The treated sewage heat pump system reuses the wasted heat in the city sewage to cool and/or heat the buildings. Biofouling

as the key problem in treated sewage heat pump systems

decreases the system efficiency and security. In this study

rotary coupon experiments were conducted

and Benzalkonium chloride

a broad-spectrum and efficient bactericide

of various concentrations was used to immerse the biofouling 10 min per day. Vital dye was used to stain the biofouling and confocal laser scanning microscope (CLSM) was used to take microphotographs of the biofouling to show the viability distribution of the bacteria cells in the biofouling. Imaris was used to calculate the biovolume of live/dead cells. The results show that benzalkonium chloride inhibits the biofouling significantly by killing most of the bacteria cells

and the inhibition effect is enhanced as the concentration increases. This research obtains insight into the biofouling inhibiting techniques and promotes the practical application of the treated sewage heat pump system by increasing the system efficiency and security.