1 Introduction

Over the past several decades, the ever-growing human population with its attendant increasing waste generation, coupled with unsustainable waste management practices, has had serious implications on public health and the environmental sanitation. The United Nations in its sustainable development goals report, Goal 6, indicates the need for adequate sanitation, wastewater treatment and an end to open defecation by 2030 (UN, 2015). As such, treatment of wastewater, particularly human excreta using several waste treatment technologies, including biogas, becomes essential in efforts made by countries across the globe towards improvement in public health and environmental sanitation. According to Abbasi et al. (2012), biogas technology has been used to efficiently treat wastewater and sewage sludge since 1895. This indicates that the efficacy of this technology in treating human waste is not under dispute.

Biogas is a renewable energy source that employs anaerobic digestion process (i.e. in the absence of oxygen) in treating biodegradable matter. Research indicates that biogas is mainly composed of methane (40%–70%), 30%–40% carbon dioxide and other gases, which can further be improved to a natural quality of 75%–99% methane (Mittal et al. 2018). Several studies have shown that anaerobic digestion is one of the oldest forms of sewage sludge treatment as well as a simple tool for managing waste (Dahiya & Joseph, 2015; Mata-Alverez et al. 2014). Sewage sludge contains mostly excreta and water in combination with other substances (Tilley et al. 2014). Furthermore, humans generate about 0.5–1.5 kg excreta per day (Regattieri et al. 2018), thus requires that wastewater is well managed to avoid or reduce environmental pollution to the barest minimum. In Ghana, off-site and on-site excreta management options such as sewerage system, septic tank systems, ventilated improved pit (VIP) latrine systems and open defecation are the predominant waste management practices used, but these are either energy intensive or environmentally unfriendly. Currently, the human excreta (Hex) management mix in Ghana stands at 21% basic sanitation (sewerage, septic tank system and VIP latrine system), 45% limited sanitation (improved facilities shared with other households), 13% unimproved (pit latrine) and 22% open defecation (Appiah-Effah et al., 2019; GSS, 2018). It is however important to note that in the urban areas, basic sanitation level is 25%, limited sanitation is 56% (mostly peri-urban settlements), unimproved is 8% while open defecation stands at 11% (Appiah-Effah et al, 2019; GSS, 2018).

The main legislation framework governing human excreta (Hex) management practices is the Local Government Act (Act 462), with the responsibility of providing sanitation services assigned to Metropolitan, Municipal and District Assemblies. Other policy documents which support the implementation of Hex management include Environmental Sanitation Policy (MLGRD 2010), which covers all aspects of environmental sanitation, including HEx management, acknowledging the challenges with HEx management especially urban/peri-urban and making households responsible for financing their own household facilities; Strategic Environmental Sanitation Investment Plan (adapted from WSUP (2017)) which proposes the establishment of a national revolving fund for household sanitation to be managed by microfinance institutions.

Unlike the others, research has established that the utility of a biogas system goes beyond only management of human excreta, to treating it and even generating renewable energy out of the excreta (Rupf et al. 2015; Arthur et al. 2011 Amigun and Blottnitz 2010). Thus, this has the potential to decrease over-reliance on other sources of energy such as fossil fuel and wood fuel, the use of which have varied adverse effects on the environment. Besides, biogas technology provides a by-product of bio-fertiliser that is rich in plant nutrients, which can partly or fully offset chemical fertilisers (Arthur et al. 2011; Mariwah & Drangert, 2011). Other benefits of biogas systems include improvement of community livelihood (employment), sanitation, reduction in emission of greenhouse gas and finally improved life and health (DFID NET-RC, 2011; Bensah & Brew-Hamond, 2010).

Presently, few households and institutions use biogas technology as HEx management practice (Osei-Marfo et al, 2018), with less than 2% biogas technology penetration target set by Strategic National Energy Plan (SNEP) (2006/2020).

The United Nations has encouraged the development and use of sustainable energy, and by extension renewable energy, by developing nations to meet their increasing energy demands in order to minimise environmental impacts (United Nations, 2011). This is necessary because in developing countries where energy is limited in supply and relatively expensive, biogas becomes the most reliable alternative source of renewable energy and thus has greater relevance than it would in developed countries. This accounts for the reason why countries like China, India, Nepal, Bangladesh, Ethiopia and Tanzania have developed keen interest in using excreta to generate biogas (Abbasi et al. 2011).

