7.2 Natural flocculant recovery by mild fractionation using ionic liquids and aqeous two-phase systems
Separation of (suspended and colloidal) particles from water is a challenge in drinking water production and wastewater treatment. Flocculation of these particles facilitates their removal by settling, (membrane) filtration or flotation. Currently this is widely achieved with synthetic polymers. However, these suffer from several disadvantages: they are expensive, non-biodegradable and can have a carcinogenic or neurotoxic nature. This presents a hazard if they are applied in (open) aquatic ecosystems and prevents reuse of the concentrated solids. Natural flocculants, due to their environmental friendliness, have gained increasing attention for water treatment and are promising alternatives. One of the natural flocculants, yet to be exploited, are extracellular polymeric substances (EPS) excreted by mixed-cultures of microorganisms. They can be produced during biological treatment of (industrial) wastewaters and in this manner contribute to a more bio-based economy. With suitable wastewaters and under certain biological process conditions very high flocculant production yields can be achieved. However, the product concentration is low and the polymers vary in chemical structure, molecular weight, charge density, etc. A cheap and sustainable extraction and purification method would allow further fractionation of the polymers for example into proteins and polysaccharides or into low and high molecular weight polymers. This would improve the quality and effectiveness of the final product. Also, this would allow exploration of other applications of the (fractionated) biopolymers.
A key process step, which is currently still undeveloped, is the extraction of EPS with ionic liquids (ILs) as solvent, because ILs have been reported as effective and green solvents. In order to keep the EPS intact, it is essential to apply mild techniques such as aqueous two-phase systems (ATPS) for the regeneration and reuse of the IL. For this purpose stimuli responsive polymers to form ATPS will be explored. The research challenges in this project are:
1) finding appropriate ILs for extraction of EPS from the broth;
2) developing stimuli responsive ATPS based on these ILs and commercial temperature responsive and CO2-responsive polymers as well as in-house developed photo-responsive polymers;
3) study on the isolation of EPS fractions of different molar weights from the polymer rich phase by applying a stimulus (temperature, light, CO2), and study the behaviour of each fraction in flocculation processes, one of the possible applications of these EPS.
The candidate has an MSc degree in chemical engineering or related field and a strong affinity with (polymer) chemistry and separation technology. An interest in developing analytical tools for biopolymers is a pre-requisite as well as an interest to co-operate with potential end-users of the products.
This project is part of the Wetsus research theme “Natural Flocculants”. Within this theme another PhD student develops a biological production method for natural flocculants from wastewater and studies their application as flocculants.
Promotor: Prof. dr. S.R.A. Kersten
Co-promotor:Dr. ir. B. Schuur (University of Twente)
Wetsus supervisor: Dr. ir. H. Temmink (firstname.lastname@example.org)
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Wetsus, Leeuwarden, The Netherlands