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

处理禽畜粪便的沼气厂产生的消化污泥应作为液体肥料循环利用到农田。为了充分保证消化污泥的安全，有必要关注沼气厂中病原指示微生物的去除/灭活。本研究在畜禽粪便处理沼气装置中，研究了甲烷发酵过程中指示微生物的失活。该工厂的建立是为了建立一个循环系统，利用北海道东部大规模奶牛养殖区牲畜饲养者的牲畜废物和当地有机资源。副产品，如沼气和液体肥料，由牲畜饲养者共同使用。本研究使用的指示微生物有：总噬菌体：病毒污染指标；粪便大肠菌群：EPA标准，2 × 10^6/gTS，消化后的污水污泥回收到农田；总大肠菌群：废水排放典型标准；粪便链球菌：丹麦政府提出的沼气厂微生物安全指标，在启动200天的时间内，对工厂各步骤的指标去除情况进行了调查。此外，还研究了牛粪和消化污泥在37、45、55、60和70℃条件下的失活情况。所有指标均呈逐步降低的趋势。热灭活污泥中的粪便大肠菌群成功达到EPA标准。该指标在植物中的去除率依次为粪便大肠菌群>总大肠菌群>粪便链球菌>总噬菌体。各温度下各项指标均随时间的延长而降低。温度对各指标的活化作用可以用奇克定律来解释。这对热失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.