Biogas Technical Note

FONERWA

BIOGAS TECHNICAL NOTE

DRAFT

August 2015

Prepared by:

Gerard Hendriksen

Consultant

1

Summary

Biogas is already widely used in Rwanda as a source of cooking energy forrural households using dung from their dairy cows and in all prisons and some boarding schools using human waste. Biogas contributes towards improvingof the environment and the reduction of greenhouse gas emissions. FONERWA already provides some support to biogas activities in Rwanda and is considering how it can interfere more strategically in this sector by upscaling current technologies and promoting new and innovative approaches.

This technical note provides up to date information on the current state of biogas in Rwanda and also draws upon to experiences of biogas in the other countries in the region and beyond which can provide lessons for Rwanda. This note should help all concerned parties with basic information on the various biogas applications and to help make informed choices for any selected options.This information in the note was collected through a desk study and draws mainly from the National Domestic Biogas Programme and the IFAD/ KWAMP programmein Rwanda and SNV’s experiences in other countries in Africa and beyond.

The table on next page provides an overview of the biogas systems as used in Rwanda and can be divided in the two systems according to their size.

a)Small domestic digesters of 4 – 10 m3 for rural households using cow dung as feeding material. The fixed dome made out of bricks and cement promoted since 2008 under NDBP is the most popular type with about 5500 operating in the country and numbers are steadily increasing. These digesters are constructed in situ by contractors trained and approved by NDBP. Prefabricated digesters made out of plastic have been tested by NDBP but did not gain ground. More recently Kenyan made flexible bag digesters were introduced and these have made considerable progress on the market because of their lower costs and quicker installation. The Government of Rwanda has a target of 100,000 digesters by 2018 and actively supports this market through a subsidy of Rwf 300,000 per digester.

b)Large digesters of 25 – 100 m3 of the fixed dome type constructed out of bricks, have been installed in all prisons (up to 1,000m3 by connecting digesters in series) and a number of boarding schools. The feeding material is human waste and in some schools this is combined with cowdung. These digesters are constructed through contractors selected through competitive tendering and largely paid through Government programmes.

Communal biogas systems have been constructed in a number of “green” villages using the same fixed dome technology.

While biogas has progressed relatively well in Rwanda there remain some challenges such as:

1)The promotion of toilet waste in combination with cowdung in rural areas to increase volume of gas, bio slurry and as well reduce environmental impacts.

2)The relative high costs of large digesters in costs per unit as compared to the domestic type

3)Opportunities for biogas in urban areas for household cooking have not yet been addressed

4)Opportunities for commercial applications of biogas and possibly generation of electricity from waste

Table: Overview of common biogas systems for Rwanda

Table of Contents

1Introduction

1.1Background of this note

1.2Biogas applications in Rwanda

2Small biogas digesters for domestic application

2.1Type of digesters for domestic use

2.2Fixed dome digester

2.3Floating drum digester

2.4Prefabricated digesters

2.4.1Chinese fibre glass digesters

2.4.2SimGas Digesters

2.4.3Plastic Tube Digesters

2.4.4Digesters based on plastic water tanks (urban applications)

3Larger and commercial applications of biogas

3.1Biogas systems for prisons, boarding schools

3.2Communal biogas systems

4Some other aspects of biogas

4.1Composition and sources of biogas

4.2Feeding materials

4.3Bioslurry

4.4Biogas and carbon credits

4.5Uptake of biogas in other countries

4.6Biogas for electricity generation

Abbreviations

ABPP Africa Biogas Partnership Programme

ARTI Appropriate Rural Technology Institute

CDM carbon development mechanism

FGD fibre glass digesters

FONERWA Rwanda’s environment and climate change fund

GIZ Deutsche Gesellschaftfür Internationale Zusammenarbeit,

IFAD International Fund for Agricultural Development

ISEA College of Agriculture, Animal Sciences and Veterinary Medicine

kVAkilo Volt Ampere

KWAMP Kirehe Community-based Watershed Management Project (IFAD)

MININFRA Ministry of infrastructure

NDBP National Domestic Biogas Programme

PE poly ethylene

PSDAPrivate Sector Development in Agriculture (GIZ, Kenya)

PTDPlastic Tube Digester

RURA Rwanda Utility Regulatory Authority

1Introduction

1.1Background of this note

This technical brief has been developed to support the FONERWA applicants and the program’s management in the formulation and the evaluation of project proposals for biogas projects. The note is intended to provide up to date information on the current state of biogas in Rwanda. The note also refers to development of biogas in the other countries in the region and beyond which can provide ideas and lessons for Rwanda. This note is not designed to limit the options for biogas proposals but instead it should help all concerned parties to provide basic information on the various biogas applications and to help justify choices for any selected options. In the case of new developments and innovations, it helps to compare with known solutions and to provide justifications for alternatives and new approaches.

