Download Survival of pathogenic micro-organisms and parasites in

Rev. sci. tech. Off. int. Epiz., 1991, 10 (3), 813-846
Survival of pathogenic micro-organisms and
parasites in excreta, manure and sewage sludge
D. STRAUCH *
Summary: The causative agents of many infectious diseases are excreted by the
faecal route and also with other excretions or secretions of the body.
Some
pathogens are also excreted from clinically healthy animals, from those with
latent infections and in cases of transmissible multifactorial diseases. In all types
of livestock housing, the pathogens finally reach the floor with the installations
for collecting manure as a solid or liquid. Under these conditions livestock owners
do not realise that manure may contain pathogens, and therefore do not take
precautions against possible spread of diseases by utilisation of manure. The
pathogens do not survive very long in stored farmyard manure because of the
temperatures and biological and biochemical activities prevailing in the middens.
But the conditions in slurry are different because the temperature does not rise
and biochemical activity is low. Therefore the pathogens survive for rather long
periods in slurry. To avoid disease transfer by utilisation of manure and slurry
as fertilisers, certain precautions are necessary and these are described in detail.
The agricultural utilisation of municipal sewage sludge is common in many
countries. However, these sludges contain pathogens which are excreted by the
human population served by the sewers and sewage treatment plants. In the sewage
purification processes most of the pathogens are reduced in number but not
completely eliminated. They are enriched by sedimentation processes in the sewage
sludge. To protect the livestock of farms utilising sewage sludge as fertiliser or
for amending soils it is necessary to sanitise hygienically dubious sludges prior
to their use. The epidemiological aspects of agricultural sludge utilisation are
discussed and details of the available sanitation technologies are given.
KEYWORDS: Bacteria - Disinfection - Epidemiology - Livestock - Manure Parasites - Sewage sludge - Slurry - Tenacity - Viruses.
INTRODUCTION
A n i m a l excreta a n d m a n u r e
In this chapter the term 'excreta' refers t o faeces a n d urine and the term ' m a n u r e ' ,
which will be used as a general t e r m , refers to animal excreta in any f o r m , with or
without b e d d i n g and dilution water. ' F a r m y a r d m a n u r e ' (FYM) refers t o a mixture
of excreta together with substantial quantities of bedding materials (e.g. straw, w o o d
shavings, sawdust, peat) dense enough to be handled as a solid. 'Slurry' is a mixture
of faeces and urine which can also contain cleaning water, rain water, small quantities
of bedding material a n d spoiled feed particles.
* Institute of Animal Medicine and Animal Hygiene, University of Hohenheim (460), P . O .
Box 70 05 62, 7000 Stuttgart 70, Federal Republic of Germany.
814
Several hundred diseases are transmitted among animals and more than 150 of
them can be passed on to h u m a n beings as zoonoses (S.L. Diesch, unpublished
findings). The pathogens causing most of these diseases are either excreted directly
by the affected animals or indirectly spread into the environment by vectors such
as nasal, pharyngeal, vaginal, placental or lochial secretions, faeces, urine, milk, sperm,
dermal and mucosal desquamations and secretions, carcasses, blood, slaughterhouse
offal, meat and meat products, milk and milk products, eggs and egg products from
dairies, solid and liquid manures (FYM, slurries). In all of these conditions the pathogens
are excreted and end up during indoor keeping of livestock on the floor and thus in
the manure, even if the pathogen is not excreted by the faecal route. The floor of animal
houses, with their installations for collecting faeces and urine, thus acts as the collecting
basin for all pathogens which are spread by the animals of a given establishment. In
every case of a clinically diagnosable transmissible disease, dung and slurry must be
considered as infectious and an inanimate vector for the pathogen. To make matters
worse there is, especially in the case of salmonellosis, a tendency for these pathogens
to occur in slurries of livestock which have never shown any sign of clinical illness.
After the second and third microbiological examination of the same slurries, the
salmonellas are not isolated again (33, 42, 47). Similar conditions may also be found
in the course of subclinical infections with other pathogenic agents. But such incidents
risk developing into multifactorially caused diseases, whereby normally harmless
infections may lead to clinically recognisable symptoms of disease released by nonmicrobial factors. When they exist in a population for months or even years a gradual
accumulation of infectious agents will result, if further factors are added, in the outbreak
of a dangerous multifactorial disease.
Today this type of disease holds a special threat for larger and specialised livestock
establishments with a lack of population heterogeneity, such as premises for fattening
of only pigs or calves or broilers. The danger lies in the fact that in most cases the
owner of such an establishment does not recognise the infection and therefore does
not take any action to prevent a spread of the pathogens in his surroundings. Hence
he is not informed about the infective potential of the excretions of his animals and
the manure to be utilised o n his fields.
For more than two decades salmonellosis has spread steadily among man and
animals in many countries. In some areas, more than one-third of pigs and more
than one-half of broilers produced for slaughter are infected with salmonellas.
This is the reason why manure from larger production units generally should be
regarded as infected, and disposed of by means of certain safety measures.
The spread of many classical h u m a n diseases such as cholera, typhoid fever or
bacillary dysentery has been controlled by insulating man from human excreta through
improvements in personal hygiene and the use of sewage and water treatment
processes. In areas of the world where such improvements have not been made or
where available systems are inefficient these diseases remain endemic. The treatment
of animal excrements with methods used for the purification of municipal sewage
is, with the exception of a few gigantic intensive units in various parts of the world,
generally considered too expensive and unsuitable for farm animal excreta. It is
therefore necessary to find simple methods to minimise the environmental hazards
of ' n o r m a l ' manure which is only possibly infected, and more sophisticated methods
to treat manures which are certainly infected in order to render them innocuous for
further utilisation as fertilisers or for other purposes (58).
815
Sewage sludge
The terms 'sewage sludge' and 'sludge' used in this chapter are defined as all
aqueous matter which is separable from municipal wastewater, except screenings,
sievings and grit. Sludge consists of the particulate matter in raw sewage (wastewater)
like faeces, food leftovers, paper, cellulose (diapers, etc.), the excess sludge of
biological treatment steps and sludge from trickling filters — which is to say, sludge
consists mainly of organic material. The water content is between 90-99%. Sludge
is a good growing medium for bacteria as it rather quickly putrefies and needs to
be stabilised before further utilisation or deposition.
It is known that sewage and sewage sludge from municipal wastewater treatment
plants do contain pathogenic agents. These germs derive from humans who use the
sewerage systems and who suffer from acute or latent infections or from known and
often unknown permanent excretors of pathogens (e.g. salmonellosis). The spectrum
and quantity of pathogens are extended by other sources connected to the sewerage
system, like hospitals, abattoirs, livestock markets and related activities.
It is known too that a certain part of the h u m a n population, companion animals
and livestock are always afflicted with an infectious disease. In view of the fact that
it is nowadays possible to isolate pathogens from raw municipal sewage without great
effort, it seems pointless to speculate about the percentage of infected individuals.
Since a variety of fairly intangible factors play a role, the estimates vary considerably
around the factor 10 (0.5-5% of the population using the sewers).
Pathogens are excreted from infected individuals via faeces, urine, secretions or
excretions of the nose, pharynx, vagina, mucous membranes and skin, depending
on the type of infection, and reach the sewage treatment plants from sewers and
sanitary installations in homes. It is therefore understandable that for epidemiological
surveys some authors consider microbiological examination of wastewater as reflecting
the epidemiological situation of the population in certain catchment areas. Sewage
sludges usually do contain considerable amounts of pathogens even after the
purification processes (57).
Farmers in industrialised countries are increasingly exercising restraint in the
agricultural utilisation of sewage sludge, because they feel it a threat to their livestock,
especially when the animals are grazing or fed with green feed. In view of the steady
increase of latent infections with salmonellas and agents of multifactorial diseases
in the intensive production of poultry, pigs and calves, farmers want to seal their
farms off from further danger of infection. In recent years many farmers have come
to believe that their soil was being slowly but surely turned into the rubbish bin of
the nation. The following pages will discuss whether and to what extent fears regarding
the danger for livestock of infection from sewage sludge are justified, and what
measures can be taken to eliminate or minimise the possible dangers.
P A T H O G E N I C A G E N T S IN E X C R E T A A N D
MANURE
Bacteria
Theoretically, the bacteria involved in cases of bacterial infection can occur in
the excreta and m a n u r e of infected animals. An expert group of the Commission
816
of the E u r o p e a n Communities (CEC) has listed those bacteria (1) which may be of
particular concern for animal a n d / o r h u m a n health under European conditions when
they are present in animal excreta and manure (Table I).
TABLE
Bacteria
of epidemiological
concern
I
in livestock
excretions
and manure
*
(1)
Salmonella
spp.
Escherichia coli (including enteropathogenic
strains and normal gut E. coli
multiply resistant to antibiotics)
Brucella spp.
