Sporopollenin : applications in water purification

• Main Author: Meichanetzoglou, Aimilia
• Format: Dissertation
• Language: English
• Published: University of Hull 2021
• Subjects: Chemistry

Water pollution from emerging contaminants is increasingly in the spotlight, as research on the impacts on the environment is revealing more about the dangers to both animals in the aquatic environment and human health. Pharmaceuticals, personal care products, surfactants and pesticides have been proven to have endocrine-disrupting properties, affecting not only the aquatic life but human life as well. Conventional wastewater treatment plants need to updated in order to deal with this family of chemicals, since they are currently incapable of removing them using traditional methods. New methods need to be developed since the current ones leave behind around 60 - 90% of the initial contaminant concentration and re-introduce it to the water cycle. Adsorption procedures have been proven to be very effective on water treatment, targeting emerging contaminants, with research focusing on developing new materials, that apart from being effective should also be environmentally friendly. Sporopollenin is the name of a bio-polymer found in nature, constructing the outer shell (exine) of the capsule of a pollen grain or spore. The capsule itself - sporopollenin exine capsule (SpEC) - evolved to protect the genetic material contained in each grain/spore, hence sporopollenin has been proven to be chemically stable and very resistant to harsh environmental conditions. SpECs can be extracted from pollen grains or spores producing empty capsules (devoid of their genetic material), presenting a variety of differently sized microcapsules and shapes depending on the plant species. These capsules are monodispersed, presenting great mechanical strength as well as permeability. The material has a high surface area due to the porous nature with many multi-directional channels leading to the core of the capsule, giving them features and properties that are ideal for contaminant adsorption. The focus of this thesis was the investigation of SpECs deriving from Lycopodium clavatum by multiple extraction methodologies for applications on emerging contaminant adsorption. Different extraction procedures were developed, as well as surface modification protocols, in order to optimise the material for the different pollutants. The resulting SpECs were tested against four different contaminants; diclofenac, triclosan, oestradiol and phosphates, under different experimental settings, either lab based or closer to real world conditions. The results revealed that SpECs offer a very promising natural material, presenting high efficiency against the tested contaminants, with low-cost production, offering an environmentally friendly approach to the problem of water purification. For diclofenac, the most efficient SpECs type was SpECs(3)AM, with a maximum adsorption capacity value of 27.4 mg/g under a packed-bed setup. For triclosan, SpECs(3) was the most efficient type, presenting a maximum adsorption capacity of 37 mg/g under packed-bed setup or a KF value of 35.14 mg(1−1/n)/gL−1/n for adsorption from a solution. For oestradiol adsorption, SpECs(1) worked the best, presenting a maximum adsorption capacity of 42.5 mg/g. For phosphates, all tested SpECs presented similar adsorption capacities, with the water/Fe loaded SpECs(3) presenting the highest, 2.1 mg/g. SpECs presented adsorption capacity values far beyond what would be required for treating hospital effluent or surface waters and very good adsorption rates, especially for diclofenac and triclosan. Although the oestradiol experiments resulted in excellent maximum adsorption capacity, the rate of adsorption was below what would be required for treating large bodies of flowing water. However all other materials exhibited very promising rates of adsorption, particularly SpECs(3)AM for diclofenac and SpECs(3) for triclosan, warranting scale-up experiments for the treatment of such volumes as hospital effluents (55 - 530 L/min). SpECs(3) and their aminated form, SpECs(3)AM were proven to be the best candidates for contaminant adsorption, with SpECs(3) ticking all the boxes for a successful adsorbent; apart from their excellent adsorption behaviour, their production is fast and low-cost, they are environmentally friendly since they derive from plant spores, the chemicals used are not harsh to the environment nor were high temperature treatments or long reaction times required and they also presented good reusability.