猪场沼液絮凝上清液的紫外线杀菌效果

Disinfection effects of ultraviolet on supernatants of flocculated digestate from swine farm

猪场沼液中含有大量的微生物,为确保其排放或循环利用的卫生和环境安全,应对其进行有效的杀菌处理,目前国内沼液杀菌相关的研究缺乏。由于猪场沼液原液的色度和浊度很高,紫外线透过率很低,采用紫外线杀菌前需要对其进行预处理。该研究采用絮凝方法处理猪场沼液,对所获取的不同透射率沼液絮凝上清液进行杀菌试验,试验以细菌总数、大肠菌群和粪大肠菌群的数量变化及其杀菌率为指标,在4种沼液絮凝上清液透射率(0.01%、0.69%、3.78%和8.54%)、3种紫外线杀菌装置内水深(1、2和3 cm)和5种水力停留时间(1、5、10、15、20和30 min)试验条件下,探讨紫外线对沼液絮凝上清液杀菌的可行性及其运行效果。结果表明,絮凝上清液透射率(T254)、紫外线杀菌装置内水深和水力停留时间等因素对紫外线的杀菌效果均有极显著影响(P<0.01),3种因素之间均有极显著的交互作用(P<0.01)。试验紫外线灯管强度为395μW/cm2,当沼液絮凝上清液的透射率为0.69%、水力停留时间15 min和紫外线杀菌装置内水深2 cm时,紫外线对细菌总数、大肠菌群和粪大肠菌群的杀菌率分别为(99.99±1.20)%、(99.99±1.43)%和(100.00±0.01)%,使沼液絮凝上清液中粪大肠菌群的数量从3.9×106个/L下降至检出限(3个/L)以下,紫外线杀菌处理出水达到现行国家标准的无害化卫生要求,该研究可能为沼液的紫外线杀菌技术的深入研究和沼液安全循环利用提供参考。

There are a large number of microorganisms in the liquid digestate from a swine farm. The liquid digestate should be disinfected prior to discharge or utilization for sanitary and environmental safety, but there is a lack of literature on the disinfection of liquid digestate from animal feeding operations. In view of the high turbidity and chromaticity, the transmittance （T254） of liquid digestate from swine farm is nearly zero, and liquid digestate must be treated prior to ultraviolet disinfection. Flocculation was applied to pre-treat liquid digestate in this study in order to obtain supernatants with different transmittances （T254） for the following disinfecting trials. In terms of total bacteria count, total coliforms, and fecal coliforms, experiments were conducted to investigate the disinfecting feasibility and the effectiveness of ultraviolet on the supernatants of flocculated digestate under 60 experimental conditions, which were formed by 4×3×5 factorial combinations of transmittances （T254） （0.01%, 0.69%, 3.78%and 8.54%）, water depth （WD） （1, 2 and 3 cm）, and hydraulic retention times （HRT） （1, 5, 10, 15 and 20 min）. Results showed that T254, WD, and HRT all significantly affected （P〈0.01） the disinfection effects of ultraviolet on the supernatants of flocculated digestate, and significant interactions （P〈0.01） were also detected among the experimental factors. The disinfection rates of ultraviolet on total bacteria count, total coliforms, and fecal coliforms were （99.99±1.20）%, （99.99±1.43）%, and （100.00±0.01）%respectively, under the condition of 0.69%T254, 2 cm WD, and 15 min HRT. In such cases, the fecal coliforms in the supernatant of flocculated digestate decreased from 3.9×106 count/L to less than 3 count/L. Therefore, ultraviolet could be applied for the disinfection of the supernatants of flocculated digestate from swine farms, and the disinfected effluent could meet the sanitary requirements of the current national standards. It is recommended that the disinfected supernatant of digestate be reused for floor-flushing in swine farms, if the farms use tap water for production. and have no land in surrounding area for digestate application.