Land disposal of mixed human and animal wastes: A review

Waste Management & Research (1989) 7, 121-134

LAND DISPOSAL OF MIXED HUMAN AND ANIMAL WASTES : A REVIEW Jill A . Snowdon*t, Dean O . Cliver*t and James C . Converse§ (Received September 1987, revised September 1988) Combining septic tank effluent and animal wastes (mixed wastes) for eventual application to land is being proposed as an alternative wastewater disposal system . Both types of waste are spread on land separately, and private practice may be to mix and spread them together, but in most of the United States mixing of these wastes for land disposal is illegal . No research has been done to assess the hazards associated with spreading mixed wastes on land . The concern is with the impact on public health of adding septic tank effluent to animal wastes for disposal as animal wastes . The effects of pathogens already present in animal waste are presumably allowed for in current U .S . regulations . Pathogens in mixed wastes include viruses, bacteria and parasites . Viruses are not always present in on-site waste disposal systems, but when present are in high numbers . Most viral particles will pass through the septic tank and will remain viable . Transmission will be prevented if these particles are retained in soil or other solids until any of several factors deprive them of infectivity . As animals are the chief reservoir of most enteric bacteria that are pathogenic to man, no additional hazards from bacteria are expected in a mixed waste system . Some parasite eggs and cysts will settle into the bottom of the septic tank, but significant numbers will pass through and will remain viable . Retention with solids will minimize transmission through food and water . In all instances it is important to match land use and waste disposal carefully . Key Words-septic tank effluent, wastewater, on-site waste disposal, fecal pathogens, human enteric viruses, environmental virology, parasites, bacteria, U .S .A .

1 . Introduction Alternative wastewater disposal systems need to be developed where local geological conditions preclude conventional septic tank percolation systems . Examples include : the rocky shoreline of the Great Lakes ; land with creviced bedrock near its surface ; land with high water tables ; or land where the soil contains large amounts of clay. The spreading of excreta on land is a common disposal practice, especially for animal waste . Dairy farmers, for example, commonly store barnyard waste and water used for cleaning in earthen storage basins (pits which may be lined with clay or cement) until it is convenient to dispose of the slurry to land (via subsurface injection or surface spreading) . It is reasonable to consider combining human wastes, in the form of septic tank effluent, with animal wastes for disposal to land as if they were animal wastes . This practice is not yet common and is often not legal . * Department of Food Microbiology and Toxicology (Food Research Institute) University of WisconsinMadison, Madison, WI 53706, U .S .A . t Presently Congressional Science Fellow, American Society for Microbiology, 1913 I Street, N .W ., Washington, D .C . 20006, U .S.A . $ To whom all correspondence should be addressed . § Department of Agricultural Engineering, University of Wisconsin-Madison, Madison, WI 53706, U .S .A . 0734-242X/89/020121 + 14 $03 .00/0

Cc 1989 ISWA



122

J. A . Snowdon

et al .

Mixed waste disposal is appealing in that it is easily implemented . involves simple design, includes efficient disposal, reduces use of clean water to dilute the manure, and avoids building a separate disposal system . It is logical to handle two similar wastes as one, and a waste disposal system that is convenient encourages compliance with the law . The risks associated with mingling animal and human wastes have not been studied . Any land disposal of excreta may complete a cycle of transport of pathogens along the food chain . 2 . Mixed wastes 2 .1 Regulations

Currently, national regulations in the U .S . governing the production of Grade A milk prohibit mixing domestic wastes with animal wastes . Other regulations governing waste disposal to land are created and enforced at the discretion of the individual state and vary widely among states . In Wisconsin, for example, septage and holding tank waste may be surface spread on land used for forage crops (if done at least 8 weeks prior to the consumption of the forage by animals), but no application on land used for vegetable crop production is permitted . A 43-state survey on mixed waste disposal carried out revealed that 67% of the respondents do not permit domestic waste to be mixed with swine, poultry, beef, or dairy manure (Table 1) . Some states permit disposal of mixed wastes only under specific circumstances .

TABLE 1 Mixed waste regulations in the U .S . State

Response

Alabama, Arkansas, California, Colorado, Delaware, Florida, Georgia, Idaho, Indiana, Louisiana, Maryland, Michigan, Missouri, Montana, Nebraska, Nevada, New Hampshire, Ohio, Oregon, Pennsylvania, South Carolina, Utah, Virginia, Washington

Do not permit the disposal of mixed wastes

Illinois*, Minnesotat, New York*, West Virginiat

"No" for some farms and "don't know" for others

Kansas, North Carolina, North Dakota

Permit the disposal of mixed wastes

Arizona§, Kentuckyjl, Massachusetts¶, Oklahoma**

Special cases

* Does not allow mixing domestic waste with dairy manure on grade A and B farms ; responded "don't know" to mixing domestic waste with swine, beef and poultry manure . t Does not allow mixing domestic waste with dairy manure on grade A farms ; responded "don't know" to mixing domestic waste with manure from swine, beef, poultry and grade B dairy farms . $ Does not allow mixing domestic waste with swine, beef or poultry manure on grade A farms ; responded "don't know" to mixing wastes on grade B farms . § A minimum of secondary treatment is necessary before re-use is permitted . "Treatment" is required before re-use of domestic waste . Has no set policy . Disposal plans and site must first be approved by local board of health and Department of Environmental Quality Engineering . ** Preliminary treatment in a septic tank or a 30-day retention in the holding pit are required .



