Biogas produced from family-sized biodigesters is used as a clean source of energy for household cooking within energy-poor communities [1]. Also, in communities with relatively developed energy systems, the technology has been suggested for manure management [2]. Biogas produced through anaerobic digestion (AD) of biodigestible organic matter is mainly composed of methane (40–75%) and carbon dioxide (15–60%) [3]. Other minor amounts of gases and halogenated hydrocarbons are also produced in the process [4]. Of the produced biogas composition, combustible methane (CH₄) is the targeted component for cooking. In response to the global agenda of meeting SDG 7, specifically its indicator SDG 7.2.1, household biogas technology has been deployed in large numbers in South and South-East Asia and in Sub-Saharan Africa (SSA). It is estimated that China alone has more than 40 million biodigesters installed [5]. Through the Africa Biogas Partnership Programme (ABPP), more than 100 thousand household biogas plants were installed from 2009 to 2021 in 11 SSA countries [3]. The increased installation of the technology for the production and use of biogas at household level is motivated by its benefits, e.g., mitigation of health issues associated with the use of solid biomass and fossil cooking fuels [6], household financial savings as a result of reducing energy expenditures [7], environmental benefits and hence global warming mitigations [8], organic manure for soil fertilisation and soil management [9] and other socio-economic benefits [10].

However, in order to achieve the aforementioned benefits of the technology, biogas production and use require proper system operations and management [11]. In some situations, feedstock may be pretreated to increase the quality and quantity of biogas production [12]. Due to the decentralised nature of household biogas technology (HHBT) systems and the fact that daily operational routines are carried out at the household level by household (HH) family members, these systems are often susceptible to inefficiencies in operation and use. This situation has led to a substantial number of nonfunctional and or poorly operated HH biogas plants within user communities [13]. Thus, there is a growing concern over the technology’s sustainable use and achieving its intended benefits [13]. It has been evidenced that even in experienced technology user communities, only about 60% of the domestic biogas plants are operated efficiently [14]. Biogas leakage is one operational issue that affects not only fuel resource conversion efficiency but also the technology’s climate benefits. Hou et al. [15] show that the annual biogas produced from 8 m³ biodigesters installed in Chinese rural dwellings vary between 47 and 176 m³ depending on the region. The same study showed that 59%–61% of the produced biogas is used, while the rest is considered as biogas leakages to the atmosphere [15]. Studies continue to report significant environmental benefits of the technology, but also caution that when the technology is not well operated, biogas leakages do affect the intended environmental benefits [16]. Jelínek et al. [17] show that there is an unfulfilled potential of HH biogas to mitigate global warming due to the fact that about 40% of biogas is lost through leakages [17]. Nevertheless, leakage sources in small-scale household biogas systems are frequently generalised, thus overlooking the social contexts of use and the technological diversity in biodigester designs.

Contrary to the small-scale HH biogas use, methane emissions from larger-scale production units have been well studied, documented, classified and tracked according to their sources [18]. At the large-scale production level, methane is emitted from flaring, venting, fugitive leakages or through a combination of these sources of emissions [18]. Such classification of large-scale uses helps estimate greenhouse gas emissions (GHGEs) and develop their mitigation pathways. As shown in Figure 1, venting is an eminent source of methane emissions from large-scale production plants [18]. However, studies on venting from decentralised small-scale use in households within the technology user communities and the possible detrimental effects of venting are lacking in the literature, leading to uncertainty in developing mitigation approaches. Biogas venting levels associated with HHBT use could be potentially worse in communities with new technology adopters, e.g. in SSA communities. This uncertainty leaves a literature gap, calling for studies on GHGEs caused by venting associated with HH biogas production and use.

Figure 1.

