GreenHeat 
Performance Evaluation 
Slurry-Separation Technology (SST) Biogas Systems in Uganda
SECURING WATER FOR FOOD
AUGUST 2019
Prepared By: Tsegay Gebremichael, Gebreyesus
BSc in Rural Development & Agricultural Extension from Haramaya University in Ethiopia; MSc 
in Sustainable Forest & Nature Management from the University of Gottingen in Germany; and, 
Master of Energy from the University of Auckland in New Zealand 
The Kaizen Company | Contract #: AID-OAA-C-15-00011 
www.securingwaterforfood.org | securingwaterforfood@gmail.com
TABLE OF CONTENTS
ABSTRACT 2
INTRODUCTION 3
BACKGROUND 7
Gender 7
Farm Size 8
Farmer’s Experience with Innovation 9
Sources of Income 12
Family Size 13
METHODOLOGY 15
Sample Selection 16
Limitations 18
RESULTS 19
EXPERIENCE WITH INNOVATION 20
BENEFITS OF INNOVATION 23
Agricultural Activities Benefits 23
Water Benefits 24
Crop Benefits 26
Income Benefits 27
Poverty Reduction Benefits 30
Gender Differences 31
Regional Difference 32
DISCUSSION 33
Usage/Availability 34
Crop Yield/Survival 35
Changes in Income 36
Gender Differences 38
Affordability 38
Impact on Poverty 39
Waste Management 40
Soil Fertility and Productivity Benefits 40
Water Benefits 41
Benefits of Innovation on Community 43
Impact on Poverty 43
CONCLUSION 45
ANNEX I 47
2 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
Green Heat was sponsored by SWFF to reach more farmers with their innovative Slurry-Separation 
Technology (SST) biogas systems in Uganda and beyond. The technology was intended to separate water 
from the waste to be reused for mixing. In addition to recycling water, the SST was expected to create an 
easily managed high-quality fertilizer product while increasing gas production for energy consumption. 
This field evaluation was conducted to evaluate the performance of biogas technology in general and 
the slurry-separation innovation in particular. The survey was conducted July through August, 2019, in 
Uganda, four years after the introduction of the slurry-separation innovation.
The sample respondents interviewed included 51 percent men and 49 percent women. Thirteen districts 
from across all four regions of Uganda were covered. Farmers’ experience with biogas technology ranged 
from two months to 11 years.
Through face-to-face interviews, respondents reported benefits of the innovation were energy for 
cooking and lighting, soil fertility and productivity, household income improvement, and environmental 
sustainability. Fifty-four percent of farmers reported very significant improvement in their household 
income, while 96 percent confirmed improvements in the survival rate of their crops. However, the 
innovation’s impact on water consumption was not as promising. Of the interviewees, 61 percent reported 
their water consumption was increased due to the innovation. This was mainly attributed to the amount 
of water required to mix cow dung. Biodigesters equipped with SST contribute toward achieving most of 
the UN Sustainable Development Goals (SDGs). However, this survey confirmed that slurry-separation 
systems were not properly used in the biogas plants visited. No communal or individual negative impact 
resulted from biogas or the SST. 
ABSTRACT
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 3
INTRODUCTION
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The Food and Agriculture Organization (FAO) estimates that more than one-half of the developing 
world’s population, or 45 percent of all humanity, is rural dwellers and about 2.5 billion depend 
directly on farming for their livelihoods. As global pollution continues to grow, demand for food also is 
surging. However, the agriculture sector is facing numerous challenges – climate variability, shortage of 
water, pollution, land degradation, etc. In addition, rural people in developing countries rely mainly on 
fuelwood and/or charcoal for cooking, heating, and lighting as they have little or no access to modern 
energy. This not only exacerbates deforestation and the impact of climate variability but also causes 
negative effects on health, labor, and time spent on agricultural activities for women and children.
Agriculture is known to be both the victim and the cause of water scarcity globally. On one hand, 
the sector is the largest water consumer, while on the other it is the main source of water pollution. 
Therefore, the agricultural sector holds the key to tackling water scarcity and sustainability of 
livelihoods reliant on water and agriculture. Biogas generated through anaerobic digestion of organic 
materials from human and animal waste, crop residue, agro-industrial waste, and other biomass 
materials could contribute to this end. Biogas digesters could provide three main benefits – energy 
security, food security, and environmental sustainability. As a result, demand for the technology has 
grown steadily. In Uganda, biogas innovations have a long history despite the country’s low adoption 
rate. To date, about 5,800 domestic biogas plants have been installed throughout the country since 
the technology was introduced in 19501
. Unfortunately, 50 percent of them fail within one year due to 
high water demand that is mostly attributed to a wasteful design.
1 Tumusiime, Edmund, John B Kirabira, and Wilson B Musinguzi. 2019. “Long-Life Performance of Biogas Systems for 
Productive Applications : The Role of R & D and Policy.” Energy Reports 5: 579–83. https://doi.org/10.1016/j.egyr.2019.05.002.
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 5
To address this challenge, Green Heat Uganda LTD introduced an innovative Slurry-Separation 
Technology (SST) to reduce water consumption by biogas plants (Figure 1). The technology creates an 
easily managed fertilizer while increasing gas production. The innovation separates water from the 
slurry to create solid fertilizer. The dry organic fertilizer can be packaged, stored, or applied directly to 
farm fields. The liquid is reused to mix wastes, replacing the need for freshwater. Green Heat provides 
biodigesters already equipped with slurry separation; however, the innovator also integrates its SST 
innovation to existing digesters. According to Green Heat, while other digesters require one liter of 
water for mixing every kilogram of waste, its digesters dramatically reduce freshwater usage because 
water is recycled through the SST. Moreover, Green Heat’s biodigesters can be fed a variety of liquids, 
such as rainwater, wastewater, and cow urine. The system is said to be eco- and gender-friendly, 
efficient, and a true cost-saver.
FIGURE 1. GREEN HEAT’S SST2
SLURRY SEPARATION
SLURRY SEPARATION TECHNOLOGY
This is what makes our biodigester 
one of a kind. Slurry is separated 
from any liquids passing through the 
system.
CUSTOM SOLUTIONS
SST or Slurry Separation is an add-on 
feature. Therefore, it can also be 
integrated into traditional pre-existing 
digesters or available with new 
biodigesters built by Green Heat.
DRIED SLURRY
With SST, the slurry dries, 
creating solid fertilizer that can be 
packaged, transported and sold, 
or applied directly to fields. Our 
fertilizer has been proven to boost 
crop yield up to 270%.
RECYCLED WATER
Separated liquids return to the system, being 
mixed with wastes entering the digester. This 
recycling of water reduces demand for water 
by 80% and nearly eliminates the need for 
constant collection of water.
2 Http://Www.Greenheatinternational.Com/Biogas/
6 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
Green Heat has rapidly increased its scope in terms of geography and product types. While the 
company is headquartered and mainly focused in Uganda, it has started to expand its market 
by installing some biogas systems in other countries, including Ethiopia, Mozambique, Rwanda, 
Togo, and Haiti. Furthermore, apart from its innovative digester, Green Heat is actively engaged 
in producing and distributing efficient briquettes and solar lamps, and finding ways to store the 
methane gas from digesters.
In 2015, Green Heat secured funds from the Securing Water for Food: A Grant Challenge for 
Development (SWFF) specifically to introduce the slurry separation system to more biogas plants. 
This field evaluation was, therefore, conducted as SWFF seeks to understand the innovator’s reach, 
barriers to adoption, and economic and development performance. The survey was intended to collect 
independent data directly from end users to provide a historical perspective on funding sustainability.
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 7
The Republic of Uganda is administratively divided into four regions – Central, Eastern, Northern, and 
Western. These regions are subdivided into districts. The field survey attempted to cover all regions 
by taking sample districts. Data was collected by using the Fulcrum mobile application. All interviews 
were recorded, and the photos were taken using Dropbox. Questions addressed these main issues: 
benefits of biogas on overall customers’ livelihoods; impact of innovation on crop yield and household 
income; challenges users face while using the technology; impact of biogas technology on water 
consumption; impact of innovation on inputs, such as fertilizer and charcoal; any negative impact 
imposed by the technology in communities; and, contribution of the innovation to women’s activities 
and empowerment. 
Gender 
The initial list of customers was composed of 1,177 individual households. Male clients accounted for 
52 percent (610), while females made up 48 percent (567). 
FIGURE 2. GENDER OF RESPONDENTS 
(N=57)
49%
51%
GENDER OF RESPONDENTS 
(N=57)
Male
Female
BACKGROUND
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While interviewing both male and female clients was mandatory, no preferential treatment was 
required to incorporate more women since their size was equivalent to their male counterparts. 
