关键词: 城镇二级出水, 微生物污垢, 污垢质量, 微观结构

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