Waste Not, Pollute Not

This is part of IEEE Spectrum's special report: Critical Challenges 2002: Technology Takes On

"Stick it right up to your nose," farmer Robert Aman told me. "You'll be pleased."

I scooped up a handful of fluffy black compost and sniffed. It smelled slightly sweet, like rich potting soil. I never would have guessed it was recycled cow manure if I hadn't seen AA Dairy's barn and its tenants: 550 Holsteins whose digestive tracts are just the starting point of Aman's system for managing his animal waste.

In the United States, animal waste, agricultural chemicals, and eroded sediment from irrigation foul over 275 000 km of waterways and account for 70 percent of the nation's water pollution. The situation is not unique to the States. "In virtually every country where agricultural fertilizers and pesticides are used, they have contaminated groundwater aquifers and surface waters," according to "Solutions for a Water-Short World," a report by the Population Information Program at the Johns Hopkins University Bloomberg School of Public Health, in Baltimore, Md.

The choices farmers make about how they farm have a direct impact on the quality of our food and the purity of our water. Sustainable farming systems minimize the use of chemical fertilizers and rely instead on the processing and judicious application of animal manures, alongside minimal tillage and crop rotation. Farms could even one day produce enough power to sustain themselves as well as their rural neighbors. But can such approaches feed a growing world population while preserving the integrity of the water supply?

Cow power

In 1997, prompted by complaints from his neighbors about a strong odor of manure, Aman visited Mason Dixon Farms Inc., in Gettysburg, Pa., looking for ideas to solve the problem. Twenty years earlier, Mason Dixon had become the first commercial farm in the United States to process its manure through an anaerobic plug-flow digester. The digester is basically a long trough with an airtight cover, which expands as anaerobic bacteria break down waste material and release mostly methane gas. The gas powers a generator and has made Mason Dixon Farms independent of other power sources.

For years, anaerobic digesters have been used to process manure in countries like Germany, Denmark, Sweden, China, India, and Zaire. The idea is finally catching on in the States, and may get a push as U.S. farmers grapple with the consequences of consolidation in the livestock industry. The last 30 years have seen more animals and more animal waste being produced within smaller geographic areas. In response, thousands of farms have constructed huge waste-storage lagoons, some of which hold millions of liters of liquefied waste. If handled improperly, the waste may spill into surface waters or leach into groundwater. Neighbors often complain about noxious odors emanating from large open-air lagoons, a stench strong enough to sting the eyes and shorten the breath.

Inspired by his visit to Mason Dixon, Aman decided to install a digester on his own large dairy farm in Candor, N.Y., located about 400 km northwest of New York City. The design engineering work was partly funded by AgSTAR, a program sponsored by the U.S. Environmental Protection Agency (EPA), in Washington, D.C. To date, AgSTAR has provided technical assistance to 31 digester installations on swine and dairy farms throughout the country.

PHOTOS: MICHAEL J. OKONIEWSKI/LIAISON AGENCY INC

In a digester installation, a manure slurry flows from the barn (1) to a receptacle where a pump (2) periodically passes it to the digester (3). Bacteria break down the manure, releasing gas, which is fed to a generator (4a), which supplies electricity to the farm. Dairy Development spreads the digested slurry on its land. AA Dairy separates out solids for compost(4b, 5b) and pumps the liquid to a lagoon (4c) where it is held until sprayed on crops (5c) used to feed the cows (1, again). It sells excess power back to the grid (5a). Click to enlarge.

The AA Dairy setup is fairly straightforward [see diagram, above]. In their barn, the Holsteins eat from a trough and eliminate on the floor, between trips to the milking parlor. Manure and urine are scraped into a receptacle and flow down into a holding tank. Periodically, a pump feeds a batch of the waste into the digester, a receptacle about 9 meters wide by 41.5 meters long and 4.25 meters deep, with an airtight cover that swells as gas is produced. Each new plug of waste pushes material further through the digester, where anaerobic bacteria feast on the sludge, releasing on average 1600 m³ of biogas per day, about 55-60 percent of which is methane. Other gases produced during the digestive process include carbon dioxide (approximately 40 percent) and a small amount of hydrogen sulfide.

