Reduction of fecal streptococcus and salmonella by selected treatment methods for sludge and organic waste

Abstract

The increasing utilization of waste water sludge and source-separated organic household waste in agriculture has brought the quality aspects into focus, among others the hygienic aspects. In this study, the reducting effect on Fecal Streptococcus (FS) and Salmonella of different methods for stabilization and methods for further treatment of sludge and organic waste has been investigated. The most common methods for stabilization, i.e. aerobic and anaerobic stabilization, only reduce the indicator organisms by approximately 1 logarithmic decade. Methods for further treatment of sludge and organic waste have shown reductions of microorganisms allowing for unrestricted utilization in agriculture, meeting the product control: FS below 100/g and no Salmonella detected. The effect of storage of sludge at summer and winter temperature respectively has been investigated. At temperatures (around 20°C) significant reductions of Salmonella were found, while the die out at low temperatures (below 10°C) was limited. FS was not reduced systematically during storage, and therefore, FS is not usable as indicator organism for the hygienic properties of sludge during storage.

Proper Sanitization of Sewage Sludge: a Critical Issue for a Sustainable Society

“…Sahlström and colleagues (77) confirmed the unsuitability of sewage sludge produced in Swedish treatment plants for arable land due to its relatively high pathogenic bacterial content, irrespective of prior stabilization procedures, including thermophilic/mesophilic anaerobic digestion, composting, and sedimentation. These results are consistent with those reported by Jepsen et al (46), who concluded that aerobic stabilization does not reduce the pathogens and indicator organisms to levels that are acceptable for the unrestricted use of sludge in agriculture. The data (46, 77) emphasize the emerging need for an additional sanitization step during sludge stabilization to achieve a product with sufficiently high microbial quality to enable recycling of organic residues.…”

“…were detected in 53% of the digested sludge samples (22). These bacteria have been consistently identified in several additional studies analyzing sludge (27,33,46,62,74,78); the bacteria reportedly survived up to 16 months on grass treated with sludge in Switzerland (43), clearly highlighting the urgent need for the international development of a proper sanitization step before sewage sludge can be used as a crop fertilizer. Spore-forming bacteria, such as Clostridium spp.…”

Effect of pre-hydrolysis on floc structure

“…Anaerobic digestion has been extensively used to stabilize sludge, because it can effectively reduce the volume of the sludge (Dohányos and Zábranská, 2001) and inactivate pathogenic microorganisms therein (Jepsen et al, 1997). The general scheme for digestion is as follows:…”

In Vitro Treatment of Different Isolates from Cattle Dung and Pig Slurry by Nisin

“…Thus, such excrements represent a potential health hazard mainly from the aspect of their using for land application (Paulsrud and Nedland 1997). Aerobic and/or anaerobic treatment in the thermophile and mesophile zones are used in dealing with a wide range of problems associated with slurry stabilization (Novák et al 1994;Jepsen et al 1997). However, these treatments e.g.…”

“…However, these treatments e.g. in mesophile zone were found not sufficiently effective for complete decontamination (stabilization) of the excrements (Jepsen et al 1997). Therefore, new ways are experimented and searched to reach higher effectiveness of stabilization processes.…”