Cities can be transformed from being only consumers of food and other agricultural products into resource-conserving, health-improving, sustainable generators of these products. In particular, urban agriculture can convert wastes into resources, put vacant and under-utilized areas into productive use, and conserve natural resources in rural areas while improving the environment for urban living.
Urban Waste as Resources
Cities of both the Third and the First Worlds are having increasing difficulty dealing with solid and liquid wastes. A paradigmatic change in the way these wastes are viewed may be starting to emerge globally. Wastes (with exceptions) are coming to be seen not as a problem to be disposed of, but as a resource for sustainable development. A vision of metropolitan areas is evolving from primarily open-loop systems with one-way flows of resources (in) and wastes (out), to primarily closed-loop systems in which the definition of wastes and resources becomes blurred. Cities can become more resourceful in both the literal and the figurative senses. Urban agriculture plays a significant role in converting the consume-dispose open loops into consume-process-reuse closed loops.
One of the main imports into urban areas is food. At the same time, cities export daily a vast volume of wastes to be disposed of in their bioregion or in adjacent regions. Historically, these wastes have been inputs into the production of a city’s food, and they can again become so. Converting food waste into fresh food reduces food costs, improves its quality, improves the environment, creates jobs, and reduces municipal management costs.
The recycling of urban organic wastes is particularly critical because without it, nutrient and pathogen pollution damage health and reduce the capacity of the environment to sustain future generations. Urban agriculture can play a significant role by recycling both waste water and solid waste.
Cities in arid and semi-arid regions have a limited availability of water for household use and irrigation. Nutrient-rich waste water provides a precious agricultural input. Its value increases with a decreasing income level, as the potential user has less capacity to pay for organic and chemical fertilizers. Its value is also enhanced as it is available close to markets.
Waste water can substitute for freshwater, which then increases the availability of freshwater for drinking, cooking, and other uses. Since urban areas produce great amounts of waste water, it makes special sense to use it for irrigation of land and aquatic crops within and adjacent to metropolitan areas.
A number of cities in Third World countries already use this resource wisely. An estimated one-tenth or more of the world’s population currently eats food produced on waste water.
- Mexico City pumps over half of its sewage 50 miles and more to the north, where it is used to irrigate over 100,000 hectares for livestock feed.
- Calcutta produces one-third of its fish in sewage-fed lagoons and a similar share of its vegetables from waste-water irrigation.
- Morocco and Tunisia have modern waste-water reuse systems.
- Singapore is a world leader in the biological treatment of waste water for agricultural applications.
Cities from China to California convert waste water safely into food. However, for each city that does so safely, there are many more cities that lack monitoring or are directly engaged in practices that spread disease through improper use.
Some obstacles confront the safe use of waste water in urban agriculture. The first obstacle is the presence of industrial chemicals in waste streams. The use of wastes as agricultural inputs is more feasible in the urban areas of Third World countries than in those of industrial ones, as their wastes contain less chemicals and toxic materials. Careful monitoring is clearly necessary.
A more serious obstacle to the use of municipal effluent as an input to food production in Third World countries is the presence of pathogens. Fortunately, waste water can be biologically treated to remove the pathogens sufficiently so that it can be safely used for irrigation and as a medium for raising fish and other aquatic crops. Low-capital intensive processes for eliminating pathogens include sunlight, time, and an intermediate plant or animal such as algae or duckweed, which is then used as organic fertilizer or animal feed.
The second approach to managing the problem of pathogens focuses on selecting crops or animals that are less prone to absorb, retain, and transmit pathogens. Many cities use waste water to grow forest crops for fuel, forage for livestock, construction materials and other non-food crops.
The most subtle and challenging hurdle to cross in the use of urban waste water for agriculture may be cultural. Irrigation with soiled water is often considered taboo and unsafe. The idea of properly "disposing of" waste water dates back to the microbe hunters of the late 19th century.
Obstacles also exist among traditional cultures and religions. In Muslim countries, for example, there is particular reticence to using waste water for food production. As the Middle East runs out of fresh water, it may need to be in the front-line of waste water agricultural research.
The transformation of waste water from a pollutant to an input is likely to be gradual. The conversion from the 19th century disposal system to the 21st century reuse system may take a generation, being phased in over the useful life of the old system or according to the capacity of urban agriculture to absorb it. It can often be introduced first in areas with non-existent or poorly developed sewage systems. The overarching aim of the waste water management system may well include the minimization of throughput. Thus, less waste water leaving a city may indicate a better system.
Rural and urban wastes dumped and leached into rivers, lakes, bays/lagoons, seas and the oceans are one of the greatest degraders of our bioregions and the biosphere. Waste water aquaculture, livestock, and farming focused on Third World urban markets can be a major tool in arresting and, in time, reversing this devastation.
Redesigning solid waste management from the point of view of the urban farmer and future generations may suggest sorting waste at the home or business and at the farm within or at the edge of the community. Such a system would aim to transform waste to fertile soil, green plants, and food within portions of a city. It would principally collect and sort what is suitable as agricultural and landscape inputs, including composting and other modifications before reuse.