The biogas passes through a series of pipes to the generator station, where a diesel engine converted to run on methane drives a 130-kW generator. The generator powers the farm by producing about 80 kW of three-phase 208-V electricity around the clock. About a year after his visit to Mason Dixon, Aman's farm began producing electricity. Now he sells 10-20 percent of what he produces back to the grid in the summer, when fans used to cool the cows push power usage on the farm to its peak. In the winter, anywhere from 35 to 40 percent of the electricity goes to the grid.

After about 40 days in the digester, the waste is pumped into a separator, which divides the solids from the liquid. The almost odorless effluent is sent to a lagoon lined with a 5-mm-thick polymer membrane that prevents any seepage into the water table. From the lagoon, the nutrient-rich liquid is pumped through a 6.5-km-long pipe to alfalfa and corn fields that Aman owns on the other side of town. The processed solids, which are 99.8 percent free of bacteria, are composted and then sold to conventional and organic farms, which pay around US $22/m³.

AA Dairy is a study in sustainable agriculture as it can be practiced by the ordinary farmer, as Aman likes to say. But it is extraordinary enough to have attracted the attention of Cornell University professor Norman R. Scott, who is investigating the feasibility of replacing Aman's current diesel-engine cogeneration system with a more efficient molten-carbonate fuel cell.

With a little help from the Swedes

Fewer than 100 digester-powered farms of all types exist in the United States, but the list is growing. Within the last year, another, larger operation has cropped up in Homer, N.Y., about an hour's drive from AA Dairy. Dairy Development International (DDI) is a joint venture between the Feed Analysis Research Management Education (Farme) Institute, Homer, N.Y., and DeLaval International AB, of Tumba, Sweden, which has half the worldwide market in milking machine equipment.

For a place that houses 850 Holsteins, DDI looks strangely clean. One reason is that the $5.5 million farm is brand new--it started milking cows only in August 2001. It's also a laboratory. The Farme Institute is a contract research organization founded by Lawrence R. Jones, who has a Ph.D. in dairy science and a background in artificial intelligence and control systems. The research conducted at DDI will affect dairy farming practices around the world. In fact, DeLaval invested in the upstate New York location because of its great similarity, climatically and geographically, to many Eastern European countries, such as Estonia, Hungary, and Poland, where DeLaval hopes its dairy farming technologies will increase milk production.

DDI is Aman's farm writ large, underwritten as it is by corporate funding and government grants. "We mimic many things we've seen from Aman's farm," said Jones.

They've also made some improvements. For instance, each of DDI's three barns will be warmed by water pipes running under the concrete floor. The hot water, which will be heated by biogas power, will keep the manure flowing into the digester even in the dead of winter. So the electricity will keep flowing, too.

That electricity will be generated by four microturbines from Capstone Turbine Corp., Chatsworth, Calif. [see "Networking Assets," IEEE Spectrum, January 2001, p. 84]. These miniature gas-fired turbines, which rotate at 96 000 rpm, are more reliable and efficient than the diesel engine used for cogeneration at Aman's farm. There, the hydrogen sulfide in the biogas contaminates the engine's lubricating oil and necessitates a weekly oil change. Microturbines, by contrast, have no liquid lubricants, hence no contamination. But DDI will still scrub the gas before it goes to the microturbines by passing it through iron-impregnated wood chips (Aman is looking at doing this, too). If the biogas is not scrubbed, the sulfur could precipitate out of the exhaust as an acid, a danger for surrounding equipment as well as the farm's 12 000 m² of aluminum roofs.

When Spectrum toured the facility early last November, DDI was still in the start-up phase. While manure was flowing into the digester, the gas produced was being flared, or burned off, and the microturbines were on-site but not yet in service. Jones expected them to be up and running by the end of December. When the microturbines go on-line, they will be fed a steady stream of biogas and will produce a total of 100 kW of 480-V electricity. This voltage permits the electricity to be transmitted and used without any reliance on transformers.

The lessons learned at both AA Dairy and DDI could go far toward helping the entire livestock industry deal with animal waste, according to Cornell's Scott. In the future he envisions huge digester facilities for rural areas. "There are actually communities here in New York talking about what they call a community digester," said Scott, who estimated that if all the manure produced on half of the largest of the dairy farms in New York were put through digesters, the resulting electricity could power all participating farms, plus 60 000 homes.

Chemical impact on groundwater

Manure pollution is conspicuous. But the effects of agricultural chemicals on our water and our bodies are subtler and are only now being rigorously investigated.