Respondents were selected from both genders proportional to the total clients. Therefore, the sample 
also consisted of 52 percent (32 out of 60) male and 48 percent (28 out of 60) female respondents – 
with similar equivalency between both sides. However, the interviewed clients changed to 51 percent 
(29 out of 57) male and 49 percent (28 out of 57) female (Figure 2). The small disparity was due to 
absentees and/or additional females who took part in the interview. 
Farm size 
Studies show that 85 percent of the farming communities in Uganda are smallholders. The average 
farm size held by these farmers is 2.5 hectares. Statistical analysis was carried out to determine 
interviewees’ farm plot size data patterns and trends (Table 1). 
TABLE 1. DESCRIPTION OF FARM PLOT SIZE (N=56)
DESCRIPTION HECTARES
Mean 5.9
Median 1.6
Standard Deviation 16.8
Minimum 0.4
Maximum 120
Although the questionnaire was designed to collect land size in hectares, fieldwork revealed that 
farmers knew or preferred to tell the size of their farm plots in terms of acres. Ninety-eight percent of 
respondents referred to acres, while only one use hectares. Another respondent refused to disclose 
his land size, apparently because it was too big. The data was then converted – one acre equals 
approximately 0.4 hectares.
Table 1 above shows a statistical description of samples in terms of their farm plot size. The average 
land size ownership among respondents was 5.9 hectares. This is more than twice the national 
average of 2.5 hectares due to a huge disparity in farmland ownership among respondents, which 
can also be observed from the range (119.6 hectares). The maximum farm size recorded was 120 
hectares (300 acres), and the minimum was 0.4 hectare (one acre). The median of the land size held 
was much less than the mean, at only 1.6 hectares. 
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 9
FIGURE 3. FARM PLOT SIZE OF RESPONDENTS 
(N=56)
14
8
4
10
18
12
16
6
2
FARM PLOT SIZE OF RESPONDENTS 
(N=56)
RESPONDENTS
Less than 0.5
8 8 8
0.5-1.5
7
15
8
1.6-3
8
16
5
3.1-6
3
8
4
6.1-12
1
5
3
More than 12
1
4
0
Males Females All
0
FARM SIZE (HA)
A big difference in farmland size was observed during the fieldwork. Plot size among respondents 
ranged from 0.4 to 120 hectares. Overall, 16 respondents owned farm plots ranging from 1.6 to 3 
hectares followed by those (15 of 56 respondents) whose farm size was 0.5 to 1.5 hectares. Four 
respondents had farm plots of more than 12 hectares (Figure 3). All respondents confirmed they had 
full ownership of their lands. When asked if they also were renting any land and how much they pay 
for it, nine percent (5 out of 56) said they rented land for UGX 450,000 to 2,250,000 per hectare per 
year. All monetary figures are in Ugandan Shillings (UGX); as of October 15, 2019, USD $1 ~ UGX 3,701.
There is a huge gap in farm size ownership between male and female respondents. Women seemed 
to own smaller size farms than men (Figure 3). All (8 of 8) of interviewees who owned farm plots 
of less than 0.5 hectares were women. Only one woman out of four respondents had a farm more 
than 12 hectares. While the number of men and women was equal in farm size ranging from 0.5 to 3 
hectares, the number of women steadily declined as plot size increased beyond 3 hectares and rose 
as the size decreased below 0.5 hectares.
Farmer’s experience with innovation 
Interviewees were asked how long they had used their biogas systems. Their experience with the 
technology ranged from only two months to 11 years. One interviewee claimed to be the first to 
introduce and use the biogas technology in the entire district. 
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FIGURE 4. FARMER’S EXPERIENCE WITH INNOVATION 
(N=57)
30
15
20
5
35
25
10
40
FARMER’S EXPERIENCE WITH INNOVATION (N=57)
RESPONDENTS
35
Less than 5 years
19
5-10 years More than 10 years
3
0
YEARS OF USE
While biogas technology has been in Uganda since the 1950s, the Slurry-Separation System is a 
relatively recent innovation. Green Heat started to distribute it to its clients in 2015. The majority of 
respondents (61 percent) have less than five years experience with biogas technology (Figure 4). Thirty￾three percent had used it from five to 10 years. Only three percent (5 of 57) had a lot of experience 
(more than 10 years) with biogas systems. The most biogas experienced farmers (three) had their 
systems for more than 11 years while the least experienced farmer (one) had it just over two months. 
FIGURE 5. SPENDING ON EQUIPMENT DUE TO INNOVATION 
(N=57)
23%
53%
12% 5%
5%
2%
SPENDING ON EQUIPMENT DUE TO INNOVATION 
(N=57)
Free
Less than 500k
500k-1m
1.1-2m
2.1-3m
More than 3m
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Users were asked how much they spent on equipment as a result of the innovation. One farmer said 
he got it free as a donation. Five percent (7 of 57) said equipment cost them UGX 500,000 to 1 million, 
and most said the costs were shared with the innovator or other donors. Expenses on innovation 
equipment for the majority (30 of 57) ranged from UGX 1.1 million to 2 million. Twenty-three percent 
(13 of 57) said they spent UGX 2.1 million to 3 million. The remaining three respondents spent over UGX 
3 million. The minimum spending, apart from the one who did not pay, was UGX 200,000 to install a 
mechanical mixer, while the maximum paid was UGX 3.8 million (1.8 million for digester and 2 million 
for toilet installations) (Figure 5). 
FIGURE 6. HOW RESPONDENTS HEARD ABOUT THE INNOVATION 
(N=57)
28%
12%
39%
21%
HOW RESPONDENTS HEARD ABOUT THE INNOVATION 
(N=57)
Neighbor
Innovation Personnel
Extension Worker
Other
Respondents were asked how they originally learned about the biogas technology. They mentioned 
neighbors, innovation personnel, extension workers, and other sources. The majority (39 percent) 
said they learned from their neighbors, and 28 percent (16 of 57) said extension workers provided 
the information. On the other hand, 21 percent cited innovation personnel as the source of innovation 
information. The remaining 12 percent (12 of 57) said they heard about the technology from other 
sources, such as workshops, training, associations, and NGOs (Figure 6).
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Sources of income 
Interviewees were asked to identify their primary sources of income (Figure 7). 
FIGURE 7. PRIMARY SOURCE OF INCOME 
(N=57)
94%
1%1% 1%
PRIMARY SOURCE
Farming
Teaching
Veterinary Doctor
Wage Laborer
Most respondents predominantly relied on agriculture for their livelihoods, with 94 percent saying 
farming was their primary source of income. According to the interviewees and field observation, 
major crops grown across all regions are banana (locally known as matooke), coffee, corn, fruits, and 
vegetables. Dairy, poultry, pig, and fish farming are practiced to some extent. Only three (six percent) 
had primary income sources other than farming, including teaching, veterinary doctor, and wage 
laborer (Figure 7).
They also were asked if they had sources of income other than their primary sources (Figure 8).
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 13
FIGURE 8. ADDITIONAL SOURCE OF INCOME 
(N=57)
61%
16%
16%
5%
2%
ADDITIONAL SOURCE 
(N=57)
Business
Wage Laborer
Farming
Pension
None
Sixty-one percent (35 of 57) said they had no source of income other than farming. Doing business 
was a secondary source of income for 16 percent. Some of the business activities included street 
catering, drug shop, public transport, school services, and rentals. Similarly, 16 percent generated 
additional income from wage laboring, such as building, tailoring, and the like. Only three (five percent) 
confirmed that farming was their secondary source of income. Two percent said they were on pension. 
Family size 
TABLE 2. STATISTICAL ANALYSIS OF FAMILY SIZE 
(N=57)
DESCRIPTION # OF PEOPLE
Mean 9
Median 8
Sample Variance 14
Range 18
Minimum 2
Maximum 20
A total of 496 family members were represented within the 57 interviewed households. The mean 
and median family size were nine and eight members, respectively. This is far larger than the national 
average household size of 4.7 members. The minimum family size recorded was only two members, 
and the maximum was 20 members (Table 2). 
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FIGURE 9. FAMILY SIZE OF RESPONDENTS 
(N=57)
49%
26% 21%
4%
FAMILY SIZE OF RESPONDENTS 
(N=57)
1-5
6-10
11-15
16-20
The highest number of sample households (49 percent) had six to 10 family members. Households 
with a family size of 11 to 15 members accounted for 26 percent. Twenty-one percent had one to five 
family members. The remaining four percent (2 of 57) of households had 16 to 20 members (Figure 9). 
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 15
METHODOLOGY
16 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
Sample Selection 
Although Green Heat also has customers in the neighboring countries of Ethiopia, Rwanda, and Togo, 
only customers in Uganda were targeted for this study. 
