Tag Archives: rural energy access

Maintenance of biodigesters and issues surrounding maintenance/service arrangements

Even in the presence of mandated service agreements maintenance for biodigesters can still be an issue. For example, time constraints on private contractors [1] from central government to install and maintain digesters, lead to a slipping in maintenance standards. In a village in Assam interviewed in the paper, no follow up visits from the contractors were had for four years, and a 20% digester failure rate was recorded. Communications issues were a key contributor to this: the fact that a provision of a half of the installation subsidy for maintenance of plants over 5 years old was not communicated to households or the contractors.

broken biogas assam india

A broken biodigester in Assam, India, having not been repaired for 6 months. Source: Raha, Mahanta & Clarke (2014) The implementation of decentralised biogas plants in Assam, NE India: The impact and effectiveness of the National Biogas and Manure Management Programme. http://dx.doi.org/ 10.1016/j.enpol.2013.12.048

One of the more overlooked aspects of biogas digester services and operation is the maintenance requirements of digesters. Older digester designs (for example dome-type biodigesters constructed from brick or earth) require a regular maintenance schedule (monthly to quarterly is common) [2] in order to maintain best performance, including maintaining the chemical balance of the digesting chamber and its structural integrity, repairing cracks in the chamber if necessary. More modern household and collective-scale designs are based off a plastic digesting chamber, usually fibreglass-reinforced plastic (FRP), and as such require less intensive maintenance (annual maintenance visits are sufficient), but still have a maintenance burden to address for peak performance (for example, maintaining the chemical balance of the digester through appropriate feedstock insertion).

However, even in the presence of mandated service agreements for biodigesters, for example delivered through a fee-for-service energy service company (ESCO), maintenance can be overlooked. A useful case study illustrating this can be obtained from India’s National Biogas and Manure Management Program (NBMMP) [1]. The NBMMP relied on local governments in India contracting the private construction sector to construct biogas digesters for rural communities. Time constraints on these contractors on installation, stemming from the prevailing climatic conditions limiting the working period of the year due to monsoons, meant that maintenance standards, for which the contractors under the tender from local government were also responsible, and the overall quality of installation of digesters, slipped drastically. Some contractors reported having to fill an annual allocation of 6,000 digester installations in just three months, at a rate of over 60 digesters per day, often for small companies of just 5-10 technicians. Hence, some digesters were not being maintained for four years or more, and there was a 20% overall digester failure rate. Communication between the public bodies and private contractors was also an issue: the NBMMP made provision of half the subsidy granted to households for purchasing digesters as a maintenance grant over a five-year period, which was barely taken advantage of due to a lack of awareness on the part of households and contractors.

This case study makes clear the necessity of accounting for maintenance arrangements in the design of any biodigester business plan or program. Ensuring the maintenance schedule is followed will extend the life of the biodigester and improve its performance, resulting in greater satisfaction with the system from the point-of-view of end-users. This fact makes biodigesters particularly suited to a fee-for-service business model: regular maintenance can easily be combined with regular payment collection visits, reducing the cost burden on the company/organisation and improving service.

The final post in this series will focus on the recent evolution of the Chinese National Biogas Program, and the lessons to be learned for cross-application in other regions globally.

– Xavier Lemaire and Daniel Kerr, UCL Energy Institute

[1] Raha, Mahanta & Clarke (2014): http://dx.doi.org/10.1016/j.enpol.2013.12.048

[2] Surendra et al (2014): http://dx.doi.org/10.1016/j.rser.2013.12.015

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The Challenges and Opportunities of Centralised and Decentralised Biodigesters

The STEPs research project explores the relative benefits and dis-benefits of larger centralised biogas systems at a village scale versus smaller family-scale systems. It also investigates the economic and financing factors (centralisation brings economies of scale but can only really be implemented by organisations/governments, family-scale systems may be out of reach of user capital without financing arrangements), environmental factors, and social and behavioural considerations (do users want to collectively cook, issues with economics of pipe gas supply meaning necessity of group facilities etc) inherent in biodigester development.

Biogas digesters can be a valuable solution to providing thermal energy services to rural and urban households in the developing world. The technology is particularly applicable in rural areas, where access to feed stock for the digesting chamber in the form of agricultural wastes and other organic wastes is greater. In general, digesters fall into two broad categories: household-scale biodigesters, and larger, centralised biodigesters.

Laramee & Davis 2013 Dome Biodigester in Tanzania

Dome-type biodigester in Arusha, Tanzania [1]

Household-scale biodigesters are often seen as the most viable option for rural communities and households. These are generally small, with digesting chambers of volumes in the 4 to 13 cubic metres range. These installations will support the cooking needs of a rural household, as well as providing biogas for heating or lighting if required. Tailoring the size of the biogas system to the availability of feedstock for the household is critical for successful functioning of the system: studies have suggested 4-6 heads of cattle is a sustainable target if using agricultural wastes for feedstock, for an average-sized family of five. Individual biodigesters can produce sufficient gas for a single person on as little as 1 kg/day of feedstock.[2]

However, one of the primary limiting factors in the adoption of household biodigesters is financing and end-user capital constraints. Household-scale systems are still relatively expensive for the majority of rural developing-world users, and experience has shown that without the provision of credit facilities in biodigester programs, or government subsidies, adoption rates remain low.

Centralised biodigester systems offer a different set of benefits and challenges. Economies of scale are the major advantage: one centralised system can serve a medium-scale settlement or several small settlements, with a reduced burden for upfront capital costs and maintenance compared to the same service with household-scale systems, in the range of US$100 – 500 per household. The Chinese National Biogas Program [which will be the subject of a later blog in this series], has been the major implementer of centralised systems, however experience also exists in other South-East Asian countries. Examples of this can be found in the centralised digesters built near Beijing to service rural villages. For an upfront cost of ~US$1 million, 1900 households are serviced through each centralised digester, with biogas available at a 20% discount compared to market LPG prices, and the additional benefit of organic effluent being made available for sale to the local farms feeding the digester.[2] The major constraint, however, to wider dissemination of centralised systems is the significantly higher up-front capital costs. This puts the systems out of reach for private users in the majority of cases, government-scale implementation is more common.

Socio-political conditions are another factor that has proved a constraint in biogas implementation projects in developing countries. Centralised biogas digesters can have difficulty with biogas supply to end-users, particularly given the poor economics of installing piped gas supply in small rural communities. Communal cooking facilities have been a solution to this problem in theory, however experience from India suggests that collective cooking is not desired by the rural population, and this has impacted upon the success of centralised digester installations. As with dissemination programs for clean cookstoves, biogas installations need to take into account the end-users needs and desires in design and installation for product use and performance.

The other posts in this series will cover the question of why biogas hasn’t succeeded in Sub-Saharan Africa as it has in South-East Asia, the maintenance question for biogas services, and lessons from the Chinese National Biogas Program.

– Xavier Lemaire & Daniel Kerr, UCL Energy Institute

[1] Laramee & Davis (2013) Economic and environmental impacts of domestic bio-digesters: Evidence from Arusha, Tanzania. http://dx.doi.org/10.1016/j.esd.2013.02.001

[2] Hojnacki et al, MIT (2011) Biodigester Global Case Studies. Available at: https://colab.mit.edu/sites/default/files/D_Lab_Waste_Biodigester_Case_Studies_Report.pdf