Bacillus
anthracis
Leptospira
Erysipelothrix
rhusiopathiae
Mycobacterium
spp. (in particular
M. tuberculosis, M. bovis,
M. avium complex, M.
paratuberculosis
and the atypical mycobacteria)
Treponema
Chlamydia
Rickettsia
spp.
hyodysenteriae
spp.
spp.
* Outbreaks involving some o f these organisms are subject to specific regulations in different countries which include
control o f the movement and utilisation o f excreta and manure f r o m infected enterprises
Since a b r o a d variety of pathogenic bacteria can be excreted by infected animals,
it may be assumed that a similar number of organisms can at some time be found
in their excretions and manure. Under practical conditions the number will be limited
by many factors, and the variety of pathogens actually isolated is comparatively small.
T h e kind of bacteria isolated will vary with the geographical location of the farm
and the animal species. Also the physical and chemical composition of the manure
may determine the types of pathogen present. Thus leptospires, which are sensitive
to extremes of p H , may be isolated only from slurries with a p H a r o u n d neutral.
Isolations and occurrence will also depend upon the age of the slurry and its dry matter
content, as well as on the number of organisms gaining access to the m a n u r e , which
will obviously affect the possibility of pathogens being present and the outcome of
attempts at isolation. Another important factor is the ease with which small numbers
of pathogens may be isolated. M a n u r e naturally contains an excess of 1010 bacteria
per ml from which the pathogenic bacteria must be separated. Small numbers of
Enterobacteriaceae, e.g. salmonellas, may be isolated because very sensitive enrichment
and identification techniques are available. Other bacteria like those causing anthrax,
brucellosis, mycobacteriosis and leptospirosis will be isolated only if larger numbers
are present and when reliable isolation techniques for the respective pathogen are
available. Therefore the number of occasions on which a pathogen has been isolated
from m a n u r e obviously cannot give a true reflection of its occurrence, and it seems
justifiable t o assume that any organism which is voided in the faeces and urine of
animals or other body fluids and excretions may be found in manure. Very few surveys
have been carried out to assess the actual prevalence of pathogens, and those which
can be referred to have usually concentrated on salmonellas, although other organisms
have occasionally been isolated (6, 2 1 , 35, 36, 37, 40).
817
The number of pathogens contained in cattle and pig m a n u r e is probably low.
Surveys in the United Kingdom did not reveal concentrations of salmonellas above
10 per ml. But the concentrations may also be higher because even apparently
healthy cattle may excrete up to 10 salmonellas per gram of faeces (34) and a similar
n u m b e r of leptospires may be excreted in the urine of infected cattle (27). Excretion
at this level by only a few animals of a herd could render m a n u r e a potent source
of pathogenic organisms. Pathogens have also been found in poultry m a n u r e but
such reports are few. This may relate to the manner in which poultry waste is collected.
It usually tends to be a solid or semi-solid material which remains aerobic and is readily
composted. Pathogens like salmonellas, colibacteria, pasteurellas and hemolytic
streptococci are killed rapidly under these conditions (48). Others like listerias or
clostridias m a y withstand the adverse conditions involved. The type of waste may
also affect the longevity of organisms, since salmonellas are killed m o r e rapidly in
built-up than in fresh litter, and this may affect the frequency of isolation (58). In
a recent investigation the tenacity of Salmonella typhimurium in faeces of laying hens
was studied in five different types of housing (intensive floor husbandry without litter,
floor h u s b a n d r y with litter, battery without aeration of the droppings belt, battery
cages with aeration of the droppings belt, and sloping floor) and two types of middens
(covered midden for the battery cages without belt aeration, covered midden for the
battery with belt aeration). The tenacity of 5. typhimurium varied between 2 and
175 days, depending on the h u s b a n d r y system (2 days in the sloping floor system
and 175 days in the midden from the battery with aerated droppings belt).
Relevant environmental factors were temperature and the dry matter content of the
m a n u r e (50).
2
7
Viruses
Information about the occurrence and tenacity of viruses in animal excrements
is not as a b u n d a n t as in the case of bacterial infections. According to a survey
on the excretion of viruses by farm livestock, based on research in N o r t h America
(Table II), it seems a likely supposition that these findings are valid not only for
N o r t h America but, with local variations, for most parts of the world. A n o t h e r
compilation gives details about the presence of various animal viruses in faecal
matter (Table III). But as these two tables show, a considerable number of virus
genera are already k n o w n to be excreted in the faeces of livestock and other
animals. Only in recent years have improvements in the isolation techniques for
viruses from heavily contaminated material led to remarkable successes in
identifying viruses in faecal matter. This development has m a d e it possible t o
consider excrements and the spent air of animal houses in epidemiological
discussions.
Enteroviruses are relatively tenacious in slurry. Quantitative investigations in slurry
samples with direct isolation of viruses showed a virus titre of about 10 T C I D
per litre, whereas in samples which yielded enterovirus only after concentration,
about 50-100 T C I D 5 0 per litre were found (19). Infections of pigs with parvovirus
are not infrequent and the survival of this virus in slurry and sewage is
documented. Transmissible gastro-enteritis virus is relatively sensitive to environmental
influences, just as are other coronaviruses. As for the influenza viruses of pigs, these
have low tenacity. Their excretion by the faecal route is considered to be unlikely,
but nevertheless they can reach the floor and thus the m a n u r e of stables with the
nasal excretions of infected pigs. Besides typical pig strains, infections of pigs with
6
5 0
818
TABLE
Viruses
excreted
by farm
II
livestock
in North
America
(18)
Host species
Non-enveloped viruses
Enveloped viruses
Cattle
Bovine enterovirus
Bovine adenovirus
Reovirus
Reovirus-like
Bovine parvovirus
Bovine rhinovirus
Bovine papillomavirus
Infectious bovine rhinotracheitis
Malignant catarrhal fever
Bovine mammillitis
Bovine virus diarrhoea
Bovine Coronavirus
Parainfluenza type 3
Respiratory syncytial virus
Rabies
Vesicular stomatitis
Cowpox
Paravaccinia
Sheep
Ovine enterovirus
Ovine adenoviruses
Rcoviruses
Porcine parvoviruses
Contagious ecthyma
Maedi-visna
Malignant catarrhal fever
Transmissible gastro-enteritis
Hemagglutinating encephalitis
Hog cholera
Swinepox
Poultry
Avian enteroviruses
Avian adenoviruses
Avian reoviruscs
Newcastle disease
Avian influenza
Infectious laryngotraeheitis
Infectious bronchitis
Avian leukosis
Marek's disease
Fowlpox
Viral arthritis
h u m a n strains o f i n f l u e n z a virus are m o r e frequently o b s e r v e d in c o n n e c t i o n with
e p i d e m i c s in the h u m a n p o p u l a t i o n . A n t i b o d i e s w h i c h react with the h e m a g g l u t i n i n s
o f s w i n e i n f l u e n z a virus are present in m a n y h u m a n sera. T h e h u m a n strains o f this
virus can persist for years in the pig p o p u l a t i o n . Pigs m a y thus be considered a possible
reservoir for h u m a n strains o f i n f l u e n z a virus.
F r o m k n o w l e d g e o f the o c c u r r e n c e and survival o f viruses o f h u m a n origin in
w a s t e w a t e r , s l u d g e , soil a n d o n plants w h i c h were fertilised with s e w a g e ( m o r e than
100 different strains o f enteroviruses were isolated), it can be a s s u m e d that the agents
o f m a n y viral diseases o f d o m e s t i c a n i m a l s are excreted in the faeces and urine of
infected a n i m a l s , a n d therefore m u s t o c c u r frequently in m a n u r e (58).
Parasites
T h e prevalence o f p a t h o g e n i c p r o t o z o a , h e l m i n t h s a n d a r t h r o p o d s in excretions
a n d m a n u r e has been d i s c u s s e d under E u r o p e a n c o n d i t i o n s (13). Cattle faeces are
regularly c o n t a m i n a t e d with large n u m b e r s o f Eimeria o o c y s t s and trichostrongyle
819
TABLE III
Presence
of various
animal
viruses in faeces,
(52, modified)
Viruses excreted primarily in faeces
Enteroviruses
Reoviruses
Rotaviruses
Bovine virus diarrhoea
Transmissible gastro-enteritis of pigs
Calf diarrhoea Coronavirus
Rinderpest
Parvoviruses
Adenoviruses
Viruses clearly present in faeces
Aujeszky's disease
Foot and mouth disease
Swine vesicular disease
Coxsackie
Classical swine fever
African swine fever
Viruses probably present in faeces
Vesicular exanthema
Rift Valley fever
Viruses unlikely to be present in faeces
Bluetongue
African horse sickness
Louping ill
Maedi-visna
Hemagglutinating encephalomyelitis
Vesicular stomatitis
Rabies
Swine influenza
Parainfluenza 3
Herpes group: infectious bovine
rhinotracheitis
Contagious pustular dermatitis
Poxviruses
secretions
and
excretions
Virus also present in high titre in:
Respiratory secretions.