World methane emissions from large-scale energy sources 2024 [18]

While studying the HHBT in the SSA technology user communities, Robinson et al. [19] used qualitative research methods to study the venting phenomenon in what they termed “opening the Pandora box”. Their qualitative findings show that venting is understudied and call for empirical research approaches, quantifying GHGEs associated with the venting phenomenon [19]. The lack of empirical studies on quantitative measurement approaches to studying biogas venting leads to a lack of knowledge of the carbon footprint of the small-scale bioenergy sector. It can potentially hinder the growth of emerging voluntary carbon markets and bonds aimed to promote HH biogas technology use in energy-poor communities. For example, Strubbe et al. [20] have generated insights on net-GHGEs as a result of HH biogas technology in Rwandan households in the Huye District. They have shown that a 4 m³ HH biodigester can satisfy up to 65% of the HH cooking energy demand for a family of six members, leading to annual GHGEs reduction of about 2.4 tCO_2,e per HH when compared to HHs using wood only as cooking fuel.

Further, Strubbe et al. [20] show that when the produced digestate is used as a soil fertiliser, the net-GHGEs reduction is enhanced, leading to an annual decrease in GHGEs of about 2.5 tCO_2,e per HH. Such results confirm the benefits of HH biogas technology. Still, their estimations are based on a general assumption that the biogas leakage is about 9% of the total produced biogas from an HH biodigester [20]. Such generalised estimations do not clearly distinguish whether leakages through outlets are intentional (venting to avoid biodigester damage) or unintentional due to damage. When the 9% [20] is compared with 40% [17] of biogas losses due to leakages, the discrepancy indicates that leakages are context-dependent and identifies a gap worthy of filling, hence contributing to the literature on the HHBT use. The discrepancies in the literature on HH biogas leakage and the lack of literature on biogas venting from HH biogas use formed the basis of our study. Thus, this paper aims to study the venting phenomenon associated with HH biogas use, and attempts to answer three research questions (RQs):

• RQ₁: What are the biogas venting levels associated with HH biogas technology use?

• RQ_2: To what extent does venting from HH biogas technology contribute to GHGEs?

• RQ₃: What are the causes of venting from HH biogas plants in rural SSA contexts?

To answer the three RQs, Rwandan HHs are used as a case for the study. The novelty and contribution of this paper can be seen in four aspects: Venting is distinguished from generalised biogas leakage in the context of HHBT use. The use of modern smart biogas meters (SBMs) together with conventional analogue pressure gauges (APGs) provides reliable data for analysing the venting phenomenon, which is not provided by the existing literature. A community-embedded research approach provided a good opportunity to establish and explain the potential causes of biogas venting from within technology-user communities. Based on established causes of venting, we propose potential mitigation approaches which call for further studies.

In this section, methods and materials are first presented in a general context and then applied to Rwanda as a case used for the study. Methods and materials used are presented in a manner that attempts to answer the three RQs step by step from RQ₁ to RQ₃.

Methods

This subsection describes the overall approach and specific procedures adopted by the authors in their experimental research on biogas venting, as well as the relationships used in the estimation of GHG emissions.

Quantifying biogas venting.

The process is guided by the recommended principles of HH biodigester design. There is a maximum (threshold) biogas pressure a biogas holder can handle for a safe HHBT operation, beyond which the produced biogas should be intentionally released (vented) [21]. In Figure 2, the upward arrows illustrate that biogas is continuously collected in the biogas holder while being produced whenever the absolute static biogas pressure (SBP) is still less than the venting threshold. When the produced biogas is underutilised and SBP surpasses the designed threshold value, the pressure can be greater than the compression forces of the biodigester and the gas holder, causing potential cracks, hence biodigester damage and biogas leakage. To avoid this, a maximum allowable SBP for a safe operation is determined based on the biodigester technology to be installed. When the biogas pressure is just above the threshold value, and no auxiliary storage is available, the produced biogas must be intentionally released (vented) to avoid the cracking of the biodigester, allowing the biogas to flow through a designed outlet.

Figure 2.