Land disposal of mixed waste

1 23

A problem common to many states is the lack of a central authority to enforce waste disposal policy . Legislation and compliance are two separate matters . A waste disposal system that is convenient encourages compliance with the law . Mixing waste has the advantage of providing an easily implemented, readily available, inexpensive means of waste disposal for those sites where conventional disposal is precluded . On these sites the home owner is required to use alternative systems such as holding tanks or mound (above-grade, sand-filled, pressure-dosed) systems . The disadvantage of a holding tank is that it imposes high operating costs whereas the mound system imposes higher capital costs . Ascertaining the public health hazards of mixing household effluent with animal manure (for disposal to land as animal manure) may clear the way for an advantageous on-site waste disposal system . 2 .2 Advantages

Mixed waste disposal (Fig . 1) is appealing in that it is easily implemented, involves simple design, includes efficient disposal, reduces use of clean water to dilute the manure, and avoids building a separate disposal system for septic tank effluent . It is logical to handle two similar items as one . Storing the household waste together with animal waste may decrease the hazards associated with disposal of septic tank effluent to the land . The waste is spread once or twice a year instead of whenever the holding tank is full . Increased detention time promotes increased retention and/or inactivation of pathogens . This enables disposal of waste material when climatic conditions are favorable to pathogen inactivation (warm temperatures) and application to soil that is neither frozen nor soaked with rain . This approach is likely to be within already established regulations for disposal of septage and holding tank wastes .

House

Ba n

Fig . 1 . Schematic representation of an existing system that mixes human and animal wastes, for eventual disposal to land, on a dairy farm in Wisconsin . Volumes in may - ' .



124

J . A . Snowdon et al . 2 .3 History

No studies have been done on the effect that adding human wastes to animal wastes would have on the public health impact of disposal of the waste to land . Research on the disposal of human waste to land usually involves urban sludge or . less often, septage . But urban waste differs from mixed wastes both as to characteristics and treatment (Bitton et al . 1980) . Urban sludge is composed of settled solids . Mixed waste is composed of septic tank effluent (the septic tank sludge or septage is not included in this system) and animal manure . Urban sludge and mixed waste are similar in the concentration of solids and in that they contain biological pathogens of fecal origin ; the similarity ends there . The chemical, physical . and microbial composition of urban sludge (settled solids from urban wastewater) is unlike that of mixed waste (clarified septic tank effluent and diluted animal feces) . A relatively large human population contributes pathogens to urban wastewater ; the concentration of pathogens is reduced by the combined volume of wastewaters . A smaller human population contributes pathogens to small scale systems, but pathogens, when present, will occur in high numbers . The treatments vary in temperature, microflora that degrade the pathogens . retention time, and the presence of oxygen . Nonetheless, the rates of inactivation of pathogens in sewage sludge provide a departure point for further study .

2 .4 Transmission pathways Any disposal of human or animal wastes to land entails some potential risk of introducing disease agents into the food chain (via animals or plants) or the water supply . The present concern is the effect on public health of adding household waste to animal wastes and treating both as animal waste-whether this practice may contaminate food and water . Although it is not likely that human or animal pathogens from contaminated soil will be taken up and translocated into non-traumatized edible plant tissue, microbial pathogens may survive on the surfaces of food plants for extended periods of time (Kowal 1982) . The crop in the field may become hazardous to consume either directly (by man or beast) or indirectly (as when man eats beast) . Routes of transmission to be considered in the mixed waste system include : --leakage from the septic tank or earthen storage basin into groundwater ; disease transmission through vectors such as flies or wild animals ; --aerosols created by pumping, mixing, transporting . and disposing of the waste ; ---percolation from the field to groundwater ; and surface run-off. To preclude disease transmission through food or water, it is important that levels of pathogens be reduced prior to discharging waste to land . The rate at which pathogens will be inactivated in mixed waste needs to be determined .

2 .5 Pathogens The biological hazards represent the more immediate concern, and may be categorized as viral, bacterial, or parasitic . Table 2 lists the major microbial pathogens in human and animal wastes . The emphasis in this presentation is on the addition of septic tank effluent to animal manure for disposal as animal manure . The potential hazards of the disposal of animal manure remain in full force ; they are not necessarily lessened by this addition . The addition of septic tank effluent to animal manure in surface storage units increases risk only in that it represents surface holding of domestic waste with minimal

125

Land disposal of mixed waste

TABLE 2 Major microbial pathogens for humans in human and animal waste* Viruses (0 .025-0 . 100 gm dia .)

Bacteria (0 .5-2 .0 µm dia .)

Parasites (> 7µm dia .)

Enteroviruses Poliovirus Coxsackievirus A Coxsackievirus B Echovirus Other enteroviruses Hepatitis A Adenovirus Norwalk-like agents Reovirus Rotavirus

Bacillus Brucella Campylobacter Clostridium Enterobacter

Protozoa (7-50 µm dia .)