The latest report published by the National Water-Quality Assessment (NAWQA) Program of the U.S. Geological Survey (USGS) states that farming accounts for 70-80 percent of the more than 450 000 000 kg of pesticides used in the United States each year. USGS researchers found at least one pesticide in almost every water and fish sample collected from streams and in more than one-half of the shallow wells sampled in both agricultural and urban areas. One-half of the samples from wells contained two or more pesticides, one-quarter contained four or more. While concentrations of these chemicals were almost always lower than current U.S. EPA drinking-water standards, these exist for only 46 of the 83 pesticides measured. Furthermore, current standards do not take into account exposure to the chemical cocktails found by NAWQA--for example, atrazine, metalochlor, and nitrate--nor do the guidelines consider seasonal spikes in chemical usage.

Some of the most frequently detected pesticides are suspected endocrine disrupters that could harm reproduction or development of aquatic organisms or wildlife by interfering with natural hormones. In fact, more than one-half of agricultural and urban streams sampled had concentrations of at least one pesticide that exceeded a guideline for protection of aquatic life. "In addition, potential effects on reproductive, nervous, and immune systems, as well as on chemically sensitive individuals, are not yet well understood," NAWQA reported in 1999.

That's a polite understatement. While something is known about the effects of pesticides on fish, precious little is known about these same pesticides' effects on people. The good news is that a major study of the potential health effects on humans is now under way. The National Report on Human Exposure to Environmental Chemicals sponsored by the U.S. Centers for Disease Control and Prevention, in Atlanta, Ga., is looking at 27 environmental chemicals, including six organophosphate pesticide metabolites (breakdown products) such as dimethylphosphate and diethylphosphate, by measuring the chemicals or their metabolites in blood or urine samples. To help track exposures over time, an updated version of the report will be published every 12-24 months and will eventually cover more than 100 chemicals.

Soil stewardship

One effective way to minimize agricultural water pollution is to eschew chemicals altogether, as with organic farming. "You don't have those soluble fertilizers and nitrates leaching into the water table," said Eugene B. Kahn, president and CEO of General Mills' Small Planet Foods, Sedro-Woolley, Wash., and founder of organic food giant Cascadian Farm. "We feed the soil, and that by definition leads us more toward sustainability."

There are many views on what makes for sustainable agricultural practices. The techniques championed by Kahn exclude the use of herbicides or insecticides. But Jonathan Moscatello, agricultural program manager for the Portland, Ore.-based Food Alliance, sees no problem with using herbicides in limited amounts, provided that the soil is not tilled. His view is all the more intriguing because the Food Alliance has developed strict standards for certifying farming practices that they believe conserve and protect soil and water resources.

Plowing oxygenates much of the active organic matter in the soil, killing many of the beneficial organisms, Moscatello contends. With the no-till technique, the stubble and stalks are left on the ground after the fall crop is harvested. Over the winter, weeds might start sprouting. When spring comes and it's planting time, the farmer sprays the land with a broad-spectrum herbicide to kill all the weeds, which add to the crop residue left from the fall harvest. The farmer then uses a special no-till planter to insert seeds through the overlying residue and into the soil.

Moscatello claims that no-till yields soil that is richer in organic matter. Such soil transfers chemicals to plants more efficiently, so that a farmer can use less herbicide and fertilizer. The result is less pollution of ground or surface water.

Some researchers disagree with Moscatello about the efficacy of no-till techniques in protecting water from chemical contamination. One study conducted by USGS in cooperation with the University of Tennessee on farms in the Beaver Creek Watershed in West Tennessee concluded that when compared with conventional tillage methods, no-till methods made no difference in the amount of chemicals that leach into groundwater. That same study also pointed out that "no-tillage has proven to be an effective BMP [best management practice] for soil-loss reduction in many studies throughout the United States."

Indeed, no-till, as well as crop rotation (sowing the same field with a different crop every year), are so effective at conserving topsoil that the practices are now heavily advocated by international agencies like the United Nations' Food and Agriculture Organization (FAO). Such conservation agriculture, as the FAO calls it, is being adopted, albeit slowly. Of the 1.5 billion hectares (15 million km²) of land farmed worldwide, the organization estimates that conservation agriculture is being practiced on only 58 million hectares, including around 20 million hectares in the United States, 13.5 million hectares in Brazil, 9.5 million hectares in Argentina, 4 million hectares in Canada, and about 800 000 hectares in Paraguay.