TABLE 3. DISTRIBUTION OF TOTAL CLIENTS IN UGANDA
REGIONS HOUSEHOLDS INSTITUTIONS
MALE FEMALE SCHOOL/
COLLEGE CHURCH CHARITY
Central 204 199 7 1 1
Eastern 179 104 3 0 0
Northern 112 112 3
Western 115 152 5 1 0
Total 610 567 18 2 1
The total list of customers provided by Green Heat and SWFF included 1,177 (567 females) households 
and 21 institutions. Since the project’s demand was to interview a minimum of 50 individual 
households, institutions were excluded from the sampling process. Households then were grouped into 
regions. Accordingly, the customers were: 403 (199 females) from Central; 283 (104 females) from 
Eastern; 224 (112 females) from Northern; and, 267 (152 females) from Western regions (Table 3).
TABLE 4. DISTRIBUTION OF SAMPLE RESPONDENTS 
(N=57)
REGIONS DISTRICT MALE FEMALE
Central
Buikwe 3 1
Gomba 4 2
Masaka 4 3
Mukono 0 3
Eastern
Budaka 3 3
Jinjia 2 2
Kamuli 4
Northern
Gulu 0 3
Kole 2
Lira 1 5
 Western
Bushenyi 1 3
Mbarara 2 0
Isingiro 3 3
Total 29 28
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Taking time, financial constraints, and scattered locations of end-users into consideration, the sample 
size was set at 60 individual households. This, in turn, was proportionally allocated into the regions. A 
total of 13 districts (four from the Central region and three each from the other regions) was randomly 
selected. The districts surveyed included Buikwe, Gomba, Masaka, and Mukono from Central; Budaka, 
Jinjia, and Kamuli from Eastern; Gulu, Kole, and Lira from Northern; and, Bushenyi, Mbarara, and 
Isingiro from the Western region. Twenty-one (10 females), fourteen (5 females), eleven (9 females), 
fourteen (7 females) respondents were randomly selected from the Central, Eastern, Northern, and 
Western regions, respectively (Table 4). However, the interview was successful with 57 (28 females) 
respondents since three were not available in their homes or farm fields during the visit. More 
samples, both districts and respondents, were taken from the Central region because it had more 
end-users distributed across several districts compared to the other regions. 
FIGURE 10. LOCATION MAP OF SAMPLE RESPONDENTS
Green Heat staff, based on advice from the Ugandan Ministry of Health, recommended avoiding 
districts that are close to neighboring countries of the Republic of Congo and the Republic South 
Sudan, which are Ebola prone areas. The recommendation was followed, and districts located 100 to 
150 kilometers from both borders were deliberately excluded from the randomization process.
18 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
All respondents were interviewed in person in their homes or farm fields. The questionnaire was 
developed and provided by SWFF. The language barrier was not a serious issue, as Uganda is a 
predominantly English-speaking nation. As such, the interview sessions mostly were conducted in 
English, although some were done in local dialects through the help of local interpreters.
Limitations
Respondents were happy to receive the interviewers as visitors and were excited to talk about their 
biogas plants for three main reasons. First, it is considered very generous of local communities to host 
visitors. Rural people in Uganda have a culture of providing a “Visitor’s Book” for visitors to fill in their 
name, address, contacts, reason for the visit, and comments. The record is kept for generations and 
is considered prestigious. Secondly, Green Heat customers were very happy to own biogas and with 
the countless benefits they make out of their systems. The plant is not only considered as a point of 
pride that needs to be visited, but also used as an opportunity to tell how great the technology is and 
how much their lives have changed since using it. Many said they did not have enough words to list all 
the advantages. Finally, but equally as important, others wanted to use the opportunity to tell about 
the challenges they have faced with their systems. They wanted to be heard and hoped their systems 
would get fixed afterward.
However, the questionnaire had numerous limitations. Many of the questions were too long, too 
quantitative, and too complicated for farmers. They demanded respondents’ literacy and a lot of their 
time. Consequently, some questions remained unanswered, took a long time to get answered, or led 
to several estimated or inaccurate answers. Some respondents left in the middle of the interview due 
to the time required to complete it. There were inconsistencies of data because at times data that 
was intended to be quantitative was provided qualitatively. A few respondents were hesitant about 
responding to some questions, especially in relation to income and land size. Others did not know how 
big their land might be in terms of specific units or how much income they make annually. Lastly, some 
target respondents were absent in their homes and farm fields. 
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 19
RESULTS
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Respondents were asked to list the main benefits of biogas innovation. Each respondent gave more 
than one and heterogeneous answers (Table 5). 
TABLE 5. PERCEIVED BENEFITS FROM BIOGAS TECHNOLOGY 
(N=57)
BENEFITS FREQUENCY %
Energy 57 100
Fertilizer 51 89
Hygiene 13 23
Environmental sustainability 7 12
Animal feed 5 9
Source of additional income 4 7
All respondents perceived energy supply as the main benefit of biogas technology. They said biogas 
provides clean and inflammable energy mainly for cooking and lighting purposes.
Providing fertilizer was the second most frequently mentioned benefit. While biogas is used to 
produce energy, the large potential of bio-slurry often has been overlooked. However, 89 percent of 
the respondents in this study said biodigesters had been providing organic fertilizers that are rich in 
nitrogen and phosphorous and helped them increase crop productivity and improve survival rates.
Hygiene or sanitation was the other benefit of biodigesters, with 23 percent (13 of 57) citing this 
advantage. They expressed the hygienic effect of biogas plants in two ways: (a) there is no more 
messy cow dung or other organic waste in their compounds as it is directly fed to the system; and, (b) 
EXPERIENCE WITH THE INNOVATION
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 21
there is no more indoor pollution from smoky kitchens using firewood or charcoal because it has been 
replaced with clean methane gas. Twelve percent said that biogas also helps maintain environmental 
sustainability. This mainly is in relation to less firewood and charcoal consumption for energy 
purposes, which means a reduced rate of deforestation, and to the organic and environmentally 
friendly nature of the slurry fertilizer they apply to their farm fields. Five respondents said they also 
used the slurry to feed their animals – pigs, poultry, and fish. Another benefit was the fact that biogas 
could become a source of additional income. They said the demand for bio-slurry is very high and not 
everyone has access to the innovation. Therefore, some (4 of 57) were able to generate additional 
income by selling surplus slurry to neighbors and friends. 
FIGURE 11. CHALLENGES FACED WHILE USING INNOVATION (N=57)
27%
10% 8%
6%
7%
34%
8%
CHALLENGES FACED WHILE USING INNOVATION 
(N=57)
Never
Shortage of water
Lack of cow/dung
Mixing is labor intensive/disguting
System not working partially/fully
Lack of knowhow/technicians/spares
Other
Clients were asked if they had experienced any challenges while using the biogas innovation. They 
expressed several problems (Figure 11). The majority (34 percent) said they never had any problems 
associated with their systems. However, 27 percent said their systems had not worked fully or partially. 
Eight percent said the lack of cow dung was their major challenge. Six percent mentioned a shortage 
of water. Lack of technical knowhow and spares were mentioned by seven percent. Eight percent 
mentioned other challenges, such as the long distance between the biogas plant and the dairy farm 
or crop field. Another challenge mentioned by 10 percent of farmers interviewed was difficulty in 
mixing cow dung. They said manually mixing dung, which is the case for many of the clients, is tiresome 
and, at times, disgusting – especially with pig dung.
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In a separate question, farmers were asked if there had been any negative impact caused by 
the innovation in their respective communities. The majority of the respondents said there was 
no negative impact whatsoever. Only two respondents mentioned that there were some jealous 
individuals who spread bad rumors about the technology.
Gender-Based Training on Fertilizer Application.
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 23
Agricultural activities benefits 
Sample farmers were asked if the biogas innovation made them change their farming practice and 
how (Table 6).
TABLE 6. CHANGE IN FARMING PRACTICES DUE TO INNOVATION (N=56)
FARMING PRACTICE FREQUENCY %
It helps me to decide which crops to plant 40 70
Introduced new crops 27 47
It helps me to decide when to plant 45 79
Changed irrigation system 10 18
Reduced water usage 11 19
Source of additional income 4 7
The majority (70 percent) of respondents mentioned they were able to decide which crops to plant 
with the help of their biogas systems. Twenty-seven percent said the innovation made them introduce 
new crops. On the other hand, 79 percent confirmed their systems assisted in deciding when to 
plant their crops. Change of irrigation system was mentioned by 18 percent, and 19 percent said the 
innovation helped them reduce their water usage. 
Farmers were asked how many times they harvest in a year (Figure 12). 
FIGURE 12. NUMBER OF HARVEST A YEAR 
(N=57)
84%
2%
12%
2%
NUMBER OF HARVEST A YEAR 
(N=57)
2 times
3 times
4 times
48 times
BENEFITS OF INNOVATION
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While the majority (84 percent) harvest two times per year, 12 percent harvest three times. Two 
percent said they harvest four times annually, and only one said he harvests every single week. 
