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Biogas digester. This EcoSan pilot project was implemented at a prison in Meru for about 1.500 inmates and 350 staff. Photo: SuSanA Secretariat via
Biogas digester. This EcoSan pilot project was implemented at a prison in Meru for about 1.500 inmates and 350 staff. Photo: SuSanA Secretariat via
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Biogas - the global green solution for health, energy, environment

John M. Hawdon

8th May 2014

Biogas digesters are a key technology for global sustainable development, writes John M. Hawdon. They simultaneously combat parasites that infect a billion people, reduce deforestation and methane emissions, and deliver vital energy to rural communities.

Preventative chemotherapy' is designed to decrease individual worm burdens and therefore illness, but it cannot eliminate or eradicate the parasites.

Soil transmitted helminths (STH) are a group of parasitic nematodes of humans that share a common transmission mechanism involving contact with the infective stage in soil contaminated with human waste.

The STHs are comprised of the large roundworm Ascaris lumbricoides, the hookworms Necator americanus and Ancylostoma duodenale, and the whipworm Trichuris trichiura.

Over 1 billion people are infected

Found throughout the tropics and subtropics wherever poverty and poor sanitation occur, over 1 billion people are infected with one or more STH species, and more than 4 billion are at risk of infection.

Over 450 million, mostly children, suffer from significant morbidity, and 44 million pregnant women suffer clinical effects from hookworm associated anemia.

Worm infections have significant effects on health, including anemia, delays in physical growth and cognition, decreased stamina and work output, and complications during pregnancy.

These infections place considerable drag on the already overburdened economies of developing countries, so there is considerable interest in developing effective control measures.

Are drugs the answer?

There are safe and effective drugs to treat these infections, and mass drug administration (MDA), in which a single dose of drug is given to school aged children annually or biannually is the current control strategy.

This 'preventative chemotherapy' is designed to decrease individual worm burdens and therefore illness, but it cannot eliminate or eradicate the parasites.

Also, people are rapidly reinfected in the same environment, and extensive use of anti-worm (anthelmintic) drugs will eventually select for hookworms that are resistant to treatment. Furthermore, evidence indicates that MDA programs do not have any positive effect on growth or school attendance or achievement.

Vaccination to the resuce?

Because of these limitations, efforts are underway to develop a recombinant vaccine against hookworms. More than $50 million has been invested so far.

However, animal models for hookworms are poorly representative of human infections, and therefore little is known about the immunology and molecular biology of infection.

The lead antigen failed Phase 1 safety testing, and while additional antigens are currently undergoing clinical trials, an efficacious vaccine is decades away, if it's possible at all.

Tackling the problem at its root

Considerable effort and resources have been, and continue to be, spent on these top-down, medical based programs to control STH infections, with little success. That's because neither approach attacks the root of the problem, namely the contamination of the environment with human waste.

STH infections were eliminated from developed nations through construction of sanitary infrastructure, and this will be the only way these infections will ultimately be eliminated from developing countries.

Proponents of the top-down approaches point out that sanitation is costly, and indeed Western sewage systems are prohibitive in many endemic areas. Furthermore, providing latrines alone often does not impact STH prevalence due to low coverage rates, poor maintenance, malfunction, or lack of use for cultural reasons.

In all cases, the type of latrine or sanitation system and community awareness and engagement determines the overall impact on STH transmission. Even when coverage is high, it does not always translate to effects on STH infections.

The manure must be rendered harmless before spreading

In areas where farmers use human feces, or night soil, as fertilizer, latrine coverage is very high, yet has little effect on STH infection prevalence. People become infected during agricultural activities from infectious stages in manure that is purposely distributed into the environment.

In this case, a sanitary option that renders the manure harmless is required. This implies that implementation of sanitary facilities that fail to account for transmission patterns and sources are destined to fail.

Therefore, well-designed, culturally sensitive sanitary facilities, designed with an understanding of transmission patterns and that will be used regularly or exclusively, are required to realize the maximum benefit from improvements in sanitation.

Fermenting faeces for biogas - a double benefit

One such system is biogas technology, which is becoming popular in China and other countries in Asia and Africa. The technology is also coming of age in industrial countries, notably Germany where it is seen as key renewable energy source for the future. (see photo)

In a biogas system, human and animal waste undergoes fermentation in a specially designed underground septic system, generating a methane gas mixture - known as biogas - that can be burned to augment or replace household energy needs like cooking and light generation.

During the fermentation process, parasite eggs and bacteria are killed, rendering the effluent microbiologically safe. This effluent from the fermentation chamber can be used as a high-quality, nitrogen rich fertilizer which will not foster STH or other disease transmission when used on crops.

Also, this effluent meets the criteria for 'organic' fertilizer, allowing access to the lucrative organic vegetable industry.

A highly profitable investment

In addition to the effects on STH transmission, biogas has several additional advantages that make it an ideal solution to rural waste disposal problems.

Because they provide a significant portion of a household's energy needs, they are highly desirable and considered to be a good investment by the farmers. With a cost under $500 with a government subsidy, a household in China can recoup the investment in 2-3 years from energy savings alone.

Other health benefits include a decrease in burning wood for cooking, resulting in less smoke and ash in the kitchen. This will lead to fewer respiratory infections, lung damage, and premature deaths from smoke inhalation.

Wider environmental and climate advantages

Less wood burning will also decrease the time women and children spend collecting fuel wood, as well as decrease deforestation and habitat destruction.

Biogas technology can help mitigate global warming by reducing methane in slurry as compared to composting organic material aerobically, and producing less CO2 from burning firewood and fossil fuels.

Methane mitigation saves carbon emissions, and can be traded as certified carbon emission credits under the Kyoto Protocol Clean Development Mechanism.

Genuine 'sustainable development'

Finally, biogas system installation and maintenance create jobs in the local community for masons, biogas technicians, and extension agents to educate farmers on their use. These factors, together with biogas energy, represent a significant economic benefit to the farmer and his community

In conclusion, current top-down control strategies for STH control suffer from serious limitations, and can at best control STH infections.

Sanitation-based systems have the ability to eliminate STH transmission. Biogas technology represents a sustainable, bottom-up, culturally appropriate and economically desirable solution to STH control in endemic areas.



The article: 'Controlling Soil-Transmitted Helminths: Time to Think Inside the Box?' is published by the Journal of Parasitology: April 2014, Vol. 100, No. 2, pp. 166-188.

John M. Hawdon is an Associate Professor in the Department of Microbiology, Immunology and Tropical Medicine at the George Washington University. He received his B.S. in Animal Bioscience from Penn State University in 1981 and his PhD in Parasitology from the University of Pennsylvania in 1991. Dr. Hawdon received post-doctoral training at Yale University, and was a member of the Research Faculty in the Department of Public Health at Yale until appointed to the faculty of George Washington University in 2001. He has spent his entire academic career studying hookworms, and has done pioneering research in the molecular biology of hookworm infection and hookworm population genetics. He first encountered biogas technology during travels in rural China, and has long been a proponent of sanitation-based solutions to worm infections.




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