Health and
Sustainable
Agriculture
Editor: Christine Jakobsson
Sustainable Agriculture
Introduction
Manure and biological waste (biowaste) from house-holds, the food industry, restaurants, slaughterhouses, toilets, etc. can be a valuable resource when used as a fertiliser on arable land. The flow of nutrients is cur-rently linear, as the excess nutrients in food mainly end up in water recipients. This causes a net loss from productive land that is commonly compensated for by application of virgin mineral fertilisers. Redirecting this linear flow back into food production could ben-efit society in several ways, by decreasing the use of natural resources and lowering environmental pollution. However, manure and biowaste may contain disease-causing microorganisms (pathogens) such as bacteria, viruses and parasites. Since recycling of biowaste cre-ates new ways of disease transmission between humans and animals, a particular area of concern is zoonoses, disease that can be transmitted between humans and ani-mals. Although pathogens occur naturally in the envi-ronment, in many cases there is a man-made reason for their presence. One way for pathogens to be introduced into ecosystems is when biowaste of agricultural,
mu-Sanitation Treatment Reduces
the Biosecurity Risk when
Recycling Manure
and Biowaste
Ann Albihn and Karin Nyberg
National Veterinary Institute, Uppsala, Sweden
Jakob Ottoson and Björn Vinnerås
National Veterinary Institute, Uppsala, Sweden Swedish University of Agricultural Sciences, Uppsala, Sweden
nicipal or industrial origin is recycled to agriculture or forestry (Albihn, 2009). Once contamination has taken place, it is often impossible to control the spread of the infective agents either in time or space. Infections may be transmitted to grazing animals or by feed and water to indoor animals. In addition, if zoonotic infections are introduced into the food chain there is a potential health risk for humans. Therefore, to minimise the biosecurity risk when using manure and biowaste on arable land, treatment of the material to reduce the load of pathogens before spreading is highly recommended.
Disease-causing Microbes in Manure and
Biowaste
Huge numbers of species and subtypes of bacteria, viruses and parasites are found in manure and different kinds of biowaste. Some of these microorganisms are pathogens and some are also zoonoses, for example Salmonella and EHEC (enterohaemorrhagic E. coli) (Table 17.1). Zoonotic parasites such as Toxoplasma and some
cies of Cryptosporidium and Giardia are expected to cause increasing problems in the developed world in the near fu-ture (Gajadhar and Allen, 2004; Mas-Coma et al., 2008).
Some pathogens can cause serious animal contagious (epizootic) diseases that spread quickly over regions, for example classical swine fever (Table 17.1). Many epizootic diseases are characterised by being highly in-fectious, so transmission via contaminated surfaces or transport vehicles within and between farms may be pos-sible. In such cases, the animals in the infected holding
Table 17.1. Examples of zoonotic* and epizootic† agents that can be transmitted via manure and biowaste.
Agent Disease Primary reservoir/host
Bacteria
Bacillus anthracis*,† Anthrax Ruminants, horses
Brucella spp.*,† Brucellosis Ruminants, swine
Campylobacter spp* Campylobacteriosis Multiple‡
Coxiella burnetii*,† Q-fever Small ruminants
Escherichia coli* EHEC (Enterohaemorrhagic E. coli) Ruminants Listeria monocytogenes* Listeriosis Multiple‡
Mycobacterium bovis*,† Tuberculosis Cattle
Mycobacterium avium subsp. paratuberculosis† Tuberculosis Ruminants
Salmonella spp.* Salmonellosis Multiple‡
Yersinia enterocolitica* Yersiniosis Swine
Viruses
African swine fever virus† African swine fever Swine
Aujeszky’s disease virus† Aujeszky’s disease Swine
Bovine herpes virus type 1† Infectious bovine rhinotracheitis Cattle
Infectious pulmonary vulvovaginitis Cattle Classical swine fever virus† Classical swine fever Swine
Foot-and-mouth disease virus† Foot-and-mouth disease Cattle, swine
Goat pox virus† Goat pox Goat, sheep
Hepatitis E virus* Hepatitis Swine Influenza A virus*,† Avian influenza Poultry
Newcastle disease virus† Newcastle disease Poultry
Porcine reproductive and respiratory syndrome virus† Porcine reproductive and respiratory syndrome Swine
Rinderpest virus† Rinderpest Cattle, goat, sheep, Asian pig
Sheep pox virus† Sheep pox Sheep
Swine vesicular disease virus† Swine vesicular disease Swine
Parasites
Cryptosporidium parvum* Cryptosporidiosis Cattle
Giardia spp.§ Giardiasis Multiple‡
Toxoplama gondii* Toxoplasmosis Cat
Trichinella spp.* Trichenillosis Swine
‡ Most warm-blooded animals can be infected § Transmission between animals and humans not clear
are culled and their carcases destroyed to interrupt further spread of the disease as quickly as possible. According to EU legislation, the disinfection process must also include treatment of the accumulated manure and biowaste.
