Elsevier

Waste Management

Volume 32, Issue 5, May 2012, Pages 933-938
Waste Management

Fate of pathogens in a simulated bioreduction system for livestock carcasses

https://doi.org/10.1016/j.wasman.2011.10.031Get rights and content

Abstract

The EU Animal By-Products Regulations generated the need for novel methods of storage and disposal of dead livestock. Bioreduction prior to rendering or incineration has been proposed as a practical and potentially cost-effective method; however, its biosecurity characteristics need to be elucidated. To address this, Salmonella enterica (serovars Senftenberg and Poona), Enterococcus faecalis, Campylobacter jejuni, Campylobacter coli and a lux-marked strain of Escherichia coli O157 were inoculated into laboratory-scale bioreduction vessels containing sheep carcass constituents. Numbers of all pathogens and the metabolic activity of E. coli O157 decreased significantly within the liquor waste over time, and only E. faecalis remained detectable after 3 months. Only very low numbers of Salmonella spp. and E. faecalis were detected in bioaerosols, and only at initial stages of the trial. These results further indicate that bioreduction represents a suitable method of storing and reducing the volume of livestock carcasses prior to ultimate disposal.

Highlights

► Bioreduction is a novel on-farm storage option for livestock carcasses. ► Legislation demands that pathogens are contained and do not proliferate during carcass storage. ► We examined the survival of key pathogens in lab-scale bioreduction vessels. ► Pathogen numbers reduced in the resulting liquor waste and bioaerosols. ► The results indicate that bioreduction should be validated for industry use.

Introduction

In order to reduce the risk of further outbreaks of animal diseases such as bovine spongiform encephalopathy and foot and mouth disease, the European Union introduced the Animal By-Products Regulations (EC/1774/2002) in 2003 (Anon, 2009). These regulations sought to improve biosecurity across all aspects of the livestock sector, from production to waste disposal. Since their implementation, the options available to most farmers to dispose of fallen (dead) livestock have been effectively limited to either rendering or incineration, whereas previously most fallen stock was buried. The regulations have led to animosity within the agricultural industry due to the considerable costs and biosecurity concerns associated with centralised collection and rendering or incineration of fallen stock (Bansback, 2006, Gwyther et al., 2011). Indeed, there is call for both a change in legislation and the development of alternative methods of disposal (Bansback, 2006).

Bioreduction is a novel technology that has shown potential as a viable option for storing and pre-treating fallen stock prior to disposal (Williams et al., 2009). Bioreduction is the aerobic biodegradation of animal by-products in a partially sealed vessel, where the contents are mildly heated and aerated and ultimately disposed of via the permitted route for ‘Category 1’ material in accordance with the EU ABPR (i.e. via incineration or rendering). The process has been shown to reduce the volume of waste and hence the frequency of collection and associated disposal cost, as well as being a practical method for industry (Williams et al., 2009).

Fallen stock may harbour a range of zoonotic agents (Milnes et al., 2008), and current methodologies for their disposal in Europe (e.g. incineration and rendering) depend on high temperatures to deactivate pathogens; however, bioreduction operates at a mesophilic temperature (approx. 40 °C) and does not utilise any chemical disinfection procedure. Rather, the active aeration coupled with the competitive and antagonistic effects of the prevalent microbes are hypothesised to reduce pathogen levels (Williams et al., 2009). For bioreduction to be approved under the revised EU ABPR (EC/1069/2009) (as described in Annex IV of EU implementing Regulation EC 142/2011) as an alternative method of storing fallen stock prior to disposal, the fate of pathogens within the system must be elucidated and the evidence presented to the European Food Safety Authority (EFSA), which then decide whether to ratify the system for industry use (Bohm, 2008). EFSA stipulate that novel disposal methods should lead to a 5-log reduction in the numbers of two indicator organisms representing bacterial pathogens, Salmonella enterica serovar Senftenberg (hereafter called S. Senftenberg) and Enterococcus faecalis (Bohm, 2008). A previous field-scale study on bioreduction of sheep recovered negligible numbers of pathogens (Williams et al., 2009), but the initial pathogen concentration was not high enough to validate whether or not a 5-log reduction in numbers had occurred. Whilst it is preferable to assess the fate of pathogens at field-scale, the logistics of growing and handling the large volumes of pathogens needed to gain a sufficient concentration in the bioreduction vessels would be problematic. Further, EFSA guidelines state that simulated systems can be used as a proxy of field-scale systems provided that they are representative of actual conditions (EFSA, 2008).

The aim of this work was to validate the effectiveness of bioreduction in reducing numbers of introduced pathogens in a laboratory-scale system. By applying the criteria stipulated by EFSA for ratifying novel disposal methods to a simulated storage process that is bioreduction, this study will help verify whether bioreduction represents a biosecure method of containing fallen stock prior to disposal. In addition to S. Senftenberg and E. faecalis, additional microorganisms (Campylobacter spp., Escherichia coli O157, and other Salmonella serovars) were also tested as they represent common zoonotic pathogens that may be introduced with carcasses into bioreduction vessels.

Section snippets

Vessel design

Laboratory-scale versions of the bioreduction vessels described by Williams et al. (2009) were constructed using 5 l polypropylene containers; 19 cm high × 13 cm wide × 26 cm long. These mini bioreducer vessels (MBVs) were placed within a darkened incubator set to 40 °C (±2 °C) and the contents continuously aerated at a maximum rate of 6 l min−1. To negate microbial contamination and odour, the outflow from the MBVs were passed through a commercial disinfectant (20% Trigene; Medichem, Kent, UK) and then an

Waste degradation

At the end of the trial, the reduction in volume of carcass components in each vessel was similar (88.2 ± 3.7% of that initially added). The discernable animal remains were predominantly identified as stomach content although there were also some fatty deposits and small fragments of bone.

Microbiological characteristics

The controls were found to have natural populations of Salmonella spp., E. faecalis, and Campylobacter spp. but no E. coli O157 were detected. Survival of the introduced Salmonella spp. and E. faecalis in the

Discussion

This trial was conducted over 3 months as it has been shown that this is the time required for most of the carcass components to degrade within a bioreduction system. Bioreduction has already proved to be effective at reducing the volume of carcass material to be disposed (Williams et al., 2009) and the findings of this trial supported this as even the bone material largely degraded. Although the system was designed to accurately mimic field-scale bioreduction, it should be remembered that the

Conclusions

This work indicates that bioreduction is efficient at containing pathogens from carcass material and hence that the system could potentially be suitably secure to store fallen stock prior to ultimate disposal. Further investigation at field-scale level that also includes other relevant organisms (e.g. indicator viruses) is required so that the system can be soundly considered for industry use and incorporation into the revised EU Animal By-Products Regulations (1069/2009).

Acknowledgments

We are grateful to BPEX, the Welsh Government and to Hybu Cig Cymru – Meat Promotion Wales for funding the work. We thank Sarah Chesworth for her technical assistance throughout the study.

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