Respiratory secretions
Maximum amount of virus found in:
Respiratory secretions, saliva
Vesicular epithelium
Vesicular epithelium
Blood
Blood
Maximum amount of virus found in:
Vesicular epithelium
Blood
Maximum amount of virus found in:
Blood
Blood
Blood
Respiratory secretions
Respiratory secretions
Vesicular epithelium
Saliva
Respiratory secretions
Respiratory secretions
Respiratory secretions
Pock epithelium
Pock epithelium
eggs. Quantitatively these constitute the prime c o n t a m i n a n t s in cattle effluents.
Fasciola eggs, though less frequently present, are also a considerable risk as they are
very resistant a n d may multiply if they find a suitable habitat where a snail host may
become infected. Other contaminants create minor hazards due to their low resistance
(eggs and larvae of Strongyloides,
Dictyocaulus
larvae), the need to enter into an
intermediate host (Dicrocoelium, Moniezia) or just their relatively low prevalence
(Toxocara vitulorum) (Table IV).
820
TABLE
Prevalence
and resistance
of parasitic
agents in cattle
and their potential
hygienic
hazard
(13)
spp.
Helminths
Trichostrongylid
spp.
Strongyloides
papillosus
Oesophagostomum
spp.
Fascioia
hepática
Dictyocaulus
viviparus
Trichuris spp.
Dicrocoelium
dendriticum
Moniezia spp.
Toxocara
vitulorum
Resistance ( )
Priority as a
hygienic hazard
+ + +
+ + +
1
+ +
+
+
+
+
+
+
+
+
+
+
+
+
+ +
+
+ +
+ + +
+
+ +
+ + +
+
+ + +
2
+
+
+
?
1
Arthropods
Psoroptes
Chorioptes
Sarcoptes
a) + + + regular
h) + + + high
+ + frequent
+ + intermediate
effluents
Prevalence (
a)
Parasite
Protozoa
Eimeria
IV
b
3
+ occasional
+ low
It was found in Ireland that 94-96% of slatted-floor slurry samples contained
trichostrongylid nematodes, mainly Ostertagia ostertagi and Cooperia
oncophora,
in contrast to FYM samples, only 7 9 % of which had these nematodes (44). Another
comparison showed similar conditions in Sweden, where 4 1 , 0, 6, 8 and 2 % of
F Y M samples were carriers of trichostrongylids, Eimeria s p p . , Moniezia
benedeni,
Trichuris s p p . and Nematodirus
helvetianus
respectively, c o m p a r e d with
contamination rates of slurry samples of 67, 6, 17, 8 and 19% (46).
Pig faeces regularly contain Eimeria oocysts and frequently eggs of several gastro­
intestinal nematodes. A m o n g these, Ascaris eggs and coccidial oocysts are the most
dangerous from the qualitative point of view due to their high resistance. Eggs of
other species are less important though they may occasionally give rise to infections
(Table V).
Broiler and hen litter will normally be contaminated by oocysts of various Eimeria
species. As these are highly resistant, they rank first among the potentially diseaseinducing contaminants. Although less frequently present in poultry litter, eggs of
Ascaridia and Heterakis are dangerous on account of their high resistance. Other
contaminants may keep the life cycle of a parasite going; however, they will give rise
to serious trouble only occasionally (Table VI).
The priority of a contaminant according to its prevalence in the effluent, and its
innate properties of resistance and survival potential, may be modified not only by
821
TABLE
Prevalence
and resistance
of parasitic
agents in pig
and their potential
hygienic
hazard
(13)
Parasite
Protozoa
Eimeria
Balantidium
Helminths
Ascaris
Oesophagostom
Strongyloides
Hyoslrongylus
Trichuris
Fasciola
V
effluents
Prevalence (a)
Resistance (b)
Priority as a
hygienic hazard
+ + +
+ +
+ + +
2
+ + +
+ +
+
+ +
+ + (+)
+ + +
1
3
+ +
+ +
+ +
+
+
+
urn
Arthropods
Sarcoptes
Haematopinus
+
+
a) + + + regular
+ + frequent
+ occasional
b) + + + high
+ + intermediate
+ low
TABLE
5
4
?
VI
Prevalence
and resistance
of parasitic
and hen effluents
and their potential
(13)
agents in
hygienic
broiler
hazard
Prevalence (
Resistance (
Priority as a
hygienic hazard
Protozoa
Eimeria
Histomonas
+ + +
+
+ + +
1
Helminths
Asear id ia
Heterakis
Capillaria
+ +
+ +
+ +
+ + +
+ + +
+ +
2
2
Parasite
a)
Arthropods
Dermanyssus
a) + + + regular
+ + frequent
b) + + + high
+ + intermediate
c) in Heterakis eggs
+
b)
?
+ occasional
+ low
the conditions in which it is kept or stored after having been shed by the h o s t , but
also by its subsequent use. T h e hygienic h a z a r d , for instance, of pig slurry is very
822
different depending on whether it is used as fertiliser on arable land, as fertiliser on
sow or cattle pastures, or as recycled feed for cattle. The variety of parasites will
also be influenced by composition and age.
The parasites discussed above and the information shown in the tables must be
modified according to the geographical area where a problem arises.
Fungi
Animal wastes are not usually considered as a source of pathogenic fungi although
solid manure may provide a good growth substrate for many species, and Petriellidium
boydii was the dominant member of the mycoflora of manure samples isolated from
three beef cattle feedlots in the USA. This organism causes mycotic abortion in
animals, pulmonary allescheriasis in man and mycetomas in both man and animals.
Two other fungal species capable of producing mammalian mycotoxins were also
isolated (8).
T E N A C I T Y O F P A T H O G E N S IN E X C R E T A A N D M A N U R E
Bacteria
It has been reported that salmonellas may multiply during storage of slurry, but
it is generally accepted that most pathogens are reduced by storage. The reason is
that pathogens are adapted to growing in the tissues of their host, and the environment
of slurry with its comparatively low temperature and the presence of other antagonistic
organisms is obviously not suited to their continued existence. The type of slurry,
storage temperature and serotype of salmonellas may all affect the survival time, which
also depends to a considerable extent on the number of salmonellas contained in the
slurry at the beginning of storage. The greater the number of pathogens present at
the beginning, the longer will be their time to extinction. Survival is also enhanced
by reduction of temperature and an increase in solids content. Survival is greatest
at temperatures below 10°C and in slurries containing more than 5 % solids (35).
The influence of p H on the survival of salmonellas in various types of slurry has
been studied. These and other observations show that differences in the viability of
salmonellas exist, depending on the animal species from which the slurry is produced.
The following relation can be postulated: survival is longest in cattle slurry, median
in pig slurry, and shortest in cage manure from poultry and calf slurry (Table VII).
There are many reports on the survival time of pathogenic bacteria in excretions
and manure which cannot be discussed here but which deserve attention (2, 5, 6, 17,
20, 28, 40, 43, 45, 60).
Viruses
Information is scanty on the survival times of viruses in farm effluents. Some
viruses survive in faeces of various kinds, depending on summer or winter
temperatures: Aujeszky's virus 3-15 weeks, Borna virus 22 days, Marek virus 7 days,
Teschen virus 3-25 days, African swine fever virus 60-160 days, foot and mouth disease
virus 21-103 days (45). In very recent investigations which were made together with
other experiments (50) it was found that Newcastle disease virus was reduced in winter
faster in battery cage faeces (22 days) than in two floor pen systems and in the middens
823
TABLE
Survival
under
VII
of different
salmonella
types in animal
natural conditions
in storage facilities
of
(58)
effluents
farms
Survival (days)
5. dublin
S.
typhimurium
S. paratyphi B
S. anatum
S. Manchester
S. gallinurumpullonun
pH
Cattle
slurry
Cattle
urine
Calf
slurry
Pig
slurry
Poultry
slurry
49
177
157
210
180
65
58
57
73
84
12
29
22
26
33
39
39
39
47
47
28
8
57
44
7.5-8.0
7.8-8.0
-
-
-
7.0-7.7
8.4-8.8
9.0-9.4
14
for s t o r a g e o f the d r o p p i n g s from the battery s y s t e m s . In s u m m e r the results were
totally different: 22 d a y s in the battery s y s t e m s but o n l y 11 days in the m i d d e n s o f
the floor pen s y s t e m s ( 2 6 ) . M a n y m o r e i n v e s t i g a t i o n s h a v e c o n c e n t r a t e d o n survival
o f viruses in h u m a n s e w a g e or soil and h e r b a g e treated with s e w a g e and s e w a g e
sludge (6). T h e c a u s a t i v e a g e n t s o f m a n y viral diseases are excreted in t h e faeces and
urine. A n u m b e r o f viral d i s e a s e s , particularly viral enteritis, s w i n e vesicular disease
and f o o t a n d m o u t h d i s e a s e c o u l d be spread by slurry, a l t h o u g h such cases h a v e yet
to be reported (35). T h i s m a y be d u e to the fact that s o m e o f these diseases are
n o t i f i a b l e and t h e r e f o r e are subject t o specific and very stringent regulations w h i c h
e m p h a s i s e the control o f m o v e m e n t and utilisation o f animal excretions from infected
f a r m s , a n d usually are b a s e d o n biological ( ' d u n g p a c k i n g ' ) or c h e m i c a l d i s i n f e c t i o n
o f solid a n d liquid m a n u r e s .
