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Context and issues

Composting with green waste and application as an organic amendment is currently the main disposal route for sewage sludge. However, the agricultural component of the Circular Economy Roadmap (RCEM) calls for innovative technologies for recycling mineral nutrients from recycled materials such as sludge. Anaerobic Digestion (AD) is a first step in this recovery scheme. AD is a biological process that converts sludge into biogas, a renewable energy source, and a digestate (raw) rich in nitrogen, phosphorus, potassium and organic matter. In addition, in order to improve biogas conversion performance, the sludge can undergo thermal hydrolysis pretreatments that lead to a high dissolution of organic matter and an increase in soluble COD in anaerobic digestion effluents. The latter can hinder the recovery of the liquid phase of the digestates.

The raw digestates from wet anaerobic digestion processes are mechanically separated (by screw press, centrifuge, sieve...) to obtain a liquid digestate and a solid digestate. Although usually supported by the addition of coagulants/flocculants, this ultimate solid/liquid separation remains difficult and should therefore be optimized.

The optimization approach could focus in particular on the development of coagulants/flocculants specifically adapted to the physicochemical properties and characteristics of digestates.

In this context, the use of functionalized biopolymers can be of great interest from two points of view: on the one hand, natural products characterized by an environmental safety necessary for relevant recovery will be used and, on the other hand, a functionalization will allow to increase the specificity of interactions with suspended matter. This functionalization will be characterized by the distribution, the type and the number of functional groups.

Objective

The objective of this project is to study and optimize the potential efficiency of a bio-based coagulant/flocculant on the solid/liquid separation of liquid digestates in order to optimize the use of fertilizing materials.

Initially, the coagulants will be synthesized by functionalization of chitosan (obtained from crustaceans or insects). Such functionalized chitosans will be evaluated as coagulants on different types of digestates whose suitability for settling and filtering will be assessed. Measurements of zeta potential, estimation of capillary suction time (CST), rheological and particle size analyses will complete these tests. This evaluation will be combined with a biochemical analysis of the supernatants or filtrates (TS, VS, COD, TOC, IC, pH, Ions (P, K, Ca, Mg, S, Na), Nitrogen (TKN, Organic N, NH4+, NH3...) in order to estimate the potential recovery of the separated digestate.

The candidate will be in contact with the researchers of the three research units involved in the project, i.e. the Laboratory of Environmental Biotechnology, the QualiSud RMU and the Charles Gerhardt Institute.

Conditions

Start date

01/10/2020 (subject to administrative procedure)

Funding

Public funding, on a project financed by the French Water Agency (Rhone Mediterranean Corsica Water Agency).

Location

The work will take place in 2 workplaces: Montpellier and Narbonne (Occitanie - France). The candidate will thus work on the respective sites of the research teams involved:

• LBE INRA
• UMR Qualisud
• ICG Montpellier

Candidate's profile

Engineer or Master's degree in Process Engineering, Chemical Engineering and Environmental Sciences. Experience, or basic training, in general chemistry would be an asset.

Scientific curiosity and rigor, taste for teamwork and multidisciplinary, good level in English (writing scientific articles and communications in international conferences).

Application

Deadline: 04/09/2020

Contact: Hélène Carrère , LBE INRA, helene.carrere (at) inra.fr

Christelle Wisniewski, UMR QualiSud, christelle.wisniewski (at) umontpellier.fr