Abstract
The aim of the study is to assess effectiveness of sewage sludge composting efficiency oil the basis of survival of Salmonella Enteritidis bacteria. Carriers containing a strain of S. Enteritidis were added to three layers of a compost pile made of dehydrated sewage sludge from a mechanical-biological wastewater treatment plant and wheat straw. The maximum time of the bacteria survival was established which was found to be the longest in the bottom part of the heap and was 58 days, whereas in the top layer of the pile the survival time of the microorganisms was the shortest, which is 49 days. In the thermophilic stage the highest generated temperatures were from 66 to 73°C for a period of 7 days. It found reflection in the fastest rate of Salmonella bacilli inactivation. A thermophilic stage was also found in the middle layer of the pile which lasted for 5 days throughout which period the temperature ranged from 66 to 72°C. Temperatures in the bottom part of the pile were found to be lower, from 30 to 61°C, whereas temperature above 60°C was reported only for 2 days.
Highlights
Sewage sludge is characterized by a significant content of organic matter, macro- and micro-components which make it suitable to be used for fertilization of rural and forest areas and recultivation of green areas [1]
In the stage a suspension containing Salmonella Enteritidis bacteria was prepared and its density was established as 9.0·108 cells/ml by using an optical densitometer (Vitek Systems ATB 1550). 100 ml of suspension with indicator bacteria was implemented into mixed sewage sludge with straw and placed in 30 perlon bags with dimensions of 7 to 10 cm
On the first day of the experiment the amount of Salmonella Enteritidis bacteria was found to be similar in the whole pile from 9.0·108 cfu/g to 9.5·108
Summary
Sewage sludge is characterized by a significant content of organic matter, macro- and micro-components which make it suitable to be used for fertilization of rural and forest areas and recultivation of green areas [1]. Long survival of most pathogenic microorganisms is a significant problem connected with biological sewage sludge management, especially its agricultural utilization, where these organisms are able to survive in the soil or plants for months and even years [5, 6]. For this reason, the sewage sludge needs to undergo the process of hygienization before it can ever be used [7]. Assessment of efficiency of sewage sludge hygienization in the process of composting involves determination of inactivation dynamics for indicator bacteria that is Salmonella, Escherichia coli and Streptococcus faecalis. The goal of the research was to assess efficiency of sewage sludge composting on the basis of Salmonella Enteritidis survival
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