Microbiological assessment of sewage sludge hygienization in the process of composting with the use of Salmonella Enteritidis

Abstract

The aim of the study is to assess effectiveness of sewage sludge composting efficiency on 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 73oC 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 72oC. Temperatures in the bottom part of the pile were found to be lower, from 30 to 61oC, whereas temperature above 60oC was reported only for 2 days.