The dependence on non-renewable resources, particularly fossil fuels, has awaken a growing interest in research of sustainable alternative energy sources, such as bioethanol. The production of bioethanol from lignocellulosic materials comprises three main stages, starting with a pretreatment, followed by an enzymatic hydrolysis step where fermentable sugars are obtained for the final fermentation process. Enzymatic hydrolysis represents an essential step in the bioethanol production, however there are some limitations in it that hinders the process to be economically feasible. Different strategies have been studied to overcome these limitations, including the enzyme recycling and the utilization of high solids concentrations. Several investigations have been carried out in different bioreactor configurations with the aim to obtain higher yields of glucose in the enzymatic hydrolysis stage; however, the commonest are Stirred Tank Bioreactors (STBR) and Membrane Bioreactors (MBR). In general, the key criteria for a bioreactor design include adequate mass transfer, low shear stress, and efficient mixing that allows the appropriated interaction between the substrate and the enzyme. Therefore, this review will address the main aspects to be considered for a bioreactor design, as well as, the operational conditions, some characteristics and mode of operating strategies of the two main bioreactors used in the enzymatic hydrolysis stage. Moreover, two types of pneumatically agitated bioreactors, namely bubble column and gas-lift bioreactors, are discussed as promising alternatives to develop enzymatic saccharification due to their low energy consumption compared with STBR.

对不可再生资源，尤其是化石燃料的依赖，引起了人们对诸如生物乙醇之类的可持续替代能源研究的浓厚兴趣。由木质纤维素材料生产生物乙醇包括三个主要阶段，从预处理开始，然后是酶促水解步骤，在该步骤中获得可发酵的糖以用于最终的发酵过程。酶促水解代表了生物乙醇生产中必不可少的步骤，但是其中存在一些局限性，阻碍了该方法在经济上的可行性。为了克服这些限制，已经研究了各种策略，包括酶的循环利用和高固体浓度的利用。为了在酶促水解阶段获得更高的葡萄糖产量，已经在不同的生物反应器配置中进行了一些研究。但是，最常见的是搅拌罐生物反应器（STBR）和膜生物反应器（MBR）。通常，生物反应器设计的关键标准包括足够的传质，低剪切应力以及有效的混合，以使底物和酶之间发生适当的相互作用。因此，本综述将讨论生物反应器设计要考虑的主要方面，以及酶促水解阶段中使用的两种主要生物反应器的操作条件，某些特征和操作策略模式。此外，两种类型的气动搅拌生物反应器，即鼓泡塔和气举生物反应器，