Behavior of indicator microorganisms in a full-scale biogas plant treating livestock waste, and risk evaluation of digested sludge as a liquid fertilizer.

处理牲畜废物的沼气厂产生的消化污泥应作为液体肥料回收到农田。为了充分保证消化污泥的安全性，有必要将我们的注意力集中在如何在沼气厂中去除/灭活病原指示微生物。本研究以畜禽粪便沼气厂为研究对象，探讨沼气发酵过程中指示微生物的灭活。该工厂是为了建立一个循环系统，利用来自北海道东部大规模奶牛养殖区的牲畜养殖者的牲畜废物和当地有机资源。本研究中使用的指示微生物如下：总大肠菌群：病毒污染的指示物粪大肠菌群：EPA标准，2 x 10^6/gTS，用于消化污水污泥回收到农田总大肠菌群：废水排放的典型标准粪链球菌：11丹麦政府提出的沼气厂微生物安全性指标，在200天的启动期内，考察了沼气厂各工序指标的去除情况。在37、45、55、60和70℃条件下，牛粪和消化污泥混合物中的指示物均呈阶梯状下降。热灭活污泥中的粪大肠菌群成功达到EPA标准。各指标的去除率依次为粪大肠菌群>总大肠菌群>粪链球菌>总大肠菌群。在每个温度下，指标都有随时间推移而下降的趋势。在激活的每一个指标与温度可以解释在奇克定律。这对热灭活工艺的设计有一定的指导意义。

Digested sludge from a biogas plant treating livestock waste should be recycled to agricultural land as a liquid fertilizer. To fully guarantee the safety of the digested sludge, it is necessary to focus our attention on how the pathogen indicator microorganisms are removed/inactivated in the biogas plant. In this study, inactivation of indicator microorganisms through methane fermentation process was investigated in a full-scale biogas plant treating livestock waste. The plant was built to establish a circulative system to use livestock waste and local organic resources from the livestock breeders in the large-scale dairy farming area in eastern Hokkaido. The by-products, such as biogas and liquid fertilizers, are co-used by the livestock breeders.Indicator microorganisms used in this study were as follows :Total coliphages : indicator of virus pollutionFecal coliforms : standard of EPA, 2 x 10^6/gTS for recycle of digested sewage sludge to farmlandTotal coliforms : typical standard for wastewater dischargeFecal streptococci : an indicator for microbiological safety in biogas plant proposed by Danish GovernmentRemoval of the indicators by each step of the plant was investigated during the start-up period for 200 days. Furthermore, inactivation of the indicators in a mixture of caw manure and digested sludge was investigated at 37, 45, 55, 60, and 70℃, respectively.All the indicators tended to decrease step wise through the plant. The fecal coliforms in the heat-inactivated sludge successfully achieved EPA standard. The removals of the indicators in the plant were in the order fecal coliforms>total coliforms>fecal streptococci>total coliphages. The indicators tended to decrease with time at each temperature. In activation of each indicator with temperature can be explained in Chick's law. This might be useful for the design of heat-inactivation process.