Water benefits 
Reducing water consumption by biodigesters, and hence increasing users’ access to water, was the 
main benefit expected of Green Heat’s intervention, particularly the introduction of SST. Based on 
this, end users were asked how much their access to water and/or water consumption had changed 
(Figure 13). 
FIGURE 13. CHANGE IN WATER CONSUMPTION SINCE INNOVATION 
(N=57)
61%
2%
16%
21%
CHANGE IN WATER CONSUMPTION SINCE INNOVATION 
(N=57)
Increased
Decreased
No change
Yet to be seen
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 25
Although they could not state it quantitatively, they were able to qualitatively articulate the changes 
as increased, decreased, no change, or yet to be seen (Figure 13). Of respondents, 61 percent (35 
of 57) said the innovation made them consume more water mainly due to cow dung mixing. Twenty￾one percent (12 of 57) said their biogas plants helped them decrease the amount of water usage. 
Respondents believe the improvement was due to the use of biogas byproduct to water crops; slurry 
fertilizer shortens the growing season, and fertile soil preserves water. Sixteen percent (9 of 57) said 
their water consumption was unchanged, including two who had not used the system since it was 
installed. One respondent said the impact is yet to be seen as the system had only been installed for 
two months. 
Furthermore, the study attempted to find out if the innovation had any impact in terms of water 
consumption as opposed to crop yield. 
FIGURE 14. WATER USAGE VERSUS CROP YIELD DUE TO INNOVATION 
(N=57)
56%
9%
3%
7%
25%
WATER USAGE VERSUS CROP YIELD DUE TO INNOVATION 
(N=57)
Used more water and increased crop yield
Used less water and increased crop yield
No change in water and increased crop yields
Had no change in water for same crop yield
Yet to be seen/Too early/System never worked
Fifty-six percent of respondents said they used more water as a result of the innovation but their 
crop yield also increased. On the other hand, 25 percent said their biogas technology made them 
consume less water to get more crop yield. Seven percent said their biogas had no impact on water 
consumption but helped them increase crop yields. The innovation seemed to have no impact on 
water consumption or crop yield for three percent of the respondents. The remaining nine percent 
said their systems never worked or it was too early to see results (Figure 14). 
26 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
Crop benefits
FIGURE 15. CHANGES IN CROP YIELDS AFTER BIOGAS
60%
9%
31%
CHANGES IN CROP YIELDS AFTER BIOGAS
Increased
Substantially increased
Other
Among interviewees, 60 percent reported their crop yield increased due to biogas, and 31 percent said 
the biogas helped them to substantially increase their crops. Only nine percent did not know the impact 
of the innovation on their crop yield because their systems never worked or were recently installed. 
FIGURE 16. IMPROVEMENT IN CROP SURVIVAL RATE DUE TO BIOGAS 
(N=57)
4%
96%
IMPROVEMENT IN CROP SURVIVAL RATE DUE TO BIOGAS 
(N=57)
Yes
No
Don’t know
Respondents also were asked if the innovation had any impact on crops’ survival rate. Ninety-six 
percent said their crops’ survival rate improved due to the use of biogas technology. Four percent said 
they couldn’t figure it out because their system was either not working or just introduced. 
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 27
Income benefits 
FIGURE 17. FAMILY INCOME IMPROVEMENT DUE TO INNOVATION
5%
96%
96%
4%
2%
FAMILY INCOME IMPROVEMENT DUE TO INNOVATION
Somewhat
Significantly
Very significantly
Too early
Not at all
When asked if their family income improved after they started to use biogas, 54 percent said income 
improved very significantly. Thirty-five percent said their household income significantly increased 
due to the use of biogas. Family income somewhat improved for five percent. While no change was 
observed in the income of five percent of the interviewees, it was too early for four percent of the 
sample to evaluate (Figure 17). 
28 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
TABLE 7. COMPARISON OF SEASONAL CONSUMPTION OF INPUTS AND EXPENSES 
CONSUMPTION OF FERTILIZER AND EXPENSES (N=44)
BEFORE INNOVATION AFTER INNOVATION
FERTILIZER (KG) COST (UGX) FERTILIZER (KG) COST (UGX)
Total 1,336 2,244,500 65 190,000
Average 30 51,011 1 4,318
Median 0 0 0 0
Minimum 0 0 0 0
Maximum 300 780,000 50 150,000
CONSUMPTION OF PESTICIDES AND EXPENSES (N=46)
BEFORE INNOVATION AFTER INNOVATION
PESTICIDES (KG) COST (UGX) PESTICIDES (KG) COST (UGX)
Total 84 1,409,000 39 798,500
Average 2 30,630 1 17,359
Median 1 11,000 0 0
Minimum 0 0 0 0
Maximum 20 320,000 10 190,000
CONSUMPTION OF HERBICIDES AND EXPENSES (N=45)
BEFORE INNOVATION AFTER INNOVATION
HERBICIDES (L) COST (UGX) HERBICIDES (L) COST (UGX)
Total 65 1,015,500 64 962,000
Average 1 22,567 1 21,378
Median 0 2,500 0 0
Minimum 0 0 0 0
Maximum 20 300,000 20 300,000
CONSUMPTION OF ENERGY AND EXPENSES (N=40)
BEFORE INNOVATION AFTER INNOVATION
CHARCOAL/
FIREWOOD (KG) COST (UGX) CHARCOAL/
FIREWOOD (KG) COST (UGX)
Total 414,701 51,661,547 20,583 11,578,373
Average 10,368 1,291,539 515 289,459
Median 473 120,000 82 24,600
Minimum 0 0 0 0
Maximum 150,000 37,500,000 15,000 6,750,000
Data for seasonal agricultural inputs consumption as well as associated costs incurred by 
respondents was recorded during the survey. Although some of the farmers did not provide specific 
figures, the majority was able to quantify their fertilizer, pesticides, herbicides, and charcoal and/
or firewood consumption trends before and after using the innovation. Everyone that responded 
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 29
was counted, even if they did not use the input/s. Of the 57 interviewees, patterns for fertilizer 
consumption were shared by 44, pesticide consumption by 46, herbicides consumption by 45, and 
energy consumption by 40. However, numerous estimations and conversions were carried out as 
respondents provided data in a wide range of units. For instance, some farmers quantified their 
fertilizer usage in terms of number of sacks, and charcoal/firewood in terms number of trucks or sacks. 
Therefore, the information may not be accurate or representative enough.
Accordingly, the total amount of fertilizer consumed in a season was 1,336 kilograms at a cost of UGX 
2,244,500 before the innovation. After using the innovation, it reduced to 65 kilograms at a cost of 
UGX 190,000, less by 1,271 kilograms and UGX 2,054,500. This is because only three respondents 
continued to use inorganic fertilizer while others completely relied on the slurry byproduct after 
the innovation. Similarly, the consumption of pesticides was reduced due to the innovation. The 
total amount of pesticides consumed was 84 and 39 kilograms before and after the innovation, 
respectively. The average cost incurred was UGX 30,630 and 17,359 before and after the innovation, 
respectively. For herbicides consumption, the amount used in a season was equivalent before and 
after innovation – 65 and 64 liters, respectively. However, there was some difference in cost. The total 
cost of herbicides was UGX 1,015,500 before biogas, but after the use of biogas it was UGX 962,000 
(less by UGX 53,500). Respondents said there are many options now and the price is cheaper. The 
biggest change was observed in energy consumption patterns of users. Forty respondents consumed 
a total of 414,701 kilograms of charcoal and/or firewood in a season before biogas. After the 
introduction of biogas, their total charcoal and/or firewood usage reduced to 20,583 kilograms. This 
is less by 394,118 kilograms (1,915%). Furthermore, the average seasonal charcoal and/or firewood 
expenses of the users decreased from UGX 1,291,539 to UGX 289,459 (Table 7). 
30 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
TABLE 8. HARVEST AND SELL OF CROPS BY FARMERS
BANANA MILLET COFFEE SORGHUM VEGETABLES CORN BEANS RICE
Number of 
Respondents 11 1 10 2 6 14 8 1
Total 
harvested (Kg) 152,900 10,000 47,110 20,500 21,550 10,120 8,110 400
Average 13,900 10,000 5,223 10,250 4,310 778 1,802 400
Median 600 10,000 800 10,250 800 600 1000 400
Average price 
(UGX/kg) 1,046 2,500 2,111 650 3,700 923 1,931 2,800
Farmers were asked what crops they harvested in the previous season and how much the crops were 
sold for. Bananas, coffee, corn, beans, and vegetables were the major crops harvested by many of 
them. The average yields of bananas, coffee, vegetables, corn, and beans harvested was 13,900, 
5,223, 4,310,778 and 1,802 kilograms, respectively (Table 8). The average price for a kilogram of 
bananas was UGX 1,046 whereas the price for coffee was UGX 2,111. Corn and beans were sold for 
UGX 923 per kilogram and UGX 1,931 per kilogram on average. 