Parasites
M a n y parasitic i n f e s t a t i o n s o f farm a n i m a l s are transmitted by ingestion o f
infective stages in materials, including pasture, contaminated with faeces. T h e viability
o f parasite eggs a n d larvae varies e n o r m o u s l y . In T a b l e s VIII a n d I X the tenacity
o f eggs o f Ascaris suum a n d eggs a n d larvae o f s t r o n g y l e n e m a t o d e s is listed. T h e
results indicate that especially Ascaris eggs and certain larval stages o f trichostrongylids
h a v e a rather l o n g survival t i m e a n d m a y give rise t o further i n f e s t a t i o n s o f a n i m a l s
after m a n u r e has been s p r e a d o n crops or pasture l a n d .
Helminth larvae are usually killed by c o m p o s t i n g o f faeces, but often remain viable
in slurry during storage. T h e y are resistant t o d i s i n f e c t i o n , and c o n c e n t r a t i o n s o f lime
in excess o f 5 % are required for effective d e c o n t a m i n a t i o n . Soil will still c o n t a i n
infective larvae o n e year after s p r e a d i n g o f c o n t a m i n a t e d slurry. E v e n p l o u g h i n g is
n o g u a r a n t e e o f d e s t r u c t i o n o f parasite eggs a n d larvae, a l t h o u g h in practice it is a
g o o d w a y o f r e d u c i n g their n u m b e r s . S t r o n g y l e and t r i c h o s t r o n g y l e eggs p l o u g h e d
i n t o soil c a n h a t c h a n d m i g r a t e t o the s u r f a c e , a n d infective t r i c h o s t r o n g y l e larvae
can survive in soil for m o r e than a year. Parasite eggs and larvae are destroyed during
ensilage as a result o f the high temperature and fall in p H , but they m a y remain viable
824
TABLE
VIII
Survival
of eggs of Ascaris suum
under different
environmental
conditions
(12)
Medium
Conditions
Dungstead manure
Liquid manure
Slurry
Slurry
Liquid manure
Pig manure
Sewage sludge
Sewage sludge and
pig manure
Cattle slurry
Cattle manure
At least 5 0 ° C / 4 0 ° C
In laboratory 8 ° C / 1 8 ° C
Storage pit, summer
Storage pit 4 ° C / 1 0 - 1 5 ° C / 1 8 - 2 6 ° C
Storage pit
Non-aerated storage pit
Dried
In storage pits
Liquid manure
Pig and cattle manure
Pig slurry
End of viability
(days)
Aerobic treatment 35-40° C
Storage pit 22-27°C/anaerobic
digester 55°C
Licom-system 53°C
Anaerobic digestion 52-54°C
Aerobic-thermophilic treatment 55°C
TABLE
Survival
19/63
85/65
75
28
365
365
1,825
810
14
57/1
2
1
1
IX
of eggs and larvae (L) of
(12)
Species
Medium
Conditions
Trichostrongylus
colubriformis
Cattle slurry
18°C/8°C
trichostrongylids
End of viability
(days)
Egg: 2 6 / 6 4
L, + L : 4 / 4
L : 37/76
2
3
Cooperia
punctata
18°C/8°C
Egg: 2 6 / 6 4
L, + L,: 4 / 4
L : 37/76
3
Ostertagia
ostertagi
Cattle slurry
+ Cooperia
oncophora
Trichostrongylids
Licom-system,
Licom-system,
Licom-system,
Licom-system,
20°C
20°C
3°C
3°C
summer 56°C
summer 56°C
winter 50°C
winter 50°C
Cattle slurry under slatted floor
Cattle slurry through the whole year
Cattle slurry through the whole year
* Possibilities for further development apparently not tested
Egg:
2
L:
4
Egg:
6
L:
6
Egg: 28
L:
28
Egg: 172
L:
160
3
3
3
3
90
92
28*
825
in hay for over a year. Fortunately parasitic infections are seldom fatal, except in
young animals, and the likely effect of spreading infected slurry is simply an increased
parasite burden on animals which are already infected (35).
EPIDEMIOLOGICAL CONSIDERATIONS
Conventional livestock units which employ bedding do not cause a special
epidemiological problem because, if proper management procedures are carried out
and enough straw is used, dungsteads develop temperatures high enough to destroy
pathogens that may be present. This can be seen from the results of a Swedish
researcher who found that in cattle herds with slurry systems infected with salmonellas,
3 5 % of slurry samples were positive for salmonellas, whereas in similar herds with
straw bedding and dungsteads, only 6 % of samples from solid manure were positive.
Five of these six positive samples, representing 6% of the study, were from the surface
of a deep litter bed, which can be regarded as a badly managed midden. F r o m this
point of view the result is even more favourable for solid m a n u r e (62).
The relative safety of this procedure is demonstrated by its being stipulated in
many countries in the official provisions of dung disinfection for the control and
eradication of notifiable infectious diseases, by means of what is called 'dung packing'.
After three weeks the dung is considered to be disinfected and can be used without
restriction.
Also in Sweden, it was found that in FYM dungsteads the temperatures were
usually below 30°C. The reason is that nowadays the 'average' Swedish cow excretes
daily 20 kg of faeces and 5 kg of urine more than 25 years ago, and that the a m o u n t
of straw for bedding used per cow and day has decreased from 4-6 kg to 0.5-1.5 kg.
Therefore the middens have too much moisture content and the composting process
becomes anaerobic, which results in a considerable reduction of the temperature, so
that the disinfection of such dung is no longer ensured (49). Since similar conditions
were found in German farms, a new technique for composting FYM was developed
which combines composting with use of granulated quicklime. By this method a
reliable disinfection of FYM can be achieved (9, 5 1 , 59).
As stored slurry is usually anaerobic, no spontaneous generation of heat that could
entail the destruction of pathogens will occur in that medium either in summer or
winter. Therefore slurries containing pathogens always pose a health hazard to the
animals of the particular farm and its neighbourhood. A certain degree of "selfdisinfection" during storage of slurry and the adverse influences of the environment
after spreading on pastures and arable land underlie the fact that there are few reports
about severe outbreaks of infectious diseases after utilisation of slurry, especially in
grazing animals (54).
As mentioned above, there is a slight possibility that the slurry of farms with
clinically healthy animals may contain certain pathogens (e.g. salmonellas), which
occur once or twice and then vanish again. To minimise this low risk the abovementioned expert group of the C E C elaborated Interim minimum guidelines in 1978
for the utilisation of " n o r m a l " slurries:
1. Slurry should be utilised on tillage crops (excluding crops
consumption), wherever possible.
for
fresh
826
2. If slurry is spread on grassland, then use on pasture for conservation, wherever
possible. If slurry is to be spread on grazing land, then:
a) store all slurry for a minimum of 60 days before spreading
b) allow 30 days before grazing
c) graze with adult or non-susceptible animals.
3. Utilisation of slurry should be related to plant nutrient requirements (1).
Several years later the same expert group discussed these guidelines again and
approved them. It was found that they were of general application but should be
modified according to circumstances, e.g. notifiable diseases where the procedures
are laid down by law, particularly resistant pathogens like some parasites, transport
of slurry to " s l u r r y / m a n u r e b a n k s " , and seasonal effects on survival of pathogens.
Some recommendations have thus been added to the minimum guidelines:
4. Whereas storing slurry for 60 days in summer may be adequate, slurry produced
in winter should be stored for at least 90 days. Storage for these periods requires
two storage tanks. Prior to its removal, slurry inside animal houses has, of course,
all the potential dangers of untreated slurry for stock in contact with it. Slurry from
copper-supplemented pigs may be harmful to sheep grazing treated pastures.
5. Despite the wide variety of infective agents - bacteria, viruses, fungi and
parasites - that can be present in slurry, there are few published records of disease
transmission to animals or man through slurry, treated or untreated. The risk does
exist, however, and it can be reduced to acceptable proportions if care is taken to
treat and use slurry according to the minimum guidelines above.
