Experimental study of the growth characteristics of microbial fouling on sewage heat exchanger surface

Urban sewage is widely used as a heat source in the heat pump system. However, the sewage contains large quantity of micro-organisms, which can encourage fouling on heat exchanger surfaces during operation. Microbial fouling can seriously affect the heat transfer efficiency. Iron bacteria (IB) and sulfate-reducing bacteria (SRB) are the main bacteria responsible for forming microbial fouling. This study investigated the fouling growth characteristics in heat exchanger. For this purpose, the IB and SRB from water in urban sewage treatment plants were separated and purified, and the runner state of sewage heat exchanger pipeline was simulated by designing the flow channel model. The wet and dry weights of the fouling formed by IB at different temperatures, fluid flow velocities and bacteria concentrations were analyzed via weighing method. The influence of these factors on the fouling formation by IB was further analyzed. In addition, a comparative study was conducted on the composite fouling after the addition of SRB. The results show that the fouling formed by IB is composed of iron precipitates and organics. At 20–40 °C, the fouling rate of IB is faster, and the fouling generated is higher, when the temperature is higher. With the increase in flow velocity, the rate of fouling reduces, and the fouling gross decreases. The concentration of IB affects the rate of fouling so that the lower the initial concentration is, the faster the fouling rate of IB is. The structure of the composite fouling after adding SRB becomes more compact.