Biosolids, also known as treated sludge, are the by-products of domestic and commercial sewage and wastewater treatment. Rich in minerals like organic nitrogen, and phosphorous and micronutrients such as zinc, magnesium and copper, biosolids are widely used in agriculture to benefit crops production and increase crop yield. When applied carefully, biosolids are able to improve soil fertility and add organic matter that enhance soil structure, moisture retention and permeability.
Biosolids have been use in various countries in North America and Europe for years and their application has been one of the most effective ways in recycling nutrients in the natural system. Although generated from sewage sludge, biosolids are treated to eliminate most complex organic molecules and pathogens.
In many developing countries, population growth is a major issue and the demand on food continues to grow over the years. However, water treatment plants are often considered a luxury in these countries and wet wastes are often just dumped into the river or land fills, putting toxics into the environment. Therefore, many developing countries especially those in south and south-eastern Asia are practicing wet waste agriculture, hoping to reuse and recycle wet waste for food production.
One example would be the East Kolkata Wetlands in West Bangel in India. It is a combination of natural and man-made wetlands and one special feature of this wetland is that it processes the city’s garbage and sewage. Since the mid-1800s people there have been dumping sewage and waste into the wetlands and slowly they realize the soil around the area becomes more fertile and the water more nutritious for pisciculture. Yet, hygienic problems started to rise as the system continues. Although they helped in production of food, these untreated sewage brings viruses and bacteria into the food, easily causing diseases.
Of course, without the proper water treatment facilities, it is also difficult for developing countries to produce safe biosolids similar to those used in developed countries. In developing countries, few cheaper methods are therefore used to produce biosolids such as lime stabilization and composting. In lime stabilization, sufficient lime is added to dewatered sludge to raise the pH, and depending on the time it maintains its pH value, different quality biosolids are produced. For composting, de-watered organic matter is biodegraded to carbon dioxide and water, producing compost, a material close to humus that can be used for agricultural fertilization.
Hydrated lime for lime stabilization
Composting
Lime Stabilization and composting may seem to be the easy and cheap method for producing biosolids for developing countries, but more improvement and studies must still be made on the matter, such as the acid treatment and anaerobic digestion. For making sustainable agriculture from wet waste in developing countries possible, much cooperation is needed from the developed countries, including funds and skills.
Notes
1. Christine Furedy, Virginia Maclaren et Joseph Whitney, "Reuse of Waste for Food Production in Asian Cities: Health and Economic Perspectives," The International Research Centre, November 2004,
http://www.idrc.ca/en/ev-30609-201-1-DO_TOPIC.html (accessed November 1, 2009).3. The Government of Ontario,"Sewage Biosolids - Managing Urban Nutrients Responsibly for Crop Production," Ministry of Agriculture Food and Rural Affairs, October 6, 2009, http://www.omafra.gov.on.ca/english/nm/nasm/info/brochure.htm#1 (accessed November 1, 2009).
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