However, the same cannot be said about Ghana whereby human excreta is perceived as an absolute waste, and for that matter local authorities spend between 50 and 75% of their annual budget to dispose of it (Cofie et al. 2005). Despite the numerous benefits associated with the use of biogas technology, there still exists a gap between behavioural attitudes/perceptions towards using human excreta for biogas production and the actual behaviour of using human excreta for biogas in Ghana. Oteng-Peprah et al. (2019) have argued that the perceptions that the public hold on an issue is very crucial, as it forms an integral part of any successful project implementation. This suggests that for a given population to accept any emerging technology, it is important to look into the perceptions they hold about the core components of that technology. This is in line with Gibson’s, 1979 (as cited by Mariwah & Drangert, 2011) assertion that “perceptions determine our behaviour and what we perceive determines what we do next” (p. 2).

It is documented that factors such as tradition, religion and culture are perceived to be potential barriers to the adoption of biogas technology (DFID NET-RC 2011). Similarly, Shane et al (2015) found that traditional beliefs made it difficult for people to adopt biogas technology in Lusaka and Copperbelt, thus attributing this to the fact that the gas was generated from animal dung and human excreta. This reveals that whereas some people do not see anything wrong with the use of human excreta for biogas generation, others attach some level of stigma to it.

Previous research has shown that behaviour change interventions based on behaviour-oriented theories are usually more effective in changing behaviour (Bartholomew et al. 2011). In this vein, Glanz and Bishop (2010) have suggested that one of the determinants of behaviour change is the individual human choice and preference, while other determinants such as cultural, political or organisational, are assumed to have effects that are mediated through these two factors. Against this background, this study sought to assess people’s perceptions regarding the use of human excreta for biogas generation in Ghana using the theory of planned behaviour, by exploring their opinions on the use of human excreta for biogas generation from religious, economic, educational and environmental points of view as the literature is silent on this aspect.

Theory of planned behaviour is a useful theory for this study because it states that a person’s behaviour can be predicted by their intentions, and formation of intention is influenced by a person’s attitudes, subjective norms and perceived behavioural control. In line with this, we hypothesise that peoples’ perceptions of the use of human excreta (HEx) for biogas is influenced by behavioural attitudes, subjective norms and perceived behavioural control, as these may be formed without prior experience or knowledge of the biogas technology. Unlike factual knowledge, perception is known to be a subjective process of obtaining, understanding, and constructing sensory information so as to form a belief about what is happening in one’s environment.

The main objective of the study is to assess the effect of people’s perception on the use of human excreta for biogas generation in Ghana. Specifically, the study addresses the following objectives:

  1. (1)

    Examine the effects of behavioural attitudes on the use of HEx for biogas generation

  2. (2)

    Assess the relationship between subjective norms and the use of HEx for biogas generation

  3. (3)

    Test effect of perceived behavioural control on the use of HEx for biogas generation.

Insights from this study will be essential for developing interventions to promote the use of human excreta (HEx) for biogas generation to increase the acceptance and the uptake rates in Ghana and other developing countries.

2 Theory of planned behaviour

This study is guided by Ajzen’s (1991) theory of planned behaviour (TPB) (Fig. 1) which provides a framework for examining peoples behavioural intentions to use HEx for biogas production. According to Armitage and Conner (2001), the TPB is a well-validated social cognitive model used to predict people’s intentions and behaviour. The theory postulates that one’s behaviour can be predicted by one’s intentions, which in turn is dependent on three aspects: attitude towards the behaviour, which is the degree of one’s favourable or unfavourable evaluation of the behaviour in question (Fishbein & Ajzen, 1975); the subjective norm, that is the perceived social pressure to perform or not to perform the behaviour (Ajzen, 1991); and perceived behavioural control, that is a person’s perception of ease or difficulty in performing the behaviour of interest (Ajzen, 2002). Therefore, in line with the TPB, the target behaviour of interest is the individual perception towards the use of human excreta for biogas. Operationally stated, attitude is defined as the degree to which the individual expects positive/good or negative/bad outcomes from the performance of such behaviour. Subjective norm refers to the level of approval from family, neighbours, religious leaders and government institutions to use HEx for biogas. Perceived behavioural control focuses on the individual’s management of beliefs about easy or difficulty in using HEx for biogas. Hence, individuals who have positive attitude towards using HEx for biogas and believe there is normative support or approval for using HEx for biogas, and feel it is easy for them to use HEx for biogas should have strong intentions to carry out the behaviour.

Fig. 1
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Theory of Planned Behaviour (Ajzen, 1991)

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3 Hypotheses development

It can be explaind from Ajzen’s (1991) TPB that people’s perceptions on the use of HEx for biogas can be understood in terms of an individuals’ attitude towards the use of HEx for biogas, subjective norms towards the use of HEx for biogas, and their perceived behavioural control over the use of HEx for biogas.

