Gomes Daniel, Gama Miguel, Domingues Lucília
Centre of Biological Engineering, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal.
Biotechnol Biofuels. 2018 Apr 16;11:111. doi: 10.1186/s13068-018-1103-2. eCollection 2018.
In spite of the continuous efforts and investments in the last decades, lignocellulosic ethanol is still not economically competitive with fossil fuels. Optimization is still required in different parts of the process. Namely, the cost effective usage of enzymes has been pursued by different strategies, one of them being recycling.
Cellulase recycling was analyzed on recycled paper sludge (RPS) conversion into bioethanol under intensified conditions. Different cocktails were studied regarding thermostability, hydrolysis efficiency, distribution in the multiphasic system and recovery from solid. Celluclast showed inferior stability at higher temperatures (45-55 °C), nevertheless its performance at moderate temperatures (40 °C) was slightly superior to other cocktails (ACCELLERASE1500 and CellicCTec2). Celluclast distribution in the solid-liquid medium was also more favorable, enabling to recover 88% of final activity at the end of the process. A central composite design studied the influence of solid concentration and enzyme dosage on RPS conversion by Celluclast. Solids concentration showed a significant positive effect on glucose production, no major limitations being found from utilizing high amounts of solids under the studied conditions. Increasing enzyme loading from 20 to 30 FPU/g had no significant effect on sugars production, suggesting that 22% solids and 20 FPU/g are the best operational conditions towards an intensified process. Applying these, a system of multiple rounds of hydrolysis with enzyme recycling was implemented, allowing to maintain the steady levels of enzyme activity with only 50% of enzyme on each recycling stage. Additionally, interesting levels of solid conversion (70-81%) were also achieved, leading to considerable improvements on glucose and ethanol production comparatively with the reports available so far (3.4- and 3.8-fold, respectively).
Enzyme recycling viability depends on enzyme distribution between the solid and liquid phases at the end of hydrolysis, as well as enzymes thermostability. Both are critical features to be observed for a judicious choice of enzyme cocktail. This work demonstrates that enzyme recycling in intensified biomass degradation can be achieved through simple means. The process is possibly much more effective at larger scale, hence novel enzyme formulations favoring this possibility should be developed for industrial usage.
尽管在过去几十年中不断努力并投入资金，但木质纤维素乙醇在经济上仍无法与化石燃料竞争。该过程的不同环节仍需优化。具体而言，人们通过不同策略追求酶的经济有效利用，其中之一是酶的循环利用。
在强化条件下，分析了纤维素酶在回收纸污泥（RPS）转化为生物乙醇过程中的循环利用情况。研究了不同酶制剂在热稳定性、水解效率、多相系统中的分布以及从固体中回收等方面的特性。纤维素酶（Celluclast）在较高温度（45 - 55°C）下稳定性较差，不过其在中等温度（40°C）下的性能略优于其他酶制剂（ACCELERASE1500和CellicCTec2）。纤维素酶在固液介质中的分布也更有利，在过程结束时能够回收88%的最终活性。采用中心复合设计研究了固体浓度和酶用量对纤维素酶转化RPS的影响。固体浓度对葡萄糖产量有显著的正向影响，在所研究的条件下，使用大量固体未发现重大限制。将酶负载量从20 FPU/g增加到30 FPU/g对糖产量没有显著影响，这表明22%的固体浓度和20 FPU/g是强化过程的最佳操作条件。应用这些条件，实施了一个酶循环的多轮水解系统，在每个循环阶段仅使用50%的酶就能维持酶活性的稳定水平。此外，还实现了令人感兴趣的固体转化率（70 - 81%），与目前的报道相比，葡萄糖和乙醇产量有了相当大的提高（分别提高了3.4倍和3.8倍）。
酶的循环利用可行性取决于水解结束时酶在固液相之间的分布以及酶的热稳定性。这两个都是明智选择酶制剂时需要考虑的关键特性。这项工作表明，通过简单方法可以在强化生物质降解中实现酶的循环利用。该过程在更大规模下可能更有效，因此应开发有利于这种可能性的新型酶制剂用于工业用途。
