Survey of Plastic Tube Digesters in Kenya: Field Assessment Survey of the Performance of Plastic Tube Digestors in Kenya

Survey of Plastic Tube Digesters in Kenya
A field assessment survey of the Performance of Plastic tube digestors in Kenya

STUDY REPORT

December, 2010

Francis Xavier Ochieng

Commissioned by:

ENERGIE
KONSULT LTD.

Published By:
Deutsche Gesellshaft für
Technische Zusammentarbeit (GTZ) GmbH

-German Technical Cooperation-


Dag-Hammarskjöld-Weg 1-5
65760 Eschborn/German
T +49 6196 79 2438
F +49 6196 79 802438
E oscar.onguru@gtz.de
I www.gtz.de

Survey of Plastic Tube Digestors in Kenya Page 1 of 49


A field survey of the Performance of Plastic tube digestors in Kenya

Study Conducted by

ENERGIE
KONSULT LTD.

GTZ – Regional Energy Advisory Platform (East Africa)

Nairobi, December, 2010


Consultancy Reference Number: INT/EK/04/2010/GTZ

Francis Xavier Ochieng

Director,

Study Energie Konsult Ltd,

undertaken P. O. Box 7764 – 00200, Nairobi, Kenya
By
Tel: +254-714-693299 / +254-20-3203802

E-mail: xavierfo@yahoo.com , xavierf@gmx.de , director@energiekonsult.com

www.energiekonsult.com

Michael Franz

Regional Energy Advisory Platform (East Africa) - REAP (EA)

German Technical Cooperation (GTZ); Utumishi Cooperative House, 5th Floor
Prepared For:
Mamlaka Road, off Nyerere Road,

P. O Box 41607-00100, GPO; Nairobi, Kenya

Email : michael.franz@gtz.de

History of Changes

Version Description of Amendment Date

01 Draft Report Issued 29/11/2010

02 Changes in data bases, PTD pricing, Integration of all questionnaire 07/12/2010
answers into report and finally provision of a video on PTD’s

03 Addition of Subsidy analysis and referencing 17/12.2010

17TH December, 2010


Acknowledgements

The German Technical Cooperation (GTZ) is through the Energizing Development Programme
(EnDev) funding the installation of 15,000 biogas digestors before December 2010 in Rwanda
(Renwick et al (2007). In achieving this target, an optimal cost effective Biogas digester has to be
adopted. It is within this framework that an assessment of Plastic Tube Digesters was undertaken.
Essentially, the study sought to ascertain the truth of the performance of digester types in the field (i.e.
practice) and also ground truth the claims of practitioners in terms of scope and applicability of the
technology.

This output informs the basis on which decisions regarding the adoption, modification or non-adoption
of the tubular biogas digesters could be made. More importantly it lays the truth regarding the industry
practices and what can be done about it.

This research would not have been possible without Dedan N. Ndungu of Modeline Electrical and
Mechanical engineers, who took the time to take me through the various sites, many of which I had no
form of contact information like telephone numbers. It is also important to mention that Dedan also
provided a video of some of the sites he has installed these PTD’s. The first part of the video gives not
only the technical information about the digesters, its costs, sizes and installation, but also provides
information on the end-users views on the use of the digester and the benefits they accrued. His
contact information can be obtained from page 7

In addition we gratefully acknowledge the support of Oscar Onguru of GTZ-REAP and Gerard
Hendriksen for their invaluable contribution in supporting and commenting on this work. Last but not
least we thank Samuel Nene of Pioneer Technologies for providing that very invaluable initial contact
list and availing the time to give the investigator more in depth understanding of the tubular digesters.

Lastly we do acknowledge that the views expressed in this report are entirely the responsibility of the
Author and may not be the official views of GTZ or its affiliated partner agencies. Thus any comments,
contributions and clarifications should be addressed to the Author. It is our hope that the work will
enrich the ongoing discussions among practitioners, policy makers and academia and welcome any
feedback and comments

Francis Xavier Ochieng,

C.E.O Energie Konsult Ltd,

P. O. Box 7764 – 00200, Nairobi, Kenya

www.energiekonsult.com


Table of Contents

ACKNOWLEDGEMENTS ..................................................................................................................... 4
TABLE OF CONTENTS........................................................................................................................ 5
LIST OF TABLES ................................................................................................................................. 6
LIST OF FIGURES ............................................................................................................................... 6
ABSTRACT .......................................................................................................................................... 7
1. ABOUT THE FIELD ASSESSMENT ............................................................................................ 8
1.1 INTRODUCTION AND BACKGROUND TO THE FIELD STUDY ............................................................ 8
1.2 STUDY PROBLEM ...................................................................................................................... 8
1.3 JUSTIFICATION / SIGNIFICANCE OF THE STUDY ............................................................................ 9
1.4 AIM, SCOPE AND EXPECTED DELIVERABLES OF THE STUDY ......................................................... 9
1.4.1 Aim of the Study................................................................................................................. 9
1.4.2 Specific objectives ............................................................................................................. 9
1.4.3 Scope of the Study .......................................................................................................... 10
1.4.4 Expected deliverables o f the study................................................................................. 10
1.5 STRUCTURE AND METHODOLOGY OF THE STUDY ...................................................................... 10
1.6 DETERMINATION OF THE SAMPLE SIZE AND DIGESTERS TO VISIT ................................................ 10
1.6.1 General overview ............................................................................................................. 10
1.6.2 Statistical determination of the Sample Size ................................................................... 11
1.6.3 Digester sampling and Survey methodology ................................................................... 13
1.7 PTD STUDY REVISED WORK PLAN ........................................................................................... 14
1.8 CHALLENGES AND LIMITATIONS OF THE FIELD SURVEY .............................................................. 15
2. RESULTS OF THE FIELD SURVEY.......................................................................................... 16
2.1 DIGESTER MATERIAL AND SIZE ................................................................................................. 16
2.1.1 Digester material and size ............................................................................................... 16
2.2 PTD COSTS ........................................................................................................................... 17
2.2.1 Costs from Pioneer .......................................................................................................... 17
2.2.2 Costs of PTD from the field/study .................................................................................... 17
2.2.3 Subsidy and cost comparisons of PTD with Fixed dome digester .................................. 18
2.3 FARM LAYOUT AND DIGESTER INLET FEEDING DESIGN CHARACTERISTICS .................................... 0
2.4 DIGESTER PERFORMANCE ......................................................................................................... 0
2.5 BIOGAS APPLICATIONS .............................................................................................................. 2
2.6 PTD PAYBACK PERIOD .............................................................................................................. 3
2.6.1 Payback period based on Charcoal use............................................................................ 3
2.6.2 Payback period for PTD and Fixed Dome Digester based on other Biomass fuels.......... 3
2.7 BENEFITS OF DIGESTER SYSTEMS ............................................................................................. 5
2.8 EXTENSION SERVICES ............................................................................................................... 5
2.9 PTD SUSTAINABILITY................................................................................................................ 5
2.10 PTD AND OWNERSHIP FINDINGS ................................................................................................ 6


