Pre-treatment in Environmental Biorefinery

Pre-treatments are applied i) to overcome the limitations of biological processes [1] such as anaerobic digestion and dark fermentation and ii) to recover high-value molecules in the frame of environmental biorefinery [2] . Main objectives of LBE researches in this area are:

• Understanding of key mechanisms involved in the processes and elucidating the impact of pre-treatment on :
  • the structure of organic matter and endogenous microorganisms of the substrate
  • the performance of biological processes
• Optimisation of the combination of pre-treatment and biological processes

The pre-treatments can be placed upstream of the biological process, on a recirculation loop at the outlet of the digester (post-treatment) or between digester and post-digester (inter-stage treatment).

Combination of pre/post/inter-stage treatments with bioreactors                           

Pre-treatments and anaerobic digestion

The rate limiting step of most of solid substrate anaerobic digestion is hydrolysis. Pre-treatments aim to solubilise hardly accessible compounds. Expected results are increased biogas yield and/or production rate allowing a decrease of hydraulic retention time in the digester. Pre-treatments may be used to store feedstocks and preserve their methane potential, such as ensiling of catch crops.

Alkali pre-treatments of sorghum

Examples of previous studies

• Sludge / Thermal hydrolysis
• Fatty waste / Saponification
• Lignocellulosic biomass / Alkali and fungal pre-treatments

Pre-treatments and fermentation

Main objective of pre-treatment is the increase of soluble sugar concentration. As fermentation can be carried with only  waste indigenous bacteria, substrate pre-treatment can also aim at selecting indigenous microorganisms.

High temperature/Pressure  pre-treatment

Examples of previous studies

• Lignocellulosic biomass:
  •     Thermal acid pretreatment hydrolysis
  •     Alkali and enzymatic pretreatment
• Organic fraction of solid waste
  •     Sonication
• Manure
  •     Microwave

Recovery of high value molecules: cascade valorisation

Main objective: to reduce lignocellulose recalcitrance so that polymeric components (molecules from the carbohydrate and from the non-carbohydrate fraction) become more accessible for further biorefinery conversion  [2].

Micro-wave pre-treatments

Examples of previous studies

• Combined micro-wave & enzymatic treatment for improving phenolic acids release from grass biomass before anaerobic digestion
• Micro-wave treatment for improving anthocyanins extraction from grape pomace

Experimental facilities

• Thermal and chemical process : low and high temperature and pressure
• Irradiation process: microwave, sonication
• Grinding : knife and ball milling, mortar grinding technologies
• Biological : enzymes, fungi, anaerobic and aerobic consortia

References

[1] Carrere et al. (2016) Bioresource Technology, https://doi.org/10.1016/j.biortech.2015.09.007
[2] Bichot et al (2022) Biochemical Engineering Journal https://doi.org/10.1016/j.bej.2022.108434.