wilson, L., 2018. Solubilized Chitosan Biopolymers for Sequestration of Organic Acids in Aquatic Environments after Biodegradation in a Constructed Wetland Treatment System. International Journal of Technology. Volume 9(6), pp. 1140-1150
Mohamed H Mohamed Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, SK., S7N 5C9
Chukwuemeka Ajaero -Faculty of Engineering and Applied Science, University of Regina, 3737 Wascana Parkway, Regina, SK, Canada, S4S 0A2 - Water Science and Technology Directorate, Environment and Climate Change Canada,
Dena W McMartin -Faculty of Engineering and Applied Science, University of Regina, 3737 Wascana Parkway, Regina, SK, Canada, S4S 0A2 - Department of Civil, Geological & Environmental Engineering, University of Saska
Kerry M Peru Water Science and Technology Directorate, Environment and Climate Change Canada, 11 Innovation Boulevard, Saskatoon, SK S7N 3H5, Canada
Vanessa Friesen Alexo Environmental Group, 104-411 Downey Road, Saskatoon, SK S7N 4L8, Canada
Monique Simair Alexo Environmental Group, 104-411 Downey Road, Saskatoon, SK S7N 4L8, Canada
John V Headley Water Science and Technology Directorate, Environment and Climate Change Canada, 11 Innovation Boulevard, Saskatoon, SK S7N 3H5, Canada
Lee Wilson Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, SK., S7N 5C9
Email to Corresponding Author


Pristine chitosan was dissolved in two different respective aqueous acids, namely acetic acid (AcA) and hydrochloric acid (HCl). The respective acid solutions were used as media to associate with naphthenic acid fraction compounds (NAFCs) from raw oil sands process water (R-OSPW) contaminants and constructed treatment wetland systems OSPW (CWTS-OSPW) samples. The results revealed selective removal of NAFCs and lyotropic effects due to variable counterion binding of chloride versus acetate with the ionized NAFCs (carboxylate species).

Chitosan; Hofmeister series; Naphthenic acids; Oil sands process water; Wetland


The development of oil sands ores has resulted in the production of large volumes of oil sands process-affected water (OSPW), which in turn, poses a concern for nearby aquatic systems (Kelly et al., 2010). OSPW is acutely and chronically toxic to a variety of aquatic organisms (Clemente & Fedorak, 2005) because it contains naphthenic acids (NAs), which are mainly associated with the toxicity of OSPW (Headley & McMartin, 2004; Morandi et al., 2015). NAs are generally identified as a complex mixture of aliphatic and alicyclic monocarboxylic acids with the general formula CnH2n+ZO2, where n = number of carbons, Z = hydrogen deficiency, by the formation of rings (Headley & McMartin, 2004). However, the application of high-resolution analytical methods that employ Orbitrap–mass spectrometry (MS) and Fourier transform ion cyclotron resonance MS (FT-ICR-MS) has shed more light on the composition of OSPW to include oxidized NAs (Ox; where x ? 3) and sulfur- and nitrogen-containing species (NOx, SOx; Headley et al., 2009; Barrow et al., 2010; Grewer et al., 2010). In a broad sense, the aforementioned compounds are generally referred to as NA fraction compounds (NAFCs; Headley et al., 2016). As a consequence of the toxicity of OSPW, there is restriction on their release, and therefore, they are kept in large-scale tailings containment sites (Giesy et al., 2010). OSPW confined in storage containment sites requires further treatment of potentially toxic components before release of contained water to the aquatic environment (Limited, 2014; Hughes et al., 2017). This situation has led to innovative technologies and treatment strategies for OSPW remediation. Many treatment processes for OSPW remediation have been applied. Some of these technologies include conventional and advanced oxidation processes, membrane filtration technology, biological treatments, adsorption technology, and constructed wetland treatment systems (CWTS) (Rodgers & Castle, 2008; Pramanik, 2016). CWTS are receiving great attention because they are feasible, economical, and ecologically viable technology for the improvement of the quality of wastewater that have found extensive application for the treatment of a variety of contaminants in different wastewaters (Kadlec & Wallace, 2008). The removal of organic contaminants in CWTS is accomplished by the synergy of plants, soil, and hydrology, providing habitat and targeted reaction conditions for beneficial microorganisms (Rodgers & Castle, 2008; Haakensen et al., 2015; Valipour & Ahn, 2016). It is generally acknowledged that the removal processes of most contaminants in CWTS are performed by microbial processes (Faulwetter et al., 2009). The advancement of the technology of CWTS has led to potential application of diverse designs and operational conditions to maximize treatment efficiency. One of the more recently documented studies monitored the feasibility of OSPW treatment in a non-aerated wetland treatment system (Rodgers & Castle, 2008); the work demonstrated that the wetland system was effective for the transformation of NAFCs in OSPW (Ajaero et al., 2018). Furthermore, past studies have shown that bio-persistent fractions of OSPW-NAFCs remain after treatment (Haakensen et al., 2015). The post-treatment of OSPW to completely oxidize the remaining fractions is essential for further improving the treatments. Therefore, a combination of CWTS and other post-treatment processes may be valuable for the ultimate reclamation of OSPW (McQueen et al., 2016).

Polysaccharide-based sorbents and their modified forms are considered inexpensive alternative materials for hazardous wastewater treatment, where such sorbent have been under investigation and development (Crini, 2005). Wilson and coworkers (2014) reviewed the utility of such modified materials for the sequestration of NAFCs from OSPW, along with studies of other biopolymer adsorbents (Mohamed et al., 2011; Mohamed et al., 2013; Mohamed et al., 2015a; Udoetok et al., 2016).


This study provides strong support for the key role of biopolymer hydration in adsorption and self-assembly processes (Dehabadi et al., 2018). Experimental support for the two hypotheses provides an account for the association of chitosan and NAFCs. Hypothesis i was related to the enhanced adsorptive surface area of the biopolymer that occurred via solubilization of chitosan in aqueous acid, revealing an enhanced sequestration efficiency and molecular selectivity toward NAFCs in aqueous media. Hypothesis ii accounted for the role of counterion hydration effects, in accordance with the differential uptake of NAFCs in conjunction with the use of different acid additives (HCl and CH3COOH). The removal capacity of NAFCs from OSPW (both raw and treated) by dissolution of chitosan into an acid solution resulted in substantially greater removal (1,000-fold) compared with a previous report on water-insoluble forms of chitosan-based sorbents (Mohamed et al., 2015a). The role of hydration effects due to chloride and acetate counterion binding with chitosan parallel the trends in lyotropy described by the Hofmeister effect for such anions, in agreement with the observed trends in uptake for NAFCs. The use of acid dopants with variable counterions (chloride versus acetate) to solubilize chitosan offers a new approach for tuning the structure–function properties of chitosan sorbents with organic anion (carboxylate) species, as revealed for ionized NAFCs. The adsorption method employed herein favors sequestration of O2-containing species, which are known to be the major cause of toxicity in OSPW (Mohamed et al., 2017). Furthermore, solubilized chitosan reveals that selective removal can be achieved in complex mixtures of naphthenates that suggest the role of ionization effects among species of NAFCs. The role of ionization effects are readily detected using electrospray mass spectrometry in negative ion mode but are not readily observed in raw and treated wetlands OSPW systems. The molecular level insight gained through this study is anticipated to contribute favorably to sustainable resource extraction and remediation of industrial tailings through the use of green chemistry and adsorption-based technology reported herein.


The authors acknowledge the support provided by the Government of Canada (Natural Resources Canada) for this research.



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