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Sanitation: Controlling problems at source: Previous page | 1,2,3,4,5,6,7

Wastewater and excreta: Hazards or resources?

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Wastewater and excreta consist of water, micro-organisms (including human pathogens), and organic and inorganic substances including nutrients. The microbial pathogens (bacteria, helminths, protozoa, and viruses), heavy metals (in municipal and industrial wastewater), nutrients, and organic compounds contained in wastewater and excreta pose a potential threat to human health and the environment.

Wastewater and excreta also contain valuable nutrients that can be used to fertilize crops and fish ponds. Most of the nutrients a person consumes end up in the excreta. Therefore, the excreta from one person over the course of a year will contain nearly enough nutrients to grow the amount of grain (250 kg) required by that person to meet their nutritional needs (Drangert, 2000). Moreover, most of the nutrients (88% of the nitrogen, 67% of the phosphorus, and 71% of the potassium) in excreta are found in the urine. Urine, generally, poses much less health risk than faecal material because it rarely contains pathogens and thus can be used as a fertilizer after minimal treatment. Faecal material can also be safely used as a fertilizer after it has been composted or stored suitably to kill intestinal worm eggs and other pathogens that might be present.

Wastewater contains large amounts of water that can be used for irrigation. It is likely that wastewater use will increase in the future due to the scarcity of fresh water in many areas. Some estimates suggest 35% of the world's population will live in areas with chronic water shortages by 2025 (Hinrichsen et al., 1998). Because irrigation is the single largest use of freshwater worldwide (Abramovitz, 1996), using treated wastewater for irrigation may allow high quality freshwater resources to be reserved exclusively for supplying drinking water. In this era of growing water scarcity, sanitation technologies will not only be required to protect public health but they will also need to promote water conservation and reuse. Using these resources in a controlled fashion also helps to reduce the environmental degradation that occurs as a result of inappropriate waste management practices.

People and waste: the infection burden

Human excreta have been implicated in the transmission of many infectious diseases including cholera, typhoid, infectious hepatitis, polio, cryptosporidiosis, and ascariasis. WHO estimates that 2.1 million people die annually from diarrhoeal diseases and that 10% of the population of the less-industrialised world suffer from parasitic worm infections related to improper waste and excreta management (WHO, 2001; WHO, 2000; WHO, 2000b). Nearly two million of these deaths are in children of less-industrialised countries (WHO, 1999). (Box 2).

Poor sanitation, hygiene and inadequate water supply are also related to the spread of other diseases, including tropical diseases such as schistosomiasis. Among human parasitic diseases, schistosomiasis (sometimes called bilharziasis) ranks second behind malaria in terms of socio-economic and public health importance in tropical and subtropical areas. The disease is endemic in 74 developing countries, infecting more than 200 million people. Of these, 20 million suffer severe consequences from the disease.

Trematode infections are caused by parasitic flatworms (also known as flukes) that infect humans and animals. Infected individuals transmit trematode larvae in their faeces. In many areas of Asia where trematode infections are endemic, untreated or partially treated excreta and nightsoil are directly added to ponds, rivers, or lakes. The trematodes complete their lifecycles in intermediate hosts and subsequently infect fish, shellfish, or encyst on aquatic plants. Humans become infected when they consume the fish, shellfish, or plants raw or partially cooked. WHO estimates that more than 40 million people throughout the world are infected with trematodes and that over 10% of the global population is at risk of trematode infection (WHO, 1995).

Box 2: Sanitation and diarrhoeal disease

Gwatkin and Guillot (1999) have claimed that diarrhoea accounts for 11% of all deaths in the poorest 20% of all countries. This toll could be reduced by key measures: better sanitation to reduce the cause of water linked diarrhoea; and more widespread use of oral rehydration therapy (ORT) to treat its effects. Improving water supplies, sanitation facilities and hygiene practices reduces diarrhoea incidence by 26%. Even more impressive, deaths due to diarrhoea are reduced by 65% with these same improvements (Esrey et al., 1991). Of the 2.2 million people that die from diarrhoea each year, many of those deaths are caused by one bacteria - Shigella. Simple hand washing with soap and water reduces Shigella and other diarrhoea transmission by 35% (Kotloff et al., 1999; Khan, 1982). ORT is effective in reducing deaths due to diarrhoea but does not prevent it.

Poor sanitation gives many infections the ideal opportunity to spread: plenty of waste and excreta for the flies to breed on, and unsafe water to drink, wash with or swim in.

The role of poor sanitation in trachoma

Infection with trachoma is the leading global cause of preventable blindness: trachoma is closely linked to poor sanitation and is one of the best examples of an infection readily preventable through basic hygiene.

Six million people worldwide are permanently blind due to Trachoma, another 146 million people with the disease are threatened by blindness.

Trachoma is spread by a combination of:

  • poor sanitation, allowing the flies that spread the infection to breed;
  • poor hygiene associated with water scarcity and poor water quality;
  • lack of education and understanding of how easily the infection can spread in the home and between people.

A review of the evidence from several studies (Pr?ss & Mariotti 2000) suggests that improving personal, domestic and community hygiene would provide a sustainable reduction in the spread of trachoma. Antibiotic treatment of active cases would also reduce the risk of person-to-person spread. The WHO Global Alliance for the Elimination of Trachoma by 2020 has adopted a strategy called ‘SAFE’ (Surgery, Antibiotics, Facial cleanliness and Environmental changes). Addressing water scarcity, hygiene practices and poor sanitation are essential parts in this strategy for the sustainable reduction and elimination of this disease.

People and waste: the toxic burden

Infectious agents are not the only health concerns associated with wastewater and excreta. Heavy metals, toxic organic and inorganic substances also can pose serious threats to human health and the environment - particularly when industrial wastes are added to the waste stream. For example, in some parts of China, irrigation for many years with wastewater heavily contaminated with industrial waste, is reported to have produced health damage, including enlargement of the liver, cancers and raised rates of congenital malformation rates, compared to areas where wastewater was not used for irrigation (Yuan, 1993).

Nitrates from waste water can build up to high concentrations in water sources underground. This is associated with methaemoglobinaemia (blue baby syndrome) when contaminated water is used to prepare infant feeds. Nutrients may also cause eutrophication - undesirable excess in nutrients - in water sources. This can result in overgrowth of algae and harmful cyanobacteria. The toxins produced by some toxic cyanobacteria cause a range of health effects, from skin irritation to liver damage.

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