A STUDY ON DEVELOPMENT OF ENERGY SELF-SUFFICIENT SEWAGE TREATMENT SYSTEM

首先，对污水处理机构进行问卷调查。我们向日本377个城市发放了调查问卷，以了解目前下水道系统的能源消耗率。296个城市提供了答案。结果表明，处理单位污水所需电量为0.46 kWh，处理后单位污水产生的污泥量为0.006 m^3。单位污水体积内的化学热容约为1000千卡，计算出如果利用未利用的能源对污泥进行干燥处理，电能的自给自足率可达60%以上。然后，对未来三种方法的污泥能量回收进行了估计。能源消耗率（ECR）是评估的一个指标。该指标是指输入能量与回收能量之比。第一个是污泥脱水和干燥过程与冷冻和解冻预处理。在该系统中，尽管在干燥过程中有效地使用了热泵，但ECR仍达到1.8。第二个是消化。ECR变为0.93。虽然假设使用热电联产过程，但ECR值接近1.0。第三是将污泥转化为含油液体。估计ECR为0.55。这个值意味着回收的能量大约是输入能量的2倍。虽然在实际工厂中存在各种问题，但污泥转化为含油液体有可能实现能源自给的污水厂。

The first, a questionnaire survey to the sewer institutions was conducted. Questionnaires were sent to 377 cities in Japan to seek for the energy consumption rate of the current sewer system. An answer was provided from 296 cities. As a result, it was appeared that a quantity of necessary electricity to treat unit sewage volume is 0.46 kWh and amount of 0.006 m^3 sludge come from unit sewage volume after treatment. Chemical heat capacity within unit sewage volume was approximately 1000 kcal. It was calculated that self-sufficient of electricity was more than 60% if unused energy was possible to apply a drying process of sludge.Next, energy recovery from sludge was estimated about next three methods. An index of estimating was energy consumption rate (ECR). This index means that a ratio of the amount of input energy to the amount of recovering energy. The first was sludge dehydration and drying processes with freezing and thawing pre-treatments. In this system ECR became 1.8 despite the effective use of a heat pump in drying process. The second was digestion. ECR became 0.93. Although using a cogeneration process was assumed, the value of ECR is near 1.0. The third was transformation to oily liquid from sludge. It was estimated that ECR was 0.55. This value means that the amount of energy recovering was approximately 2 times of input energy. Although various problems in actual plants, the transformation to oily liquid from sludge has some possibility of actualizing a energy self-sufficient sewage plant.