August 18, 2008
Water-based sewage disposal, first introduced into the United States around the turn of the 19th century, provided a more expedient, and seemingly more hygienic, system to dispose of human waste. But these systems lead to increases in water use for waste disposal and increased pollution to surface and groundwater.
It seemed like a good idea-initially. Sewage was channeled to the nearest body of water where it was diluted, a practice generally unchallenged until the 1910-20s when sanitarians realized it might be prudent to treat sewage prior to its discharge. At the time, towns were concerned that sewage treatment would impose costs they could not afford. It’s no coincidence that shortly after the advent of these water-based systems, “sewage farming” (applying raw sewage to farm land) began to gain popularity in the U.S. Western states with their vast, uninhabited lands and little rainfall, first adopted the practice. Sewage farming was less popular in highly populated Eastern states. The short-lived sewage farming “experiment” in the U.S. ended by the 1930s – brought to an end largely because of poor management and because it was deemed a nuisance, and potentially dangerous to health. It should be noted that long before sewage farming was adopted, the practice was under scrutiny by the scientific community. One noted scientist, Thomas Baldwin, in 1874, asked, “What guarantee is there that the contagium of any infectious disease which may be in the sewage is destroyed?”
Flush Toilets for food animals
In the 21st Century sewage farming is back. This time it is being applied to the waste produced by our food animals. With the exception of poultry, most large confined animal feeding operations (CAFOs) have switched to water-based systems that essentially flush waste from the floors of vast facilities where animals are housed, and channel the slurry into large pits for temporary storage. These systems require tremendous volumes of water. Where flush cleaning is practiced, for example in large dairy operations, water use can reach 150 gallons a day for each cow. A 5,000 swine CAFO can consume an estimated 340 million gallons of drinking water and flushing water each year. The contaminated wastewater is then used to irrigate agricultural lands consisting mainly of corn and soy beans-commodities used in the production of nearly everything we eat or drink.
Like the household flush toilet, the use of flush systems in animal agriculture increases the volume of waste and the odors. Waste pits, referred to as “lagoons”, are the most common waste handling system in U.S. swine production. Although some contamination controls are in place-concrete -lined pits and locating pits indoors, underneath the floors where pigs are raised-there are increasing concerns of the incidence of odors and spills due to poor management and storm events. Water-based systems, if connected to a wastewater treatment plant, can work effectively, but require significant investment and maintenance-costs beyond affordability for the average farmer.
Treatment Standards: Animal waste vs. Human waste
In the U.S. there are major differences in treatment standards required for human wastewater and wastewater from animals prior to land disposal. Sludge from human wastewater treatment plants must be stabilized through a number of processes to reduce pathogen levels, odor and volatile solids content, vector attraction, and metal content. Human waste is treated and classified as either Class A or Class B biosolids, based on the concentration of fecal coliforms and the treatment process applied. Class A biosolids are assumed to be pathogen-free and can be land applied without any pathogen-related restrictions. Class B biosolids must have a fecal coliform below a required level, or must have been treated by a “process to significantly reduce pathogens”. Class B biosolids cannot be packaged and sold or given away, or used in sites where the public could become exposed.
In contrast, no treatment-process control requirements, or prescribed pathogen criteria, have been established for animal waste, even though levels of pathogens in the waste can be equal to or even higher than levels found in human waste. Moreover, many pathogenic organisms, such as Salmonella and E. coli are regularly found in animal feeding operations. To make matters worse, pharmaceuticals are often added to the feed, eventually ending up in the waste.
To Flush or not to Flush
Animal producers often believe that risks from spreading waste are exaggerated, and that the waste represents a nutrient resource that should be used. But, the demographics of animal agriculture has changed to the point that this is no longer true.
Historically, U.S. farmers had fewer animals per area of land and relied on this larger land base to treat the waste, which was almost exclusively handled in a dry form. In 2001, the average small animal feeding operation (50-299 animal units) had 3.5 acres per animal unit (an animal unit is approximately 1000 lbs of live weight or equivalent to one beef cow) versus 0.18 acres per animal unit at large concentrated animal feeding operations (CAFOs). Although there are instances where small animal feeding operations can pose a public health risk, the increased volume of waste, the unavailability of land and the water-based waste handling methods used at large CAFOs has led to lawsuits driven by public concern. Problems of waste management are exacerbated when operations apply waste on steep slopes, near waterways and natural drainage-ways, or when certain weather or soil conditions exist, such as rainfall, snow covered land, frozen land, or saturated soil.
Managing waste in a dry form, such as on-farm composting carried out under controlled conditions, could be a more suitable method for treating waste. Although less technologically advanced, this method can effectively raise the temperature of the waste, reducing the number of intestinal microorganisms. It can also decrease the likelihood of spills and control odors associated with anaerobic conditions of flush-and-discharge systems.
Dry systems, however, are not without problems. They require proper management to ensure optimal conditions and prevent ammonia emissions. Additionally, shifting to a dry system would change the current design of animal feeding facilities, towards hoop housing (Photo 4) for example, and potentially decrease the number of animals that could be raised at one facility. Since water would no longer be used to flush the waste from the floor, there would be an increase in demand for labor to manage the waste. Producers would likely view this more labor-intensive method as a step backwards and more costly. In contrast, communities would likely benefit from this change – less odor, fewer spills, and a potentially treated end product.
Animal welfare would be improved with a change in the design of animal feeding facilities. For example, hogs raised in nonbedded confinement systems exhibit more aberrant behavior and suffer more injuries than hogs in bedded hoop housing.
Some believe that principles of sanitary engineering can and should be applied to animal waste management, but so far, these technologies are far too expensive for farmers. Under current farmer-producer contracts, farmers are fully responsible for waste management, although in most cases–at least in poultry and swine operations–it is the integrators (i.e. companies) who control the feed inputs and own the animals. With sanitary engineering beyond the financial grasp of most farmers and with integrators shirking the responsibility to provide proper waste management or give farmers incentives to do so, the public may be forced to seek regulation to through expensive lawsuits-likely aimed at farmers.
The increased production efficiency realized by food animal producers, based in part on water-based flush systems, calls for improved waste management and monitoring to safeguard human and ecological health. Sewers have worked well for moving waste from houses, however, proper treatment remains elusive in a number of cities; much more so for animal feeding operations.