Smart Storage of Biomass to Enhance its Technological Conversion – STOCKACTIF

The research has been conducted at multiple scales: a few grams to select the most
effective fungi, a few hundred grams to find the best conditions and explain the
mechanisms and several kilos to identify industrial extrapolation difficulties and make a
technical, economic and environmental study as realistic as possible.
For the transformation, solid state fermentation (SSF) methods were used. The
conversion was measured by end-use representative tests (biogas potential, hydrolysis
tests, ethanol potential) and also by mechanical measures to quantify how the biological
pre-treatment could decrease the grinding energy of the raw material. Biochemical
reactions were followed by molecular biology methods and methods to distinguish the
relative transformation of lignin compared to sugars (3D spectrofluorometry, pyrolysis
coupled to chromatography and mass spectrometry).
An industrial process configuration was designed and first steps have been tested by the
industrial partners of the project. This configuration provided the framework for the
technical, economic and environmental comparison which was conducted by a specialized
partner, using data obtained at different scales.

Research at the laboratory scale have identified a strain of fungus (among 175 tested)
with particular characteristics and have allowed to define its optimal conditions. On a
larger scale the possibility of the Stockactif pretreatment using a «starter« in the solid
state has been demonstrated. The strain and pre-treatment process have been patented.
This strain has also been studied into a wider program of international collaboration.
Innovative methods (in the field of FMS) and new equipment (in the field of mechanical
measurements and grinding) were developed and published. These achievements are
now available to be used routinely in the participating laboratories. in particular , an
innovative mechanical measuring equipment was reproduced in four copies to equip the
partner’s laboratories.
The techno-economic and environmental assesments made under the hypothesis of
industrial scale units show that the additional investment costs related to the installation
of the Stockactif pretreatment platform are relatively low (a few %), but are not
balanced by a reduction in operating costs: these costs are equivalent in the case of
ethanol and higher in the case of biogas, due to the mass loss. From the environmental
point of view, the results are mixed, with a significant improvement of the LCA criteria
for the ethanol pathway and a slight deterioration for the biogas pathway, which is
already inherently efficient and suffers again the effect of the mass loss related to pretreatment.

Scientifically, this project was the starting point to at least two national collaborative
projects interested in the potential of fungal treatments on solid media for obtaining
specific molecules. Furthermore, the Stockactif patented strain has been, with others,
integrated into a broad international functional genomics program managed by the Joint
Genome Institute (JGI) of the Department of Energy of the USA (US-DOE). This
opportunity allowed us to sequence its genome and use those results for the
transcriptomic study conducted as part of the Stockactif project. The tests conducted on the Stockactif “solid-state starter” production on several hundred
kg has identified the key points of the compromise to find. At short term, existing
industrial equipments are not suited to handle this compromise, but in the medium term
this subject could be reactivated if a particular use of Stockactif process is desired,
especially to transform with a low environmental impact some particularly recalcitrant
raw materials.

The project was the opportunity to host two doctoral students, one in teams of BBF in
Marseille and of FARE in Reims, the other in the LBE team in Narbonne. In addition to
their thesis, the doctoral fellows writed or participated in writing 12 scientific articles and
presented more than 9 comunications and posters.
A patent involving three public laboratories has been filed. It's called «Pretreatment of
lignocellulosic biomass by filamentous fungi for the production of bioenergy«.

The rationale of this project of « smart storage » is to take advantage of the idle time between biomass harvesting and its utilization in a biorefinery : this time would be used for preparing biomass deconstruction via lignolytic bioprocesses. In other words, it would look as a kind of controlled ensiling fitted to the new utilization of biomass, namely its potentialities to be transformed in energy (bio-ethanol, biogas), in platform molecules (through white biotechnology of sugars coming from cellulose or hemicelluloses or as a source of phenolic compounds).

This idea raises the question of the balance between the transformation of lignins and the losses of sugars during such a storage, but other issues are pregnant, like contamination or piloting the storage. This project deals with all of these by using solid state fermentation methodology and lignolytic fungus strains.

The benefit would be at the same time energetical and environmental : for all kinds of biomass utilization, the two first steps in a factory (size reduction and pretreatment) are strong consumers of energy (grinding, cooking, steam explosion, ….) and possibly of chemical reactives (acid pretreatment, alkali pretreatment, organosolv pretreatment, …) which need to be filtered out and which deteriorate the environmental impacts. So a pre-conditioned biomass which would enable to lower, or to suppress, the pretreatment would be a noticeable benefit. In case of biogas production, a pre-conditioned biomass could gain wider possibilities of uses if its biodegradation kinetic fits with the classical substrates ones .

In our approach, the essential difference in comparison to an industrial process is the time, which turned from hours to weeks. In fact, the background of the proposal is not new, as it is close to the « biopulping » process developed in papermaking industry around ten years ago, but the present project is designed to address new issues :
- keep as max as possible the « utilization potential » of the biomass for ethanol (and so saccharification) and biogaz production
- describe the operating parameters for piloting the storage, in order to be able to obtain a repeatable degree of transformation, whichever be the external perturbations, including the problem of contamination by sugars-consuming bacteria
- set up the technico-economical balance between the possible loss of end use potential and the gain for pre-treatment and anaerobic digestion, particularly in terms of energy and environmental impacts
- plan the use of this smart storage principle in a simple, low cost and realistic way by comparing a few pre-industrial solutions

The research work is mainly cognitive, as the field to address is wide and it is necessary to handle the effects of several parameters to find an optimal solution. This work is managed through four main work-packages :
- the screening for best suited fungus strain(s) and the choice of the level and the conditions of efficient inoculation methods
- the description of the controlling parameters for solid state fermentation
- the characterization of the products obtained regarding subsequent steps of process, and particularly grinding, bio-ethanol and biogas production
- the influence of fungus preconditioning on the technico-economical and environmental balance.

Thanks to the partnership of four industrial companies, the solutions will be tested at a pre-industrial scale. This step will also be an opportunity to test the prototype of an on-site device designed to sensor complex biological reactions, developed by a start-up company during this project. The private companies partnership is also a guarantee of moving the five academic research teams towards a robust and realistic solution for this smart storage principle.