Poverty reduction benefits 
FIGURE 18. INCOME BEFORE AND AFTER INNOVATION 
(N=29)
20000000
10000000
25000000
30000000
15000000
5000000
INCOME BEFORE AND AFTER INNOVATION 
(N=29)
INCOME (UGX)
Median
5000000
Average
5581724
Range
24980000
Minimum
20000
Maximum
25000000
0
Before After
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 31
Respondents were asked to share their annual income before and after the innovation. Only 51 
percent (29 of 57) were able to determine their income in quantitative terms. Others, although they 
could express it qualitatively (Figure 17), were unable to provide numerical data. The majority shared 
annual data while others gave seasonal data, which was then multiplied by the number of seasons 
to determine income per year. The average, median, range, and maximum income all were higher 
after the innovation than before (Figure 18). The median was 60 percent higher after the innovation. 
Whereas, the maximum income earned was UGX 16 million and UGX 25 million before and after the 
innovation, respectively. 
TABLE 9. WHAT DO FARMERS DO WITH THE NEW INCOME?
NEW INCOME SPENT ON FREQUENCY %
Send and/or keep children in school 45 79
On investment in farming 37 65
Improving house 15 26
Social functions such as weddings 3 5
Others 6 11
Since the majority of sample households confirmed that biogas had enabled them to increase their 
household income, they were asked what they do with the new or additional income generated due 
to the innovation. Sending or keeping children in school was the most frequently mentioned use for 
the new income. The second most commonly mentioned purpose was on investments in farming. 
Improving their house was identified by 26 percent of the respondents. Three households mentioned 
they also spent it on social functions, such as weddings. For the remaining six households, it was either 
too early or their systems never worked so they had no new income, or they didn’t answer (Table 9). 
Gender differences 
TABLE 10. HOW HAS THIS INNOVATION HELPED YOU?
USAGE MALES % FEMALES %
Helps by lower cost of inputs 13 45 12 43
Helps women farmers as well as men 13 45 20 71
Reduces crop wastage 2 7 0 0
It helps me to decide when to plant 14 48 9 32
It helps me to decide which crops to plant 5 17 7 25
Improves the health and strength of 
livestock 1 3 0 0
Increases my yield through timely 
forecasts 13 45 13 46
They made a special effort to include 
women farmers 1 3 4 14
Helps in producing more of our most 
important crop 6 21 9 32
Makes Water Reusable 1 3 3 11
Helps reduce labor 2 7 1 4
32 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
Any difference in gender in terms of how has the technology helped end users was explored. The 
most frequently mentioned benefit by male respondents (48 percent) was helping to decide when to 
plant crops. However, most female respondents (71 percent) stated helping women farmers as well 
as men as a benefit of the innovation. Forty-five percent of males and 43 percent of females said 
biogas helps lower the cost of inputs. Increasing crop yield through timely forecast was the second 
most mentioned benefit by both males (45 percent) and females (46 percent). The least frequently 
mentioned benefits by males were making water reusable, making a special effort to include women 
farmers, and improving the health of livestock. No female mentioned the benefits of reducing crop 
wastage or improving the health of livestock (Table 10). 
Regional differences 
FIGURE 19. REGIONAL DIFFERENCE OF EXPERIENCE WITH INNOVATION
 
10
5
15
REGIONAL DIFFERENCE OF EXPERIENCE WITH INNOVATION
RESPONDENTS
14
Less than 5 years
11
10
1
6
5-10 years
4
2
8
0
More than 10 years
0 0
2
0%
Central Eastern Western Northern
Clients from the Northern region of Uganda seemed to be more experienced than those from other 
regions. The two respondents who used biogas for more than 10 years were from the Northern region. 
Of the 36 respondents who used biogas for less than five years, 14 were from Central, 11 from Eastern, 
10 from Western, and one from Northern regions. The majority of those who had five to 10 years 
biogas experience were from Northern followed by those from Central (Figure 19).
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 33
DISCUSSION
34 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
As the fieldwork started, there was some confusion from the field evaluator concerning whether the 
interviewees were the right targets/customers. While administering the question “how long have you 
been using the innovation” in the questionnaire, some respondents answered as having used it for 
eight to 11 years. Meanwhile, the list of clients provided by both Green Heat and SWFF showed that 
the earliest SST was installed in 2015, meaning four years maximum usage. With this unexpected 
heterogeneity in mind, Green Heat personnel were contacted and confirmed that many of the 
customers had used biodigesters for a long time and SST was installed onto their existing systems. 
Despite this information, it was still not fully clear, whether to only focus on SST or the entire system. 
Fortunately, a field “Check-in Call” was set up by SWFF for this type of inquiry. It was confirmed by 
SWFF that the interest was to study the impact of the entire biogas systems equipped with SST on 
clients’ livelihoods. 
Usage/Availability 
Of the interviewed farmers, 34 percent have used their biogas systems properly and never had 
problems. Others, however, revealed that their systems had not worked fully or worked partially for 
various reasons. Two respondents said their biogas plants never worked since they were installed, 
and the owners believed that lack of professionalism of those who built it was the reason. In one 
village in Northern Uganda, respondents said only four of the 20 systems installed in that village were 
functioning at the time of the interview visit. It also was observed that many lighting units were not in 
service although the systems were still running.
The partial or complete failures of biogas plants were in association with several other factors as 
well. Eight percent of respondents said lack of cow dung had been their major challenge. They said 
their cows died or were stolen, and they no longer had access to dung to feed to their systems. 
Several farmers collected cow dung from neighbors to keep their systems running. Another challenge 
mentioned by 56 percent of respondents was the shortage of water. A majority of the farmers said 
their biogas plants made them consume more water due to mixing, and they did not use recycled 
water to mix the dung. Non-functioning systems due to lack of cow dung or water were observed. 
Lack of technical knowhow and spares were mentioned as a challenge which directly or indirectly 
caused the failure of many systems. Respondents said they did not have the expertise to fix defects 
in their innovations regardless of the seriousness of the failures nor did they know who to contact 
for spares, where to get spares, or to address any issue pertaining to their biodigesters. During the 
survey, it was witnessed that many of the faults required only basic spares and technical knowhow as 
the interpreters/guides were able to fix some issues during the field visit without using any spares or 
special tools. As a result, those respondents who had their problems solved by the interpreters/guides 
were thankful they were part of the field team.
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 35
Crop yield/survival
The majority of respondents reported positive impacts of the biogas innovation on yield and survival 
of rates of crops. Ninety-six percent confirmed improvements in the survival rate of their crops due to 
biogas technology. Sixty percent said although they had to consume more water to run the innovation, 
their crop yield increased as a result. Thirty-one percent said the biogas helped them to substantially 
increase their crop yields. Users mentioned that the fertilizing effect of the slurry is very high and organic. 
During the field survey, it was learned that a farmer was about to launch a local association named 
“Buyernga Bamalakulabako Farmers Group.” The association aims at producing and packaging high￾quality slurry (both liquid and solid) to the market. The farmer claimed their bio-slurry concentrate would 
contain 20 percent cow dung, 30 percent nitrogen, five percent phosphorus, five percent potassium, 
and 40 percent water. He said it can increase crop yield by as much as 200 percent. Although this is a 
little less than the 270 percent increase in crop yields set by Green Heat, one can easily imagine how 
effective the bio-slurry can be in increasing crop productivity and survival rates. 
Through the anaerobic reaction that takes place in the digestion chamber, the methane gas, which 
would otherwise burn crops if cow dung was directly applied to the farm fields, gets separated. 
Moreover, the same process decontaminates the slurry from any potential pests that would be 
Systems out of service
36 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
caused if raw cow dung was used as fertilizer. Some farmers mix the liquid component of the bio￾slurry with local ingredients and use it as pesticides. The bio-slurry helped users to not only choose 
when to plant and which crops to plant, but also reduce their agricultural inputs consumption such as 
inorganic fertilizers, pesticides, and herbicides. This means farmers no longer need to buy such inputs 
or can use them to a much lesser extent. It is to be recalled that 70 percent of the interviewees were 
able to decide which crops to plant, and 79 percent were able to decide when to plant their crops due 
to biogas. Farmers also were able to introduce new farming techniques, such as intercropping, due to 
the use of slurry. One farmer who had his biogas system connected to the toilet said that he also was 
able to get additional crops on his farm plot pollinated from human waste.
Changes in income 
An increased income was reported by 89 percent of the interviewees due to the use of biogas, of 
whom 54 percent reported a very significant improvement in their household income. Five percent 
said family income improved somewhat. Households’ average annual income after the innovation 
was UGX 5,581,724, up by 32 percent as compared to the average income before of UGX 3,787,302. 
Respondents said not only had the innovation helped them boost their crop productivity but also had 
reduced costs on inputs such as fertilizer, herbicides, and pesticides.
