Journal of Pure and Applied MicrobiologyVol. 8 No. 2

Occurrence and Removal of Enterohemorrhagic Escherichia coli O157:H7 in Four Full-scale Sewage Treatment Systems in Beijing, China

Zhang Zhennan1, Zheng Shaokui2, Xu Yahui1, Li Juan1 and Liu Xinchun1*

1College of Resources and Environment, University of Chinese Academy of Sciences, Beijing, 100049, People?s Republic of China. 2MOE Key Laboratory of Water and Sediment Sciences/State Key Lab of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing, 100875, People?s Republic of China.

Received on 14 October 2013 and accepted on 30 December 2013

 

ABSTRACT

Enterohemorrhagic Escherichia coli O157:H7 (EHEC O157:H7) is zoonotic pathogen linked with severe human illnesses. In order to evaluate risks of the pathogen in wastewater treatment process, the occurrence and removal of them were studied in four municipal wastewater treatment systems every three months from November, 2011 to July, 2012. Real-time PCR for E.coli O157:H7 was performed on extracted DNA using primers targeting eaeA gene. The method was used to detect E.coli O157:H7 in raw wastewater, mixed liquor, secondary clarifier effluent, excess sludge and sludge liquor of the four systems mentioned above. The quantity of E.coli O157:H7 in raw wastewater varies with the season, ranging from 103 to 105 copies per milliliter(copies/ml) in summer, from 102 to 103 copies/ml in winter. However, effluent keeps relatively steady, 10 to 102 copies/ml. The removal of E.coli O157:H7 was about 1 to 3 orders of magnitude in copies per milliliter. The amount in sludge liquor is more close to influent than in effluent, which showed the sludge liquor should not be discharged into natural water bodies directly as it still threatens people?s health. The result also indicated that EHEC might not be a kind of bacteria joining to make up zoogloea. In order to understand the mechanism of the removal of EHEC, the quantity of E.coli O157:H7 in effluent in copies per millimeter was compared with that of excess sludge, and the latter makes up a proportion ranged from 54.22% to 96.14%, which means the majority of E.coli O157:H7 came into returned sludge in secondary sedimentation tank. Thus, temporary transference from water phase to sludge is one reason of E.coli O157:H7 decreasing.

Keywords : Enterohemorrhagic, Escherichia coli (EHEC), real-time PCR, wastewater treatment.