2.11 SECOND HAND PTD.................................................................................................................. 6
3. LESSONS LEARNT AND CHALLENGES EXPERIENCED ......................................................... 7
3.1 LESSONS LEARNT ..................................................................................................................... 7
4. RECOMMENDATIONS .............................................................................................................. 10
4.1 FRAMEWORK FOR PTD INSTALLATION AND OPERATION MANUAL ................................................ 10
4.2 RECOMMENDATIONS FOR THE PTD ADOPTION IN RWANDA ....................................................... 10
4.3 RECOMMENDATIONS FOR FURTHER SCIENTIFIC RESEARCH AND FIELD STUDIES .......................... 11
4.4 RECOMMENDATIONS FOR BETTER MARKET DELIVERY MODELS ................................................. 11
4.5 END-USER RECOMMENDATIONS ............................................................................................... 12
4.6 RECOMMENDATIONS TO POLICY MAKERS.................................................................................. 12
5. APPENDICES ............................................................................................................................ 13
5.1 TOOLS USED IN FIELD SURVEY ................................................................................................ 13
5.1.1 Institutional Questionnaire ............................................................................................... 13
5.1.2 End-User Questionnaire .................................................................................................. 17
5.2 INITIAL PTD’S LIST FROM PIONEER TECHNOLOGIES LIMITED ..................................................... 20
5.3 REFORMATTED AND UPDATED LIST OF CONTACTS .................................................................... 23
5.4 PTD DATA BASE..................................................................................................................... 28
6. REFERENCES........................................................................................................................... 32

List of Tables

Table 1: Sample size at 95% confidence level with a degree of variability P of 0.5 ............................. 12
Table 2: Selection of Digester sites based on pre-determined sample size ......................................... 13
Table 3: Selection of final sites to visit based on household location type ........................................... 14
Table 4: PTD performance study – Revised Work plan ........................................................................ 14
Table 5: Performance of Installed PTD in Sample and in total population............................................ 16
Table 6: Comparative assessment of costs and subsidies of PTD and Fixed dome digesters .............. 0
Table 7: Overall performance of PTDs.................................................................................................... 0
Table 8: Payback period of different digesters based on different Biomass fuels .................................. 4
Table 9: Assumptions for a household of 5 people ................................................................................. 4
Table 10: Current and potential Companies installing Plastic Tube digesters in Kenya......................... 7

List of Figures

Fig 1: Trend analysis of PTD’s prices and installations over the years................................................. 18
Fig 2: Biogas Cook stove, with the feed inlet pipe being shown ............................................................. 2


Abstract

This report documents the results of a field survey of Plastic tubular digestors (PTD) in Kenya. Using a
precision level (e) of 17% of the total probable biogas digestors installed by a local company –
Pioneer Technologies Limited, 34 biogas digestors were visited, Of these 28 were working, 3 were not
working, two had been dismantled and replaced with masonary ones and the last one had been
installed at Jomo Kenyatta University of Agriculture and Technology for experimental purposes, whose
objects have since been achieved, and the PTD’s operations there stopped.

The implications of this is that of the expected countrywide installations of PTDs about 82.4% are
working, while 8.8% are not working, 5.9% have been decommisioned and masonary ones installed in
thier place and lastly 2.9% have been decommissioned/abandoned and nothing replaced in thier
stead.

Findings indicate that most of the end-users, who are mostly farmers were quite satisfied with the
PTD, however some did express dissapointment on the challenges they face. These included low gas
pressure during the morning and evening cooking periods, low/insufficient gas production as energy
needs increased and lastly insufficient farmer training on how to feed and maintain the Biogas
digesters. These challenges are mainly a user management problem on what the digester if fed with
and how frequently it is fed. Nevertheless, the issue of low gas production during morning and evening
cooking period is more of how well the digester is insulated from the elements, which is a training
issue. The use of UV treated double layer plastic did not seem to be a problem only in as far as the
Platic tube was not pierced.

The opportunity cost of not collecting firewood, and the utilisation of animal waste for energy, seems to
be the main motivator for the uptake of PTD’s. In essense, Household cooking and general sanitation
of the farm were also, in many cases, the key motivating factor for wanting a biogas digester in Kenya.
In order however to scale up and/or replicate this experience in other places, it is important that priority
be given to extension services and maintenance.

Equally important is optimizing gas production by correct retention time, research into the effects of
adding cattle urine, toilet waste, using other locally available material and recycling of slurry.
Furthermore, the success of the biogas project is dependent on the farmers' payment of the digesters,
which can be achieved by establishing an efficient credit system.


1. About the Field Assessment

1.1 Introduction and Background to the Field Study

The German Technical Cooperation (GTZ) is through the Energizing Development Programme
(EnDev) funding the installation of 5,000 biogas digestors before December 2010 in Rwanda. This is
undertaken within the framework of the National Domestic biogas programme (NDBP). The NDBP
aims at installing 15, 000 Biogas units by December 2011 (Rwanda, 2009). , and targets rural
households in Rwanda that have 2 -3 cows. The fixed Dome biogas digestor type with a capacity of
between 6 – 10 m² is being considered by the NDBP as a technology of choice for promotion.

However, for many of the rural households the cost of installation of the digestor at about € 1,000 is
too high despite a € 350 subsidy and a bank credit. Thus the November 2009 project review mission
recommended assessment of cost reduction opportunities. Based on GTZ experience in some South
American Countries, the possibility of an alternative biogas technology apart from the fixed dome is
now being considered. (GTZ Terms of reference for the Survey of plastic tube digesters in Kenya)

The Plastic Tube Digestors (PTD’s) as experienced by GTZ in the aforementioned countries provides
such an option. Within the Eastern Africa region institutional memory exist in form of Pioneer
Technologies who claim that they have since the year 2006 installed about 300 PTD’s in Kenya.
However, no independent surveys of these PTD’s to verify these claims have been undertaken

Initial studies to verify these claims have been undertaken by the consultant applying for this study
under the auspices of the Institute of Energy and Environmental Technology (IEET) of Jomo Kenyatta
University of Agriculture and Technology (JKUAT). The Consultant together with his team have tested
the performance of the Pioneer Technologies PTD’s at IEET and done preliminary site/field visits of
the Pioneer Technologies installed PTD’s.

Subsequently, the GTZ PTD’s study furthers the Scope of work done by the Institute and provides an
even greater sample space to draw scientifically valid lessons which can be used to deal with the
challenge facing NDBP of which this study seeks to solve.

1.2 Study Problem

NDBP is interested in assessing the potential of the PTD technology as another option for the farming
households in Rwanda. While there are claims that a Pioneer Technologies has installed over 300
PTD’s in Kenya, no independent surveys have been done to verify these claims (apart from the single
performance study and preliminary studies done by the applying consultant who is based in IEET –
JKUAT).


Therefore a need exist to survey the PTD’s installed by Pioneer Technologies. More knowledge of
Kenya’s experience with PTD is required to gauge if and how they can be used in Rwanda. This
should then enable NDBP make a sound judgment on whether or not to pursue the introduction of
PTD’s in Rwanda.

1.3 Justification / Significance of the study

The study will collect data and other relevant information to enable the NDBP make a sound
judgement on whether or not to pursue the introduction of PTD’s in Rwanda. This is necessitated by
the realisation that the installation of Fixed dome Digestors is out of reach of the rural households with
2 – 3 cows, despite the a € 350 subsidy and a special bank Credit.

In addition the study will verify the claims made by Pioneer Technologies that it has since the year
2006 installed about 300 PTD’s in Kenya of which about 90% are operational. The significance of a
positive or negative verification of this claim will provide lessons on technology adoption, adaptation
and fuel further research in the area of PTD’s.

