Biohydrogen production: towards an innovative added-value bioprocess in anaerobic digestion-based waste treatment plant – ProBHyM

The methodology consists of addressing the following five sub-objectives:
(1) Optimization of the bioH2 production at laboratory scale from the organic fraction of municipal solid waste (OFMSW) and residues generated from agro and food industries,
(2) Operation in continuous process with variable real waste to estimate the production performances in a simulated environment.
(3) Integration of bioH2 and CH4 bio continuous processes with assessment of the overall energy conversion efficiencies.
(4) Influence of scaling up the bioH2 process from laboratory to pilot scale,
(5) Evaluation of the impacts of implementing a bioH2 process (life cycle analysis and technico-economic studies).

For this, the project is structured in 4 interdependent workpackages :
Task 1: Optimization of bioH2 operating parameters at lab scale
Task 2: Optimization of H2/CH4 process coupling at lab scale
Task 3: Feasibility tests at pilot scale
Task 4: Assessment of the environmental, social and techno-economic impacts

To date, during the first period of the project, research efforts have mainly focused on the optimization of H2 production at laboratory scale.
In task 1, thermal pretreatment of complex substrates (OFMSW) showed very little impact on H2 production performances, except on microbial communities in several cases. It was shown that the application of substrate pre-treatment affected mainly the microbial communities. Following conservation tests of heat-treated microbial inocula (digestate, leachate, WWTP sludge) on the fermentation of complex substrates (OFMSW and agro-industrial waste), the addition of an external microbial inoculum was not necessary. Nonetheless, the addition of efficient, stored and pre-treated inoculum was favorable to make the process more reproducible and stable. These results are subject to a joint publication between the partners. Beyond this finding, threshold inhibitory values of the H2 fermentation by microbial co-product accumulation were determined. Descriptive and explanatory models of the fermentation pathways in the presence of inhibitors are under construction.
In tasks 2 and 3, first tests showed the ability of endogenous microorganisms to produce hydrogen from real substrates in batch culture at laboratory and pilot scale (250 L).
In task 4, a first technico-economic pre-study was carried out in order to determine whether the solution of producing biohydrogen by fermentation was suitable and viable within an actual industrial anaerobic digestion unit (TRIFYL site as example). This pre-study highlighted the different equipment / processes necessary to produce bio-hydrogen, and opens new ways of process improvement.

In the second part of the project, optimization strategies for the H2 fermentation bioprocesses will be tested in order to overcome the inhibitions due to the accumulation of microbial metabolites and further maximize the conversion of model substrates to H2.
The energy performances after coupling the two processes (hydrogen and then methanation) will be assessed and compared to a simple anaerobic digestion step (usual treatment process) on real wastes.
At the pilot scale, the tests will be continued by integrating the parameters for removing the identified inhibitors.
Finally, the technological choices will be refined and impact studies (LCAs, regulatory study) will be carried out.

- K. Dauptain, A. Schneider, M. Noguer, P. Fontanille, R. Escudie, H. Carrere & E. Trably (2020) Impact of microbial inoculum storage on dark fermentative H2 production. Bioresource Technology (under revision)
- K. Dauptain, A. Schneider, C. Barrau, P. Fontanille, N. Bernet, H. Carrère & E Trably (2020). Impact of microbial inoculum on dark fermentaive H2 production. WHEC 2020 (World Hydrogen Energy Conference) (postponed to 2022)
- Poster presentation of the PROBHYM project at the Journées Recherche Industrie JRI Biogaz Méthanisation (Toulouse, 8 -10 September 2020)

While anaerobic digestion has regained a lot of interest with intensive industrial development in the field of waste treatment, fermentation processes represent a great potential way of innovation, particularly for the production of hydrogen, as emerging energy carrier. The main objective of the ProBHyM project is to study and evaluate the optimal parameters of fermentation process operation with a view to intensifying the production of hydrogen as an additional mean of energy recovery in waste AD plants. In particular, the fermentation process will be investigated on : (i) the mechanisms of inhibition (metabolic and/or populational) in relation to the accumulation of these by-products, including H2 in the medium (ii) the long-term operation and the impact of fermentation step on downstream AD, (iii) the upscaling and (iv) an economic and environmental analysis. The ProBHyM project will provide essential answers on the potential and limits of the production of H2 by dark fermentation.