Biogas pressure in the gas holder below the venting threshold; arrows indicate that the produced biogas under this condition (if no cooking event) is collected in the biogas holder

The venting phenomenon is illustrated in Figure 3. The bidirectional arrows indicate that during venting events, any produced biogas that causes the SBP to exceed the venting SBP must be released through designated outlet(s). The intentional release can be done by triggering (through designated biogas valves) or by biodigester design, e.g. differential height, a design mechanism used for fixed dome HH biodigesters. Based on this safety design principle, the vented biogas volume (in m³) can be recorded, and the associated GHGEs can be estimated. In this study, the vented biogas volume is logged onto the server by using the SBMs, which are described later in the material section.

Figure 3.

Biogas pressure in the gasholder above the venting threshold; the upward arrows indicate biogas being produced, while the downward arrows indicate biogas being vented

Validating logged data.

APGs are used as conventional measurement tools for the SBP of biogas available in the biogas holder. However, as APGs cannot record volumetric biogas utilisation unless calculated from the recorded SBP, they are not convenient for recording instant changes in SBP. As such, SBMs are used as alternative and flexible biogas measurement tools for remote data logging, visualisation, and analysis of HH biogas utilisation for a specific HH, and within a particular time frame. Data validation is first done by the use of APGs to verify the reliability of results from data collected with SBMs. The SBP samples are recorded using APGs during field visits. The SBP is sampled before and after short cooking sessions at the respective technology users’ HHs. The sampled SBPs are used to calculate the biogas consumption by using Boyle’s law, presented in eq. (1) [20], and the barometric formula in eq. (2). The calculated volume of consumed biogas using APGs is compared with biogas consumption recorded with SBMs for validation. To minimise the potential effect of the produced biogas during these cooking sessions, p₁ and p₂ are recorded from very short cooking sessions. These sampled cooking sessions are made very short so that biogas being continuously produced from AD during the sampled cooking sessions is assumed to be negligible.

V cons = ( p 1 − p 2 )× V hol p alt (1) p alt = p o × e ( −Mgh RT ) (2)

Where V_cons [m³] is the volume of biogas consumed during the sampled cooking sessions, p₁ [kPa] and p₂ [kPa] are SBPs recorded at the start and end of a specific short cooking session, V_hol is the volume of the biogas holder (2 m³, in this case), p_alt [kPa] is the local atmospheric pressure at the altitude of a specific HH, p₀ is the standard atmospheric pressure of 101.325 kPa, M is the molar mass of air of 0.029 kg/mol, g is the acceleration due to gravity 9.81 m/s², h [m] is the altitude at which the biodigester is installed, R is the universal gas constant of 8.314 J/(mol·K)], T [K] is average absolute temperature (T [°C] +273.15).

Estimating greenhouse gas emissions.

After validating that the volume of biogas consumed recorded from SBMs is almost equal (with negligible differences) to the calculated values from recorded data using APGs, the biogas consumption and venting are monitored and recorded with SBMs. Using the recorded data of biogas vented over a specific period, GHGEs are estimated. Considering the average local temperature over the data collection period and the local altitude, the ideal gas law is used to determine respective gas densities of CH₄ (ρ C H 4 ) and CO₂ (ρ C O 2 ) by using eq. (2) and eq. (3).

ρ C H 4 = p alt R C H 4 T ρ C O 2 = p alt R C O 2 T (3)

Where R C H 4 of 518.3 J/(kg·K) and R C O 2 of 188.9 J/(kg·K) are ideal gas constants for CH₄ and CO₂, respectively. Using eq. (4) and eq. (8) and the recorded data on biogas venting [m³], the GHGEs associated with the venting phenomenon over the study period are estimated. The values m, k, v, ρ, and E_tot, represent the masses and percentages of CH₄ and CO₂ in the produced biogas, volume, density, and total emissions, respectively.

E tot [ kgCO 2,e ]= E C H 4 [ kgCO 2,e ]+ E C O 2 [kg] (4)

Where E_tot [kgCO_2,e] is the total emission in kilograms of CO₂ equivalent, E C H 4 [ kgCO 2,e ] is the methane-related emission in kilograms of CO₂ equivalent, and E C O 2 [kg] is the carbon dioxide-related emission. The methane-related emissions are obtained as in equation (5).