Clients reported using their new income from the innovation for various purposes. The additional 
income was used by the majority to send or keep their children in school. Sixty-five percent reinvested 
it in their farming business, and 26 percent reported using it for improving their houses.
Beans intercropped with bananas
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 37
Five percent of target farmers could not report any additional income, as it was too soon after getting 
the innovation. The remaining two percent said they never saw any improvement in their family 
income from the innovation because their systems never worked since being installed. 
The interviewees also reported several other non-income benefits from the biogas, such as increasing 
the value of land which, in turn, improves their access to credit schemes. The innovation also helped 
farmers reduce the usage of agricultural inputs, such as inorganic fertilizer which, in turn, reduces 
cost and enhances savings. Moreover, biogas has become a source of additional income for many 
of the clients interviewed. The slurry byproduct was used as fertilizer, to feed animals, and as a 
product for sale. Blended with maize grains, it was used to feed animals, particularly pigs, poultry, 
and fish. A woman from Lira, in Northern Uganda, said: “If you feed bio-slurry to a chicken, it can gain 
2.5 killogram in weight in just three months and be ready for sale.” Due to the limited or no negative 
environmental impact coupled with a high fertility effect, there is high demand for bio-slurry among 
farmers. Since not everyone owns the biogas innovation, some users were able to generate additional 
income by selling surplus slurry to others. 
Cow on an SST Biodigester Farm (left). Bio-slurry for sale @ UGX 40,000/Barrel (right).
38 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
Gender differences 
Overall, no major difference was observed between genders relative to the innovation. However, when 
asked to prioritize the benefits of biogas for farming activities, the innovation’s contribution toward 
enabling decisions on when to plant was the most frequently chosen benefit by male respondents 
(48 percent). Among females, however, the fact that biogas helps both male and female farmers was 
mentioned by the majority (71 percent). Lowering the cost of inputs and helping both female and male 
farmers were similarly chosen by 45 percent of male respondents. For 46 percent and 43 percent 
of female respondents, increasing crop yield through timely forecasts and lowering the cost of inputs 
were prioritized, respectively (Table 6). 
Affordability 
Due to the high cost of installation, respondents said, “Not everyone can afford biogas.” They indicated 
many of their friends and neighbors would like to adopt it if not for the high cost of equipment or lack 
of a cow. Cow ownership is an essential requirement for biogas adoption but the price of a cow is 
unaffordable to many rural farmers. Another affordability challenge mentioned by farmers was the 
large space required to install a biogas plant. Respondents indicated that lack of space was why 
some of their peers were unable to introduce the innovation. Interestingly, one farmer suggested if 
the biogas components (from mixing chamber to the outlet) could be arranged somehow vertically 
instead of laying them horizontally, people with small land size could use it. 
Data on overall expenses spent on biogas systems was recorded during the survey. Although one 
respondent received it as a donation, the cost of equipment ranged from UGX 200,000 to 4 million, 
the minimum being only maintenance cost covered by the farmer. Some farmers got their systems 
in a cost-sharing mode between themselves and the innovator or other NGOs. Some respondents 
reported that they also were supported with cows.
Two types of bio-digesters were observed during the fieldwork – Fixed Dome and Flexible Balloon 
options (Photo 5).
Fixed Dome type (left). Flexible Balloon type (right).
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 39
While the ultimate purpose remains the same in both options, they significantly vary in cost of 
installment and maintenance. These two options not only vary in cost but also in the space they 
require. The Fixed Dome occupies a larger space than the Flexible Balloon Option. Fixed Dome is a 
sub-surface digester that ranges from four to 50 cubic meters and is also known for offering long￾term solutions for effective waste management. The majority of systems visited were of this nature. 
The Balloon Option is a portable digester that is quicker and easier to install and is best suited for 
small farms and households. The plastic casing is fed with organic waste and expands as gas is 
produced. The Balloon Option is relatively cheaper and lays on a relatively smaller surface. This option, 
however, has not yet been widely used by farmers because it is a relatively newer technology. Only 
one respondent had this type of biogas system. 
Energy benefits
The principal benefit farmers would expect from biogas is energy generation. In this particular survey, 
100 percent (57 of 57) mentioned the benefit of energy (Table 3). A woman from Jinjia in the Eastern 
region of Uganda said, “Because of biogas, our cooking task has become easier, faster, cleaner, and 
safer.” It has enabled farmers to save time required for cooking and to have more time to engage in 
their farm activities. Moreover, the innovation helped clients to reduce not only their energy expenses 
but also the pressure on forest resources and the wider environment. Most of the rural people in 
Africa rely on forest resources as their source of energy, mainly for cooking, heating, and lighting 
purposes. This is causing a high rate of deforestation and environmental degradation. Biogas is 
providing alternative clean energy to the end users. Those farmers whose systems worked properly 
said they no longer bought or used charcoal or firewood or they consumed less compared to the 
amount they used before the innovation. Due to the cleanliness of the methane gas generated from 
their systems, users said they no longer suffer from indoor pollution, recalling when they cried while 
cooking with firewood. Clients also compared cooking with conventional gas to cooking with biogas. 
With biogas, users said even young children can do the cooking which would not be possible with the 
conventional gas due to its flammable nature. 
Although lighting facilities were not in service in many of the biogas plants visited, two respondents did 
have working lighting systems and had replaced the use of kerosene. 
Methane gas being used for cooking and lighting
40 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
Waste management 
One of the challenges rural dwellers in Africa have in common is the lack of proper sanitation facilities. 
They rarely have access to proper latrines, and animal dung adds to the problem. Humans do not live 
far enough from their livestock, causing chronic hygienic challenges.
In this field evaluation, however, it was found that the biogas innovation also provided rural users 
with sanitation benefits. Sanitation was the third most frequently mentioned (23%) benefit (Table 3). 
Farmers said before the innovation, they had piles of cow dung in their backyards or scattered all 
along their compounds, causing problems such as pest infestation and mosquitoes. A compound 
littered with cow dung also affected the appearance of their houses. Now that clients have biogas 
plants to use the cow dung, it is no longer considered as waste but rather as raw material or “gold.” 
Moreover, to ensure sustainability and reliability of their systems, a couple of households had built 
toilets and connected them to their systems. Many more respondents wanted to or planned to do 
the same. By doing so, users keep their systems running and steadily generate outputs while also 
maintaining their indoor and outdoor hygiene. “Thanks to the biogas innovation, everything in our 
home is recycled. Cow dung and the waste from our latrine are directly fed into the system; we apply 
slurry from the system to seeds in our farm plot; we use the crop yields for our consumption and the 
crop residues for our animals. We no longer need rubbish bins to collect and dispose organic wastes,” 
said a female respondent from Gulu district, Northern Uganda. 
Soil fertility and productivity benefits 
The Green Heat innovator reports that the dry fertilizer separated by the SST is proven to boost crop 
yield by as high as 270 percent. Similarly, the respondents in the field were appreciating the high 
fertilizing effect of the bio-slurry byproduct. Enhancing soil fertility, and hence productivity, was the 
second most frequently stated benefit of biogas (98 percent) (Table 3). In the field, various farming 
practices were observed for the slurry, including crops grown on banana stems with slurry, vegetables 
grown in sacks full of slurry mixed with soil, and mushrooms grown in hanging plastic bags filled with 
slurry and soil. Farmers said the bio-slurry made the task of growing food easier and more flexible. 
The farmer pictured below said even people who live in rented houses can still grow crops on things 
such as a banana stem. He said, “Even if your landlord kicks you out, you can still move with your crops 
carrying your banana stem.” For such good reasons, there is a very high demand for slurry, and not 
everyone has biogas plants.
 
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 41
Water benefits 
Green Heat says its slurry separation system enables biodigesters to consume less water or reduces 
water needs of biogas plants by as much as 80 percent. In principle, water by-products are separated 
during the process of slurry separation and re-used to mix with organic waste later in the system – by 
replacing freshwater. This survey, however, shows a completely different outcome. Shortage of water 
was one of the major challenges identified by clients in relation to the innovation. Sixty-one percent of 
the interviewed households said their water consumption increased since they started to use biogas, 
mainly due to cow dung mixing. Only 21 percent said their water consumption was reduced due to 
biogas. But even that was because of some indirect effects of the byproduct. Respondents believed the 
reasons for improvement was due to the application of semi-liquid bio-slurry to crops, the slurry fertilizer 
shortening the growing season, and the fertile soil preserving the water. 
When asked what they use the slurry for, most farmers said they directly apply it to their farm fields. 
Some said they sometimes reuse it to feed their system instead of cow dung but not as water. When 
Food being produced in many ways using bio-slurry
42 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
further asked why they wouldn’t use recycled water to mix dung instead of freshwater, they said the 
residual or slurry is too thick to be used for mixing which was also confirmed during field visits. Farmers 
said they can only use the slurry to re-feed their systems, especially when there is a shortage of cow dung.