This information in the note was collected through a desk study and draws from the MININFRA’s National Domestic Biogas Programme as well as from the Africa Biogas Partner Programme[1] (ABPP) operating in five other countries in Africa. Also the IFAD/ KWAMP programme[2] has been implementing a biogas programme in Kirehe district and their experience has been included in this note. This has been followed up through email and skype conversations. There was no opportunity to carry out field visits to exchange views with the various stakeholders and validate what was found in the different reports.

The results and views presented in this report and any possible errors or omissions are the responsibility of the consultant and do not necessarily represent those of FONERWA or the sources of information mentioned in the report.

1.2Biogas applications in Rwanda

Biogas was introduced in Rwanda in the 1980s but uptake was limited. In the early 2000s, the Rwanda Government initiated the construction of large biogas systems in prisons to reduce the environmental impacts of the toilet waste on the environment and provide cooking energy. The National Domestic Biogas Programme became operational in 2007 and focused in domestic biogas for households owning a small number of dairy cows.

Table 1 provides an overview of the different systems in Rwanda. The rest of this note is divided in:

Chapter 2 which deals with small biogas systems for domestic purposes

Chapter 3 describes the use of biogas for larger institutions such as boarding schools.

Chapter 4 deals with the theoretical back ground of biogas, the use of bioslurry, the potential for carbon credits and the opportunities of electricity generation.

1

Table 1: Overview of common biogas systems for Rwanda

• Proven technology using local skills and materials
• Low maintenance
• Requires little space (digester underground )

• Investments costs dropping but remain high
• Construction process takes several weeks

• Standard product quality
• Quicker installation
• Digesters can be moved (with some costs)

• No local manufacturer (as yet?)
• Special skills and tools needed for assembly
• No proven production and market as yet

• Fast installation
• Easy transport to site
• Digesters can be moved to other location
• Shorter retention time

• Life span not yet proven
• More easily damaged
• Above ground design, requires more space

• Uses household waste
• Quick to install
• Can be moved easily

• Investment costs high Rwf 160- 400,000/ m3
• Sensitive quality and quantity of feeding materials,
• Market not proven yet

• Proven design
• Significant impact on fuel wood savings
• Improvements in hygiene

• Requires strong/ dedicated management
• Investment costs high
• Limited number of contractors

• Combination of human and animal waste

• Investments costs appear higher than individual systems
• The distribution of gas production between households can be challenge

1

2Small biogas digesters for domestic application

2.1Type of digesters for domestic use

There are many different types of digesters for domestic applications and the table below provides a quick overview of the popular models and some have found wide scale application in Rwanda.

Table 2: Overview of biogas options for domestic applications

2.2 Fixed dome digester

The fixed dome digester is the most popular type in Rwanda and since 2008 about 5,500 units have been in the country under the National Domestic Biogas Programme. Digesters are constructed at the farmer’s homestead by local contractors trained by the programme. NDBP provides a subsidy provided the digester meets pre-determinedquality standards.

Figure 1; Fixed dome digester

Sizes of digester vary between 4 and 10 m3 but the most popular model is 6 m3. It requires about 40 kg of fresh cow dung per day (2 – 3 cows using zero grazing) and a similar amount of water. Urine collected from the stables can replace most of the water needed to mix with the dung, improves the performance of the digester and adds value to the bioslurry. A 6 m3 generally provides sufficient cooking gas for a family of 5 persons for most days. In certain types of food or quantities, households have to supplement with firewood.

The table below shows typical investments costs for the digesters supported under NDBP. During the initial years of the programme the use of burnt bricks was banned and digesters were constructed out of stones and concrete. More recently burnt bricks are used fully or partly in the design depending on availability and costs. Construction costs also vary slightly depending on location, availability of building materials and the costs of the contractor.