Lastly the study will complement the initial studies that had been undertaken by the applying
consultant on PTD’s at the institute of Energy and Environmental Technology of the Jomo Kenyatta
University of Agriculture and Technology (JKUAT). It will enable the orientation of the further research
in dealing with the design and performance issues noted in the initial studies, since only a small
sample space was used.

1.4 Aim, Scope and expected deliverables of the study

1.4.1 Aim of the Study

The main aim / objective of the assignment is to assess the performance of the Plastic Tube Digestors
(PTD’s) installed by Pioneer Technologies in Kenya to inform the Rwanda biogas program about
possible introduction into the country.

1.4.2 Specific objectives

Specifically the study will seek to attain the following:

1. Compilation of a list of PTD’s installed by Pioneer Technologies in Kenya. The list will contain
the contact details and other pertinent information on the PTD like status, digestor
specifications and performance

2. Site visits of 30 randomly selected PTD’s from the aforementioned list above to assess their
performance and obtain their technical details.


3. Creation and Verification of a Data base of PTD’s installed in Kenya.

4. Provision of report indicating the status of PTD’s in Kenya and lessons learnt in the
experience. This report will be based on the findings of the above objectives

1.4.3 Scope of the Study

The study being limited in both time and depth of assessment will confine itself to the general
assessment of the working condition of 30 randomly selected Plastic tube digestors. The aim is to give
a general picture on the performance of these digestors.

1.4.4 Expected deliverables o f the study

Two main deliverables are provided by this study:

1. A report detailing the status of PTD’s in Kenya and lessons learnt in the experience. This
report will be based on the findings of the aforementioned specific objectives

2. A verified data base of PTD’s installed in Kenya

1.5 Structure and Methodology of the study

The Study essentially utilised Stratified random sampling to identify about 26% of the total installed
PTD’s. This translated to about 30 PTD’s sampled and visited.

From original list obtained from Pioneer Technologies (5.2), a corrected and reformatted list which
included Counties as per the First Schedule, Article 6(1) of the Constitution of Kenya (AG, 2010) was
developed. The need for including counties is based on the demands of the stratified random sampling
wherein, in determining the sample size, the data is stratified / divided in accordance with
administrative divisions i.e. Counties. Appendix 5.3 is the results of this correction and stratification.

1.6 Determination of the sample size and digesters to visit

1.6.1 General overview

Determination of the number of digesters to visit (sample size, n) out of the total number of digesters
(expected population size, N) is a bit complex but nevertheless simplified using on a number of
scientifically proven statistically techniques, and which unfortunately end up giving a slightly different n
from the pre-determined sample size given in the Terms of Reference (ToRs).

In determining the size of the sample n a number of factors are considered including: purpose of the
study, population size, risk of selecting a “bad” sample and the allowable sampling error. In studies


involving a lot of variables and/or high precision demands, then more stringent sample determination
are utilised. In simple studies like this one, simple formulas can be applied.

It is however, the question of the population size that tends to seriously impact on the determination of
the sample size. Various methods have evolved for determining N (Israel, u.d, Bartlett et. al. 2001).
For our purpose an initial sample size of 300 was given.

In terms of reducing the risk of selecting a “bad” sample, where a bad sample in this case would refer
to selecting only the working digesters or the ones that are not working. The constituents of the
sample have to be selected randomly, both in time and space. The implications of this to our study
being that the sites visits were done both during weekdays and weekends, morning, afternoons and
evenings. It also meant that different geo-administrative locations were visited. Lastly it implied that the
telephone contact numbers we had were called randomly and whoever agreed to meet us, irrespective
of status of digesters, or even its existence/presence was visited. No preference was given to whether
the digester was installed by the main study client (i.e. Pioneer Technologies Ltd) or not.

Lastly an acceptable/allowable margin of error, which is also known as the level of precision (e) has to
be defined. This is the range at which the true value of the estimated population is estimated to be.
Generally researchers increase this value when a higher margin of error is acceptable or decrease it
when a higher degree of precision is needed. In our case, based on uncertainty in the true population
(or number) of the PTDs’ in the field a higher e value than the normal one of ± 5% can be utilised. This
is further discussed below.

1.6.2 Statistical determination of the Sample Size

This study is based on the realisation that the total population of PTDs’ installed countrywide in Kenya
is unknown. Consequently, certain assumptions based on scientifically accepted statistical approaches
have to be utilised. In the case of survey research, this normally means use of random samples that
are generally assumed to cover the whole population. The determination of sample size based on
scientific approaches cannot be underscored. This is mainly done to avoid to common errors in survey
research (Bartlett et. al. 2001)

Subsequently, Yamane (Israel, u.d) provides such a formula for calculating the sample size (Eqn 1):

Eqn 1: Simplified formula for determining sample size

(Israel, u.d)


Based on Eqn 1 the following Table 1 was derived.

Table 1: Sample size at 95% confidence level with a degree of variability P of 0.5

Sample size (n) at a Desired Precision level (e) of
Expected population (N) 30% 20% 17.0% 15.0% 12% 10% 8% 5% 3% 1%
30 8 14 16 18 21 23 25 28 29 30
40 9 15 19 21 25 29 32 36 39 40
50 9 17 20 24 29 33 38 44 48 50
60 9 18 22 26 32 38 43 52 57 60
70 10 18 23 27 35 41 48 60 66 70
80 10 19 24 29 37 44 53 67 75 79
90 10 20 25 30 39 47 57 73 83 89
100 10 20 26 31 41 50 61 80 92 99
116 10 21 27 32 43 54 67 90 105 115
118 10 21 27 32 44 54 67 91 107 117
120 10 21 27 32 44 55 68 92 108 119
121 10 21 27 33 44 55 68 93 109 120
130 10 21 27 33 45 57 71 98 116 128
150 10 21 28 34 47 60 77 109 132 148
180 10 22 29 36 50 64 84 124 155 177
210 11 22 30 37 52 68 90 138 177 206
240 11 23 30 38 54 71 95 150 197 234
270 11 23 31 38 55 73 99 161 217 263
300 11 23 31 39 56 75 103 171 236 291
330 11 23 31 39 57 77 106 181 254 319
500 11 24 32 41 61 83 119 222 345 476
600 11 24 33 41 62 86 124 240 390 566
700 11 24 33 42 63 88 128 255 429 654
800 11 24 33 42 64 89 131 267 465 741
900 11 24 33 42 64 90 133 277 497 826
1,000 11 24 33 43 65 91 135 286 526 909
2,000 11 25 34 43 67 95 145 333 714 1667
4,000 11 25 34 44 68 98 150 364 870 2857
5,000 11 25 34 44 68 98 152 370 909 3333
10,000 11 25 34 44 69 99 154 385 1000 5000
100,000 11 25 35 44 69 100 156 398 1099 9091
300,000 11 25 35 44 69 100 156 399 1107 9677
1,000,000 11 25 35 44 69 100 156 400 1110 9901
(Author)

From Table 1 it is noted that the higher the number of PTD expected to be actually installed (N), so will
a higher sample size (n) be obtained. Subsequently based on the initially pre-determined sample size
of 30, only two options are open to us in terms of the precision level (e): Either we assume e is 1% and
hence N is 30 or we take a higher value of e and subsequently have a wider choice of N.