Based on observations, one main reason is that the separation process or SST was not effectively 
being executed. When inspecting the systems, it was noted that only a few had the facility to 
undergo the separation. For effective separation and recycling water, the outlet of systems need to 
be partitioned into two containers – one for the solid fertilizer and another for the liquid component 
(Photo 8, right). Unfortunately, most of the biogas plants visited had only one outlet where both 
components accumulate in the same container or directly flow to farm plots (Photo 8, left). 
But Green Heat also reports that its biodigesters can be fed with a variety of liquids such as rainwater, 
wastewater, and cow urine. This was confirmed during the field visits. Customers were observed 
harvesting rainwater and collecting cow urine, including from their neighbors, to use for mixing. A 
male farmer from Buikwe district in the Central region of Uganda expressed the benefits of biogas 
innovation and said, “Thanks to the biogas technology, nothing of this cow is thrown away anymore. 
Her dung is used to feed our system to generate energy and her urine is used to mix the dung. Her 
milk is used to feed our children and the remaining is sold out to generate income. The more you feed 
her, the more she gives you dung and urine hence energy and fertilizer, and milk.” 
Single outlet (left). Partitioned outlet (right).
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 43
Benefits of innovation on community
Respondents reported a wide range of knowledge and skill-sharing about biogas among their 
communities, and some consider themselves as “biogas promoters.” Many users said they frequently 
receive visitors to see their systems. Some respondents adopted the innovation due to the experience 
of their friends or neighbors. Only two respondents mentioned that some community members made 
up stories of biogas plants causing pest infestation, such as mosquitoes. On the contrary, however, 
farmers used the fluid from bio-slurry as an organic pesticide by mixing it with unidentified locally 
available ingredients. 
Impact on poverty 
Sixty-one percent (35 of 57) of respondents relied on agriculture as their primary source of income. 
However, farming is costly and requires a number of inputs, such as fertilizer, pesticides, herbicides, 
water, labor, and seeds. These could be reduced by using improved agricultural technologies, such 
as bio-slurry. Therefore, to determine the impact of the biodigesters equipped with slurry-separation 
innovation on users’ livelihoods, a comparison of input consumption, expenses spent on inputs, the 
amount harvested, and income earned before and after the use of the systems was calculated. 
As a result, it was observed that the increase in crop yields and household incomes, as well as the 
reduction in consumption of inputs and associated expenses, was remarkable.
Cow urine being used for mixing dung
44 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
Based on observation, the impact of the technology on poverty alleviation was very visible. As 
shown in Table 7, users spent 1,081 percent less on inorganic fertilizers (mainly urea and dap) after 
the innovation. Each farmer spent UGX 46,693 less on average in a season. After the introduction 
of biogas and later SST, users switched to organic bio-slurry. But at the same time, crop yield and 
income of their households were increased. The average annual income of the sample households 
was UGX 3,787,302 before and UGX 5,581,724 after the innovation, a 47 percent increase. Similarly, 
the impact of the innovation on pesticides and herbicides consumption was promising. Farmers used 
less or no chemicals to prevent pests or herbs after the innovation. Moreover, clients’ average energy 
expenses dramatically reduced after the innovation (346 percent less). Users said access to clean 
energy also improved their health and safety conditions. Fifty-four percent of farmers reported their 
income improved very significantly as a result of the innovation. Most of them sent their children to 
school with the new income. 
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 45
CONCLUSION
46 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
Green Heat was sponsored by SWFF to reach more farmers with their innovative Slurry-Separation 
Technology (SST) to biogas systems in Uganda and beyond. The intention of the SST was to enable 
biogas plants to separate water from the waste to be reused for mixing. Apart from recycling water, the 
technology was expected to create an easily managed, high-quality fertilizer product while increasing gas 
production for energy consumption. According to the innovator, the Green Heat SST would result in reduced 
water demand of biogas systems by as much as 80 percent, and the fertilizer would increase crop yield 
by as high as 270 percent. This field evaluation was, therefore, carried out to evaluate the performance 
of the biogas technology in general and the slurry-separation innovation in particular. The field survey 
was conducted in July and August, 2019, in Uganda. Although the biogas technology had been there for 
a long time, it was over four years since the slurry-separation innovation had been introduced.
The sample respondents interviewed included both men (51 percent) and women (49 percent) from 
13 districts scattered across all the four regions of the Republic of Uganda. The average family size 
of samples was nine members, whereas, the average farm land holding was 5.9 hectares. Farmers’ 
experience with biogas technology ranged from two months to 11 years.
Through the face-to-face interviews and personal observation, it was realized the innovation benefits 
users in many ways. Every respondent (100 percent) picked energy generation for cooking and lighting as 
the main benefit of the innovation. Enhancing soil fertility, and hence productivity, was the second most 
frequently mentioned benefit (98 percent). Fifty-four percent reported very significant improvement 
in their household income due to the innovation. Twenty-nine respondents said their average income 
increased by 32 percent annually after the innovation. The maximum yearly income registered before 
was UGX 16 million, and after the use of the Green Heat innovation, it elevated to UGX 25 million – up by 
56 percent. Ninety-six percent confirmed improvements in crop survival rate. However, the innovation’s 
impact on water consumption was not as promising as expected. Sixty-one percent of the interviewed 
households confirmed their water consumption increased after they started using biogas, which was 
attributed to the amount of water needed to mix dung. Only 21 percent reported their water consumption 
was reduced after biogas, but that was due to some indirect impacts not related to recycling. Moreover, 
the shortage of water was one of the major challenges identified by users. During the field visits, it was 
noticed that the SST was not being used by many of the farmers as intended to recycle water. 
Overall, the project achieved countless remarkable successes toward improving farmers’ livelihoods. 
The biogas systems offered users with clean energy, hygienic services, and environmental 
sustainability. In addition, the SST provided high-quality organic fertilizer that increased crop 
productivity and household incomes. However, some improvement is needed to properly administer 
and utilize the SST for recycling water. Through their wide range of purposes, biodigesters properly 
equipped with SST could contribute toward achieving most of the UN Sustainable Development 
Goals (SDGs). Among them are SDG 1: “Ending poverty in all its forms everywhere;” SDG 2: “Ending 
hunger, achieving food security and improved nutrition, and promoting sustainable agriculture;” 
SDG 6: “Ensuring availability and sustainable management of water and sanitation for all;” SDG 7: 
“Ensuring access to affordable, reliable, sustainable and modern energy for all;” and, SDG 13: “Taking 
urgent action to combat climate change and its impacts by regulating emissions and promoting 
developments in renewable energy.”
No communal or individual negative impact caused by biogas, or the SST in particular, was observed 
during the field survey. 
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 47
ANNEX I
48 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
FARMER INFORMATION
NAME 
AGE 
DATE TIME 
GROUP INTERVIEW? o Yes o No
GROUP INTERVIEW NOTES
HOW MANY FAMILY MEMBERS LIVE WITH YOU? 
GENDER o Male o Female
WHAT IS YOUR PRIMARY OCCUPATION?
o Farming
o Wage Labor
o Seasonal Migrant Labor
o Small Enterprise
o Other: 
DO YOU HAVE ANOTHER OCCUPATION?
o Farming
o Wage Labor
o Seasonal Migrant Labor
o Small Enterprise
o Other: 
WHAT IS THE NAME OF YOUR VILLAGE/TOWN? 
HOW MUCH LAND DO YOU OWN? 
HOW LARGE IS YOUR FARM/PLOT? 
o Large
o Medium
o Small
o Very Small
HOW MUCH IS LAND RENT? 
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 49
OTHER LAND NOTES
HOW LONG HAVE YOU BEEN USING GREEN HEAT? 
DID YOU PARTICIPATE IN AGRICULTURAL ACTIVITIES THIS YEAR? o Yes o No
HOW MANY MONTHS IS THE PRIMARY GROWING SEASON? 
HOW MANY TIMES DO YOU HARVEST PER YEAR? 
FARM INFORMATION
WHAT CROPS DO YOU GROW AS A RESULT OF GREEN HEAT? LIST FROM MOST IMPORTANT TO 
LEAST IMPORTANT:
1. 
2. 
3. 
DID THE MOST IMPORTANT CROP BENEFIT FROM GREEN HEAT? o Yes o No
DID THE SECOND MOST IMPORTANT CROP BENEFIT FROM GREEN HEAT? o Yes o No
DID THE THIRD MOST IMPORTANT CROP BENEFIT FROM GREEN HEAT? o Yes o No
WHAT IS THE WATER SOURCE FOR YOUR IRRIGATION OF CROPS?
o Own pond
o River
o Groundwater
o Innovation Source
o Other 
50 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
WHAT IS YOUR METHOD OF IRRIGATION?
o Drip feed
o Flooding
o Hand watering
o Rainfed
o Other 
HOW MUCH HAS YOUR WATER USAGE CHANGED SINCE USING GREEN HEAT, IF AT ALL? 
