The development of zero waste biorefineries is a promising yet challenging pathway towards a sustainable bioeconomy. Deep insights on the composition of biorefineries side streams along with the development of green technologies are mandatory to achieve such goal. In this paper, a sustainable pilote scale membrane process was used to recover valuable organic matter dissolved in the main side stream of a thermomechanical pulping (TMP) plant. A great number of analytical tools were combined to get an extensive characterisation of the generated fraction, including ICP-AES, HPIC-PAD, FTIR, SEC, 13

Catalytic depolymerization of lignin is a challenging process due to competitive repolymerization reactions. In this paper, the oxidative depolymerization of lignin was catalyzed by a commercial laccase both in a batch experiment and in a membrane bioreactor using the same catalytic conditions. The membrane bioreactor was previously optimized to reach high permeation flux (25 L.h-1 .m-2) during lignin diafiltration. While the lignin was exclusively condensed in the batch experiment leading to high molecular weight macromolecules (from 9 to 16 kDa), its depolymerization was effective in the bioreactor producing fragments of less than 1 kDa thanks to the in-situ extraction of the reaction products. This paper demonstrates that the reactor configuration is playing an essential role in triggering or preventing lignin condensation. It also reports the first proof-of-concept demonstrating that in-situ membrane extraction of the reactive fragments of lignin from the bulk medium can be useful against detrimental repolymerization reactions.

Membrane process is a viable option for valuable compounds such as lignin and lignans recovery in aqueous discharges of thermomechanical pulp industries. Recovery of lignin and lignans with continuous mode ultrafiltration/nanofiltration installation has not been studied in detail previously. After flotation used to remove lipophilic matter of pulp mill effluent, the three steps membrane process was composed of a clarification step by a 150 kDa ultrafiltration used to remove suspended matter, followed by two nanofiltrations of 1 kDa and 300 Da to respectively retain lignin and lignans. A techno-economic evaluation of this process has been performed. The process with a plant capacity of 60 m 3 .h-1 was able to produce 12 tons of lignin and 825 kg of lignans per month. The influence of plant capacity between 0.1 and 60 m 3 .h-1 on extracts production cost allows determining a production cost equal or below 10 €.kg-1 as plant capacity reached 10 m 3 .h-1. Valorization of lignin and lignans as parts of the formulas of high added value products could allow thermomechanical plants to head towards 2 biorefinery and cleaner production concepts. Furthemore, the 300 Da permeate possessed the required characteristics to be re used and save fresh water utilization.

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