Fate of pathogens in a simulated bioreduction system for livestock carcasses
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.
References (31)
- et al.
The environmental and biosecurity characteristics of livestock carcass disposal methods: a review
Waste Manag.
(2011) - et al.
Assessing genetic structure and diversity of airborne bacterial communities by DNA fingerprinting and 16S rDNA clone library
Atmos. Environ.
(2005) - et al.
Influence of biotic and abiotic factors on human pathogens in a finished compost
Water Res.
(2004) - et al.
The role of indigenous microorganisms in suppression of Salmonella regrowth in composted biosolids
Water Res.
(2001) - et al.
In-vessel bioreduction provides an effective storage and pre-treatment method for livestock carcasses prior to final disposal
Bioresour. Technol.
(2009) - et al.
Risk of escape of prions in gaseous emissions from on-farm digestion vessels
Vet. Rec.
(2010) - Anon, 2009. The Animal by-Products Regulations, vol. 1069/2009, European Commission,...
- Bansback, B., 2006. Independent Review of the National Fallen Stock Scheme and Company. Available from:...
The Experimental Validation and the Organisms to be Considered in the Context of the ABP Regulation
(2008)- et al.
Comparison of different primer sets for use in automated ribosomal intergenic spacer analysis of complex bacterial communities
Appl. Environ. Microbiol.
(2004)
Inactivation of Salmonella Senftenberg strain W 775 during composting of biowastes and garden wastes
J. Appl. Microbiol.
Luminescence-based detection of activity of starved and viable but nonculturable bacteria
Appl. Environ. Microbiol.
Direct detection of Salmonella cells in the air of livestock stables by real-time PCR
Ann. Occup. Hyg.
The ecology, epidemiology and virulence of Enterococcus
Microbiology
Cited by (15)
Cardinal acuity on the extraction and characterization of soluble collagen from the underutilized abattoir junks for clinical demands
2022, Process BiochemistryCitation Excerpt :Slaughtering, the prime supplier of solid and liquid wastes which were reflected as a burdensome in anaerobic management owing to the presence of organic matters such as high proteins and lipids [1] and also hazardous pathogens [2].
A critical review on risk evaluation and hazardous management in carcass burial
2019, Process Safety and Environmental ProtectionCitation Excerpt :In the case of a disease outbreak, animals within a certain area are culled and require safe disposal that is practical and economically prudent (Kim and Pramanik, 2015). Several methods including burial, incineration, rendering, composting, anaerobic digestion, and alkaline hydrolysis are available for carcass disposal (Gwyther et al., 2012; Delgado et al., 2014). Each method has advantages and disadvantages for large scale mortality events (Table 1).
Lab-scale evaluation of aerated burial concept for treatment and emergency disposal of infectious animal carcasses
2018, Waste ManagementCitation Excerpt :Aerobic carcass degradation carried out in small underground vessels was reported as a novel technology that provides an effective option for storing and pretreating of animal (sheep) carcasses prior to final disposal in the UK (Williams et al., 2009). It was shown that high numbers of bacteria Salmonella enterica (serotypes Senftenberg and Poona), Enterococcus faecalis, Campylobacter jejuni and coli, and Escherichia coli O157) in sheep carcasses were inactivated in the digestate within 3 months of AeD (Gwyther et al., 2012). Combining aeration with burial raises questions that have not been researched.
Method for sampling and analysis of volatile biomarkers in process gas from aerobic digestion of poultry carcasses using time-weighted average SPME and GC–MS
2017, Food ChemistryCitation Excerpt :The temperature of process gas was 28 ± 0.5 °C, and relative humidity was 100%. Laboratory-scale AeD system was designed, constructed and validated for this research with similar features to (Gwyther et al., 2012; Williams et al., 2009). For the TWA-SPME method: gas samples were collected from AeD reactors using 250 mL gas sampling bulbs (Supelco, Bellefonte, PA, US) with a flow rate at 3 L min−1 (air mass flow controller model GFC 17, Aalborg, Orangeburg, NY, US).
Semi-continuous anaerobic digestion of solid slaughterhouse waste
2014, Journal of Environmental Chemical EngineeringCitation Excerpt :Slaughterhouses generate substantial amounts of animal by-products, which are defined as parts of the animal not intended for consumption, either because they are not fit for human consumption or because there is no market for them. This type of waste typically contains large amounts of organic matter, mainly composed of proteins and lipids [4] and pathogens, and its disposal can lead to serious environmental problems [3,7,9,10]. European Commission Regulation (EC) [11] No. 1774/2002 categorizes different animal by-products and indicates how they should be used, commercialized and eliminated.
Why must we rush to bury our dead (pigs): The option of excarnation by exposure
2021, Canadian Veterinary Journal