Enteropathogenic

Entamoeba Giardia Toxoplasma Escheri-

chia coli Leptospira Listeria Mycobacterium Pseudomonas Salmonella Shigella Staphylococcus Yersinia

Metazoa (> 50 pm dia .) Nematodes (roundworms) Ancylostoma Ascaris Necator Strongyloides Toxocara Trichuris

Cestodes (tapeworms) Echinococcus Taenia

* Adapted from Kowal 1982, Little 1980 & Sobsey 1983 .

pretreatment . The usual precautions to detain the waste and prevent surface run-off or leakage into groundwater supplies are still necessary . 3 . Viruses 3 .1 Characteristics and transmission

Viruses may be considered to be obligate intracellular parasites . They often have a very limited host range and are replicated only by their host cells . Consequently, upon release to the environment outside of the gastrointestinal tract, they will either persist or diminish in numbers, never increase . Viruses of concern in waste disposal are enteric viruses . Enteric viruses are characterized by the ability to withstand pH 3 and are thus capable of passing through the stomach (Melnick 1982) . The genus Enterovirus includes the polioviruses, coxsackieviruses A and B, echoviruses and hepatitis A virus . Enteric viruses are transmitted, directly or indirectly, via the fecal-oral route . Epidemiological studies have shown that enteric virus infections occur most frequently in infants and young children, who then transmit them to siblings, other children, and adults in households and other settings where fecal-oral transmission is likely, such as day care centers, schools, and play groups (Evans 1982 ; Kapikian et al. 1982 ; Melnick 1982) . Indirect transmission, by vectors such as flies or vehicles such as food or water, may occur when human waste is applied to land . Routes to target hosts include : direct contamination of food crops ; contamination of the water supply (through surface runoff or through groundwater) ; or infecting the workers that load, haul, spread and incorporate the waste into the soil . At any time, only a few percent of the population are likely to be experiencing an enteric virus infection and actively shedding viruses in feces . Infectious particles will usually be present in human excreta only during the several days or weeks that a person



126

J. A . Snowdon

et al .

experiences an enteric virus infection . No gastrointestinal distress need accompany the infection . It is estimated that feces may contain from 10 6 to 10 10 viral particles per gram (Kowal 1982) . Enteric viruses have been observed in raw sewage at concentrations exceeding 102 plaque forming units (PFU) per ml (Englande 1983) . The population which contributes waste to a septic tank is smaller than that which contributes to urban wastewater . The probability of enteric virus being present is much smaller, but if virus is present in septic tank wastewater, it is likely to be present in higher numbers . For example, Hain and O'Brien (1979) recovered from 800 to 7500 PFU ml - ' in septic tank effluent . Levels in groundwater have been reported to range from 0 .004 to 0 .025 PFU ml - ' (Hain & O'Brien 1979) . The precise number of plaque forming units needed to cause infection is unknown . It is supposed that low numbers of viral particles (1 to 200) will result in infection . Since large numbers are shed and low numbers cause disease, the potential for widespread disease is large where sanitation is not effective . 3 .2 Persistence in septic tanks

Strainer (1984) determined that one-half of the viruses entering the septic tank are solidsassociated . Due to the low settling velocities of virus particles (Sproul 1976), septic tanks will only remove viruses that are adsorbed to or entrapped within large settling solids . Viruses in the sediment may be reintroduced into the overlying waters during activities that disturb the sediment (Goyal et al. 1977 ; Van Donsel & Geldreich 1971) . Inactivation of viruses within the septic tank sludge is affected by the temperature, pH and the lack of oxygen ; i .e ., viruses are inactivated more slowly in anaerobic systems than when aerated (Lund & Nissen 1983 ; Lund et al. 1984) . Sedimentation within the septic tank or dilution and displacement of the agents from the septic tank with its effluent occur much more rapidly than death or inactivation . Significant numbers of viruses will pass through a septic tank . 3 .3 Persistence in soil The fate of viruses in soil is pertinent to mixed wastes because : mixed wastes will be applied to land, and some factors that determine virus survival in soil may be similar to the factors that determine virus survival in mixed wastes . 3 .3 .1 Determining factors The survival of virus in the environment is a function of many variables . Temperature, microbial activity, and the types of virus are the most influential determinants ; but in soil, saturation, chemistry, and association with particles also play a role (Sobsey 1983) . Work done here earlier (Green 1976 ; Salo & Cliver 1976) indicates that temperature is a predominant factor in determining the inactivation rate of enteroviruses . Microbes in general, and viruses in particular, survive longer at lower temperatures, and conversely are inactivated by heat . Green (1976) found a 97% reduction in 28 days when poliovirus type I was held at 20°C v . a 57% reduction when it was held at 7°C . Lund et al . (1984) reported that the degradation of both porcine and human enteroviruses was primarily temperature dependent . They also noted that greater inactivation occurred in the presence of oxygen . Observations by Hurst et al. (1980) indicate that appreciable virus inactivation due to microbial activity in soils may occur only under aerobic conditions and at moderate to high temperatures . Temperature and oxygen both strongly influence microbial activity, which, in turn,



Land disposal of mixed waste

127

influences viral persistence . Known microbial predators of enteric viruses are bacteria . These microbes may produce metabolites that adversely affect virus particles or may use the virus capsid as a nutrient source (Cliver & Herrmann 1972) . Sobsey et al . (1980) found shorter viral inactivation times in non-sterile suspensions of wastewater . Green (1976) found no significant differences between survival of poliovirus I in sterile and non-sterile sand columns . Ward (1981) reports loss of viral infectivity in activated sludge due to microbial activity . Herrmann et al. (1974) found that two enteroviruses were inactivated more rapidly in a lake than in sterile lake water . These authors found that poliovirus 1 is susceptible to proteolytic enzymes of some microbial species .

