固定化细胞反应器包括以下几种类型：细胞再循环系统（Cell recycle systems ）、 固定床反应器（Fixed bed reactors ）、流化床反应器（Fluidized bed reactors ）、絮凝 细胞系统（Flocculated cell systems ）。 1、细胞再循环系统（Cell recycle systems ） In a fermenter with cell recycle the cells are separated from the effluent and then recycled back to the fermenter; thus minimising cell removal from the fermenter Cell recycle system Cell recycle is used in activated sludge systems. A portion of the cells are separated in a settling tank and returned to the activated sludge fermenter. Biomass recycling for product or biomass production is more difficult due to the need for maintaining sterility during cell separation. Centrifugation which is a faster process than settling would be used to separate the cells. Biomass recycle systems can be easily modelled. 2、固定床反应器（Fixed bed reactors ） In fixed bed fermenters, the cells are immobilized by absorption on or entrapment in solid, non-moving solid surfaces. In one type of fixed bed fermenter, the cells are immobilized on the surfaces of immobile solid particles such as plastic blocks, concrete blocks, wood shavings or fibrous material such as plastic or glass wool