The Changes Of Nutrient Elements, Enzymatic Activity And Microbes During Vermicomposting For Sewage Sludge

The vermicomposting technology is a highly efficient, environmentally friendly processing method for city sludge. The dynamic changes of enzyme activities, microbe and nutrient elements were monitored during the out of door vermicomposting experiment. The formal vermicomposting experimental conditions were found out by a preliminary experiment with fresh activated sludge. As for the formal experiment, four groups were set up, the Basket①to③are parallel for test groups inoculated with earthworms, and the Basket④was a control one without earthworms. During the period of35days, the main works were done as following:(1) The conditions, such as temperature and pH, etc., was tried in order to optimize the environment of vermicomposting.(2) The dynamic changes of organic matter and nutrient elements in the composts were periodic tested in order to understand the composting process.(3) The enzyme activities of the composting materials and earthworm feces were also periodic tested in order to determine key enzymes.(4) The microbe quantities of three major groups were monitored so as to determine the dynamic change and its possible relationship with earthworms. As results:(1) The earthworms could adapt well to the fresh sludge environment. The average earthworm body weights increased about1times, and breeding was in good condition during a period of35d composting process.(2) The environmental conditions were changing obviously during the composting process. The temperatures of four composts reached the highest at fifth day, and then declined in fluctuation. As the body volume was relatively small, the compost temperature was significantly influenced by the environment. The original sludge was acidic, and finally became weak acid. The conductivity had small fluctuations during the early stage, and rose obviously in the late.(3) The organic content of compost in every basket was reduced by70%or so during a35d composting process, mainly because of the heavily decomposition of organic matter under the action of microbes and earthworms. That of nitrate nitrogen showed a trend of growth in the composting process, it was lower in the early stage, but increased rapidly after21d. This might be caused by the actions of moisture, microorganism, ammonification and nitrification. The available p content increased steady, but it was different among the four groups, may be related to the mineralization of organic matter, and phosphatase activity, etc. The available k content increased considerably for each of the four groups, especially in the late stage (28d-35d).(4) The urease activity increased at early stage however, it began to decline after7d. The urease activity of basket (1)-(3) showed a slight rise during the later period, but this phenomenon was not found in the compost of basket (4). Furthermore, the urease activity was not detected in feces at the same time. Thus, this might be associated with earthworm body secretions. The phosphatase activity was rose up at first, and then dropped down at the later stage during the composting process. At the early stage, the composting temperature increased, and the phosphatase activity also increased. So, this might be associated with temperature. As the acceleration of organic matter decomposition, the organic phosphorus content decreased at the late stage, the phosphatase activity reduced at the same time. Soil proteinase came from microbes, plants and animals. So, the protease content was low in the composts because of no animal and plant activity. With the increase of earthworm quantity and weight at the early stage, the earthworm activities and protease activity was growing. However, the earthworm weight increased slowly, leading to a fall in protease activity due to the decrease of organic matter content in the later period.(5) The microbial activity was reduced at the first7days the respiration increased after7d, and then reached the top at21d for all of the four groups. At the end of composting, the activities for test groups were higher than that of the control one, so the action of earthworm increased the microbial activity. The numbers of bacteria were about2.4x10-9/g, relatively abundant in the initial sludge. It decreased before14d, and then had a rising trend for all of the test groups. The temperature rise prompted the increase of fungi activity and number. The number of fungi for test groups began to reduce during the period of7to14d, and then began to rise in small increments, resulted at slightly higher ones than those of the initial stage. However, the fungi number changed a little. The numbers of actinomycetes were not higher in initial sludge, and experienced a "rise-decrease-rise" process during composting, and so did in the control one. Thus, the earthworms had no obvious impact on actinomycetes.