3 .3 .2 Length of persistence The survival time of viruses in waste systems is highly variable, but should be considered in terms of days, weeks, or months as opposed to minutes or hours . Enteroviruses are reported to survive for 3 to 170 days in soils of various compositions at various temperatures, and from I to 23 days on crops (Kowal 1982) . Substantially longer survival is expected at cold temperatures, as human enteric viruses are routinely stored in the laboratory at - 18 ° C for up to a year with only a one-log (90%) decrease in infectivity . Prolonged detention is one key to the prevention of viral transmission . There is nothing particularly antiviral in septic tank waste . Viral inactivation is largely a function of post-septic-tank treatment . Consequently, disposal of virus-laden septic tank effluent after mixing with animal manure slurry and detention in a storage basin looks very attractive . A mixed waste system entails increased detention time, increased microbial load, and exposure to temperatures which may be higher than in a septic tank, all factors which should contribute to inactivation of the virus (Snowden et al. 1989) .

4. Bacteria 4 .1 Characteristics No additional bacterial concerns are expected to result from addition of septic tank effluent to barnyard waste for disposal to land as animal waste . Animals are the chief reservoir of enteric bacteria that are pathogenic to man . Bacteria present in animal slurry constitute a numerous and diverse population . Animal wastes contain an enormous quantity of bacteria . For example, when 159 samples of swine effluent and sludge were examined the total bacterial counts ranged from 7 x 10 6 to 3 x 10" colony forming units ml - ' (Strauch 1978) . Dudley et al. (1980) developed a comprehensive screen for the enumeration of pathogenic bacteria from sewage sludge which includes over 40 different species . Neither the concentration nor the variety of bacteria is expected to change appreciably upon the addition of septic tank effluent to barnyard wastes . Those bacteria which are specific for livestock species represent no additional threat to public health in a mixed waste system (as they cannot infect humans) . Those few bacteria of exclusively human origin (V . cholerae and Shigella) cannot infect animals, and are not likely to multiply or survive very long outside of their enteric origins . Shortened survival times are due to adverse temperatures, low levels of nutrients, and competition from other microflora . The high concentrations of soluble materials present in a manure pit have been reported to minimize bacterial growth (Berry 1966) . Further protection is afforded because grazing animals are not easily infected (Jones 1977) ; large numbers (10 5 microbes and greater) of bacteria must be present in the forage



128

J . A . Snowdon

et al .

to result in an infection . Bacterial infection is more likely to occur under extreme conditions of prolonged exposure to heavy contamination or when the susceptibility of cattle is unusually high . Pathogenic bacterial genera that may be recovered from feces include : Brucella, Campylobacter, Clostridium, Klebsiella, Mycobacterium, Pseudomonas, Salmonella, Shigella, Staphylococcus, Yersinia, and others . Coliform bacteria, implicitly associated with feces and wastewater, include : Citrobacter, Enterobacter, Escherichia, Klebsiella, Proteus and Serratia, some of which are not of fecal origin and most of which are not pathogens . Other bacteria that are neither in the coliform group nor are pathogens may be recovered from feces . Of the pathogens which could be spread in slurry, Salmonella is considered to be the most important and probably provides a model for other bacterial diseases (Havelaar 1986) . 4 .2 Persistence Survival periods for hazardous bacteria in soil--plant--wastewater ecosystems range from minutes to weeks . Persistence for 12 weeks is not uncommon . Rates of inactivation vary . Reddy et al. (1981) calculated first-order die-off rate constants (k) from published data for various pathogens and indicator organisms . The average die-off rates were 1 .33 per day (k = 0 .21-6 .93) for Salmonella, and 0 .68 per day (k = 0 .62-0 .74) for Shigella sp . The mean half-life from his list of over 120 bacteria was 76 h . Die-off rates approximately doubled with a 10°C rise in temperature (in the range of 5 to 30°C) . Salmonella have been reported (Jones 1977) to survive in cattle slurry for as long as 150 days, but 90% die during the first 2 to 4 weeks . Factors affecting bacterial survival in soil or on pasture include the initial number of organisms, temperature, frost, moisture content and humidity, sunlight, oxygen tension, hydrogen-ion and inorganic salt concentration, soil permeability and particle size, the presence of usable organic material and the antagonistic, predatory and beneficial effects of other microorganisms (Jones 1977) . The diversity of these variables easily accounts for the differing survival rates that are reported . While manure slurries must be handled as potentially hazardous, the addition of septic tank effluent hardly contributes any additional bacterial burden to this microbiological collection . It is important to match the type of sludge being disposed to the type of use that the land will get . Prudent practices such as storage of the slurry for at least I month, no grazing animals for I month after spreading, special precautions for young a nimals . n o application to crops eaten raw by humans (or a 12 month delay prior to planting), and avoidance of surface run-off should be observed . A mixed waste system includes an additional treatment step for the household waste . Pike (1986) reports that the use of lagoon storage or cold anaerobic digestion removed greater than 99% of Salmonella . From a bacteriological viewpoint this system represents a clear advantage for safe waste disposal . 5 . Parasites 5 .1 Characteristics A parasite may be defined as an organism that obtains its nutrition from the tissues or body fluids of another organism that is called the host . The term parasite is restricted in this work to protozoa and metazoa that infect animals including man . Parasites that have stages in their life cycle which are adapted to long survival in the