Three hypotheses were developed to bring into focus the coherence of the TPB model as follows:

Hypothesis 1

Attitudes (health risk, environmental protection, bio-fertiliser and energy for cooking) have significant effect on the use of HEx for biogas generation (Oteng-Peprah et al., 2019).

Hypothesis 2

Subjective norms (family, neighbours, religion and institutions) have positive relationship on the use of HEx for biogas generation (Osei-Marfo et al, 2020).

Hypothesis 3

Perceived behavioural control (HEx knowledge, stigma, subsidy and cost) have positive influence on the use of HEx for biogas generation (Shane et al, 2015).

4 Methodology

4.1 Background and study area

Two study areas were selected in Ghana: Cape Coast Metropolitan Assembly (CCMA), located in the Central Region and Ablekuma North Municipal Assembly, located in the Greater Accra Region both in the Republic of Ghana (Fig. 2). Cape Coast is located on longitude 1° 15′W and latitude 5° 06′N covering an area approximately122 square kilometres, while Ablekuma North lies between latitude 5° 33′ N and on longitude 0° 12′ W also covering 60 square kilometres. The CCMA was selected because residents of the suburban coastal communities around the Cape Coast Castle have turned the shoreline into an open defecation ground. Meanwhile, Cape Coast Castle is a major tourists’ site that generates enormous income for the Government of Ghana due to the unique role it played in the era of the trans-African Slave Trade. Apart from that, about 45 tonnes of wastewater that is generated daily within the Metropolis is improperly disposed of on bare land at a dumpsite located some five kilometres away from the central business area, thus posing a potential serious health threat to residents of the metropolis (CCMA, 2014). In essence, despite the huge amounts of wastewater generated within the metropolis, the Cape Coast Metropolitan Assembly does not have any wastewater treatment plant or sewage system to hygienically dispose of this waste, thus the need to promote the use of biogas technology to avoid the harmful practice of discharging wastewater onto bare grounds at the dumpsite. The choice of Ablekuma North, being part of the Accra Metropolitan Area and within the capital city of Ghana, was based on reports of increased open defecation in the area which does not only affect public health but also puts Ghana’s position on open defecation at seventh (7th) globally and second (2nd) in Africa, respectively (Osumanu et al., 2019). Besides, it is known that one of the key causes of perennial flooding in Accra that often claims many lives is the illigal disposal of waste into waterways, thus choking the drainage systems (Asumadu-Sarkodie et al., 2015). Most household waste thrown into drains in the city contain human excreta tied in coloured polythene bags, largely coming from unscrupulous people living in housing units without toilet facilities. Additionally, there is no sewage system in the Ablekuma North Municipal Assembly. Moreover, both Cape Coast and Ablekuma North are metropolitan areas that have residents with vast differences in their cultures, traditions, religions, educational levels and socioeconomic status.

Fig. 2
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Map of study area

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4.2 Elicitation study

The study began with an elicitation survey, following suggestion by Fishbein and Ajzen (2010) within four communities in Greater Accra and Central Regions using convenience sampling. This survey was conducted to identify salient beliefs underlying peoples’ perceptions on the use of HEx for biogas generation. An open-ended questionnaire was administered, and the likely outcomes summarised in Table 1. The participants were asked to indicate: (a) the advantages/benefits and disadvantages/challenges of using HEx for biogas for domestic purposes, (b) persons or groups of people who would approve or disapprove of their actions with respect to using HEx for biogas, and (c) the factors that could facilitate or discourage them in using HEx for biogas for domestic purposes. A total of 120 respondents participated. A content analysis was then carried out, and the most frequent beliefs and knowledge underlying peoples’ perceptions were included in the formulation of TPB questionnaire. The TPB questionnaire was administered on 130 participants as a pre-test to test for consistency, ambiguity, understandability and psychometric properties prior to the main study. Modification and correction were made based on the responses to improve clarity and easy comprehension. A Cronbach’s alpha of 0.709 was obtained, indicating that the scale was adequate.

Table 1 Summary of salient beliefs
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4.3 Main study

The main study was conducted over a period of three months from July to September 2017. The total population of the study areas was 366,918, which composed of a combination of all residents of Cape Coast Metropolitan Assembly (169,893) and of Ablekuma North Municipal Assembly (197,024) (GSS-PHC, 2012). The researchers targeted all adult residents of Cape Coast Metropolis and Ablekuma North in Accra Metropolis who did not own or use biogas technology but depend on other excreta management technologies such as septic tank system, ventilated improved pit latrine or open defecation. Though the respondents had not received any biogas training, they indicated that they had heard of it through friends, family members or neighbours who own or have received training or campaign on biogas.