6. Evidence was presented at the workshop to suggest that the guidelines are not
sufficiently well known to farmers. Each country should ensure that steps are taken
to make their contents widely known through the media - print, radio and television
- as well as at agricultural meetings, shows and markets.
7. Despite the relative lack of unequivocal evidence that slurry transmits disease
to man or livestock, it is recommended that the existing guidelines should be adapted
to meet the particular needs of individual countries. Further research is needed:
a) to determine the levels of contamination of pasture with pathogenic organisms
that may result from treating it with slurry; and
b) to evaluate methods for the disinfection of slurry without decreasing its value
as a fertilising agent.
8. The workshop agreed that future activities should concentrate on communicable
diseases rather than manure-associated problems. In accordance with the C E C , special
emphasis should be placed on campylobacteriosis as an emerging disease and also
on listeriosis. Attention should also be given to other zoonoses (2).
Since the risks of infection associated with the spreading of slurry on farmland
have not yet been clearly established, the safest procedure will be to aim at the best
possible decontamination of infected slurry during the storage phase, e.g. before
spreading. To achieve this purpose the decimal reduction time ( T ) for given
pathogens under specific storage conditions has been used to calculate the holding
time in batch storage of slurries (21).
90
827
S u c h use o f T90-values will require:
1. K n o w l e d g e o f t h e initial c o n c e n t r a t i o n in t h e slurry o f the p a t h o g e n i c a g e n t s
concerned.
2. A d e c i s i o n as t o w h a t s h o u l d be regarded as the " a c c e p t a b l e final l e v e l " o f
the p a t h o g e n s in the slurry after b a t c h s t o r a g e .
3. T h e presence o f m o r e than o n e storage facility o n a farm as a s a f e g u a r d against
the i n t r o d u c t i o n o f freshly i n f e c t e d slurry d u r i n g batch s t o r a g e .
A l t h o u g h o u r k n o w l e d g e is s c a n t y regarding the initial c o n c e n t r a t i o n s o f
p o t e n t i a l l y p a t h o g e n i c bacteria in fresh slurry, several reports are available o n the
c o n c e n t r a t i o n o f certain bacteria. S o far, n o d e c i s i o n has a p p a r e n t l y b e e n reached
with respect t o an " a c c e p t a b l e final l e v e l " o f v a r i o u s p a t h o g e n i c bacteria in relation
to d e c o n t a m i n a t i o n o f slurry.
R e g a r d i n g Salmonella
bacteria, the view m i g h t be t a k e n for practical p u r p o s e s
that a reduction in n u m b e r s t o a level w h e r e , using special f a v o u r a b l e p r o p a g a t i o n
m e t h o d s in the l a b o r a t o r y , for e x a m p l e , not o n e Salmonella
c o u l d be d e m o n s t r a t e d
per 10 ml o f slurry (i.e. log10 to the bacterial c o n c e n t r a t i o n : < - l ) w o u l d be
a c c e p t a b l e . In t h e o r y , o f c o u r s e , it c a n n o t be e x c l u d e d that, under special
circumstances, even minute a m o u n t s o f pathogens m a y give rise to cross c o n t a m i n a t i o n
a n d / o r a risk o f i n f e c t i o n in a n i m a l s and m a n .
D e s p i t e the o b v i o u s l i m i t a t i o n s in the applicability o f these results, their clear
t e n d e n c i e s and relative u n i f o r m i t y within the individual bacterial species and
e x p e r i m e n t a l g r o u p s give reason to a s s u m e that the T90-values f o u n d m a y be used
p r o v i s i o n a l l y as a g u i d e l i n e for r e c o m m e n d e d h o l d i n g times for batch s t o r a g e o f
infected slurry (21).
A n e x a m p l e for the c a l c u l a t i o n o f required r e d u c t i o n levels is g i v e n in T a b l e X .
TABLE
X
Storage time for slurry infected with S. typhimurium,
calculated on the basis of T90- values for anaerobic and aerobic
storage in winter and in summer
(21)
Storage time in weeks
Winter T90
Summer T
anaerobic
aerobic
anaerobic
aerobic
x 5.9
x 1.6
X
2.0
x 0.6
Required
reduction
9 0
4
From 1 0 / m l
to < 1/10 ml
30
8
10
3
From lOVml
to < 1/10 ml
12
3-4
4
1-2
Similarly, Tyo-values for other p a t h o g e n i c agents m a y p r o v i d e an a p p r o x i m a t e
i n d i c a t i o n o f r e c o m m e n d e d b a t c h s t o r a g e t i m e s for infected slurry in v a r i o u s
situations.
828
These calculations may provide a basis for further consideration of needs and
possibilities in setting up general or special guidelines for decontamination of infected
slurry by batch storage. Reflections on ecological and technical-economic aspects of
this and other possible decontamination methods should also be included in such
considerations.
Further investigations with this method are also necessary to prove its applicability
to slurries infected with viruses and, perhaps, parasites.
In the case of parasitic diseases, the epidemiological situation may be somewhat
different from that of bacterial and viral diseases. Tables IV, V and VI provide lists
of parasites which may occur in animal effluents in Europe. They require modification
for parasitological situations in other parts of the world. In contrast to the
epidemiological facts of infectious diseases caused by bacteria and viruses, parasites
may need more than one host for their final development and they may have several
larval stages, each differing in sensitivity to environmental influences. Furthermore,
certain measures make it possible to interrupt chains of infection for parasites without
disinfection of the inanimate vector, e.g. utilisation of pig slurry on cattle pastures
and cattle slurry on pig pastures.
A detailed account of the complex epidemiology of parasitic diseases is impossible
in the context of the agricultural utilisation of manure and slurry. However, the
recommendations in Table XI are based on the viability of some important parasitic
eggs and larvae under certain environmental conditions listed in Tables VIII
and IX (12).
TABLE
Hygienically
XI
safe utilisation of manure and slurry in
from a parasitological point of view
agriculture
(12)
Medium
Stockpiled manure
Fresh cattle slurry
Fresh pig slurry
Stored cattle slurry
Stored pig slurry
Poultry manure
-
Cultivated crops
Vegetables Potatoes Sugar Corn Grain Green Meadow Pasture
beets
fodder
+
--
+
+
+
+
+
+
+
+
+!
+!
+!
+!
+
+
+!
+!
+
+
+
+
+
+
+
+
+
+
+
+
—
-
—
+!
+!
+
—
—
—
+!
+!
+
i
i
+
Not applicable
!
I f possible insert one cut for silage or hay winning
+ ! After topdressing with slurry do not feed fresh (dry or silage beforehand); avoid direct harvesting from the soil
+ Applicable without restrictions
In some countries with very high densities of livestock in a given area, it is becoming
common to store slurry jointly in large tanks, each with a capacity of several thousand
cubic metres. This development is subsidised by the governments. These joint storage
facilities raise the risks of disease spread, because the pathogen content of the
829
individual slurry is not k n o w n and the slurry mixture is distributed to all members
of the facility. Even under very strict conditions it is not possible to eliminate this
hygiene risk completely. Farms involved in such a joint storage system must therefore
be willing to bear an acceptable risk. For this new development, important
recommendations have been issued recently (32).
In cases of notifiable diseases, all countries have special legal regulations on how
the excreta and manure should be disinfected and handled thereafter. Solid manures
are usually incinerated or composted, and slurries chemically disinfected. Since many
of the chemicals which are used for slurry disinfection can be toxic for soil, plants
or water, some ecologically desirable chemicals are listed in Table X I I .
TABLE
Suitable
XII
chemicals for the disinfection
Disinfectant
Dosage *
(kg/m )
Reaction time
(days)
9-15
25-40
8-12
40
4
4
4
4
3
Formalin
40% calcium hydroxide suspension
Sodium hydroxide (NaOH)
Peracetic acid 15% **
of slurry
* Lower value: effective against enveloped viruses
Upper value: effective against bacteria
** Only to be recommended for disinfection o f small amounts, due to the heavy formation o f foam
Some larger livestock enterprises use anaerobic digestion of slurry to produce
biogas. Most of these biogas plants are operated at mesophilic temperatures in the
range of 30-35°C and the operators believe that pathogens are destroyed by the
anaerobic digestion process. This opinion must be corrected because the mesophilic
temperatures are not sufficient to destroy the pathogens. Only in the thermophilic
range of 55°C can it be expected that the effluent of the digesters is disinfected.
Therefore the effluent of biogas plants with mesophilic digestion has the same
hygienic status as any slurry stored in a tank (30, 53, 66).
Further ways of disinfecting m a n u r e by biological, biological-technical and
chemical methods have been proposed, along with discussions on how to protect the
environment from chemical disinfectants (3, 7, 40, 58, 60).
P A T H O G E N I C AGENTS IN SEWAGE SLUDGE
Bacteria
As mentioned in the introduction, most pathogens enter sewage treatment plants
from sewers. Their range depends largely on the epidemiological conditions in the
particular region.