Land disposal of mixed waste

129

environment outside of the gastrointestinal tract are the parasites that might possibly be transmitted to man or domestic animals through the application of sludge, septage, animal waste slurries, or mixed waste to land . These life forms must be relatively resistant to a wide range of environmental conditions ; they include the eggs of helminths and the cysts of some protozoa . These forms are microscopic in size (helminth eggs are about 100 µm and protozoan cysts 30 µm) and are passed in the feces of their host . Even in a relatively light infection millions of these eggs or cysts may be shed daily . Numerous species are transmitted through feces . Forty-six pathogenic protozoa and helminths of major concern in wastewater have been listed by Kowal (1982) . Few data are available on the actual prevalence of parasites in waste . Reimers et al . (1981) surveyed sludge samples from 27 municipal plants in the southern U .S .A . for the type and quantity of parasites present, which resulted in a substantially smaller list (Table 3) . The most frequently recovered helminth eggs were those of Ascaris, Toxocara and Trichuris species . Viable eggs of at least ten other helminths and cysts of a few protozoa were also found in lower numbers and less frequently . Similarly, Arkhipova (1979) found Ascaris, Diphyllobothrium, Enterobius, Taenia and Trichuris species in samples of mixed human and farm waste (the only report found in the literature of mixed wastes applied to land) . Protozoan species are likely to be missed in these surveys as they are not as readily recovered by currently available analyses . Kowal (1982) states that only three protozoan species are of major significance as causes of disease transmitted to humans through wastewater Balantidium coli, Entamoeba histolytica and Giardia lamblia . TABLE 3 Parasites in urban sewage sludge* Incidence in 27 treatment plants

Parasite Ascaris Toxocara Trichuris Hymenolepis diminuta eggs Entamoeba coli-like cysts Capillaria eggs with striations Giardia cysts Capillaria eggs with pits Trichosomoides-like eggs Ascaridia-like eggs Coccidia oocysts Toxascaris leonina eggs Cruzia-like eggs Taenia spp . eggs Acanthocephalan eggs

27 27 26 23 23 il 9 7 7 7 6 2 1 1 i

* Adapted from Reimers et al. 1981 .

5 .2

Prevalence

The types and levels of parasites actually present in waste depend upon the levels of infestation in the contributing human and animal populations . Estimates of the frequency of occurrence of some parasites, such as Giardia, Taenia saginata and Ascaris are available . These species represent : protozoan parasites ; a helminth with a two-host



130

J. A . Snowdon et al .

life cycle ; and a helminth of which eggs are extremely persistent outside of its host . In 1977 and 1978, 4% of the stool specimens submitted to state laboratories in the U .S .A . were positive for Giardia ; the carrier rate ranges between 1 .5 and 20% (Jakubowski 1984 ; Davies & Hibler 1979) . The incidence of infection with Taenia saginata in the U .S .A . is estimated at less than 1 % (Yeager 1980) . Public health laboratories surveyed by the U .S . Center for Disease Control (CDC) found evidence of adult taeniid tapeworm infection in 209 (0 .05%) of the 414 820 human fecal specimens examined (Warren et al. 1974) . The incidence is also low in cattle, but is very important because the economic consequences of an infected herd are devastating (Hammerberg et al. 1978) . In 1967 the U .S . Federal inspection of 28 million cattle revealed that 14 407 (or 0 .05%) had cysticercosis . Comparable data over nine years (1959-1967) average 0 .06% incidence (Schultz et al . 1970) . The prevalence of Ascaris in humans in the U .S .A . was estimated to be about four million in 1972 (Warren 1974) . Ascaris is, however, enzootic in livestock . An infected human adult may shed millions of cysts or eggs daily . If 1 % of the population were infected with Giardia, and 200 000 000 cysts are shed daily by an infected adult, the concentration of cysts in raw sewage would be 9600 cysts L - ' (Jakubowski 1984) . People infected with a helminth parasite such as Taenia may excrete up to one million ova per day (Greenberg & Dean 1958) . In one study raw sewage contained 0 .78 helminth eggs L', and treated sewage contained 0 .46 helminth eggs L - ' (Wilkens 1982) . Although one might expect to find one helminth eggs L - ' of wastewater, many more protozoan cysts would be likely to occur . Not all of the cysts and eggs recovered from environmental samples are infective . These surveys do not determine the viability of the parasites and hence may overestimate the hazard . Small scale waste systems would be less likely to contain parasite ova and cysts, but if ova and cysts are present they would be present in much greater numbers than in urban treatment plants . Most of the parasites would collect in the sludge, but many will fail to settle in the sludge, or will be resuspended and will continue out of the septic tank with the effluent . 5 .3 Persistence outside ofthe host

The survival of protozoan parasites outside of the gastrointestinal tract may be measured in terms of days or months, depending upon ambient conditions . E. histolytica produces cysts that are relatively short-lived : 6-8 days in soil and 8-40 days in water (Burge & Parr 1980) . Giardia cysts can survive up to about 77 days in water at 8°C, 5--24 days at 21 °C, and 4 days or less at 37°C (Bingham et al. 1979) . Protozoan cysts are highly sensitive to drying . Although protozoan cysts deposited on plant surfaces may be expected to die off rapidly, they can and do survive long enough to get into the human food supply under conditions of poor management . Tay et al. (1980) found high levels of protozoan cysts on the wastewater-irrigated fruits and vegetables in Mexico City's marketplace . The persistence of the eggs of metazoan parasites outside of the gastrointestinal tract has been reported to be anywhere from a few days to 15 years, depending upon the species and the surrounding conditions . Reports of the persistence of Taenia eggs range from 2 h to 120 days . Nansen & Henriksen (1986) reported their persistence for 69 days at 30°C, 5 .2 h at 50°C, and 1 .4 h at 60°C . Müller (1953) presented the classic study of the survival of Ascaris eggs in soil, and found that they remained infectious for at least 5 to 7 years . Bürger (1982) thoroughly reviewed the subject and cited examples of the survival of A . suum eggs from I day to 1 year, depending primarily upon temperature and moisture . Ascaris eggs sprayed on leafy vegetables, for example, were completely degenerated after 27 to 35 days . Little (1980) says



