Conceived and designed the experiments: JR LC EYWS. Performed the experiments: JR LC EYWS. Analyzed the data: JR LC EYWS. Contributed reagents/materials/analysis tools: LC. Wrote the paper: JR EYWS.
The authors have declared that no competing interests exist.
Cooking and heating remain the most energy intensive activities among the world's poor, and thus improved access to clean energies for these tasks has been highlighted as a key requirement of attaining the major objectives of the UN Millennium Development Goals. A move towards clean energy technologies such as biogas systems (which produce methane from human and animal waste) has the potential to provide immediate benefits for the control of neglected tropical diseases. Here, an assessment of the parasitic disease and energy benefits of biogas systems in Sichuan Province, China, is presented, highlighting how the public health sector can leverage the proliferation of rural energy projects for infectious disease control.
First, the effectiveness of biogas systems at inactivating and removing ova of the human parasite
Sustainable strategies that integrate rural energy needs and sanitation offer tremendous promise for long-term control of parasitic diseases, while simultaneously reducing energy costs and improving quality of life. Government policies can enhance the financial viability of such strategies by introducing fiscal incentives for joint sanitation/sustainable energy projects, along with their associated public outreach and education programs.
Cooking and heating remain the most energy intensive activities among the world's poor, and thus improved access to clean energies for these tasks has been highlighted as a key requirement of attaining the major objectives of the UN Millennium Development Goals
Digestion of organic waste material under anaerobic conditions generates “biogas,” the primary constituent of which is methane which can be used for cooking, heating and lighting. China provides a prime example of the rapid investment in this simple technology, as government financial support for rural biogas projects, funded mainly by the Ministry of Agriculture, has increased from 1 billion CNY in 2003 to over 2.5 billion CNY in 2006
To support the rapid adoption of these systems among households, various benefits of their use have been cited including improved rural sanitation, reduced labor requirements for wood collection (especially among women), reduced greenhouse gas emissions, improved respiratory health in kitchens, and increased agricultural productivity through improvements in soil quality
What is more, where the diffusion of biogas technology has been limited, a lack of community acceptance of the technology has been faulted
The study was conducted in 10 villages with historically high schistosomiasis infection prevalence in three townships (Daxing, Chuanxing, and Gaojian), near the city of Xichang in Sichuan Province, PRC (E102°18′ N27°52′;
Nearly three million household biogas systems are in use in Sichuan, representing nearly a fifth of total biogas systems installed in PRC
The main challenge of assessing the effectiveness of biogas systems at removing/inactivating schistosome ova is the extremely low concentration of eggs in the typical system. Owing to this limitation, three separate experimental approaches were undertaken to determine removal in the spring and summer of 2004. These experiments were designed to separately assess removal by biochemical inactivation and removal by sedimentation, both of which are active pathogen removal mechanisms in biogas systems
In the first experiment, an operating biogas system was seeded with a single pulse of highly infected stool, and the effluent was analyzed weekly for two months (May and June) for the presence of viable ova. The egg density of 2.4 kg of homogenized infected stool was determined to be >100 epg using a triplicate 41.5-mg per slide Kato-Katz thick smear method
A second experiment conducted in two biogas systems was designed to quantify the biochemical inactivation of schistosome ova in biogas chambers. Egg density of a homogenized infected stool sample was determined (epg = 10) by the Kato-Katz thick smear method, and 40 g samples of stool were seeded into nylon mesh bags (
A third experiment was designed to isolate removal by sedimentation in biogas systems using
In 2003, 33 heads of household representing a total of 162 household members in two schistosomiasis endemic villages, Xinlong 7 and Xinming 3, were randomly selected to participate in a pre-biogas questionnaire to profile their current energy usage, and to assess, using multiple measures, the perceived value of implementing biogas in their homes. In 2007, a follow-up, post-biogas survey was conducted in 10 endemic villages (which included the 2 villages from the pre-biogas survey) in Xichang County with approximately 25 heads of households randomly selected in each, representing approximately 875 household members. Participants were asked again about their energy usage, whether they had a household biogas system, and if so, how the system was being used and their satisfaction with the system's operation. To examine the influence of the ongoing government program, the larger survey was designed to be more comprehensive, including villages that were and were not included in the biogas subsidy program. All surveys were administered with the free and informed consent of participants by trained personnel from the Sichuan Institute of Parasitic Diseases and the Xichang County Schistosomiasis Control Station.
Socio-demographic data were obtained from a baseline survey of household characteristics conducted in 2000, as part of a larger epidemiologic study of schistosomiasis transmission in these villages. These data were used to explore differences in sociometric variables between villages. No significant differences existed between villages with respect to gender ratio (male∶female of 51∶49), age structure (23%<14 years, 29% 14–29 years, 37% 30–49 years, and 11% 50+ years), education (12% illiteracy, 85% having at least an primary school education), and occupation (the majority, 58.3%, being farmers). Household characteristics such as median numbers of individuals per household (3–4 individuals) and median numbers of pigs per household (2–3 pigs) were consistent between villages, while median household incomes ranged from 1,500 to 7,500 CNY. Logistic regression was used to evaluate the effect of pig ownership, household size, and income on interest in biogas in the pre-biogas survey, and on the presence of biogas in the post-biogas survey.