Organic farmers enrich the soil with compost like this from AA Dairy.

What drives change?

In developed countries, any drive to cultivate more land using conservation agriculture will in the end come from consumers, whose demand for organic food has for a decade been growing at 15-20 percent per year in the United States and much faster in Europe. This trend has attracted the interest of large food companies and prompted General Mills to acquire Kahn's Small Planet Foods in 2000. "As a consumer-driven food company, General Mills wants to stay on top of consumer trends and meet consumer need," Kahn told Spectrum.

While Kahn contends that to those who choose it, organic food is "just lunch," leading consumer advocate Andrew Kimbrell, director of the Center for Food Safety, Washington, D.C., believes that people realize that "every food decision they make has implications for the earth." And, he added, "They're voting with their consumer dollar for technologies, techniques, and foods that reflect their new consciousness about their own personal health and the health of the natural world."

Consumers who can pay premium prices for organic food may have some say in how certain crops are cultivated, but will have less to say in addressing the 1.36 trillion kilograms of animal waste produced by eight billion U.S. farm animals. Solutions to that problem will likely depend on regulatory imperatives and government incentives. The EPA's AgSTAR program is one step down a trail blazed by European countries like Denmark, where the government entices farmers to produce power from biogas by allowing them to sell excess power back to the grid at premium prices. For now, U.S. farmers seem more concerned about the government eventually compelling them to deal with their animal waste in a more efficient manner. Some farmers have told Cornell's Scott that they are investigating digesters not only because they view themselves as the ultimate stewards of the land, but also because they want options if and when any new environmental regulations come down the pike.

Larger dairy and swine farms are particularly interested, Scott noted, and these are the kinds of operations that can afford to buy efficient, technologically sophisticated power generators like microturbines. In fact, one of Scott's students has just left Cornell to run a 4000-head dairy operation in California that will be installing microturbines. Scott suggests that, once prices for advanced cogeneration systems drop into line with farmers' wallets, farms could become a lucrative niche market for microturbines and even for fuel cells.

Other market opportunities in sustainable agriculture are currently being exploited by farm equipment manufacturers like Yetter Manufacturing Co., Colchester, and John Deere & Co., Moline, both in Illinois. Bob Nelson, a spokesman for John Deere, said that the company has been making planting equipment for farmers who over the last 20 years have been attracted to the no-till method, and he stressed that the company continues to develop the technology. Deere is also building global positioning system (GPS) receivers into its tractors and combines to help farmers plant, spray, and harvest more precisely, cutting the amounts of chemicals applied and fuel used. Nelson estimated that 10-20 percent of U.S. farmers already use GPS as part of an overall precision agriculture approach and that their ranks are "growing every day as the systems improve."

In poor and developing countries, though, changes in agricultural practice will have less to do with tractors equipped with the latest bells and whistles or consumers demanding organic tomatoes than with getting the most out of the land as cheaply, and with as little soil degradation, as possible. Fertile soil and clean water are precious commodities in countries struggling to feed their people [see "Safe Water Saves Lives"]. Conservation agriculture and minimum tillage in particular have been proven to prevent topsoil erosion. Moreover, by not tilling the soil, farmers can save between 30 and 40 percent of time, labor, and fuel costs compared to conventional cropping, according to the United Nations' Food and Agricultural Organization.

Conservation agriculture for crop cultivation can work equally well in both the developed and developing worlds. For livestock operations such as dairy farming, however, one person's sustainable solution can be another's ticket to destitution.

Aman tells the story of a visitor from India who recently toured his farm. Since the mid-1970s, the Indian government has been supporting the installation of anaerobic digesters in rural, cow-owning households as an alternative to wood and kerosene for cooking and heat. But when Aman suggested his visitor build a modern dairy based on AA's design, he politely demurred. In his opinion, the Indian government would never sanction such an operation because the socioeconomic costs are too high.

Approximately 70 million Indians eke out a living from dairy cows. Not only would a highly efficient, industrial dairy farm such as Aman's be beyond the means of even most wealthy Indian farmers, but such operations, if they were to proliferate, would also rob millions of subsistence. In developing countries like India, the implementation of sustainable agricultural techniques often involves striking a balance between ensuring local self-sufficiency and protecting the water supply, and controlling the dissemination of technology in such a way that it supplements human labor without replacing it entirely.