E C H 4 [ kgCO 2,e ]= m C H 4 [kg]×GW P C H 4 (5)

Where m C H 4 [kg] is the mass of methane and GW P C H 4 (equal to 28) is the global warming potential of methane. The methane mass is calculated as in equation (6).

m C H 4 [kg]= v biogas [ m 3 ]× k C H 4 × ρ C H 4 [kg/ m 3 ] (6)

Where v_biogas is biogas volume [m³], k C H 4 is the methane fraction in the produced biogas, and ρ C H 4 is the methane density. Similarly, carbon dioxide-related emissions are obtained in equation (7).

E C O 2 [kg]= m C O 2 [kg] (7)

Where the mass of CO₂ [kg] is calculated as in equation (8).

m C O 2 [kg]= v biogas [ m 3 ]× k C O 2 × ρ C O 2 [kg/ m 3 ] (8)

In equations (6) and (8), the values of CH₄ and CO₂ fractions (k C H 4 and k C O 2 ) reported in empirical literature are used.

Establishing causes for venting.

Venting is the result of the underutilisation of the produced biogas. Thus, the causes for underutilisation, and hence venting, are analysed through a close observation of HH’s cooking practices, usage patterns, interactions, and unstructured interviews during field visits.

Applying Methods and Materials to the Case

Research methods presented earlier were customised to Rwandan HHs as a case for the study because Rwanda is one of the SSA countries with a national domestic biogas programme (NDBP) [25], and its small geographical area allowed for reaching research sites flexibly. A prior literature review and interactions with biogas project officers showed that HH biogas plants deployed in Rwanda used three types of technologies: fixed dome, flex bags, and floating drum, although the latter is not common [26].

Because existing HH biogas plants in Rwanda, installed in the framework of NDBP, were not customised to accommodate sensor-based data collection systems, new installations had to be done at selected sites. Installation of new HH plants was necessary if: (a) existing HH biodigesters installed under NDBP had technical and operation issues and had affected Rwanda’s NDBP, (b) distinguishing venting from leakage required high standards of supervised installations, maintenance, and contracts obligating frequent leakage tests and reporting, (c) pipe diameters had to follow the recommended specifications from the SBMs manufacturer. Based on the knowledge above gathered in the local context, this study followed a four-phase research method depicted in Figure 4.

Figure 4.

The four phases of the research design

In addition to researchers’ experience and literature on Rwanda’s NDBP, the local authorities recommended research sites (HHs) based on the set criteria: owning at least three cows, reliable access to a piped water supply and willingness to cooperate during data collection. A review of Rwanda’s biogas programme indicates that biodigesters of 4 m³, 6 m³, 8 m³ and 10 m³ satisfy 42%, 62%, 82% and 104% of HH cooking energy demand in Rwandan HHs, respectively [26]. Installing 10 m³ would not be economical as it would lead to the underutilisation of biogas, while installing biodigesters below 8 m³ would lead to insufficient gas production. Thus, 8 m³ biodigesters were chosen for installation on the selected sites. Four HHs were selected for the study to ensure a daily close follow-up on the technology use, and based on the available budget. After selecting HHs (research sites), 8 m³ HH fixed dome biodigesters were installed for research purposes.

Fixed dome technology was selected because: (a) fixed dome dominated existing deployments, and this would be close to simulating existing Rwanda’s NDBP, (b) all construction materials could be sourced locally, and (c) fixed dome technology has a longer lifespan compared to flex bag (balloon-shaped polyethene biodigesters) technology also installed in Rwanda. After installation, the HH plants were fitted with SBMs to measure SBP and DBP. Conventional APGs were installed adjacent to each other to allow for data comparison and validation during fieldwork. The research process was reviewed and approved under research permit N°:NCST/482/438/2023 issued by Rwanda’s National Council for Science and Technology. The SBMs were configured by researchers, while biodigesters were installed by the experienced local contractor who installed HH biodigesters through NDBP.