For this studies purpose an e value of 17% was chosen. This was based on a two point criteria: First,
that we have an e that can cover as wide a range of known and unknown Population (N), and
secondly to have a sample size (n) that is as near as possible to that given in the ToRs. A much bigger


sample space will mean more time and resources (money, transport etc) to undertake the survey than
was initially agreed upon or allowed by the contract. Subsequently an e value of 17% allowed the
study to be able to choose a sample size that covers not only the final list given to us by Pioneer
Technologies of 116 installed PTDs but more importantly to also cover their initial claim of 300
installed PTD’s. In addition it allows us to have a sample size that can cover a possible potential of
exceptionally high numbers of installed PTD’s – since no census of the number of installed PTD’s has
been done or is known. .

It is thus for the above reasons that the initial suggested sample size of 30 PTD’s was increased to 34.
This allowed us to be able to cover between an expected population of between 30 to 10,000 installed
PTD’s.

1.6.3 Digester sampling and Survey methodology

The study was undertaken using a stratified sampling methodology, based on Geo-administrative units
referred to as counties. Whereas other sample methods could have been used to determine the
sample size (Bartlett et. al. 2001), the Terms of Reference (ToR’s) had already a pre-determined
minimum sample size of 30 digesters which was increased to 34 based on statistical analysis (section
1.6.2). Thus the sampling of digesters in Appendix 5.3 resulted in the following selection of sites
(Table 2) based on a stratified sampling approach.

Table 2: Selection of Digester sites based on pre-determined sample size

Household Number of % of digesters Sample size per Sample or sites
County
location Type digesters in population county visited
Embu Rural 3 3% 1 0
Kajiado Rural 2 2% 1 1
Kiambu Rural 67 58% 18 18
Kisumu Rural 6 5% 2 0
Machakos Rural 7 6% 2 1
Meru Rural 2 2% 1 0
Muranga Rural 5 4% 1 3
Nairobi City Urban/peri-urban 3 3% 1 8
Nakuru town Urban/peri-urban 12 10% 3 0
Nyeri Rural 3 3% 1 0
Taita Taveta Rural 2 2% 1 0
Uasin gishu Rural 4 3% 1 0
Total 116 100% 31 31
[Author]
Realizing that the household location types were similar in certain areas, sampling of the counties was
done on the basis of whether they are in rural areas or Urban/peri-urban areas. Which allowed the
research to concentrate only on certain parts of the country and not transverse the whole country.
Results of this geo-administrative sampling based on Counties to be visited is shown (Table 3). It
meant in principle that site visits would be made of Kajiado, Kaimbu, Machakos, Muranga and Nairobi


City counties, while ignoring the rest, since the location types of the ignored sites are similar to the
ones visited.

Table 3: Selection of final sites to visit based on household location type

Household location Number of % of digesters Sample size per Sample or sites
Type digesters in population county visited
Total Rural 101 87% 27 23
Total Urban/peri-urban 15 13% 4 8
Total 116 100% 31 31
[Author]

Based thus on the selected sites above, questionnaires were developed (appendices 5.1.1 and 5.1.2)
and by use of Geographical position system, a former engineer from Pioneer technologies and the
tools indicated in the appendices above, the sites were visited in accordance with the indicated work
plan (Table 4).

1.7 PTD study Revised Work plan

In achieving the study, the following work plan (Table 4) was utilised. It will be noted that names of the
localities to be visited are also correlated to the aforementioned counties (Table 2)

Table 4: PTD performance study – Revised Work plan

Tues, Wed, Thur, Frid, Sat, Sun, Mon, Tue,
Localities to be Mon,
23rd 24th 25th 26th 27th 28th 29th 30th
visited 1ST Dec
Nov Nov Nov Nov Nov Nov Nov Nov
Kajiado,

Nairobi City
Kiambu,

Site Visits Machakos
Kiambu,

Muranga
Nairobi City,

Kiambu
Data analysis
Draft report
writing, data
base creation
Receipt of
comments
Submission of
final report

and cleaned
data base


[Author]

1.8 Challenges and limitations of the Field survey

1. Distribution and accessing the digesters:- The biggest challenge in the study was in not only
identifying the digestors but also in accessing them. As will be noted, the original list obtained
from Pioneer technologies was pretty scarce on information, especially contact details.
Subsequently use had to be made of someone who has been installing the PTD’s to
personally take the Author to the sites. This was both expensive and difficult since there were
areas where the vehicle could not access and one had to make the journey on foot. The
distance between one site to the other was also huge, and meant transversing huge distances
to reach only one site.

2. Things not covered in performance Assessment: - The performance assessment has not
covered the more technical aspects of the gas composition nor the digestor temperature. But it
is assumed that these are in within the acceptable ranges based on the fact that the gas is
actually burning on the stove and is almost odourless. Other aspects not covered in the survey
include size of the households, their incomes and even household energy expenditure before
and after installation of the Biogas systems.

3. Time frame constraints: - The study was constrained by time not because of poor planning but
mainly due to unexpected events. This has got to do with the delay in obtaining the initial
contact list and even in having the first interview with Pioneer Technologies. It took almost 4.5
weeks before these could be accomplished, hence leaving only 1.5 weeks for going to the
field.


2. Results of the Field Survey

2.1 Number of digesters installed
After initial analysis and data base verification we can now state that based on the studies undertaken
that the data base has a total of 147 installed PTD’s countrywide. Of these based on the statistical

analysis indicated in Table 7 that the following is the current situation of the installed digesters as per

the new data base.

Table 5: Performance of Installed PTD in Sample and in total population

Sample Total
PTD performance Units % population
Working 28 82.40% 121
Not working 3 8.80% 13
Upgraded to masonry type (Floating or fixed dome) 2 5.90% 9
Abandoned / decommissioned 1 2.90% 4
Total 34 100% 147
[Author]

The above presents a statistical analysis with a margin of error of 17.5% in both the upward and
downward direction. However, it does give an indication that quite a number of the Digesters are
working, though they may not be doing so satisfactory as indicated by the responses of the farmers
who felt that the digesters did not meet all their needs like lighting and during the morning and evening
periods gas pressure was quite low that cooking took a bit longer than expected.

2.2 Digester material and size

2.2.1 Digester material and size

Based on discussions with Pioneer Technologies, it was realized that the company has been selling
Plastic Tube Digestors since 2006 on commercial basis; however, further discussions with Dedan
Ndungu indicated that the Plastic Tube digester work actually began sometime in 2002 with the 1st
generation of Plastic Tube digester which was essentially two layers of Polythene.

Various modifications led to the 2nd Generation PTD. This consisted mainly of an elastic /expandable
tube like that of a bicycle inner tube. The 3RD generation was a modification of the 2nd Generation
whilst the 4th Generation consisted mainly of a double layer UV treated Polythene material with Glass
reinforced Fibre (GRF) again. The digester has thickness gauge of about 300 micron, making it quite
long-lasting, with an estimated lifespan of about 5 - 15 years depending on the maintenances and
feeding capacity and frequency.


The aforementioned changes from the 1ST generation to the current 4TH generation have had
significant impacts on the quality and performance of the PTD. These include longevity (life span), UV
protection of the digester, and the general aesthetics of the digester. A comparative analysis in terms
of analytical performance was not undertaken.