Spore-forming bacteria such as Bacillus and Clostridia species are often present in manure and biowaste, but most of these species are common soil bacteria and non-patho-genic. However, some pathogen species of spore-form-ing bacteria may be present, for example B. anthracis, which causes the zoonotic and epizootic disease anthrax,
and C. chauvoie, which causes black-leg in ruminants. Both these diseases may result in high mortality. In addi-tion to the listed pathogens (Table 17.1), there are several non-listed organisms that can be present in manure and biowaste, and new disease-causing agents will always be found. In developing countries, infectious diseases of both animals and man are more frequent than elsewhere, caus-ing a heavy load of pathogens in manure and biowaste.
Exposure Pathways
The use of biowaste from society creates new routes for the spread of pathogens between animals, humans and the environment. Pathogens can enter a farm environment via incoming manure and biowaste, or via other sources such as purchased live animals, feedstuffs or equipment. There is also a risk of pathogen transmission from neighbouring farms via vector animals, e.g. birds, rodents or insects. Humans can also spread pathogens, e.g. if toilet waste is added to slurry tanks. In high-density livestock areas, excess manure may have to be transported to other re-gions, a practice involving a risk of long-distance spread of pathogens.
On-farm spread of pathogens can occur via storage, transport and use of manure. From fertilised land,
fur-ther spread may occur via surface runoff, leakage to groundwater, dust particles and harvested crops. Grazing animals can pick up pathogens and further transmit them directly to other animals, humans or into the food chain. Recycling of manure and biowaste may also affect water quality if freshwater recipients are contaminated, e.g. af-ter heavy rainfall or flooding. The highest risk of humans acquiring zoonotic infections is via consumption of in-fected food or water (Bemrah et al., 1998; Cassin et al., 1998), but humans can also be infected directly through contact with live animals or the environment.
Survival and Proliferation of Microbes in
the Environment
The survival and proliferation of pathogenic microor-ganisms in the environment varies depending on differ-ences between species, but also on factors such as ag-ricultural management strategy and climate conditions (Mitscherlich and Marth, 1983; Hutchison et al., 2004). It is well known that bacterial endospores, from species such as Bacillus and Clostridia, can survive for decades in soil. However, survival for over one year is also possible for some vegetative bacteria, if conditions are favourable (Mitcherlich and Marth, 1983). Different soil types affect microbial survival owing to the combined effects of soil texture, pore space, surface activity and moisture-hold-ing characteristics. The presence of manure or biowaste also affects pathogen survival in soil due to availability of essential nutrients and organic material to which the pathogens can adhere (Nyberg et al., 2010). Survival of pathogens on crops has also been reported. Bacteria may be incorporated into biofilm on plant surfaces or even colonise internal structures (Heaton and Jones, 2008). Zoonotic parasites such as Toxoplasma and some subspe-cies of Cryptosporidia and Giardia can also survive for long periods of time in the environment, and their abil-ity to resist many natural and artificial conditions makes them most difficult to control (Feachem et al., 1983).
The method used for application of manure or biowaste to land is another important factor for the survival of path-ogens. Due to the ammonia emissions from field-applied manure, incorporation directly after application by tillage
Figure 17.1. Pathogens can enter a farm environment via incoming ma-nure and biowaste to be used as a fertiliser or from other sources such as purchased live animals, feedstuff or equipment. Also, vector animals may transmit pathogens from neighbouring farms. Grazing animals can pick up pathogens and further transmit them directly to other animals, humans or into the food chain. Photo: M. Löhmus, SVA.
is mandatory. This procedure reduces animal exposure, but persistence is considerably prolonged within soil com-pared with on the soil surface, partly because the pathogens are protected against deteriorating UV-light (Hutchison et al., 2004). The reliability of natural inactivation factors on plant surfaces, in soil and in feed and foodstuffs should not be overestimated. In addition, some pathogenic bacte-ria such as Salmonella, E. coli and Bacillus can multiply in favourable circumstances, such as in warm and humid weather (Mitscherlich and Marth, 1983).
Other Unwanted Organic Material in
Manure and Biowaste
Apart from pathogens, hormones, antibiotics and other phar-maceutical residues are also found in manure and biowaste (Vinnerås et al., 2008). Antibiotic-resistant bacteria that end up in the environment may spread their resistance genes to better-adapted indigenous bacteria, thereby increasing the environmental resistance reservoir (Kühn et al., 2005).
Unwanted organics in soil can affect plant growth but the higher density of microorganisms in soil than in water probably results in higher degradation of unwanted organ-ics in the soil. The main negative effect of pharmaceutical residues is reported to be on aquatic life, e.g. reproductive disorders in fish (Sumpter and Johnsson, 2005).
Treatment and Handling of Manure and
Biowaste to Reduce the Biosecurity Risk
Current large-scale livestock production, epizootic dis-eases and globalisation increase the need for biosecurity. Practices that have been considered adequate for decades may not be sufficient any longer. By introducing a barrier to disease transmission early in the food chain, food safety can be increased. Manure treatment differs depending on tradition and local conditions and, in general, large farms have more opportunities for treatment. Some examples of treatment methods for producing hygienically safe end products are described below, and some of these meth-ods offer opportunities to co-treat manure with biowaste. Effective treatment can prevent ecosystem contamination and dissemination of pathogens. In order to be sustain-able, suitable treatment methods must combine biosecu-rity aspects with environmental, economic and nutrient recycling aspects. As an extra safety precaution, the use of a particular end-product on farmland may be restricted, or there may be a quarantine period between spread of the end-product and crop harvest or grazing.