A differential height of 80 cm between the throat and outlet level of 8 m³ fixed dome technology was designed based on the contractor’s experience. The designed venting threshold pressure in this case was ~8 kPa, a value which is dependent on the bioslurry density, differential height and acceleration due to gravity. After initial feeding, a hydraulic retention time (HRT) of 45 days was allowed based on the local contractor’s experience [26]. The initial feeding was monitored correctly, and plants were later donated as an HH cooking lab to study the HHs’ cooking practices, biogas utilisation and the venting phenomenon. After handing over the HH plants to the selected users, data were collected for seven months, between 1^st June–31^st December 2024. A monthly inspection was carried out by the contractor to ensure that biodigesters are leak-tight. Portable electronic biogas detectors were used to detect possible biogas leakage, and monthly inspection reports were submitted to researchers. In addition to the monthly inspection report submitted by the contractor, researchers conducted soapy water tests to detect possible biogas leakage through pipes during field visits. Such leakage preventive mechanisms were put in place to differentiate venting from other potential biogas leakages. Further, a number of demarcations were set, and SBP patterns were used to differentiate venting from other possible leakages.

Setting demarcations.

Venting was classified as any release of the biogas through designed outlets whenever the SBP just exceeded a set threshold value (8 kPa in this case). As such, venting events could be predicted. On the contrary, any other SBP drop event that would occur due to any unpredictable, unintentional, and uncontrolled phenomena not caused by a cooking session was classified as biogas leakage.

Assumed SBP behaviour.

It was presumed that whenever a venting event occurred, the SBP (absolute) remained relatively constant. The implication is that during venting events, the biogas holder has reached its maximum storage capacity, defined by the system’s threshold pressure, including the designated safety margin, beyond which additional biogas cannot be retained. Under this assumption, the threshold SBP (8 kPa) is treated as a constant threshold pressure at which venting occurs, recognising that biogas production varies with factors (e.g. temperature, feedstock conditions, and pH). Thus, during a venting event, it is assumed that any biogas continuously produced is vented so that the gas-holder pressure does not rise above the SBP threshold. In other words, the volume of gas being produced is balanced by the volume being vented, maintaining the pressure at the set limit. Thus, the constancy of SBP in this assumption reflects the digester’s venting mechanism under leak-tight conditions, rather than an assumption of constant gas production.

Figure 5.

Biogas underutilisation pattern sampled at one of the HHs on 13th June 2024, between 1 am and 12 am

Using a WA, described in the material section, three variables were remotely monitored: the average absolute SBP [kPa] in the biogas holder, the average biogas flow rate [m³/h] from the biogas holder to the biogas stove during cooking sessions, and the biogas consumption [m³] in a specific cooking duration [h]. For example, Figure 5 depicts a sampled event of biogas underutilisation, leading to biogas venting. It can be observed that the SBP remains relatively constant at an average SBP of about 8.5 kPa, just above 8 kPa (venting threshold), between 3 am and 11 am. On the contrary, Figure 6 indicates a recommended usage pattern, keeping SBP within a proper operation range. Selecting subsequent time slots for biogas utilisation analysis, WA enhanced by MLA helps to display biogas consumption (usage), venting, and leakage as indicated in Figure 7. To this end, using equations (1)–(3), data in Table 1 were generated. Further, using these data as input to equations (4)–(8), together with recorded biogas vented [m³] from biodigesters installed at the respective participating HHs, the GHGEs were estimated.

Figure 6.

Recommended biogas utilisation pattern sampled at one of the HHs on 1st December 2024, between 1 am and 12 am

Figure 7.

A sample of WA display, enhanced by MLA indicating biogas consumption (usage), venting, and leakage from the four HHs from 15th to 17th July 2024

Table 1.

