Abstract: Treated sewage is an important carrier of urban waste energy,which can be used as a suitable heat source in heat pump systems.A treated sewage source heat pump system was designed and used at Beijing Olympic Village in 2008 to provide heating and cooling,which is a green approach to recovering urban heat.However,treated sewage contains components that can cause fouling,such as heterotrophic bacteria,microbial nutrients and suspended substances.These could not be completely removed during treatments conducted by the wastewater treatment plants,and biofouling inevitably occurs in the plate heat exchangers of the treated sewage used in the heat pump systems.In order to understand the characteristics of the biofouling,an experimental system,which mimicked the treated sewage water and simulated the relevant fouling formation process,was developed in our laboratory.The flow cell in the system,which was used to imitate plate heat exchangers,allowed sample surfaces properly retrieved and analyzed.Extensive experimentations including process monitoring and microstructure development in biofilm were conducted and the results presented in this paper showed the possibility of reducing the biofouling in the future.Under typical heating and cooling conditions of heat pump,the growth curves of biofouling were generated from different weight values,the micromorphic evolution of biofouling was characterized by using Environmental Scanning Electron Microscopy.A series of quantitative information was obtained and discussed.In particular,the effects of flow velocity and bacterial concentration were investigated,which clearly influenced the biofilm development,thus impacting the thermal resistance created.It was found that the biofouling growth rate changed synchronously with the micromorphic evolution,and the effect of flow velocity on biofouling formation was non-monotonic.Biofouling would be neglected when the bacterial concentration decreased to 10³ CFU·ml^-1(CFU,colony formine unit).The results are instructive to choose the cleaning time points and develop mitigating and cleaning technology.

Key words: municipal secondary effluent, biofouling, fouling mass, micromorphic evolution

摘要： 城镇二级出水所含致垢微生物将导致其热能回用过程中在换热面上形成以微生物污垢为主的混合污垢，影响换热、流动效率。以可控微生物种类及浓度的模拟二级出水为介质，对典型热泵供暖、制冷工况下微生物污垢在模拟板式换热器的竖直不锈钢壁面上的形成过程进行了研究，关注起始阶段垢层微观结构演变与宏观垢量生长特性，并考查了流速、菌浓度对成垢过程的影响。实验表明：垢层微观结构演变与宏观垢量增长存在同步关系，污垢生长速率对应于微观结构演变；流速对于成垢过程影响呈非单调性；菌浓度低至10³ CFU·ml^-1（CFU，菌落形成数）时成垢量可忽略。实验结果可指导除垢时间点的选择及改进抑垢、除垢方法。

关键词: 城镇二级出水, 微生物污垢, 污垢质量, 微观结构