One example is a farm in Jakarta located on the property of a horse racing club. The farmers recycle the track’s wastes and those of the surrounding neighborhood. Glass, metal and cloth go to a recycling center and organic material is composted on site. Everything moves by handcart. What remains to go to landfills is very limited, and jobs and fresh food are generated within the community.
The urban farm can be organized to collect and process as much of the nutrient-providing wastes as possible. The household with a backyard or a rooftop garden can be set up to reuse its own organic waste. The primary constraint to the ecological use of solid waste seems to be organizational, whereas in the instance of waste water, the significant constraints may be more sociocultural attitudes and technical matters.
Under-Utilized Urban Land and Water
Not only should the waste by-products of the urban areas be inputs into urban agricultural production, but the urban setting itself can be seen as a resource to be tapped for the same productive purposes.
Cities in Third World countries are widely perceived as solidly built up with no area to spare. Agriculture and urbanization are commonly viewed as conflicting activities. A closer look reveals however that there are considerable land and water areas in the urbanized sphere that are available for agricultural use. Furthermore, the agricultural use of areas at the edge of cities should not be regarded as a marginal use, but rather as an integral part of that urban area’s productive system.
All cities and towns have a number of vacant and under-utilized land and water surfaces that can be used for agriculture. These surfaces include:
- areas not suited for built-up uses
- idle public and other lands
- lands that can have an interim use
- community lands
- household areas: rooftops, patios, walls, etc.
Wetlands and steep slopes are ideal for certain types of agriculture. The approach paths to airports are not suitable for housing or workplaces but are good for agriculture. Every city has idle public land like roadsides, utility rights-of-way, university grounds, and so forth. Community areas are common spaces for small-scale horticulture, typically school grounds and park space, but also vacant lots. The horse racing club in Jakarta, mentioned above, does not lose its value because agriculture is an added use. Lakes, ponds, reservoirs, and bays can often add aquaculture to their current use and be cleaner and prettier.
A little space around the home can go a long way to enhance food security and augment income. Sarajevo is our best-known example this year. Both the Wall Street Journal and CNN Network News have reported on the universal practice of keeping small animals and growing food as a means of family survival.
Conservation of Resources
Urban agriculture also conserves resources. The food in a supermarket in the United States travels an average of about 1,300 miles between its point of production and its point of consumption. With increased urban agriculture, this average distance can be cut significantly. In other countries, the distance saved may not be as great but the impact may be greater. The resulting savings in energy and transport costs are obvious. Not so obvious are the savings in storage, including cold storage, and the savings in product lost due to handling and transport damage.
The concept of fungibility is crucial here. Fungibility means that some resources can be substituted for others, which are then freed for alternate uses. For example, recycling a newspaper does not save the tree from which that paper came, but rather helps save another tree that would be cut to make another newspaper. Similarly, urban agriculture can be seen as allowing rural agriculture to become more focused on those methods and crops where there is a clear advantage for generating income.
At the household level, this concept of fungibility has the most important implications. In many large urban areas, lower-income households spend over half their incomes on food. As the largest component of a household budget, any saving on food expenditures translates into a significant portion of the income becoming available for other non-food expenditure. Similarly, if urban agriculture results in surpluses that are sold, the resulting additional income can be sizable. Either way, household resources are expanded or freed for reallocation. It is not unusual for women working part-time in urban agriculture to earn as much and more than their husbands with government or semi-skilled jobs.
The concept of fungibility can also be extended to the conservation of bioregions and their resources. Urban agriculture can reduce the pressure to convert deserts, mountain slopes and rain forests into cropland, as well as the pressure to cut woodlands for fuel. The much higher yields from urban agriculture techniques when compared to those from rural agriculture can make these reductions in pressure particularly significant. Likewise, aquaculture has been one of the fastest growing farming systems of the 1980s and 1990s. As cities grow their own fish and other aquatic crops, the pressure on the fisheries outside metropolitan areas can be reduced.
A Source of Sustenance
Urban agriculture offers opportunities to some groups in particular and thus has positive impacts on equality. In many cultures and places, urban agriculture is women’s agriculture. Moreover, urban agriculture by its nature is a low-capital, high-labor industry and attracts low-income entrepreneurs and employs part-time and temporary low-skilled workers. Thus, the urban agriculture industry provides income to new arrivals in the city, teenagers, retired persons, and those caring for children.
Urban agriculture is the largest and most efficient tool available to transform urban wastes into food and jobs, with by-products of an improved living environment, better public health, energy savings, natural resources savings, land and water savings, and urban management cost reductions. It contributes to social sustainability while increasing ecological sustainability.
The Urban Agriculture Network is a global resource center working to promote agricultural production in urban areas. 1711 Lamont St., NW, Washington, DC. 20010; 202/483-8130; e-mail firstname.lastname@example.org.