Local altitudes, temperatures, atmospheric pressures, CH4 and CO2 densities

Sites	Altitude, h [m]	T [°C]	palt [kPa]	ρ C O 2[kg/m3]	ρ C H 4 [kg/m3]
Bugesera site	1440	21	85.69	1.54	0.56
Huye site	1800	19	82.15	1.49	0.54
Musanze site	2280	18	77.56	1.41	0.51
Rubavu site	2090	18.5	79.41	1.44	0.52

In this section, results are presented step-by-step to answer the RQs from RQ₁ to RQ₃. It is worth noting that no biogas leakage was detected during the data collection period. If biogas leaked, it was too negligible to be detected by the biogas leakage detectors or by the SBMs.

Figure 8 shows monthly biogas consumption and venting from the four participating HHs. Biogas vented in a seven-month period (during data collection) was 44.5 m³, 36.4 m³, 28.3 m³, and 25.6 m³ for the Bugesera (Eastern), Huye (Southern), Musanze (Northern) and Rubavu (Western) sites, respectively. Thus, the total biogas consumed by the participating HHs in seven months was 2,172 m³, while 135 m³ was lost through venting. As such, results showed that the ratio of total biogas consumption to venting was 16:1. Using recorded volume of biogas vented, equations (1)–(8), ratios of CH₄ and CO₂ in biogas produced from anaerobic digestion [3], and assumptions stated in methods section, the average GHGEs associated with biogas venting ranged between 33–56 kgCO_2,e per month per HH as shown in Figure 9.

Figure 8.

HH biogas monthly consumption and venting from the four HH biogas plants over a period of seven months

Figure 9.

Average monthly GHGEs per HH

Although different HHs showed different utilisation patterns, results showed that venting levels were generally higher in June, November and December compared to other months. An overall decrease in biogas utilisation was recorded in the dry season (July to early October) because of observed intermittent biodigester underfeeding at the Musanze and Rubavu sites, leading to less biogas production. Whenever biogas was used and the SBP dropped below ~1.5 kPa, the biogas flow to the stove became weak, and HHs were advised to wait until the biogas pressure builds up. This approach resulted in a noticeable decrease in biogas utilisation during dry seasons. Although biogas production typically decreased during the dry season, making venting unlikely, venting events were still recorded.

Interactions with participating household members revealed that the types of meals typically prepared during the dry season were largely incompatible with the design and functionality of locally fabricated biogas stoves. The locally cooked bread prepared from corn and cassava flour requires continuous mingling and intensive physical manipulation, which is not supported by the locally fabricated biogas stove structure. Dry beans harvested in June dominated the HH’s meals in the dry seasons and required prolonged cooking, which requires high heat not produced by unpurified biogas used directly from anaerobic digestion. Further, the supply of fuel wood was found to be more reliable in the dry season than in the rainy season, and HHs confirmed that they preferred to cook such staple meals with fuel wood. This contributed to a low biogas utilisation in July, August, September, and October.

This work answers three research questions rooted in the identified research gap, enhancing the literature on venting associated with small-scale HHBT use, specifically in SSA. The venting levels are quantified with an approach that distinguishes venting from general biogas leakage. Results showed that vented biogas led to an average monthly GHGEs of 33 to 56 kgCO_2,e per household. Quantifying and distinguishing venting from generalised leakage can help to mitigate GHGEs associated with such a phenomenon. In this section, this study’s contributions, limitations and potential future work are discussed, thereby offering a nuanced understanding of small-scale biogas utilisation and the associated GHGEs.

On the Materials Used and Practical Limitations

Data collected by using the APG during data validation often resulted in slightly lower values compared to the logged data from the SBMs. The absolute differences are graphically presented in Figure 10, ranging between 0.01 and 0.04 m³. The differences may be due to the analogue readings of SBP [kPa] from the APG, which are not as precise as digital data from SBMs, and/or the assumed gas laws presented in the methods section. The SBMs provided a convenient way for remote and timely acquisition of data on biogas utilisation and venting compared to APGs, which do not offer instant data, require the physical presence of researchers, and require the conversion of recorded biogas pressure from kPa to m³. Although normalised cubic meters [Nm³] are generally preferable, the off-the-shelf SBMs used in this study did not have the capacity to capture the continuous (e.g. temperature, atmospheric pressure) data required for accurate normalisation. Applying assumed corrections risked introducing additional uncertainties, which we avoided by recording biogas volumes in m³ for consistency. While differences from Nm³ values may exist depending on temperature and pressure, these are not expected to alter the study’s conclusions.