Table 3: Typical investment costs for fixed dome digesters (Rwf)

*) based on the average type of dairy cows in Rwanda. In case of larger animals, the number can be reduced.

The NDBP with support of SNV has established an elaborate skills development programme to masons and other artisans who want to be officially registered with the programme as contractors/ service providers[3].

The biogas digesters installed under the NDBP are equipped with a second inlet enabling connection to a toilet. However, uptake of this option has been very limited despite the additional benefits in terms of sanitation, production of more biogas and bio-slurry. There are technical and cultural barriers that need to be overcome. In some Asian countries (China in particular), the use of human waste for biogas is more accepted.

Table 4: Fixed dome digesters: pros and cons

RURA, the Rwanda Utility Regulatory Authority, has issued technical guidelines for the construction of domestic fixed dome biogas plants[4]. The document has been prepared to assist the biogas plant operators to successfully carry out their anticipated roles in constructing good-quality biogas plants

2.3Floating drum digester

The digester is in many aspectssimilar to the fixed dome. The main difference is that the generated gas is caught in an inverse steel drum which “floats” on top of the fermenting slurry. The biggest advantage of this type of digester is the more consistent pressure of the gas. However, the costs are substantially higher than for fixed dome digesters and the system requires more maintenance. The system has been relatively popular in Kenya but never gained ground in Rwanda. It is not promoted under NDBP because of the extra costs.

Figure 2: Floating Drum Digester

Table 5: Floating biogas digesters: pros and cons

2.4Prefabricated digesters

2.4.1Chinese fibre glass digesters

Prefabricated digesters manufactured out of plastic reinforced with fibre glass are popular in some countries including China and Indonesia. Prefabricated digesters are promoted for the following reasons a) installation is quicker than the fixed dome, b) quality of product easier to maintain than in case of individually constructed digesters and c) expected lower costs of the systems. The system has been tested in Rwanda with Chinese pre-fab digesters and more recently with the GesiShamba digesters manufactured by Simgas Tanzania.

Figure 3: Prefabricated digesters

In 2007 MININFRA imported 100 fibre glass digesters (FGD) and accessories from China under a contract that included the provision of technical expertise. Most of these digesters were installed by the Ministry in the Kirehe district. The performance of these digesters was assessed in a study carried out in 2009[5]. The study found that the construction time for FGD was 13 days compared to 20 days for the fixed dome type (not taking into account the time needed for negotiation of contracts, other preparations and the initial filling of the digesters with dung after completion). The report also estimated that the gas production of the fixed dome type was higher than of the FGD digesters but this was partly contributed to the management by the users.

The report estimates the costs of the FGD to be Rwf 764,000 (or about Rwf 125,000/m3. The initial expectations were that prices of the FGD digesters would come down if produced locally instead of imported in knocked down versionbut this was never tested as the program was discontinued.

2.4.2SimGas Digesters

The SimGas Company[6]from the Netherlands established a production unit for digesters in Tanzania from where it supplies other countries in East Africa. Initially the focus was on digesters for urban households using organic waste as feeding material (see page11for further information on urban biogas). More recently the company introduced pre-fabricated digesters of a modular design for rural areas (GesiShamba) which allows digesters to be assembled in sizes from 2 – 20 m3. A number of digesters has been installed in Kenya and Tanzania to fully test the design. Some modifications are currently being implemented before the product will be officially launched and marketed. Final prices are not yet fully established but it is now reported that these will be comparable or even slightly higher than for the fixed dome types. A manufacturing price of USD 750 in Rwanda has been quoted in some earlier documents. Simgas wasalso considering local manufacture of the digester elements in Rwanda but no final decision has been taken as yet. Key factor will be the number of digesters that can be sold in the country and which can justify to high investment costs for production facilities

Table 6: Pre-fabricated biogas digesters; pros and cons

2.4.3Plastic Tube Digesters

Plastic tube digesters (PTD) made out of polyethylene sheeting material (thickness of 300 micron)have been installed in a number of countries and have been particularly successful in South America in Bolivia. The costs for a 3- 6 m3 plastic tube digester are reported to be as low as € 100 – 150. Gas storage and pressure of these plastic tube digesters are relatively low and in some designs storage capacity is increased through the addition of extra storage bags.