2.3 PTD Costs

2.3.1 Costs from Pioneer

Thus, the current PTD in the Kenyan market is essentially a 4th generation tube, of which, as per
Pioneer Technologies, comes in two sizes: Standard and large

1. Standard type (Length=10m, Diameter=1.5m, total volume=6m³), with a daily Gas production
of =2.4m³/day and costing about KES 42, 000/- (ca. US$ 5251 /-)

2. Large type (Length =10m,Diameter=2.6m,Total Volume=16m³), with a daily Gas production
of 3.2m³/d and costing about KES 65, 000/- (ca. US$ 812.50 /-)

The aforementioned costs generally include Transportation to most parts of Kenya, the stove, gas
pipes, Biogas Digester bag and installation costs. It does not include the cost of digging the Trench
where the digester will lie in.

2.3.2 Costs of PTD from the field/study

The results from the field however indicate a different cost from that given by Pioneer Technologies.
From the study it was noted that the cost ranged between US$ 250 and US$ 562.50. Two main
reasons are attributed to this discrepancy: first quite a number of the PTD’s in the sample were not
installed by Pioneer as such, but by a one Dedan Ndungu before he joined Pioneer in 2006 and also
by other Companies.

Secondly, a trend analysis over the years (Fig 1) shows a slow increase in the general prices of both
PTD’s sizes, which maybe attributed to increased cost of raw materials. For Pioneer’s competitors it
was found out based on 2009 – 2010 figures, that for the Standard type it costs about US$ 488, while
the large sized costs about US$ 563, making them 7% and 31% cheaper than Pioneer’s respectively.
Raising the question of sourcing of raw materials and allowable profit margins, which do impact on the
final digester price.

1 Exchange rate being 1 USD = KES 80


Fig 1: Trend analysis of PTD’s prices and installations over the years.

Large sized PTD
Trends in PTD's prices and installations over the years
Small sized PTD
600

500
Cost of installation in KES

400

300

200

100

0
05/11/2001
13/02/2002
24/05/2002
01/09/2002
10/12/2002
20/03/2003
28/06/2003
06/10/2003
14/01/2004
23/04/2004
01/08/2004
09/11/2004
17/02/2005
28/05/2005
05/09/2005
14/12/2005
24/03/2006
02/07/2006
10/10/2006
18/01/2007
28/04/2007
06/08/2007
14/11/2007
22/02/2008
01/06/2008
09/09/2008
18/12/2008
28/03/2009
06/07/2009
14/10/2009
22/01/2010
02/05/2010
10/08/2010
18/11/2010
Date of installation

[Author]
Analysis of Fig 1 shows that generally 65% of Digesters are of Standard size while 35% are the large
size type. It is postulated that the choice for more Standard sized Digesters is based on its
comparatively lower price. However, Fig 1 shows an increase in prices of both standard PTD’s
(35.7%) and large sized PTD’s (55.6%). The increase in digester prices can be attributed to the
general increase in input material costs, transport and labour charges. Nevertheless, as farmers come
to experience the advantages of bio-digesters and/or as the number of cows they keep increase, the
tendency of farmers to move from standard sized PTD, to large sized ones and/or masonry based
fixed or floating type bio digesters increased.

In fact during the site visits, 2 sites were found where initially PTD’s had been installed, but they were
no longer there. The Farmers had decommissioned them to the much bigger Fixed dome Biogas
digesters due to demand for more gas (especially for lighting) and also as a way of maintaining
sanitation and reducing bad odours from Cow dung due to the large numbers of zero-grazed cows.

The Standard type can work with 1 dairy cow, whilst the large type may require between 1 - 3 cows. In
the event of local indigenous cows the number of the cows will range from 1 to 4 depending on the
size of the cow, the quantity of dung it removes and the frequency of dung removal.

2.3.3 Subsidy and cost comparisons of PTD with Fixed dome digester

Renwick et. al. (2007) in a study of Biogas digesters in Africa provided the following costs for
installation and maintenance of a fixed dome biogas digester which we compare with a PTD (Table 6).
In determining the probable costs of a PTD in Rwanda, certain assumptions were made these
included:

1. That the subsidy level being given for fixed dome digesters in Rwanda will be extended to


the plastic tube digesters

2. That the possibility of local manufacture of the PTD exists in Rwanda

3. That the in-kind contribution with respect to PTD’s is significantly less than that of fixed
dome and mainly include labour for digging the trench and putting up a protective fence. In
case a protective roof is put over the PTD the contribution will rise slightly.

4. The annual repair and maintenance basically deals with repair of the protective fence and
roof. In case of Digester being pierced (which is assumed not to be a common
occurrence) the costs will go up significantly

From the comparative analysis it is clear that a locally produced PTD with subsidy will cost far less
than similar sized fixed dome ones. It should be pointed out that the production costs for locally
produced PTD in Rwanda has been assumed to be similar to that of Kenya. In reality if this is a
Government of Rwanda project, and efforts are made to establish a local manufacturing plant, then the
cost of the net cost of the PTD to the end user may be far cheaper than the half net cost of the 6 m³
fixed dome i.e. below the US$ 236 mark.


Table 6: Comparative assessment of costs and subsidies of PTD and Fixed dome digesters

Annual
Proposed in-kind Net cost of
Average Total cost of Subsidy repair &
Country / Region Digester Type subsidy contribution digester
plant size plant (US$) (%) maintenance
(US$) (US$) (US$)
(US$)
Uganda Fixed dome 8 m³ 770 200 26% 77 11.6 493.00
Rwanda Fixed dome 6 m³ 859 300 35% 86 12.9 473.00
Ethiopia Fixed dome 6 m³ 747 186 25% 75 11.2 486.00
Sub-Saharan Africa Fixed dome 6 m³ 750 200 27% 75 11.3 475.00
Plastic Tube
Kenya
Digester 6 m³ 563 0 0% 15 5 548.00
Rwanda (estimated) -
Plastic Tube
locally made with 6 m³ 563 196.62 35% 15 5 351.38
Digester
subsidy
Rwanda (Estimated) -
locally made with no
Plastic Tube
subsidy - Assuming 6 m³ 563 0 0% 15 5 548.00
Digester
same production
costs as Kenya
Rwanda (Estimated) -
imported from Kenya
with subsidy
Plastic Tube
(additional charges 6 m³ 731.9 255.61 35% 15 5 461.29
Digester
include a 30%
transport & taxes
charge)
[Author, Renwick (2007)]

2.4 Farm layout and Digester inlet feeding design characteristics
The general farm layout with respect to the design characteristics and placement of the PTD’s was on
average similar. For most parts, 1 – 3 cows were kept in an enclosure with a cement floor (zero
grazing unit) and their dung by way of either cemented drainage canals or manual collection using
buckets, was brought to the digestor site. At the digestor site, two approaches were witnessed in terms
of feeding frequency:

1. Either a rectangular trench was dug, wherein the fresh dung was placed, such that whenever
the digester was to be fed, a bucket were used to collect the dung from this trench for feeding
into the digester

2. A second more advanced approach involved a masonry modification of the above. The inlet
pipe of the digester was enclosed within a 40 – 60 cm high square masonry tank. The inlet
pipe being at the bottom. A second masonry tank that feeds the aforementioned one is also
built. The two tanks share a inner wall, which has a gate that allows the contents of the latter
tank to flow into the former and into the digester. Both tanks are sized in such a manner as to
have a total volume of 160 litres (80 litres each). Fresh dung is thus poured into the latter tank,
after releasing its previous contents to the former tank with inlet pipe. This ensures proper
mixing of water and dung, and also proper volume feeding into the digester.

