健康风险与喷洒污水产生的喷雾中微生物浓度的关系

与喷洒处理后的生活污水产生的喷雾相关联的细菌健康风险难于控制.在Rolleston 污水处理厂进行喷雾取样,符合取水权条件.Rolleston 采用延时曝气, UV 处理和土地喷雾灌溉.虽然喷洒液中有大肠杆菌,即使采用非选择性媒介,用Andersen 采样器收集不到.在微小杆菌芽孢计数为 1000 /100 ml,在暴露在相当于一个人靠近喷雾器站两小时的空气体积的琼脂皿上只生长出三个菌群.三个芽孢可能没有暴露在空气中,因为可能被污染了.因为存留在空气中的液滴体积较小,微生物存在的机会较低,除非喷洒液中微生物浓度较高.如果排放物中某微生物含量10,000 /100 ml ,则直径100 (m 的颗粒含有一个或多个微生物的机会是0.005% . 进行了野外实验,以确定排放物中微生物数量和喷雾雾珠大小比例关系,该雾珠可能进入人的肺部且含有微生物. 两株小芽孢杆菌是一样的,只对两种抗生素的抵抗力不同,混入水中喷洒.用装有含适当抗生素琼脂皿的几对六级Andersen 采样器收集雾珠/ 颗粒.结果表明,当喷洒悬浮液中芽孢浓度平均大一百倍时,六级Andersen采样器收集(即可能进入人肺)的雾珠/ 颗粒数量平均大五十倍.因此,如果始终(就像食品厂进行有害分析和关键点控制)可检测排放物,确保要喷洒的排放物中致病菌水平始终较低,则对于公共健康风险,这应当是比监测大气更容易更可靠的测试.

Relationship Between Health Risks and the Concentration of Microbes in Aerocsols Generated During Spraying of Wastes

Monitoring the microbial health risks associated with aerosols generated during the spray application of treated domestic wastes is difficult. Sampling of aerosols was carried out at the Rolleston waste water treatment facility to comply with conditions of a water right. Rolleston uses extended aeration, UV treatment and spray irrigation onto land. While coliform bacteria were present in the liquid sprayed they were not collected by the Andersen sampler even though a non-selective medium was used. At Bacillus subtilis endospore counts of 1000 /100 ml only 3 colonies grew on agar plates that had been exposed to a volume of air equivalent (assuming the Andersen sampler adequately mimics the human lung) to a person standing close to the sprayers for two hours. The 3 endospores may not have been in the air as they may have been contaminants. Since the volume of the droplets that remain airborne is small, the chance of a microbe being present is low unless the concentration of that microbe in the effluent to be sprayed is high. If the effluent contains 10,000 of a particular microbe /100 ml then there is a 0.005% chance of a 100 (m diameter particle having one or more of that microbe. A field experiment was set up to determine the relationship between number of microbes in an effluent and concentration of aerosols of a size that would be carried into the human lung and contain the microbe. Endospores of two identical strains of Bacillus subtilis, except for their resistance to 2 antibiotics, were mixed in water and sprayed. Droplet/particles were collected using pairs of six stage Andersen samplers loaded with agar plates containing the appropriate antibiotics. Results showed that when the concentration of endospores in the sprayed suspension was on average 100 times greater, the numbers of droplets/particles collected in the six stages of the Andersen sampler (i.e. would have entered the human lung) were on average 50 times greater. Thus if the effluent could be checked at all times (in the same way that food factories are applying Hazard Analysis and Critical Control Points) to ensure that the pathogen level in the effluent to be sprayed was consistently low, then this should be an easier and more reliable test of public health risk than monitoring the air.