Land disposal of mixed waste

131

"While the eggs of Ascaris, Trichuris and Toxocara are capable of surviving for several years in the soil when environmental conditions are ideal, they undoubtedly survive over much shorter periods in most instances" .

5 .4 Transmission The addition of septic tank effluent to stored animal waste may add species of parasites that would not otherwise be present in the animal waste . Man travels further than most host species and can transport parasites to new geographic regions . The ability of both metazoan and protozoan forms to resist extreme environmental conditions for extended periods of time (unlike viruses) adds to the concern of transmitting parasites through the disposal of mixed wastes to land . One can only speculate as to whether animal wastes may degrade parasites ; no published information suggests such an effect . The risk of transmitting parasites through mixed waste is dependent upon the type of parasite present . Regulations that effectively protect public health cannot be made based on current knowledge . Research results on rates of inactivation of selected parasites will be reported elsewhere .

6 . Summary Alternative on-site wastewater disposal systems need to be developed where local geological conditions preclude conventional percolation systems . One alternative is to combine human wastes with animal wastes (mixed wastes) for disposal to land as if they were animal wastes . Mixed waste disposal is simple, efficient, inexpensive and logical . Regulation of waste disposal, in the U .S .A ., discourages mixed waste disposal . New regulations must be based on knowledge of the public health impact of this disposal practice . It continues to be important to match land use and waste disposal carefully . Minimum interim guidelines for the use of slurry were drafted by a working group of the Commission of the European Communities (Kelly 1978, as cited in Bürger 1982) . They state clearly (Table 4) that slurry should be preferably applied on tillage land and applied only in a restricted manner on grassland . Effective minimum storage times are still subject to debate pending availability of more data . The disposal of a mixture of household waste and animal manure to land represents an easy and efficient waste disposal system . Mingled wastes appear to enhance the demise of microbial pathogens

TABLE 4 Guidelines for disposal of animal slurry to land : drafted by a working group of the Commission of the European Communities (1) Slurry should be applied on tillage crops (excluding crops for fresh consumption), wherever possible (2) If slurry is spread on grassland then : (a) apply on pasture for conservation, wherever possible ; (b) if on grazing land: (i) store all slurry for minimum of 60 days before spreading ; (ii) delay of 30 days before grazing ; (iii) graze with adult or non-susceptible animals (3) Application of slurry should be related to plant nutrient requirements From Kelly 1978, as cited in Burger 1982.



132

J . A . Snowdon et al .

that are a threat to human health . The risk of re-entry of enteric pathogens into the food chain is diminished by the ease with which a mixed waste system may be implemented . An easy and effective waste disposal technique encourages compliance and reduces the risk of inappropriate and hazardous disposal . Pathogenic material may be transmitted through contaminated food or water . The pathogens of concern may be classified as viral, bacterial, or parasitic . Viruses are likely to persist in the septic tank and be discharged in the effluent . Temperature, oxygen, and microbial predators influence the longevity of viruses in a mixed waste system . Enteroviruses are reported to persist in soil for days to months depending upon the conditions . As animals are the chief reservoir of enteric bacteria that are pathogenic to man, the addition of septic tank effluent to animal wastes is not expected to increase the bacterial load or the bacterial hazard . Parasites, like viruses, are likely to persist in the septic tank and some will be discharged in the effluent . Soil type, moisture, temperature, exposure to direct sunlight, and destruction by other microbes are all factors which may inactivate parasites . Depending upon the species, parasites may persist for days or years . Transmission of parasites can be precluded only if they are retained until inactivated . These enteric pathogens are shed in high numbers, but often ingestion of only a few is needed to transmit disease . The levels of pathogens in waste must be reduced before spreading it on land . The mixed waste disposal system presents an opportunity to reduce the levels of pathogens and to limit transmission by retaining the pathogens on fecal solids . Pathogens need to be retained until inactivating forces decrease their numbers ; association with solids also minimizes entry of pathogens into the food chain . Land use and waste disposal must be matched carefully to preclude disease transmission .

References Arkhipova, N . S . (1979) Role of pasture irrigation with sewage effluent in the epizootiology of cattle cysticercosis . Veterinary Bulletin, 49, 335 . Berry, E . C . (1966) Requirements for microbial reduction of farm animal wastes . In : Proceedings National Symposium on Animal Waste Management . American Society of Agricultural Engineers Publication No . SP-0366, Michigan State University, pp . 56-58 .

