Intensification of Biological Carbon Redirection in Wastewater Treatment Plants – Study of a High-Rate Activated Sludge Reactor under Real Operating Conditions. Project CAPTURE 2

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INRAE presentation

The French National Research Institute for Agriculture, Food, and Environment (INRAE) is a major player in research and innovation. It is a community of 12,000 people with 272 research, experimental research, and support units located in 18 regional centres throughout France. Internationally, INRAE is among the top research organisations in the agricultural and food sciences, plant and animal sciences, as well as in ecology and environmental science. It is the world’s leading research organisation specialising in agriculture, food and the environment. INRAE’s goal is to be a key player in the transitions necessary to address major global challenges. Faced with a growing world population, climate change, resource scarcity, and declining biodiversity, the Institute has a major role to play in building solutions and supporting the necessary acceleration of agricultural, food and environmental transitions.

Work environment, missions and activities

The research unit (UR) REVERSAAL (Reduce, Reuse, Recover Resources from Wastewater) at INRAE’s Lyon-Grenoble-Auvergne Rhône-Alpes Center focuses primarily on the treatment and recovery of resources from wastewater. (https://reversaal.inrae.fr/).

Wastewater treatment plants are evolving into water resource recovery facilities, incorporating the valorization of organic carbon within a circular economy framework. Upstream redirection of carbon prior to biological treatment helps minimize its oxidation and enhances its recovery as biogas or other valuable co-products. High-rate activated sludge (HRAS) reactors play a key role in this redirection, but their treatment and settling performance can be affected by hydraulic and organic load fluctuations. Optimizing these processes requires better control of operational parameters and solid-liquid separation strategies to enable carbon redirection after the biological reactor. This industrial PhD (CIFRE), conducted in collaboration with the Saur Group (https://www.saur.com/), is based on pilot- and demonstrator-scale experiments aimed at optimizing high-rate activated sludge reactors under real operating conditions. The study is part of the CAPTURE 2 project, led by INRAE’s REVERSAAL research unit and the Saur Group, which investigates the integration of both physico-chemical and biological carbon redirection strategies

The proposed approach is based on several sequential steps:

• Impact of upstream pre-treatment processes;
• Optimization of operational parameters to maximize carbon redirection;
• Evaluation of solid-liquid separation strategies for the produced sludge;
• Valorization potential of the sludge and its impact on biogas production.

Particular attention will be given to microbial dynamics and floc structure within the biological reactors. Microscopic observations, supplemented if necessary by metagenomic analyses, will be used to investigate floc architecture, interactions between bacterial populations, and the production of extracellular polymeric substances (EPS). These data will be analyzed in relation to sludge settleability and valorization potential, particularly for biogas production.

This work aims to improve the understanding of microbiological and physico-chemical mechanisms influencing carbon redirection in wastewater treatment plants and to optimize the performance of treatment processes and resource recovery.

 

You will be specifically responsible for:

Assessing the performance of high-rate biological reactors under dynamic conditions and analyzing the impact of upstream pretreatments: Continuous experiments on a pilot column will be conducted to evaluate organic carbon redirection based on operational parameters (hydraulic retention time, sludge age, dissolved oxygen) and upstream pretreatments. Primary settling (with or without chemical additives) will be compared to cloth filtration to assess their impact on carbon capture, floc dynamics, and effluent quality. Measurement of soluble, colloidal, and particulate Chemical Oxygen Demand (COD) fractions will help elucidate biosorption, aggregation, and settling mechanisms. Particular attention will be paid to floc structure and strength, as well as EPS composition (extraction and quantitative/qualitative analysis of carbon and nitrogen compounds via TOC and TKN). Real-time monitoring with specific probes will allow performance tracking under varying load conditions, hydraulic fluctuations, and wet weather events, with the aim of optimizing flow regulation and aeration.

Optimizing intensification strategies for high-rate biological reactors: Several intensification strategies will be implemented to improve the performance of high-rate biological treatment processes. The addition of ferric chloride (FeCl₃) will be tested to enhance flocculation by promoting the formation of more compact, dense, and shear-resistant sludge. The efficiency of solid-liquid separation will be compared under different configurations, such as doubling the settling surface area or using filtration. The impact on sludge production and its methane potential will be assessed through biodegradability tests, the proportion of readily hydrolysable organic matter, and its suitability for anaerobic digestion. The full-scale demonstrator developed by the Saur Group will provide an opportunity to validate the results obtained under controlled conditions.

Capitalizing on results and defining recommendations for large-scale integration: The results will be disseminated through scientific publications and transferred to the Saur Group in the form of technical recommendations. A techno-economic analysis based on the PhD outcomes will estimate investment and operating costs associated with the process deployment. The optimization of operational conditions and intensification strategies will be assessed considering existing infrastructure constraints. Finally, the impact of various configurations on process stability, robustness under hydraulic fluctuations, and bacterial community composition will be incorporated into the final recommendations.
 

Special working conditions: remote working possible

Training and skills

• Recommended education: Master’s degree (or equivalent) in Process Engineering or Chemical Engineering
• Desired knowledge: Reactor operations, wastewater treatment, applied chemistry and microbiology, good laboratory practices
• Preferred experience: Prior experience in the wastewater field is essential
• Required skills: Proficiency in English (reading, writing, speaking), data analysis, summarizing, and scientific writing
   

INRAE's life quality

By joining our teams, you benefit from (depending on the type of contract and its duration):

- up to 30 days of annual leave + 15 days "Reduction of Working Time" (for a full time);
- parenting support: CESU childcare, leisure services;
- skills development systems: training, career advise;
- social support: advice and listening, social assistance and loans;
- holiday and leisure services: holiday vouchers, accommodation at preferential rates;
- sports and cultural activities;
- collective catering.

How to apply

I send my CV and my motivation letter