Gao W, Smith D W, Li Y
Department of Civil Engineering, Lakehead University, Thunder Bay, ON, Canada P7B 5E1.
Water Res. 2006 Jul;40(12):2321-6. doi: 10.1016/j.watres.2006.04.021. Epub 2006 Jun 5.
Inactivation capacity of E. coli (strain ATCC 15597) in water by natural freezing was examined via two freezing methods: spray freezing and freezing in a freezer. The effect of freezing temperature (-5, -15 and -35 degrees C), storage time, freeze-thaw cycles on the survival of the test organism were investigated. In addition, the number of cells injured by the freezing process was also examined by using different growth media. The bacteria frozen at the warmer temperature (-5 degrees C) was most sensitive to storage and freeze-thaw cycles as compared to those frozen at -15 and -35 degrees C. In general, greater inactivation efficiencies were achieved under longer storage time and warmer freezing temperature conditions. Freezing and thawing caused cell injury. More cells were injured when frozen at -15 degrees C. The percentage of cells injured decreased as freeze-thaw cycles increased. The spray-freezing process was found more effective in killing the cells. On average, the log reduction rate for the spray ice with two-day storage time was about 4 log units higher than those without any storage after freezing. The results indicated that the natural freezing processes are not only cost-effective techniques for chemical and physical contaminant removal from wastewater or enhancing sludge dewaterability in cold regions but also effective in reducing E. coli concentration.
通过喷雾冷冻和在冰柜中冷冻这两种冷冻方法，研究了天然冷冻对水中大肠杆菌（ATCC 15597菌株）的灭活能力。考察了冷冻温度（-5、-15和-35℃）、储存时间、冻融循环对受试微生物存活的影响。此外，还通过使用不同的生长培养基检测了冷冻过程中受损细胞的数量。与在-15℃和-35℃冷冻的细菌相比，在较高温度（-5℃）下冷冻的细菌对储存和冻融循环最为敏感。一般来说，在较长储存时间和较高冷冻温度条件下能实现更高的灭活效率。冷冻和解冻会导致细胞损伤。在-15℃冷冻时更多细胞受到损伤。随着冻融循环次数增加，受损细胞的百分比降低。发现喷雾冷冻过程在杀死细胞方面更有效。平均而言，储存两天的喷雾冰的对数减少率比冷冻后未储存的喷雾冰高约4个对数单位。结果表明，天然冷冻过程不仅是从废水中去除化学和物理污染物或提高寒冷地区污泥脱水能力的经济有效技术，而且在降低大肠杆菌浓度方面也很有效。