Bingham, A . K ., Jarroll, E . L . Meyer, E . A . & Radulescu, S . (1979) Introduction of excystation and comparison of dye-exclusion versus excystation . In : Waterborne Transmission of Giardiasis, (Jakubowski, W . & Hoff, L ., eds) . USEPA-600/9-79-001, pp . 217-229 . Bitton, G ., Damron, B . L ., Edds, G . T . & Davidson, J . M . (eds) (1980) Sludge Health Risks of Land Application, Ann Arbor Science Publishers, Ann Arbor, MI . Burge, W . D . & Parr, J . F . (1980) Movement of pathogenic organisms from waste applied to agricultural lands. In : Environmental Impact of Non-Point Source Pollution, (Overcash, M . R . . Davidson, J . M . eds), Ann Arbor Science Publishers, Ann Arbor . MI, pp . 107-124 . Bürger, H . J . (1982) Large scale management systems and parasite populations : prevalence and resistance of parasitic agents in animal effluents and their potential hygenic hazard . Veterinary Parasitologv, l1, 49-60 . Cliver, D . O . & Herrmann, J . E . (1972) Proteolytic and microbial inactivation of enteroviruses . Water Research, 6, 797-805 . Davies, R . B . & Hibler, C . P . (1979) Animal reservoirs and cross-species transmission of Giardia . In : Waterborne Transmission of Giardiasis, (Jakubowski, W . & Hoff, J . C ., eds .), USEPA-6001 9-79-001, U .S . Environmental Protection Agency, Cincinnati, pp . 104-126 . Dudley, D . J ., Guentzel, M . Neal, Ibarra, M . J ., Moore, B . E . & Sagik, B . P . (1980) Enumeration of potentially pathogenic bacteria from sewage sludges . Applied and Environmental Microhiology, 39, 118-126 . Englande, Jr ., A . J . (1983) Incidence and fate of viruses in sludges . In : Sludge Characteristics and Behavior, (Carberry, J . B . & Englande, Jr., A . J ., eds), Martinus Nijhoff Publishers (in cooperation with NATO Scientific Affairs Division), Boston, MA, pp . 280-293 .



Land disposal of mixed waste

133

Evans, A . S . (1982) Surveillance and seroepidemiology . In : Viral Infections of Humans, 2nd edition, (Evans, A . S ., ed), Plenum, New York, pp . 43-64 . Goyal, S . M ., Gerba, C. P . & Melnick, J . L . (1977) Occurrence and distribution of bacterial indicators and pathogens in canal communities along the Texas Coast . Applied and Environmental Microbiology, 34, 139-149 . Green, K . M . (1976) Sand filtration for virus purification of septic tank effluent . Ph .D . Thesis, University of Wisconsin-Madison . Dissertation Abstracts number DDJ76-15992 . Greenberg, A . & Dean, B . H . (1958) The beef tapeworm, measly beef, and sewage-a review . Sewage Industrial Wastes, 30, 262-269 . Hain, K . E . & O'Brien, R . T . (1979) The survival of enteric viruses in septic tanks and septic tank drain fields . New Mexico Water Resources Institute Report, NMWRRI 108, Project No . A052-NMEX. New Mexico State University, Las Cruces, pp . 1-73 . Hammerberg, B ., Macinnis, G . A . & Hyler, T . (1978) Taenia saginata cysticerci in grazing steers in Virginia . Journal of the American Veterinary Medical Association, 175, 1462-1464 . Havelaar, A . H . (1986) General epidemiology of Salmonella . In : Epidemiological Studies of Risks Associated with the Agricultural Use of Sewage Sludge : Knowledge and Needs, (Block, J . C ., Havelaar, A . H . & L'Hermite, P ., eds), Elsevier, London, pp . 15-20 . Herrmann, J . E ., Kostenbader, K . D . & Cliver, D . O . (1974) Persistence of enteroviruses in lake water. Applied Microbiology, 28, 895-896 . Hurst, C . S ., Gerba, C . P . & Cech, 1 . (1980) Effects of environmental variables and soil characteristics on virus survival in soil . Applied and Environmental Microbiology, 40, 10671079 . Jakubowski, W . (1984) Detection of Giardia cysts in drinking water-state of the art . In : Giardia and Giardiasis-Biology, Pathogenesis, and Epidemiology, (Erlandsen, S . L . & Meyer, E . A ., eds) . Plenum Press, New York, pp . 263-286 . Jones, P . W . (1977) Health Hazards Associated with the Handling of Animal Wastes . Commission of the European Communities . Animal and Human Health Hazards Associated with the Utilization of Animal Effluents . European Economic Community Workshop in Dublin, Ireland . Kapikian, A . Z ., Greenberg, H . B ., Wyatt, R . G ., Kalica, A . R ., Kim, H . W ., Brandt, C . D ., Rodriguez, W . J ., Parrott, R . H . & Chanock, R . M . (1982) Viral gastroenteritis . In : Viral Infections of Humans, 2nd edition (Evans, A . S ., ed) . Plenum Medical, New York, pp . 283326 . Kelly, W . R . (Ed) (1978) Animal and human health hazards associated with the utilization of animal effluents . ECSC-EEC-EAEC, Brussels-Luxembourg, 304 pp, as cited in Bürger, H . J . (1982) . Kowal, N . E . (1982) Health Effects of Land Treatment . Microbiological . Health Effects Research Laboratory, U .S . EPA Cincinnati, OH . Little, M . D . (1980) Agents of health significance : parasites . In : Sludge-Health Risks of Land Application, (Bitton, G ., Damron, B . L ., Edds, G . T . & Davidson, J . M ., eds) . Ann Arbor Science, Ann Arbor, MI, pp . 47-58 . Lund, E . & Nissen, B . (1983) The survival of enteroviruses in aerated and unaerated cattle and pig slurry . In : Agricultural Wastes, (Hobson, P . & Taiganides, E . P ., eds) . Applied Science, Essex, pp . 221-233 . Lund, E ., Lydholm, B . & Nielsen, A . L . (1984) Demonstration of viruses in treated wastewater, sludges, and liquid manures . In : Enteric Viruses in Water, (Melnick, J . L ., ed) . Karger, Basel . Melnick, J . L . (1982) Enteroviruses . In : Viral Infections of Humans, 2nd edition, (Evans, A . S ., ed) . Plenum, New York, pp . 187-251 . Müller, G . (1953) Investigations on the lifespan of Ascaris eggs in garden soil . Zentralblatt für Bakteriologie, 159, 377-379 . Nansen, P . & Henriksen, S . A . (1986) The epidemiology of bovine cysticercosis in relation to sewage and sludge application to farmland . In : Epidemiological Studies of Risks Associated with Agricultural Use of Sewage Sludge : Knowledge and Needs, (Block, J . C ., Havelaar, A . H . & L'Hermite, P ., eds) . Elsevier, London, pp . 76-82 . Pike, E . B . (1986) Recent UK research on incidence, transmission, and control of Salmonella and parasitic ova in sludge . In : Epidemiological Studies of Risks Associated with Agricultural Use of Sewage Sludge : Knowledge and Needs, (Block, J . C ., Havelaar, A . H . & L'Hermite, P ., eds) . Elsevier, London, pp . 72-75 .