830
Table XIII lists the bacterial pathogens which may be encountered in the central
part of Europe and which have been isolated from wastewater already. The table
contains all current bacteria of greater or lesser importance for the epidemiology of
infectious bacterial diseases. Although a given germ may be missing from this list,
its occurrence in sewage can still not be excluded. It may be a constant inhabitant
of the wastewater in certain regions (11, 14, 22, 31).
TABLE
Bacterial
pathogens
XIII
to be expected
in sewage
(14, 39, 64)
and sewage
sludge
Primary pathogenic
Secondary pathogenic
Salmonella s p p .
Shigella s p p .
Escherichia coli
Pseudomonas
aeruginosa
Yersinia
enterocolitica
Clostridium
perfringens
Clostridium
botulinum
Bacillus anthracis
Listeria
monocytogenes
Vibrio cholerae
Mycobacterium s p p .
Leptospira s p p .
Campylobacter s p p .
Staphylococcus
Streptococcus
Escherichia
Klebsiella
Enterobacter
Serratia
Citrobacter
Proteus
Providencia
Viruses
In the case of viruses t o o , a compilation of their regional range must vary. It is
known that more than 100 viruses are excreted from humans in the faeces. Nearly
every day new ones are added, some of which still await identification. They pass
through the digestive tract in a typical manner and are excreted by infected persons
in large a m o u n t s . The clinical signs which they provoke may have trivial to severe
or even fatal consequences (22, 23, 24, 4 1 , 63, 64).
A combination of increased awareness regarding the environment, improvements
in laboratory techniques and the discovery of new viruses which are pathogenic for
humans has led to an intensification of scientific activities, reflected in several hundred
scientific publications on excreted viruses. There can be no doubt that a compilation
of viruses excreted by humans (Table XIV) will undergo many changes in the coming
years as a result of the characterisation of new viral agents and of a further
differentiation of taxonomy. All of these viruses can, with regional differences, appear
in the sewage.
Viruses are also excreted with the faeces of animals, and viruses occurring in birds,
dogs and cats can reach the sewers. Equally, it cannot be excluded that viruses derived
831
TABLE
Viruses
Virus group
excreted
by humans which
in sewage and sewage
(23, 41 modified)
Number of
types
Enteroviruses
Poliovirus
Coxsackievirus A
3
24
Coxsackievirus B
6
Echovirus
New enteroviruses
Adenovirus
Reovirus
XIV
34
4
30
3
Hepatitis A virus
can be
sludge
expected
Diseases or symptoms caused
Poliomyelitis, meningitis, fever
Herpangina, respiratory disease, meningitis,
fever
Myocarditis, congenital heart anomalies,
meningitis, respiratory disease,
pleurodynia, rash, fever
Meningitis, respiratory disease, rash,
diarrhoea, fever
Meningitis, encephalitis, respiratory disease,
acute haemorrhagic conjunctivitis, fever
Respiratory disease, eye infections
Not clearly established
Infectious hepatitis
Rotavirus
?
Astrovirus
?
Calicivirus
7
Coronavirus
Vomiting and diarrhoea
7
Vomiting and diarrhoea
Common cold
Norwalk agent and other
small round viruses
7
Vomiting and diarrhoea
Adeno-associated virus
4
Not clearly established but associated with
respiratory disease in children
from livestock may enter wastewater in various other ways. It is known that h u m a n
viruses occur in domestic animals (Table XV). Unfortunately it remains an open
question whether and to what extent the agricultural utilisation of municipal sewage
and sludge contributes to this transmission.
Parasites
Parasitic infestations of humans and animals play a certain role. Under the
conditions of Central Europe the number of parasites is rather limited compared with
subtropical and tropical areas, where parasitic diseases may have top priority in
frequency and importance.
The range of parasites in Central Europe has certainly been enlarged by the influx
of immigrant workers, refugees and resettled persons from various regions of the
globe. But there are no indications that parasitoses have been transmitted to the native
population to any considerable extent. Table XVI does not contain 'exotic' parasites
but is restricted to those which belong to the usual range in Central Europe (29, 64).
832
TABLE X V
Human
viruses
associated
with
(41)
domestic
animals
Recovered from
Virus identity
Cattle
Enteric viruses
Poliovirus 1
Coxsackievirus A5
A6
A9
A10
A20
B3
B5
Echovirus 2
6
8
10
19
Reovirus 1, 2, 3
Respiratory viruses
Influenza virus A 2
Mumps virus
Cats
Dogs
Goat
Horse
+
+
+
+
Swine
Infection
produced *
Cattle
+
+
+
+
+
+
+
+
+
+
+
Swine
Dogs
Dogs
Dogs
+
+
+
+
+
Cats
+
+
Cattle, dogs,
cats
+
+
+
+
Cats, swine
Dogs
* Infection determined by clinical or serological evidence
Due t o biological peculiarities in the life cycle of most parasites, h u m a n s and animals
play a similarly i m p o r t a n t role as intermediate and final h o s t s . The developing and
final stages of these parasites reach the sewage directly from faeces.
TABLE X V I
Parasites
to be expected
in sewage
(29, 64)
and sewage
sludge
Protozoa
Cestodes
Nematodes
Entamoeba
histolytica
Giardia lamblia
Toxoplasma
gondii
Sarcocystis spp.
Taenia saginata
Taenia solium
Diphyllobothrium
latum
Echinococcus
granulosus
Ascaris
lumbricoides
Ancylostoma
duodenale
Toxocara canis
Toxocara cati
Trichuris
trichiura
Yeasts and fungi
P a t h o g e n i c yeasts a n d fungi are p r o b a b l y of less i m p o r t a n c e for the
epidemiological discussions of sludge utilisation (Table XVII). They can infect humans
833
and animals, cause allergic diseases a n d / o r produce mycotoxins. But there have also
been suggestions that one should not underestimate the significance of this group
of micro-organisms for public health, especially in connection with the agricultural
utilisation of sewage and sewage sludge. At present, the significance of these microbes
in public health has not yet been properly estimated (10, 56).
TABLE
XVII
Pathogenic yeasts and fungi to be expected
in sewage and sewage sludge
(10, 56)
Yeasts
Fungi
Candida
albicans
Candida krusei
Candida
tropicalis
Candida
guillermondii
Cryplococcus
neoformans
Trichosporon
Aspergillus s p p .
Aspergillus
fumigatus
Phialophora
richardsii
Geotrichum
candidum
Trichophyton s p p .
Epidermophyton
spp.
Effects o f s e w a g e t r e a t m e n t o n p a t h o g e n s
In line with our present knowledge of the effects of sewage treatment on pathogens
in wastewater, it can be stated that most pathogenic agents can survive the treatment
processes of wastewater, but in reduced numbers. Some of them are adsorbed to or
enclosed in faecal particles and remain within sludge during the various sedimentation
processes. Therefore sewage sludge is rightly described as a concentrate of pathogens
(11, 15, 22, 23, 31).
S U R V I V A L O F P A T H O G E N S IN T H E E N V I R O N M E N T
EPIDEMIOLOGICAL SIGNIFICANCE
Given that in many countries between 4 0 % and 8 0 % of sludge is disposed of in
agriculture, this is a very serious aspect. The problem is all the more serious if one
considers the viability of s a l m o n e l l a s in greater detail. In an extensive survey,
303 samples were examined after digested sludge was distributed on agricultural land
from tankwagons in the usual way. Salmonellas were found on grass in 2 6 % of all
samples taken until the fifth week. The samples were negative only after six weeks.
In 5 9 % of the samples from topsoil, salmonellas persisted until the tenth week. In
the crust of sludge which can be found during dry weather periods on pastures for
several weeks (when the sludge is not tilled into the grass and the topsoil), 8 4 % of
all samples taken until the sixteenth week contained salmonellas (55).
In our own experiments, the survival of salmonellas and Ascaris
ova was
investigated during sludge utilisation in forestry. Salmonella senftenberg
survived on
and in the soil after a single application of infected sludge in summer to experimental
plots of eleven different forest stands between 424 and 820 days. After application
of sludge in winter the survival times were between 104 and 350 days. Ascaris ova
did not survive for longer than 78 to 107 days (61).
834
Experience in Switzerland has shown that such investigations are important. In
that country the farmers favour the use of sewage sludge on their pastures, and in
many cases they store the sludge from sewage treatment plants together with liquid
manure from their pigs or cattle in tanks on the farm before spreading it on pastures.
An epidemiological causal relationship was found between the agricultural utilisation
of municipal sewage sludge and salmonella infections in cattle herds. In an analysis
of nearly 27,000 cases within ten years (Fig. 1), there was unequivocal accumulation
of infections with salmonellas during the green fodder period. The first increase of
infections was traced to the spreading of sludge during the winter and the culmination
of cases in August/September to the massive spreading of sludge after hay making
and the subsequent short mowing intervals. This investigation shows that it is a
perversion of hygienic principles for more and more sewage to be collected and treated
with more and more sophisticated methods in plants if the sludge - which consists
mainly of human faeces — is then distributed over large areas without being disinfected
(11).