2.5 Digester performance

Results of the survey (Table 7) indicate the following status in terms of the sampled digesters:

Table 7: Overall performance of PTDs

PTD performance Units Sample %
Working 28 82.4%
Not working 3 8.8%
Upgraded to masonry type (Floating or fixed dome) 2 5.9%
Abandoned / decommissioned 1 2.9%
Total 34 100%
[Author]

Table 7 is summarised from four main factors which in totality ascertain the performance of the PTDs.

These are:-

1. Digestion process: - 82.4% of the sample size indicated that their digestor was producing gas
regularly an indication of normal digestion process in the digester. Of this 82.4%, 5.9% (2
sites) had problems with the digester bag. In both cases the digester bag had developed

hole(s) due to piercing from Animals or children. For the Kiserian Site, the owner had repaired
it using a bicycle repair kit normally used to repair punctures in the elastic inner tube of the
bicycle tyre. For the other site in Ngome area, the owner had tried using Super Glue ™ but
gas leakage was still experienced. This however, did not adversely affect the gas production
nor the digestion process. Hence, the digester was still working till date. A key lesson was
thus learnt regarding the 4TH generation PTD – i.e it is possible for the digester bag to be
repaired using normal puncture repair kit for elastic tube – provided the hole or tear is not so
big.

2. State of the Digester bag (the PTD itself):- Of the Sampled digesters

8.8% were not working due to the digester bag having bursted /torn or thick scum forming
due to infrequent feeding or inappropriate feeding material. One case, the owner digester
was not being utilised, though the problem was simply that the connecting gas transfer
pipes from the digester to the kitchen had become detached at one point.

The remaining 82.4% had the digester bags still working, some since 2004. It was also
observed that 90% of the sample had the digester bag whose outside appearance was
clean and in most case shaded from direct sunlight.

3. State and performance of the cooking equipment: -

• For all those receiving gas from the digester, 100% had their cooking stove
working and producing sufficient heat for a long period to allow satisfactory
cooking.

• The data analysis revealed that the number of cooking hours ranged from 2 to
about 6, the average being about 5 hours. Based on the general eating habits of
rural and urban populance in Kenya, this meant 1 hour in the morning, 2 hours
during lunch time and 2 hours during the evening period. However for meals
requiring longer cooking hours like “Githeri” – a mixture of beans and maize,
which incidentally is very common among the rural populations in Central parts of
Kenya, the hours would probably change with 3 to 4 hours being utilised to cook it
during mid-day, when incidentally there was more Biogas production.

• There was however a concern that during the morning and late evening’s gas
production is a bit low, limiting the cooking duration and heat intensity. However
during mid-day on sunny days, the gas production is quite high. This is indicative
of a problem with temperature that allows the digestion bacteria to function. A
possible solution to this would be the availability of a gas storage bag, of which of
the 100% sampled none had a gas storage bag.

4. State and performance of gas transmission pipes and water traps: - 100% of the sample did
not have a water trap to capture the condensate coming out of the digester. Rather, the gas


transmission pipe had been made in such a manner as to slope from the Kitchen area back to
the digester, hence allowing the condensate to flow back to the digester. 100% of the gas
transmission pipes were quite in order. Choice was however being made between PVC low
density pipes and recommended flexible gas pipes.

Based on the above it was noted that apart from the singular incident of one person whose digester
bag had a leak all the other had PTD system that was function quite well. This leads us to the
conclusion that 82.4% of the Biogas digesters were operation quite well without any trouble.

2.6 Biogas applications
In all cases (100%) Biogas was being used for cooking using a cooking stove (Fig 2), and in some
cases even baking using a modified biogas baking oven.

Fig 2: Biogas Cook stove, with the feed inlet pipe being shown

[Author]
Wherein some had expressed interest in the utilisation of biogas for lighting, it was noted that this was
not possible mainly because of gas pressure issues. Like in the cases of Uganda (Pandey et.al.,
2007:51), the low gas pressure normally meant that lighting is not feasible when using PTD nor is it
possible to have many biogas cook stoves connected to one PTD, since it had a corresponding
increase in the amount of time spent cooking due to decreased gas pressure. Consequently, none of
the sampled sites had biogas based lighting systems nor more than one Biogas cook stove. In two
cases the owners due to demand for more gas at higher pressure especially for lighting,
decommissioned the PTD and installed the Masonry types.

Nevertheless, many of the owners / end-users from the sampled were quite happy with the benefits
that system was giving especially in terms of savings in the use of charcoal and firewood, the
reduction of indoor air pollution (hence less expenditure on health) and the simple convenience and
Cleanliness of the gas.


A key application of the Biogas was the utilisation of the slurry. In all the sites visited where the biogas
was in good working condition, the slurry obtained was mainly used as an organic fertilizer and soil
conditioner. In addition farmers quoted the benefits of the digester as a sanitizer, since it decomposes
the cow dung which when in huge quantities would lead to foul smelling air.

2.7 PTD payback period

2.7.1 Payback period based on Charcoal use
It is estimated that the biodigestors can pay for themselves between 15 to 43 months, depending on
the type of fuel the digester is replacing, its cost (or what one would pay for it, if bought) fuel use., and
based on the assumption that the Bio-digestors could be used instead of charcoal for 54% or more of
the household cooking.

The determination of the payback period for the PTD is calculated as:

Cost of investment / savings per month

Or Cost of investment / 2.31 times the price of a sack of charcoal per month

The calculation assumes that a household of about 5 people will use an equivalent of 15.1 Kg of
charcoal per week, which translates to about 0.54 of a sack of charcoal, leading to 64.7kg per month
(about 2.31 Sacks of charcoal). A sack of charcoal is about 28 Kg.

In our case based on the average digestor cost of KES 45, 040, the payback period based on the
current prices of a sack of charcoal going for KES 900. The payback period translates to about 16.25
months and is calculated as follows:

PTD payback period = Cost of investment / (2.31 * price of a sack of charcoal/month)

= KES 45, 040/ (2.31 * KES 1,200/month)

= KES 45, 040 / (KES 2,772 / month) = 16.25 Months ~ 17 months

It is however noted that the lower the price of charcoal the longer the payback. Realizing then, that the
price of charcoal is increasing due to a diminishing resource base (less trees being replanted and
increased desertification and denudation of forests), it is feasible that the prices will be on an upward
trend, leading to increased attractiveness of PTD digesters.

2.7.2 Payback period for PTD and Fixed Dome Digester based on other Biomass fuels
In Rwanda and many other rural East African Countries, use of fuelwood and biomass residues like
maize cobs is quite common. An comparative analysis was thus done on the payback period of not
only the PTD but also the Fixed dome “Chinese Design” Biogas digester based on different Biomass


fuels (Table 8). The assumptions underlying Table 8 is based partly on Table 9 and also on studies

done. For instance the Biogas (2008) provides a Rwandan cost for 6 m³ Fixed dome digester used in
the calculation since obtaining the cost in Kenya for such a small digester was not possible

Table 8: Payback period of different digesters based on different Biomass fuels

Masonry (Fixed dome) -
"Chinese design" Plastic Tubular
Cost (KES) (installations,
68,720.00 45,040.00
materials, accessories)
Cost (US$) (installations, 859.00 (Source: Biogas,
563.00 (In Kenya)
materials, accessories) 2008)
When polythene is used Lifetime is
less than 5 years, but when butyl
Lifetime 20 years or more rubber is used lifetime is
comparatively longer (greater than 10
years)
Digester Size (M³) ~6 ~6
Biogas production (M³/day) ~3 ~3