134

J. A . Snowdon et al .

Reddy, K . R ., Khaleel, R . & Overcash, M . R . (1981) Behavior and transport of microbial pathogens and indicator organisms in soils treated with organic wastes . Journal of Environmental Quality, 10, 255-266 . Reimers, R . S ., Little, M . D ., Leftwich, D . B ., Bowman, D . D ., Englande, A . J . & Wilkinson, R . F . (1981) Project summary : Parasites in southern sludges and disinfections by standard sludge treatment . USEPA-600/S2-81-166 . SSWMP (Small Scale Waste Management Project) (1978) University of Wisconsin, Madison . Management of Small Waste Flows, USEPA-600/2-78-173 . Salo, R . J . & Cliver, D . O . (1976) Effect of acid pH . salts, and temperature on the infectivity and physical integrity of enteroviruses . Archives of Virology, 52, 279- 282 . Schultz, M . G ., Hermos, J . A . & Steele, J . H . (1970) Epidemiology of beef tapeworm infection in the United States . Public Health Reports, 85, 169--176 . Snowden, J . A ., Cliver, D . O . & Converse, J . C . (1989) Inactivation of poliovirus one in mixed human and dairy animal wastes for land disposal . Waste Management and Research 7, 135-142 . Sobsey, M . D . (1983) Virology Considerations in Soil Absorption of Wastewater : Review of the Literature and Research Needs . Presented at the Workshop on Research Needs Relating to Soil Absorption of Wastewater . Colorado State University, Fort Collins, CO, pp . 126-152 . Sobsey, M . D ., Dean, C . H ., Knuckles, M . E . & Wagner, R . A . (1980) Interactions and survival of enteric viruses in soil materials . Applied and Environmental Microbiology, 40, 92- 101 . Sproul, O . J . (1976) Removal of viruses by treatment processes. In : Viruses in Water, (Berg . G . et al., eds) . American Public Health Association, Washington, D .C ., pp . 167-179 . Stramer, S . L . (1984) Fates of poliovirus and enteric indicator bacteria during treatment in a septic tank system including septage disinfection . Ph .D . Thesis, University of Wisconsin-Madison, Madison, WI . Strauch, D . (1978) Identifying the priority contaminants microbiological agents, Commission of the European Communities . Animal and Human Health Hazards Associated with the Utilization of Animal Effluents . European Economic Community V Workshop, Dublin, Ireland . Tay, J ., DeHaro, I ., Salazar, P . M . & Castro, M . De L . (1980) Search of cysts and eggs of human intestinal parasites in vegetables and fruits . International Symposium on Renovation of Wastewater for Reuse in Agricultural and Industrial Systems, Morelos, Mexico, 15-19 December . van Donsel, D . J . & Geldreich, E . E . (1971) Relationship of Salmonellae to fecal coliforms in bottom sediments . Water Resources, 5, 1079-1087 . Ward, G . D. (1981) Onsite treatment disinfection and disposal of septage . In : Individual Onsite Wastewater Systems . National Sanitation Foundation Eighth National Conference, pp . 319-331 . Warren, K . S . (1974) Helminthic diseases endemic in the United States . American Journal of Tropical Medicine and Hygiene, 23, 723-730 . Wilkens, S . (1982) Risk of infection of cattle by Taenia saginata and Sarcocystis spp . from irrigated sewage plant effluents and in vitro trials on the rate of sedimentation of helminth eggs . Veterinary Bulletin, 52, 2081 . Yeager, J. G . (1980) Risk to animal health from pathogens in municipal sludge . In : Sludge-Health Risks of Land Application . (Bitton, G ., Damron, B . L ., Edds, G . T . & Davidson, J . M ., eds) . Ann Arbor Science, Ann Arbor, MI, pp . 173-199 .