Composting
Composting can be used for both small-scale household kitchen waste and large-scale solid waste treatment, e.g. in windrow composting. Both open and closed systems are used, or a combination in different steps. During com-posting, bacterial activity in the treated material gener-ates heat and, if well managed, temperatures up to 70ºC can be obtained. If a high temperature can be maintained for long enough, an adequate reduction in pathogens can be achieved. However, studies have shown that there is a risk of pathogen re-growth in cold outer zones of the compost pile, especially if the material is relatively fresh (Elving et al., 2010).
Figure 17.2. One way of studying the survival and proliferation of path-ogens under outdoor conditions is by the use of lysimeter systems, which consists of soil-filled polyvinyl tubes lowered into the ground with separate collection of drainage water. Photo: K. Nyberg, SVA
Anaerobic Digestion
In biogas plants, manure and biowaste can be co-treat-ed. According to European legislation, heat treatment is compulsory when animal by-products, e.g. from slaughter houses, are being processed (EC 1774/2002). Pasteurisation at 70°C for 60 min gives a sufficient re-duction for most pathogens (Mitscherlich and Marth, 1983; Sahlström et al., 2008). However, the reduction in heat-resistant viruses is limited, and bacterial endospores and prions are not reduced at all (Bagge et al., 2005). Outside the EU, heat treatment before digestion is not as common and the reduction in pathogens through the di-gestion process is limited, most often 1-3 log10, although with higher reduction rates at longer hydraulic retention times (Yen-Phi et al., 2009).
Ammonia Treatment
Ammonia treatment involves application of either ammo-nia in solution or urea, which upon being dissolved are de-graded by the naturally occurring enzymes in manure. The resulting increase in pH (to approximately 9) increases the concentration of uncharged ammonia, which is the active substance. Ammonia has shown to be an efficient bacte-ricide, irrespective of temperature, starting from concen-trations of 10mM. The effect on the parasite Ascaris spp. has been shown to be considerably greater at temperatures above 20°C and ammonia concentrations above 40mM (Nordin, 2010). The reduction effect on enveloped ssRNA viruses such as avian flu is also reported to be sufficient at a range of temperatures (Emmoth, 2010).
Formic Acid
Formic acid is used in Sweden for stabilisation of milled slaughter house waste intended for incineration. Addition of approximately 1% formic acid decreases the pH below 5 and the material is then stabilised and safer to handle during transport and storage. This treatment has been shown to sufficiently decrease pathogenic enterobacteri-ases, e.g. Salmonella. However, it has only a limited ef-fect on viruses.
Liming
Increasing the pH by application of hydrated lime (calci-um hydroxide) to a value over 11 effectively reduces the numbers of pathogenic bacteria present, although a pH
above 12 is required for a long time to remove the highly chemically resistant Ascaris spp. Faecal coliforms and
Salmonella are rapidly inactivated after liming, reaching
no-detection levels within periods shorter than 24 hours (Bennet et al., 2003; Bean et al., 2007). However, there is a risk of re-growth of pathogens and therefore the pH value needs to be kept high for a certain amount of time. In addition, liming is most effective in materials with a high water content, as the inhibitory effect is dependent on free ions in aqueous solution. When treating manure with lime the high pH induces formation of carbonates, e.g. CaCO3, which precipitate and form a thick sludge in the manure tank.
Storage
Manure slurry is relatively convenient to handle, but san-itisation through storage is not reliable (Himathongkham
Figure 17.3. Manure slurry is relatively convenient to handle, but sanita-tion during storage is not reliable. A proper hygiene treatment before spread on arable land is recommended, e.g. by composting, anaerobic digestion or treatment with ammonia or lime. Photo: B. Ekberg, SVA.
et al., 1999). Levels of indicator organisms vary over time during storage, indicating that pathogen levels may fol-low a similar pattern. In addition, a long period of storage without adding fresh material is generally impossible, since on-farm storage capacity is usually limited.
Conclusions
Manure and biowaste are resource for agriculture. However, the potential health risks associated with plant nutrient recycling in the food chain must not be ignored. Recycling of manure and biowaste to agricultural land can inadvertently spread infectious diseases, although opinion differs concerning the risk levels. The biosecurity risk for animals and humans may be sufficiently reduced if the material is properly sanitised before being spread on agricultural land. In order to be sustainable, suitable treatment methods must combine biosecurity aspects with environmental, economic and nutrient recycling aspects. Examples of treatments are composting, anaerobic diges-tion or treatment with ammonia, formic acid or lime. To obtain general acceptance for the use of biowaste as a fertiliser, a hygienically safe end-product is needed.
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