Due to economical, environmental, and government restrictions, paper mills are trying to reduce water consumption and discharge. Recently, China government has released a “water ten plan policy” which will greatly limit to the fresh water usage in the pulp & paper industry. This situation forces paper mills to reduce the incoming water usage as well as recycling some of its process waters. Reduction in fresh water usage by recycling the process water has brought several consequences in the wet end process. Various physical and chemical parameters greatly change which cause imbalance in wet end stability. Changes will also happen in the microlfora and microfauna populations in wet end and the problems caused by these changes are different. These includes the generation of odorous chemicals, microbiological influenced corrosion (MIC), iflamentous sludge bulking, higher BOD/COD in eflfuents, and faster slime buildups in paper machine. This paper reveals the changes in microorganisms population in wet end as the impact of higher water closure, together with the mechanisms and problems caused by the change. Possible solution to the problems is also provided.%迫于成本控制、环境保护及政府管控的压力，造纸厂都在努力降低水耗并减少排放。而中国政府刚刚颁布实施的《水十条》更是极大地限制了制浆造纸工业的清水取用。在这种形势下，工厂被迫降低水耗同时循环使用部分流程水。降低水耗并循环使用流程水给纸机湿部带来了不少问题。许多物理和化学参数都发生了变化，从而导致了纸机湿部的稳定性下降。湿部的微生物数量也发生了变化，并导致一系列不同的问题。可能是产生了有异味的物质，或是导致了微生物诱导腐蚀，或形成了丝状菌沉积，或污水的高BOD/COD值，同时使纸机的菌泥沉积加快。本文揭示了纸机水循环的高封闭条件如何导致湿部微生物数量的变化，以及这些变化产生的机理及其导致的问题，同时也提供了解决这些问题的可能途径。
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