FIG.
1
S e a s o n a l distribution o f s a l m o n e l l a i s o l a t i o n s f r o m dairy cattle
approx. 27,000 samples (11)
The parasitic eggs in sludge create problems in areas with pasture farming because
they survive on soil and plants for many months. It is known that Ascaris eggs survived
for two years in soil which had been irrigated with sewage. They were even found
on plants which had been irrigated with chlorinated sewage.
Our knowledge of the behaviour of viruses on plants and in soil is less adequate
than in the case of bacteria. But it appears that the viability of viruses in soil is of
the same order as in sewage, where they survive for over 100 days. The few available
investigations were made with sewage. In 2 of 25 samples, viable enterovirus was
found on plants irrigated with sewage. In addition, poliovirus I survived on sewageirrigated vegetables for 36 days. The same virus survived after artificial infection on
835
plants of cabbage, pepper and tomatoes for 4, 12 and 18 days respectively. Two other
groups of researchers have shown that viruses may penetrate into the root system
of plants and then into the stem. They concluded that internal as well as external
contamination of plants is possible (22, 23, 25, 4 1 , 63).
Of all the pathogens which survive the wastewater purification processes, parasite
ova have the longest survival times in the environment. Eggs of Ascaris suum survive
up to fourteen years in soil, others between several months and six years. They also
tend to be resistant to chemicals, e.g. 2 0 % formalin for two years, but are killed
by temperatures above 55°C in approximately ten minutes. Sewage sludge and faecal
excretions are the only way by which parasites specific for h u m a n beings can reach
the environment (29, 56, 65).
In the case of h u m a n infections with Taenia saginata the circumstances are similar
to those of salmonellosis. The agricultural utilisation of sewage sludge and sewage
is only one link in the epidemiological chain. But everything possible should still be
done to break such a link and to work on further links like the sanitation of
campgrounds, recreation areas, parking lots and picnic areas on motorways.
In conclusion, it can be stated that pathogens occur in sewage and that they are
enriched in sewage sludge, which raises concern not only for public health but also
for domestic animals and livestock. This has been shown in Switzerland where
fertilisation of pastures with sewage sludge which has not been disinfected resulted
in a spread of salmonellosis in dairy cows. These animals are therefore a link in the
infection cycle of h u m a n and animal salmonelloses. The economic losses caused by
salmonellosis in the western states of the Federal Republic of Germany in 1977 were
calculated for the sector of human medicine as 107 million DM (approx.
US$ 59 million) and for livestock (cattle, calves, pigs and poultry) another 132 million
DM (approx. US$ 73 million) (38). For damage caused by viruses and parasites in
sewage sludge no figures are available. Connections have been proved only for Taenia
saginata. In any case, the agricultural utilisation of hygienically dubious sewage sludge
poses a risk for the whole national economy. This can be prevented only by sanitation
measures like disinfection of sludge prior to its utilisation in agriculture.
MEASURES FOR SANITATION OF SEWAGE S L U D G E
To prevent damage to agriculture and public health by the utilisation of hygienically
dubious sewage sludge, the C E C issued a "Directive on the use of sewage sludge in
agriculture" on 12 J u n e 1986. Within three years Member States had to apply the
laws, regulations and administrative provisions contained in this Directive (16).
In the Federal Republic of Germany the government issued an " O r d i n a n c e on
sewage s l u d g e " which went into effect on 1 April 1983. This ordinance stipulates
that the use of sewage sludge on pasture and forage land is no longer allowed if it
is not "hygienically s a f e " (sanitised, disinfected) (4). Since the legislators did not
define the term "hygienically s a f e " , a working group was formed to elaborate a
definition and also to define the appropriate technologies for achieving "hygienically
safe" sludge. These definitions are presented below as an example, because they are
more precise and more detailed than in other countries.
836
Definition
To be sanitised (hygienically safe) according to Paragraph 2, Article 2 of the
German " O r d i n a n c e on sewage sludge", a sludge has lo be treated by a sanitation
process for which appropriate investigation has proved that:
a) the number of indigenous or seeded salmonellas is reduced by at leasl four
powers of ten (logs); and
h) indigenous or seeded eggs of Ascaris are rendered non-infectious;
furthermore, the sanitation process must result in a sewage sludge in one gram of
which, directly after the treatment,
c) no salmonellas can be detected; and
ilj not more than 1,000 Enterobacteriaceae can be detected.
In addition to these forms of System Control (a, b) and Process Control (c, d),
a continuous Operational Control is provided for. Supervision is required so that
the process conditions, which are necessary for the effective sanitation of the sewage
sludge, are continuously observed. The Operational Control is performed In
controllable continuous recording of the process conditions which are representative
and specific for each sanitation system.
Sanitation technologies
According to the above definitions, six established technologies have been
evaluated from the aspect of ensured sanitation.
/. Sludge pasteurisation
- Process
(pre-pasteurisation)
description
During pasteurisation raw sewage sludge is to be heated to temperatures
below 100°C, but at least 65°C, for at least 30 minutes. This is done prior to a
stabilisation process and is known as pre-pasteurisation. Comminution of larger
particles before the pasteurisation process is also necessary. To ensure that all sludge
particles arc exposed to the reaction temperature and time, their size may not exceed
5 mm.
Other temperature/time combinations can also be used, for example: 70°C for
25 min, 75°C for 20 min or 80°C for 10 min.
Even at higher temperatures a reaction time of less than ten minutes is not allowed.
— Process
control
The process conditions of the technology, especially:
a) the temperature in the reactor; and
b) the reaction time
are to be recorded by continuous plotting.
837
2. Aerobic-thermophilic
stabilisation
of sludge
(ATS)
- Process
description
In the course of the ATS process caused by air (oxygen) supply, exothermal
microbial degradation and metabolic processes result in a rise of temperature and
of pH up to values of about 8. Provided that the reaction vessel is well insulated,
that the air supply is correctly calculated and that the sludge has a sufficient
concentration of organic dry matter, temperatures can be reached which provide for
stabilisation and also sanitation of the sludge.
ATS processes should be operated in two-stage reactors (two vessels connected
in series) at least, to avoid the microbiological disadvantages of hydraulic shortcircuits. Detention times of at least, five days are required when both reactors have
the same volume.
Based on the batch-type operation (e.g. one hour feeding per day) and 23 hours
stabilisation (reaction time) and of the temporary decrease of temperature inevitably
connected with this type of operation, the following reaction times and temperatures
are necessary: 23 h at 50 C. 10 h at 55°C or 4 h at 60"C.
Process control
To supervise the process conditions, the following parameters are to be recorded
by continuous plotting:
a) the temperatures and their reaction times in the reactors in at least two positions
with recording instruments
b) the pH values of the raw sludge and of the effluent of the ATS process
c) the daily sludge volume flow, from which the reaction time can be calculated
using known volumes of the reactors.
3. Aerobic-thermophilic
stabilisation
of sludge (A TS) with subsequent
anaerobic
digestion
- Process
description
In the aerobic-thermophilic first stage the sludge is sanitised. The sanitation is
ensured by sufficiently high temperatures in the sludge, which can be produced by
additional heating with extraneous energy and exothermic microbial processes during
the partial stabilisation. In the course of subsequent anaerobic, mesophilic or
thermophilic stabilisation, the necessary security of the sanitation process is ensured.
By treatment in this two-stage process the sludge is considered as sanitised if in
the first stage either the conditions of pre-pasteurisation are fulfilled or if the reaction
temperature of at least 60°C is kept continuously for at least four hours. During these
four hours no raw sludge may be added. In the second (anaerobic) stage a process
temperature of at least 30°C must be maintained.
- Process control
To supervise the process conditions, the following parameters are to be recorded
by continuous plotting:
a) in
bj in
the first stage:
the temperature in two positions
the reaction time
the second stage: the temperature.
838
4. Treatment
of sludge with lime as Ca(OH)2 (lime hydrate,
— Process
slaked
lime)
description
C a ( 0 H ) 2 (calcium hydroxide, lime hydrate, slaked lime) is used for sanitation of
liquid sludge before use, or for conditioning sludge before dewatering. In both cases
the addition of lime increases the p H as a function of the a m o u n t of lime added and
the properties of the sludge. Wet addition of lime as a suspension should be preferred
to lime powder because of the better mixing and sanitising effect.
The initial p H of the lime-sludge mixture must be at least 12.6 and the mixture
must be stored for at least three months (reaction time) before use.
— Process
control
T o supervise the process conditions of each batch produced, the following
parameters are to be recorded:
a) the initial p H value
h) the reaction time.