Payback period with Charcoal
24.79 16.25
(months)
Payback period with Firewood
42.95 28.15
(bought) in Months
Payback period with Biomass
residue (maize cobs etc) in 65.45 42.90
months

Exchange rate (1 US$ is equal to KES) 80
[Author, Fao (2001), ]

Table 9: Assumptions for a household of 5 people

Assumptions for a household of 5 people
Usage per Fuel use per Fuel use per
Fuel type Unit costs (KES) month / unit month (KES) Month (US$)
Charcoal (2.31 times the
price of a sack of
charcoal) 1,200 2.31 2,772 34.65
Firewood (how much
would be spent if bought) 400 4 1,600 20.00
Biomass residue (how
much would be spent if
bought) 150 7 1,050 13.13
[Author, Karanja & Kiruiro (2003), ]

Generally, from the PTD comparative analysis (Table 8), the PTD has a slightly shorter payback

period as compared to the fixed dome of similar size. The only challenge as has been identified from
the field is the temperature fluctuations hence subsequent gas production fluctuations. This is
attributed to the exposure of the PTD digester bag to the elements, while the fixed is normally fully
enclosed within the ground affording it constant temperature for microbial activity.


2.8 Benefits of Digester systems
The main benefits indicated by the farmers / end-users being accrued from the Biogas digesters were:

1. 90% of the respondents indicated that the PTD helped them in save in the use of paraffin,
charcoal and fuelwood, allowing the money so used to be channelled to other things like
Education, obtaining more cows etc

2. No respondent in the survey (0%) indicated the possible reduction of indoor air pollution
(hence less expenditure on health)

3. About 10% of the survey sample indicated the benefits obtained by the simple convenience
and Cleanliness of the gas.

4. Of the 28 working digesters visited, all of them indicated the benefits the obtain from using the
Slurry as an organic fertilizer and soil conditioner. However other uses like Hydroponics, use a
feeding supplement for pigs and fishes were not indicated.

2.9 Extension services
Of the sampled, 96.7% had experienced some form of contact with the PTD installer after its
installation. This took the form of Telephone support (38%) or site visits (62%). The frequency of the
extension occurred ever since the installation was done (29%), or whenever they have a problem
(61%) or between 0 to 3 months after installation and nothing since then (10%).

It was further noted in all cases (100%) the farmers were given either a face to face training or a
manual (user guide) or both training and manual that describes not only the workings of a Biogas
digestor, but that also explained how and when the digester should be fed. Most of the problems to
arising with the Biogas digester were noted to emanate mainly from the low pressure and low gas
production matrix.

2.10 PTD Sustainability
The sustainability of the PTD’s was noted to be significantly reduced due to poor end-user
management of the especially the gas tube. More specifically, infrequent feeding, over-feeding and
under-feeding were the causes of low pressure and/or low gas production. In a bid to deal with the
hardened scum formed due digester feeding issues, 3% of the users had attempted to agitate the tube
by stepping on it. The end result being that the tube burst.


It is thus realized that with proper maintenance, and end-user education including proper extension
services these PTD’s can last up to 15 years, making them the most sustainable of all cooking fuels
currently available.

2.11 PTD and ownership findings
It was noted that the 97% of the users who had bought the digesters with the own money, took better
care of their digestors as compared to those (3%) who had obtained their digesters either through
subsidy or through donations.

This led to the question of Ownership and financing mechanism of the digesters. From the field survey
it was noted that a process whereby the farmer actually spends his/her own money to obtain the
digester generally tended to take better care of the system than the ones who had received it wholly
through some charitable organisations.

In view of the Rwandan situation, a mix of farmer’s contribution and subsidy or a total loan programme
approach may be recommended to allow for ownership development. Additionally, ownership issues
are a sub-set of the how well the farmer has been trained to use the digester including the attendant
extension services. The well trained farmers who received regularly extension services (97%) of the
study tended to take better care of their digesters.

2.12 Second hand PTD
About 5.9% of the surveyed had switched from plastic tubular digesters to Masonry ones. The main
reasons for these is the increased energy demands in terms need for Biogas lighting and increased
biogas use due to increased cooking activities. In addition other reasons for the switch include the low
gas pressure during the early morning and late evening periods, leading to non-effective and rather
long cooking times.

In the case where the Farmers upgraded to Masonry digester, they normally gave out the PTD to one
of their relatives. However, it can be postulated that if they were to sell it after 3 years, a probable
costs would less than KES 24,772 (US$ 309.65) for the Large sized digester. This is based on a
straight line depreciation of 15%.


3. Lessons Learnt and challenges experienced

3.1 Lessons learnt

1. Companies installing PTD’s in Kenya:- It was noted that a number of companies exist (

2. Table 10), which are installing PTD’s in Kenya these include:

Table 10: Current and potential Companies installing Plastic Tube digesters in Kenya

1. Dedan N Ndungu 2. Samuel N. Nene,
Modeline Electrical and Mechanical Pioneer Technologies Limited
Engineers P. O. Box 32910 – 00600, Nairobi, Kenya
P. O. Box Tel: +254-(0)20 253442
Tel: +254-(0)723 389642 Mobile: +254-(0)722 552505
Email: modelinetechnologies@yahoo.com Email:- pioneerteknik@yahoo.co.uk
3. E. K. Kahiga 4. Samwel Kinoti
Biens Limited, Skylink innovators,
P. O. Box 57859 Nairobi, P. O. Box 64459 - 00620 Nairobi,
Tel: +254-(0)778030 / +254-(0)737521242 http://skylinkinnovators.blogspot.com
Email: ekahiga@yahoo.com Email: skylinkinnovations@gmail.com

[Author]

The 4th Company, Sky link Innovators is one of the top five East African energy SMEs in the
Access to Clean Energy Challenge and a winner of the GVEP-I Ashden Award . Skylink also
has received financial training and expect further funding in 2011 for piloting a plastic biogas
digester from Mexico from the Access to clean Energy Challenge promoters.

However, it was noted that due to the rather cut-throat competition, none was willing to give
information or even acknowledge the existence of the other competitor, thus the study was
unable to get more contact details of other competitors.

3. Installation methodology: - Simple approaches have been devised to allow for proper
feeding. This has taken the form of either a masonry tank or rectangular trench. In other
cases, used 200 litres oil drums are used to store the fresh cow dung before it is
transferred to the digestor.

4. After sale services and end-users training: It was realized that with this 4TH generation


Plastic tube digestor that proper end-user training in form of manuals and/or face to face
training is key in dealing with the inherent problems of digester breakdown. This couple
with a robust after-sale / extension service will definitely enable the PTD’s to last up to
their expected lifetime of 15 years.

5. Failure of PTD’s:- The main cause of failure of the PTD’s is mainly related to end-user
maintenance and utilisation of the tubular digestor on one hand and poor or inadequate
extension service on the other contribute to the digestor failing or under-performing.

6. Multiplying and Upgrading / scaling up of digestors: - It was noted that those farmers /
end-users who have managed to acquire the PTD and also been blessed with an increase
of cows tend to install a bigger Biogas digestor. In most case this being the fixed dome or
the floating dome.

7. Essentially the problems experienced with the PTD's in Kenya are a combination of either
Management issues (managing / taking care of the digester by the end-user) or After-sale
service from the installing company. The Technology itself (the current PTD being the 4th
generation one) is sound.