The study was approved by the Committee for the Protection of Human Subjects at the University of California at Berkeley, and the Institutional Review Board of the Sichuan Centers for Disease Control, Chengdu, PRC, prior to data collection. Written informed consent was obtained from all study participants, and all research procedures were conducted according to the principles expressed in the Declaration of Helsinki.
No viable eggs were recovered in the effluent collected weekly from two biogas systems for two months following seeding with highly infected stool. Likewise, zero viable eggs were recovered (no hatched miracidia observed,
The pre-biogas survey in two villages in 2003 revealed that participants made use of diverse fuels for daily activities such as lighting and cooking (
Percentage of households using energy source | |
Lighting | |
Electricity | 98 |
Candles | 10 |
Kerosene | 7 |
LPG | 2 |
Cooking | |
Electricity | 2 |
Kerosene | 5 |
LPG | 5 |
Coal | 88 |
Wood | 57 |
Percentage who cited as their primary reason… | |
…for wanting a biogas system | |
Inexpensive energy | 79 |
Improved health | 14 |
Improved quality of fertilizer | 7 |
…for not wanting a biogas system | |
Expense of construction | 70 |
Expense of upkeep/maintenance | 7 |
Reliability | 7 |
Reduced fertilizer quality | 7 |
Not enough animals | 7 |
Positive interest in biogas was associated with an increased number of pigs in the household. Indeed, gas production is largely determined by the quantity of input waste, pigs being the dominant source by mass
Respondents in the pre-biogas survey estimated the cost of biogas installation at 2,100 CNY (range 800–8,000 CNY). Two-thirds of respondents in the pre-biogas survey indicated that they would be willing to pay 800 CNY (approximately US $100 at the time of survey) for a system, and as would be expected, this group nearly exactly coincided with respondents indicating interest in installing a system in their home. Half of those with interest in a biogas system expressed the need for a loan to help cover the costs of construction.
A total of 254 households in 10 villages participated in the post-biogas survey. Of these, 54 households (21%) had biogas systems. Biogas systems were found in half of the villages surveyed, and only in villages where government subsidies were available (
Village | Respondents | # have biogas | % |
Daxing Xinming 3 |
26 | 18 | 69 |
Daxing Xinming 7 |
25 | 6 | 24 |
Daxing Shian 5 |
25 | 10 | 40 |
Daxing Jianxing 6 | 25 | 0 | 0 |
Chuanxing Jiaojia 4 | 26 | 0 | 0 |
Chuanxing Hexing 1 | 25 | 2 | 8 |
Chuanxing Minhe 1 | 26 | 0 | 0 |
Chuanxing Minhe 3 | 26 | 0 | 0 |
Chuanxing Xinlong 7 |
25 | 18 | 72 |
Gaojian Tuanjie 2 | 25 | 0 | 0 |
Total | 254 | 54 | 21 |
Villages where biogas subsidies were made available.
Every household with a biogas system in use reported that they received a subsidy to build their system. These subsidies were valued at 1,000–1,500 CNY, with one household reporting only 300 CNY. On average villagers estimated the total cost of each system to be 2,900 CNY (range 1,300–14,000 CNY), and they estimated that on average they save approximately 600 CNY (range 100–1,000 CNY) per year in reduced household energy costs. Because subsidies were provided in the form of construction supplies and accessories such as pressure gauges and biogas appliances (e.g. rice cooker, single-burner range), the installation of a biogas system was often associated with other household improvements; 98% of the families installed improved toilets at the same time as their biogas system. Since most of the systems were relatively new, no maintenance costs were reported, except for one respondent who spent 40 CNY to fix a system, but ultimately stopped using the system altogether.
The dominant reason provided in the post-biogas survey for why a household did not install a biogas system was not cost, but rather lack of sufficient space on their property to build a system. There were no significant differences in household incomes between those having systems versus not having systems. Similarly, there was no significant difference in average educational level between those with and without biogas.
The typical household biogas system relies upon the input of both human and pig waste into the system to produce biogas. On average for those using biogas there were 4.7 persons in the household (range 2–9) and 2 pigs (range 0–5). Some households (38% of those surveyed) reported that they had to purchase additional pigs shortly after the system was installed to generate sufficient quantities of biogas. When we administered our survey, nearly all families reported that their system produced sufficient biogas to fuel their desired use of biogas-operated appliances. The only family not using their system reported a system leak and insufficient gas production.
Nearly all households (98%) reported using biogas fuel for cooking, which is consistent with the subsidy program that provided kitchen appliances at no cost. Prior to using biogas many households used a combination of energy sources for cooking. Households reported using some wood (94%), coal (49%), crop waste (2%), and electricity (28%; sum greater than 100% due to use of multiple fuels). All respondents reported that switching to biogas resulted in cleaner and less smoky kitchens, and that cooking with biogas was easier than using their previous cooking fuel. On average, respondents' systems produced sufficient biogas to support 1.2 hours of cooking time per day (range 0.2–3 hours).