USING GREEN HEAT HAS YOUR ACCESS TO WATER:
o Had no change
o Improved
o Fundamentally improved (Improved a lot)
o Other: 
PREVIOUSLY GROWN CROPS: DID YOUR FARM PRODUCE DIFFERENT CROPS IN THE PAST THAT 
ARE NO LONGER GROWN HERE? IF SO, WHICH ONES? 
MASS OF PRODUCE: WHAT YIELDS DID YOU HAVE FOR EACH CROP YOU MENTIONED?? 
MASS OF PRODUCE 2: WHAT YIELDS DID YOU HAVE FOR YOUR CROPS BEFORE USING GREEN 
HEAT? 
USING GREEN HEAT HAVE YOU, FOR EACH CROP:
o Used more water
o Had no change in water use
o Used less water
o Other: 
USING GREEN HEAT HAVE YOUR CROP YIELDS (ASK FOR EACH CROP):
o Declined
o Remained the same
o Increased
o Substantially increased
IS THERE A DIFFERENCE IN THE SURVIVAL RATES OF YOUR CROPS DUE TO GREEN HEAT? 
o Yes o No
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 51
HOW MUCH OF YOUR PRODUCE DID YOU CONSUME IN YOUR HOUSEHOLD? (PERCENTAGE – 
NOTE IF DIFFERENT FOR EACH CROP) 
HOW MUCH OF EACH OF THE FOLLOWING INPUTS DID YOU USE BEFORE GREEN HEAT?
FERTILIZER (KG)
PESTICIDE (KG)
HERBICIDE (L)
CHARCOAL (KG)
WATER (TOTAL)
LABOR (DAYS)
OTHER 
HOW MUCH DID YOU SPEND ON EACH OF THE FOLLOWING INPUTS BEFORE GREEN HEAT? 
FERTILIZER (KG)
PESTICIDE (KG)
HERBICIDE (L)
CHARCOAL (KG)
WATER (TOTAL)
LABOR (DAYS)
OTHER 
HOW MUCH OF EACH OF THE FOLLOWING INPUTS DO YOU USE AFTER GREEN HEAT?
FERTILIZER (KG)
PESTICIDE (KG)
HERBICIDE (L)
CHARCOAL (KG)
WATER (TOTAL)
LABOR (DAYS)
OTHER 
HOW MUCH DID YOU SPEND ON THE FOLLOWING INPUTS AFTER GREEN HEAT? 
FERTILIZER (KG)
PESTICIDE (KG)
HERBICIDE (L)
CHARCOAL (KG)
WATER (TOTAL)
LABOR (DAYS)
OTHER 
52 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
HOW MUCH DID YOU SPEND ON EQUIPMENT BEFORE AND AFTER GREEN HEAT GREEN HEAT?
HOW MUCH DID YOU SPEND ON TRANSPORT AND STORAGE BEFORE AND AFTER GREEN HEAT? 
 
DO YOU HAVE PROBLEMS FINDING A MARKET TO SELL YOUR CROPS IN? o Yes o No
PLEASE EXPLAIN. 
 
DO YOU HAVE PROBLEMS GETTING YOUR CROPS TO THE MARKET? o Yes o No
PLEASE EXPLAIN. 
OTHER FARM NOTES (OPTIONAL).
INCOME AND EXPENDITURES
WHAT IS YOUR ANNUAL HOUSEHOLD INCOME? 
HOW MUCH INCOME DID YOU MAKE BEFORE GREEN HEAT? 
AFTER GREEN HEAT? 
HAS GREEN HEAT IMPROVED YOUR FAMILY INCOME? 
WHAT PERCENTAGE OF YOUR INCOME DO YOU GET FROM NON-FARM SOURCES? 
HOW MUCH PRODUCE DID YOU SELL FOR EACH OF YOUR CROPS IN THE LAST SEASON AND THE 
LAST YEAR? 
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 53
WHAT IS THE PRICE PER KILO YOU RECEIVED FOR EACH OF YOUR CROPS FOR THE LAST SEASON?
USING GREEN HEAT HAS YOUR ACCESS TO CREDIT:
o Not improved
o Improved
o Improved and have been able to repay over a short period
HOW DO YOU CURRENTLY FINANCE AGRICULTURAL ACTIVITIES?
o Own savings
o Credit and savings scheme
o Other credit
HOW MUCH DO YOU PAY FOR GREEN HEAT? 
HOW MUCH ARE YOU WILLING TO PAY FOR GREEN HEAT?
o Nothing
o GREEN HEAT is free
o The same as what I pay now
o 50% less
o 50% more
o Other: 
HOW HAVE YOU SPENT YOUR NEW INCOME?
o N/A (if no new income)
o Send children to school or keep children in school
o Social functions (like weddings)
o Investment in farming
o Improving house
o Other: 
OTHER INCOME NOTES (OPTIONAL)
54 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
PERCEPTIONS OF GREEN HEAT
WILL YOU USE GREEN HEAT IN THE FUTURE (5 TO 10 YEARS)? o Yes o No
PLEASE ELABORATE: 
HOW, IF AT ALL, HAVE YOU CHANGED YOUR FARMING PRACTICES DUE TO GREEN HEAT?
o No change
o Introduced new crops
o Changed irrigation system
o Reduced water usage
o It helps me decide when to plant
o It helps me decide which crops to plant
o Other: 
HAVE YOU FACED ANY DIFFICULTIES OR PROBLEMS USING GREEN HEAT? o Yes o No
HOW CAN GREEN HEAT BE IMPROVED? 
HOW DID YOU HEAR ABOUT GREEN HEAT?
o Wealthy farmer
o Neighbor
o Innovation personnel
o Extension worker
o Other: 
WHAT FACTORS INFLUENCED YOU TO TRY GREEN HEAT?
o Demonstration from neighbor’s farm
o Innovation is free from extension services
o No alternative water source
o Other: 
DO YOU SHARE YOUR KNOWLEDGE SKILLS FROM GREEN HEAT WITH OTHERS? o Yes o No 
IF SO, HOW? 
SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019 55
WHAT DO YOU FEEL ARE THE BENEFITS OF GREEN HEAT? 
HAVE YOU HEARD ABOUT CLIMATIC VARIATION? HAVE CHANGES IN RAINFALL OR TEMPERATURE 
AFFECTED YOUR FARMING PRACTICES OR CROP YIELDS COMPARED TO YOUR HISTORICAL 
RAINY/DRY SEASON PERIODS? o Yes o No
PLEASE SPECIFY HOW. 
HOW HAS GREEN HEAT HELPED YOU? PLEASE RANK THE TOP 3 AND EXPLAIN POSITIVES/
NEGATIVES.
 Makes water reusable 
 Helps women farmers as well as men 
 They made a special effort to include women farmers 
 Helps in producing more of our most important crop 
 Increases my yield through timely forecasts 
 Helps by lowering cost of inputs 
 Improves health and strength of livestock 
 Helps reduce labor 
 Reduces crop wastage 
 Helps me decide when to plant 
 Helps me decide which crops to plant 
 Other: 
WOULD YOU RECOMMEND GREEN HEAT?
o No
o Yes
o Yes, would strongly recommend
56 SECURING WATER FOR FOOD: GREEN HEAT PERFORMANCE EVALUATION | AUGUST 2019
ARE THERE NEGATIVE IMPACTS FROM GREEN HEAT IN THE COMMUNITY? o Yes o No
IF YES, PLEASE EXPLAIN. 
IF THERE HAVE BEEN ANY NEGATIVE IMPACTS, HAVE EFFORTS BEEN MADE TO RESOLVE THEM? 
o Yes o No
EXPLAIN. 
DO YOU HAVE PROBLEMS FINDING A MARKET TO SELL YOUR CROPS IN? o Yes o No
EXPLAIN. 
DO YOU HAVE PROBLEMS GETTING YOUR CROPS TO THE MARKET? o Yes o No
EXPLAIN. 
HAVE CHANGES IN RAINFALL OR TEMPERATURE AFFECTED YOUR FARMING PRACTICES OR 
CROP YIELDS COMPARED TO HISTORICAL RAIN/DRY SEASON PERIODS? o Yes o No
OTHER
INCOME/POVERTY NOTES
GENDER OBSERVATIONS
QUESTIONS/REQUESTS
OTHER NOTES
Securing Water for Food has sourced and invested in a portfolio of innovative 
solutions that aim to help farmers use water more efficiently and effectively, 
improve water storage for lean times, and remove salt from water to make more 
food. Our cohort of innovators are helping people in 35 low-resource countries 
with tools they need to produce more food with less water.
To learn more about Securing Water for Food, 
visit www.securingwaterforfood.org.