5. Treatment
of sludge with lime as CaO (quicklime,
— Process
unslaked
lime)
description
By adding CaO to dewatered sludge, the lime-sludge mixture is heated to
temperatures between 55°C and 70°C by exothermic reaction of the calcium oxide
with available water, when the insulation is adequate. The initial pH of the limesludge mixture must reach at least 12.6 and the temperature of the whole mixture
at least 55°C for two h o u r s .
— Process
control
T o supervise the process conditions of each batch produced, the following
parameters are to be recorded:
a) the mixture ratio of lime and dry matter of sludge
b) the initial p H of the lime-sludge mixture
c) the temperature at least two hours after mixing in three positions, one of which
must be in the outer zone of the mixture.
6. Composting
— Process
of sludge in
windrows
description
The sanitation of sludge by composting in windrows with bulking material (e.g.
municipal refuse, straw, sawdust, wood shavings) is caused by the heat generated
during composting by microbial processes. Besides this temperature and the reaction
time, microbial metabolic substances having antibiotic effects are also of importance.
For the sanitising effect to occur, it is necessary to have a sufficient aeration of
the mixture of sludge and bulking material by technical means, for example, by turning
the heaps or by forced aeration (for windrows or piles which are not turned). The
effective temperatures must prevail in each part of the composting material for the
necessary reaction time.
839
The initial water content of the composting material must be 40-60% and the
reaction temperature in the heap at least 55°C for three weeks.
- Process
control
To supervise the process conditions for each windrow, the following parameters
are to be recorded:
a) the initial water content of the mixture
b) the temperature measured at least daily in three positions and at different
distances from the surface of the heap; one position in the central part and one in
the outer zone
c) the composting time and turning (number, date).
7. Composting
- Process
of sludge in
reactors
description
The sanitising of sludge by composting in reactors (in-vessel composting) with
bulking material (e.g. sawdust, wood shavings, bark, reflux material) is caused by
the heat generated during composting by microbial processes. Besides temperature
and reaction time, microbial metabolic substances having antibiotic effects are also
of importance.
For the sanitising effect to occur, it is necessary to have sufficient aeration
the mixture of sludge and bulking material by technical means. The steadiness
desired temperature profiles in the reactors can be influenced and controlled
techniques of aeration, filling and emptying. Effective temperatures must prevail
each part of the composting material for the necessary reaction time.
of
of
by
in
The initial water content of the composting material should not exceed 7 0 % . The
complete mixture should be exposed to a temperature of at least 55 °C during a passage
time through the reactor of at least ten days. In addition, the composting material
should not pass the " h o t z o n e " with a temperature of at least 65°C sooner than in
48 h o u r s .
T h e reactor passage shall be followed by a phase of curing the material in heaps
or piles for at least two weeks with at least one turning, or in a second reactor to
provide the necessary security for the sanitation process.
Successful sanitation depends to a large extent on an undisturbed operation of
the composting process. W h e n disturbances of operations are connected with a
decrease in temperature, the batch of compost must either be used as reflux material
and thus pass the reactor a second time, or must be composted again in a heap under
the conditions described for composting of sludge in heaps.
- Process
control
T o supervise the process conditions, the following parameters are to be recorded:
a) the initial water content of the mixture
b) the temperature in at least three positions: one before the compost reaches the
" h o t z o n e " , one in the " h o t z o n e " and at least one in the peripheral zone of the reactor
840
c) the storage time and turning of the curing heaps (date, number) or reaction
time in the second reactor
d) disturbances of operations (causes, duration).
To make it easier to assess the sanitising effect of thermal technologies, the
time/temperature combinations are summarised in Fig. 2. These ensure the destruction
of some selected pathogens. The lines in the diagram represent the carefully evaluated
upper limits for the thermal destruction of the mentioned pathogen, which requires
estimation of the particular time/temperature combinations. A sanitation technology
whose time/temperature effects lie in the "safety z o n e " should destroy all pathogens
in the treated sludge. The combinations shown in Fig. 2 which mark the border of the
"safety z o n e " are at least: one hour at > 6 2 ° C , one day at > 5 0 ° C or one week at
> 4 6 ° C . For further details concerning other pathogens see the original publication (25).
FIG. 2
Effect o f t e m p e r a t u r e a n d time o n s o m e selected p a t h o g e n s isolated
f r o m s e w a g e s l u d g e and septic t a n k s
(25)
841
SURVIE DES MICRO-ORGANISMES P A T H O G È N E S ET DES PARASITES D A N S LES
DÉJECTIONS A N I M A L E S , LE FUMIER ET LES BOUES D ' É P U R A T I O N . - D . Strauch.
Résumé: De nombreux agents pathogènes responsables de maladies
infectieuses
sont présents dans les sécrétions ou les déjections animales, fécales ou autres.
Certains agents sont également excrétés par des animaux cliniquement
sains,
ou victimes d'infections latentes, dans le cas de maladies contagieuses à étiologie
multiple. Dans les différents élevages, les germes pathogènes
gagnent les
installations qui collectent les excréments en vue de leur utilisation
comme
fertilisants, sous forme de fumier ou de lisier. Dans ces conditions, les éleveurs
ne sont pas conscients de la présence des germes pathogènes dans le fumier,
et ne prennent donc pas les mesures nécessaires à la prévention des maladies
qu'entraîne son utilisation. Les germes pathogènes ne survivent que difficilement
dans le fumier de ferme, du fait des réactions thermiques,
biologiques
et
biochimiques qui se produisent au sein de ces matières organiques. Par contre,
dans le cas du lisier la température reste stable et l'activité biochimique
réduite,
ce qui favorise la survie des germes pathogènes. Il est donc nécessaire de prendre
certaines précautions lors de l'utilisation du fumier et du lisier comme engrais.
L'utilisation par les agriculteurs des boues provenant des eaux usées des
agglomérations
urbaines est courante dans de nombreux pays. Ces boues
véhiculent cependant des germes pathogènes d'origine humaine, qui ne seront
pas totalement
éliminés par les procédés
d'épuration.
Au contraire,
la
sédimentation
des dépôts favorisera leur multiplication.
Afin de protéger le
bétail, Il est donc nécessaire de traiter les boues potentiellement
contaminées
avant de les utiliser comme engrais dans les fermes.
L'auteur décrit les
conséquences épidémiologiques
de l'utilisation des boues d'épuration à des fins
agricoles, ainsi que tes traitements possibles de ces boues.
MOTS-CLÉS : Bactéries - Bétail - Boues d'épuration - Désinfection Epidémiologie - Fumier - Lisier - Parasites - Résistance - Virus.
SUPERVIVENCIA D E MICROORGANISMOS P A T Ó G E N O S Y P A R Á S I T O S EN
DEYECCIONES A N I M A L E S , ESTIÉRCOL Y LODOS D E A L B A Ñ A L . - D . Strauch.
Resumen: Los agentes causantes de numerosas enfermedades infecciosas son
excretados por vía fecal y otras secreciones del organismo. Algunos
agentes
patógenos también son excretados por animales clínicamente sanos o que sufren
de infecciones latentes, en caso de enfermedades
transmisibles de etiología
múltiple. En todos los establecimientos pecuarios, los patógenos llegan al suelo
a través de ¡as instalaciones que recogen el estiércol en forma sólida o líquida.
En tales condiciones, los productores no se clan cuenta de que el estiércol puede
contener agentes patógenos y no toman las precauciones necesarias para evitar
la difusión de enfermedades a través de su uso. Los patógenos no sobreviven
mucho tiempo en el estiércol almacenado en las granjas, debido a las reacciones
térmicas, biológicas y bioquímicas que se producen en estas materias orgánicas.
Sin embargo, en el caso del estiércol licuado, la temperatura es estable y la
actividad bioquímica reducida, lo que favorece la supervivencia de los gérmenes
patógenos. Por lo tanto, para evitar la difusión de enfermedades por el uso
de estiércol como fertilizante,
es necesario tomar ciertas
precauciones.
El uso agrícola de ios lodos de albañal urbano es corriente en muchos países,
pero dichos lodos contienen agentes patógenos de origen humano que no llegan
842
a ser destruidos totalmente por los procedimientos
de depuración, sino que,
por el contrario, son multiplicados por la sedimentación de los depósitos.
Por
consiguiente, para proteger al ganado, es necesario tratar los lodos que puedan
estar contaminados antes de utilizarlos como fertilizantes o abonos en las granjas.
El autor describe las consecuencias epidemiológicas del uso agrícola de los lodos,
así como las tecnologías disponibles para el tratamiento de los mismos.
P A L A B R A S CLAVE: Bacterias - Desinfección - Epidemiología - Estiércol Estiércol licuado - Ganado - Lodos de albañal - Parásitos - Resistencia - Virus.
*
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