8. Lessons learnt in terms of Performance of the digestors

Number of digesters installed: - based on the initial figures provided by Pioneer
Technologies of having installed 116 Biogas digestors, and realizing that of the
sampled PTD’s visited only about 20% were installed by pioneer, being indicative
of the scale at which different players are installing PTD’s in Kenya. The
installation however is from our study mainly in former Central province of Kenya
with forays into Rift valley and parts of Western Kenya.

Ratio of Bio digesters working to those not working (statistical analysis): It was
noted that only 8.8% of the Biogas sampled are not working as compared to the
82.4% working ones. The reasons for the 3% not working are based mainly on
maintenance issues.

Savings w.r.t. to charcoal use: A savings of KES 2,772 (US$ 34.65) is made
monthly in avoided cost of buying 2.31 sacks of charcoal. Savings are made in
reduced deforestation due to acquisition of firewood. In addition savings in terms
of avoided costs of buying the fuel source are made for fuelwood (US$ 20) and
US$ 13.13 for Biomass residues like maize cobs.

Sustainability – Unlike the previous generation of PTD’s which were made of
heavy gauge Polythene, the 4TH Generation PTD will probably last much longer
than 5 years in contrast to what many literature indicate. The exact time span is
however not clear, since they have only been around since 2003 (about 7 years
as at the time of undertaking this study).


Though quite a number of the consumers were satisfied with the PTD, a number
of them expressed disappointment that the digester could not meet all their needs
like lighting and further that the fluctuation in gas production especially during
morning and late evenings was very inconvenient. It was on this reason that about
5.9% of the sampled decommissioned their PTD digesters and moved to the
Masonry type.


4. Recommendations

4.1 Framework for PTD installation and operation manual

It is recommended that 12 page, double sided A5 user guide or operational manual, in the event
PTD’s are to be installed elsewhere, be developed. The manual will among other things cover the
following issues:

1. The process occurring inside a biogas digestor – use of diagrams and photographs is
highly recommended (about 2 pages)

2. A brief description including a measurement based schematic / cross-sectional diagram of
the Plastic tubular digester ( about 1 page)

3. A brief description with diagrams of the layout and installation of the plastic tubular
digestor (2 to 3 pages)

4. How to feed the Biogas digester, including feeding frequency and use of simplified
formulas for retention time, daily feeding capacity and frequency, and expected gas
amount ( about 1 page)

5. A diagrammatic how to section dealing with things like digestor feeding, digestor repair,
digestor agitation in case of scum formation etc ( 4 pages)

6. Frequently asked questions (trouble shooting ) (2 pages)

7. Contact details of local installer, local extension officer and/or artisan who can repair the
digestor (back cover)

4.2 Recommendations for the PTD adoption in Rwanda
Based on the above, it seems quite recommendable to suggest PTD for the Rwandan programme, but
certain things will need to be in place, to make up for the shortfalls experienced in the Kenyan
Programme. Such issues include:

1. Proper end-user support programmes and training

2. Developing of the local capacity to repair the digestor using modified Bicycle tube puncture repair
kits.

3. Support of a local company to be able to produce Double layer UV resistant Plastic material,
gauge 300 micron. For this butyl rubber or other relevant material can be used.


4. Exploring ways to ensure that end-user takes ownership of the digestor, i.e. the digester should
not be a gift.

5. Exploring the need of whether to incorporate a gas bag in the whole setup.

4.3 Recommendations for further scientific research and field studies

It is also recommended that further scientific research and field studies be done with respect to:

1. Determination of the life span of the Plastic tube digester, including the best kinds of cost effective
materials to be used in manufacture and repair of Tubular digesters. Of particular interest in such
a research is the Ultra-Violet light protection mechanism of the tube, its thermal capacity (ability to
retain or lose heat) and its thickness which is important in terms of light piercing of the digester

2. Efficiency Benchmarking:

• Determining the quality and quantity of gas produced by both a PTD and masonry
type digester like Fixed dome and/or floating drum

• Determining on a comparative basis the performance of the digester (PTD, fixed dome
and floating drum) based on time of day, feeding frequency, feeding quantity, feeding
type, effect of temperature fluctuations on gas production etc

3. Investigating cost-effective, easily adaptable and locally available approaches to repairing a

• Torn / bursted plastic digester bag

• Pierced Plastic digester bag

4. Development and piloting of a PTD value chain and also of a sustainable PTD market delivery
model. This will specifically target the problems experienced in terms of

• End-user support

• Extension services

4.4 Recommendations for Better Market delivery models

1. Supporting on a local scale in Rwanda, an industry or a number of Small and medium Enterprises
(SME’s) to mass produce UV protected thick double layered PTD tubes

2. Support of local skills upgrading in Biogas installation and repair


3. Support industry in availing affordable PTD repair kits

4. Government support in extension services for small scale farmers owning PTD’s

5. Local industry support for biogas equipment and accessories. These would include gas valves and
biogas stoves.

4.5 End-user recommendations

1. Development of a PTD end-user manual (section 4.1) and wide distribution to end-users in a
language they can understand

2. Regular user support visits from Government extension officers and installers

3. Protection of the PTD against animals, children and other harm

4. Farmer training on type of feeding material and feeding frequency for digester

5. Development and dissemination of a video on PTD installation, operation (feeding, cleaning,
troubleshooting etc), repair and gas use. An example of such a video is given for a short time
period at this link: http://www.energiekonsult.com/consultancy/GTZ-REAP/

4.6 Recommendations to policy makers

1. Undertake study on effect of subsidies on end-user management of the PTD’s (See section 2.3.3
and Table 6)

2. Determination and piloting of best financing mechanism of PTD’s for poor households in the
context of ownership creation and sustainability

3. Scaling up of the whole programme region-wide


5. Appendices

5.1 Tools used in Field survey

5.1.1 Institutional Questionnaire

Questionnaire with Pioneer Technologies:

Aim:

1. Understand the history of the company and its staffing level including branches and/or
outposts

2. Distributors / retailers and suppliers of their products or manufacturing material

3. Understand their scope of activities (installation areas, costs / area, what they do
(activities)

4. Understand the technology and its processes

5. Understand the challenges they are experiencing

6. Obtain a database of all their installed plants including names of clients, their contact
details, location of installation, date of installation, frequency of monitoring & evaluation,
Cost of installation at that time,

7. Their extension processes.

Interviewee _________________________________ Tel ____________________________

Contacts _____________________________________ Position ______________________

Main issue Sub-issues Responses

Company Contacts

Branches

Staffing levels

Branches /outputs

History (when it started,
people involved, growth
record)

Delivery network Distributors

Retailers

Suppliers of the materials /



material availability

Scope of Installation areas (provinces,
activities districts, locations)

Installation costs (stratified
per installation area)

Number of installed PTD’s &
area of installation (geo-
referencing?)

Any other activities they are
involved in

Technology Who manufactures it

How it works

Operation parameters (PH,
Temp, etc)

Feedstock type

Lifespan

Average gas production / day

Manufacturing costs and
energy

Challenges Production

Transportation

Installation



End-user operation &
Education

Extension (end-user) support

Policy

Others

Extension Who does extension?
processes

What kind of extension?
(Education, O&M, marketing
etc)

Who pays for it?

Database Location of installation
compilation
Geo-reference

Names of client

Contacts (postal, mobile, e-
mail)

Installation date

Cost of installation at that time

Frequency of M&E,


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