While we are aware of the use of biogas for lighting in other counties in Sichuan Province, in the villages surveyed here, no households reported this use. This may reflect the fact that lighting equipment was not supplied as part of the subsidy program. What is more, the subtropical summer climate and reduction in biogas production in winter months precludes use of biogas fuel for household heating.
In most households, effluent from the biogas digester is used as a natural fertilizer for agriculture. All respondents felt that there was a sufficient quantity of fertilizer produced by their systems. Most households (82%) reported that the quality of the fertilizer was better having passed through the biogas system, 16% felt it to be roughly the same as pit-stored stool, and 2% felt it to be inferior. Villagers attributed large changes in fuel usage (by mass) to the installation of biogas systems, including a 68% decrease in household coal usage, 74% reduction in wood, and 6% drop in crop waste. In contrast, use of electricity was reported to increase by 3% (by CNY) subsequent to biogas installation, possibly a result of the introduction of modern electrical devices and appliances into villagers' homes.
Overall, 96% of respondents were satisfied with their decision to build the system. The primary and secondary reasons for a household's decision to implement the biogas system are listed in
Percentage of households | |
Primary reason for implementing a biogas system | |
Inexpensive energy | 48 |
Improved health and sanitation | 42 |
Convenience and saving time in cooking | 6 |
Subsidies | 4 |
Secondary reason for implementing a biogas system | |
Improved health and sanitation | 43 |
Inexpensive energy | 23 |
Improved quality of fertilizer | 19 |
Convenience and saving time in cooking | 11 |
Subsidies | 4 |
The post-biogas survey responses were largely consistent with those of the pre-biogas survey in identifying energy costs, health, and subsidizing construction costs as important factors in determining whether to implement a biogas system. The one difference, however, was that the post-biogas survey also identified convenience as an important benefit to biogas.
Private benefits to households in terms of the consumptive use of biogas for cooking have been emphasized and estimated in various regions, including China
Data were available to quantify biochemical inactivation at
As is common in experimental removal studies, this study was limited by a small sample of biogas systems in which removal was estimated. In cases where government subsidies are applied, the Ministry of Agriculture plays an active role in overseeing the design and construction of the systems, which may reduce the variability in removal rates among systems by ensuring uniform design and construction quality. While evaluation of a larger number of systems across multiple seasons would increase confidence in the estimates presented here, our findings in a limited number of systems suggest that the development of biogas infrastructure in endemic areas could offer a significant reduction in parasitic ova contamination from nightsoil use, with important implications for human disease. Simulation studies based on the results presented here suggest the community benefit of reduced worm burden is almost linearly proportional to biogas coverage: a 10% reduction in eggs in a village for 1 year, for example, resulted in a 12% infection intensity reduction in comparison with no control measures
Although they were developed collaboratively with the local schistosomiasis control authorities, the surveys in this study lack rigorous validation that would make them useful in different regions of China. Moreover, we acknowledge the limitations of a direct comparison of the pre- and post-biogas surveys. The differences in number of villages and minimal overlap in households between the two surveys did not allow for a formal paired comparison of household perceptions. Thus, our results are meant to be descriptive. We note, however, that the reported reductions in household coal, wood, and crop waste use for energy were based solely on the post-biogas questionnaire, which asked the relatively larger sample of households with biogas systems about energy usage the year before and after the installation of the biogas system. Still, economic development may confound comparisons of energy usage before and after the installation of biogas. An indicator of this development was electricity usage, which increased a modest 3%. Moreover, the post-biogas survey, with its larger sample of households allowed us to assess the association between objective household metrics (particularly household income) and adoption of biogas systems.
The most striking finding from the post-biogas survey was the importance of subsidies in implementing the systems at the village level. In villages without the subsidies, no new biogas systems were constructed. Interestingly, the respondents did not perceive the subsidies to be a critical factor in their decision to implement a system. This suggests that, along with the monetary subsidy, the outreach, education and marketing of biogas benefits that occur with an organized governmental program are key to community adoption.
While the subsidies covered a portion of the construction cost, villagers were still required to pay a considerable amount of money to implement these systems. On average, these systems cost roughly 23–32% of a household's estimated 6,000 CNY annual income. With energy savings valued at roughly 600 CNY per year, 2–3 years are required to recoup the capital cost incurred by a household. Villagers indicated their belief that their systems would last a long time (mean response was 14 years). Moreover, a large percentage of respondents (89%) reported their system still operated as well as when they first had it installed.
Biogas systems offer a number of benefits which are highly valued in this community despite the capital requirements of installation. Villagers perceive both improved sanitation and cleaner kitchens (especially with respect to black carbon) associated with biogas system use. Indeed, the health benefits from improvements in indoor air quality resulting from reductions in indoor burning of coal, wood, and crop residues benefits have been shown elsewhere to be considerable
The focus of schistosomiasis control in China has been on chemotherapy and control of the intermediate snail host
The authors wish to thank our colleagues at the Xichang County Anti-Schistosomiasis Station, and to Kang Junxin, Director of the Sichuan Center for Disease Control and Prevention (Chengdu, People's Republic of China) for their continued support and collaboration.