Figure 10.

Data validation output from short samples of cooking sessions

Using SBMs with Machine Learning Algorithms (MLAs) embedded in the WA provided direct readings of data required for the study. Due to the growing need for remote data acquisition in the energy sector, developing cost-effective and small-scale embedded electronic modules for HH biogas technology monitoring could enhance technology data acquisition, lead to data-driven HHBT designs and policies, and thus enhance intended benefits. Powering such devices can be an issue due to the remoteness of technology user communities, but the increasing use of pico-solar modules and portable batteries can mitigate such challenges [30].

Through this study, it has been realised that contractors installing HH biogas plants in the framework of Rwanda’s NDBP do not account for the effect of altitude on atmospheric pressure. This approach can lead to misestimations in the design of threshold biogas pressure for venting. Rwanda’s terrain is hilly and mountainous, especially in the northern and western provinces. Using the same differential height of 80 cm for an 8 m³ fixed dome biodigester at all sites might have marginal effects on the results.

Limitations and Potential Future Work

This study relied on measured data and equations without modelling the anaerobic digestion (AD) process. Practically, during sampled cooking sessions for data validation, however short they may last, there is a continuous gas production through AD, and this might have marginal effects on estimations. Further studies combining anaerobic digestion modelling and the use of SBMs can add more insights to the findings of this study. Also, this work quantified the HH biogas venting levels and GHGEs associated with the venting phenomenon, and established causes of venting from HHBT by using data from an 8 m³ fixed dome biodigester. The results obtained using different sizes and biodigesters’ designs could broaden the literature on the use of HHBT technology and the associated venting phenomenon. The locally fabricated and distributed biogas stoves, see Figure 11, do not follow a well-standardised and regulatory framework and do not support local cooking practices and needs. Hence, technical studies focusing on how to improve and customise biogas stoves to local cooking practices, as well as the use of auxiliary biogas gas storage instead of venting, are required to ascertain how such modifications can impact the technology use. Further still, during field work visits, it was observed that HHBT use depends on daily HH livelihoods. Thus, though this study generated insights on causes of venting, a mixed-method research approach combining in-depth qualitative and quantitative data can broaden the understanding of how HH livelihoods affect the HHBT use, contributing to its sustainable use.

Figure 11.

Locally fabricated and distributed biogas stove

This study recorded venting levels from HH biogas plants installed in energy-poor communities. Underlying causes of HH biogas venting from HHBT use were established, and GHGEs associated with such venting phenomenon were calculated. Results show that vented biogas led to an average monthly GHGEs of 33–56 kgCO_2,e per household. When such results are extrapolated over a whole year, this leads to average annual GHGEs of 0.4–0.7 tCO_2,e per HH. Thus, HH biogas venting not only causes loss of the biogas energy carrier but also contributes to GHGEs. Even when there is sufficient biogas for cooking, HHs opt for fuel wood to cook specific local meals, which cannot be cooked using the locally fabricated biogas stoves supplied with the HH biogas plants. Research work focusing on technical development to customise the technology, especially the biogas stoves to the cooking practices of local meals, cost-effective purification methods and auxiliary biogas storage can minimise venting and enhance the envisaged technology benefits.

In addition to technical measures, demand-side practices can also help reduce venting by better matching gas availability with cooking demand. Where culturally feasible, HHs could adjust cooking times so that meal preparation overlaps more closely with peak gas production, thereby reducing pressure buildup and subsequent venting. Cooking durations may also be shortened to make biogas more suitable for foods that are typically avoided due to long simmering requirements, such as dry beans (e.g., through pre-soaking). Although some HHs may be reluctant to adopt pre-soaking dry beans because of taste preferences, such measures can be introduced as optional household-level adaptations that improve biogas utilisation and further minimise venting.