A two-stage stratified sampling design was adopted for the representative survey. The sampling frame used for the study is the frame of the Ghana, (2010) Population and Housing Census (PHC) provided by the Ghana Statistical Service (GSS), which is a complete list of all census enumeration areas (EAs). An EA refers to a geographic area covering an average of 145 households. Two residence strata (urban and peri-urban: Urban refers to settlement with high population density, concentration of administrative bodies and infrastructure, and a diverse set of livelihood and income levels while peri-urban refers to settlement mostly concentrated in low-income urban areas usually located on the outskirts of cities (CEUP, 2016)) were created, and we selected equal numbers of EAs in each of our two residence strata. This design was chosen since it allowed us to evenly distribute the sample across the strata, thus ensuring that there is sufficient sample size in each strata type. The stratification was done for the two areas, which when multiplied by the two stratum types gave four strata. Within each of the four strata, we randomly selected two EAs, thus giving us initial sample of eight EAs.

After having generated the first-stage sample of EAs, our research assistants listed all the households in the eight identified EAs. Then 40 households were randomly selected from each EA. Thus, the target sample was 320 representative households, of which 308 households were interviewed due to expression of unwillingness to participate by some households. At least two persons were interviewed in each household, which included the household head and any other male or female resident in the house. Any adult aged 20 years and above who has spent not less than twelve months in the household was eligible to participate in the survey. In total, 610 respondents consented to participate in the study, which included 282 from CCMA and 328 from Ablekuma North, respectively.

5 Questionnaires

The instrument for collection of data was a questionnaire. The questionnaire comprised three sections. The first concerned demomographic characteristics including age, gender, education, monthly income of an individual, ethicity and religion. The second focused on knowledge on benefits of biogas and perceptions of HEx for biogas, and the third dealt with TPB constructs on using HEx for biogas. The second and third sections had items measured on 7-point Likert scale. Six trained research assistants supported in administering the questionnaires.

5.1 Knowledge on the benefits of biogas

Knowledge on the benefits of biogas was measured with seven items. Knowledge on the benefits of biogas is explained in terms of the perceptions of fuel, electricity, bio-fertiliser, sanitation improvement, job opportunities, public health improvement and environmental identity. The questionnaire assessed participants knowledge concerning the benefits of biogas (e.g. “Biogas can be an alternative fuel for cooking”. 1 = strongly disagree, 7 = strongly agree).

5.2 Perception on human excreta for biogas

Perception on using human excreta for biogas was measured with three items. Perceptions on human excreta for biogas is explained in terms of subjective beliefs of being negative practice, dangerous and safe use. The questionnaire assessed participants understanding or belief concerning the use of human excreta for biogas (e.g. “Using human excreta for biogas is negative”. 1 = strongly disagree, 7 = strongly agree).

5.3 Attitude (A)

Attitude was measured with four items using behavioural beliefs and their corresponding outcome evaluations. These items include health risk: the possibility that an individual can fall sick, environmental protection: maintaing the quality of the natural environment, bio-fertiliser: digested excreta and energy for cooking: biogas obtained from the use of HEx. Participants rated the likelihood that using HEx for biogas would produce each of the outcomes and rated the importance of each outcome (e.g. “Using human excreta for biogas will expose me to health risk”. 1 = strongly disagree, 7 = strongly agree). The overall attitude score was obtained according to an expectancy-value model (Fishbein & Ajzen, 2010), Eq. (1), in which the score for the likelihood of an outcome is multiplied by its corresponding score of importance. This is expressed as follows:

$${\text{A = }}\sum {b_{i} e_{i} }$$
(1)

where A is the attitude towards the use of HEx for biogas behaviour under consideration, bi is the strenght of belief i that performing the behaviour will produce outcome i, and ei is the evaluation of outcome i. The same expectancy-value model was applied to obtain the overall score for each belief-based measures indicated below.

5.4 Subjective norms (SN)

Subjective norm was measured using four items to assess participants normative beliefs and their motivation to comply. These items are family: members of both nuclear (spouse and children) and extented family (siblings and parents), neighbours: people living next door or in the same vicinity, religion: influence of religious leaders and institutions: government agencies. Participants rated the approval of important refernts or people and whether their opinions have any influence on their decision to use or not to use HEx for biogas (e.g. “My family would…..me making use of human excreta for biogas”. 1 = strongly disapprove, 7 = strongly approve).

5.5 Perceived behavioural control (PBC)

Perceived behavioural control was measured with four items using control beliefs and power of control factors. These items are HEx knowledge: an individual’s information about human excreta, stigma: the shame associated with using human excreta, subsidy: money granted by government and cost: price of biogas construction. Participants assessed factors that would facilitate or hinder their ability to use HEx for biogas (e.g. “I need to acquire special knowledge on how to use human excreta for biogas”. 1 = strongly disagree, 7 = strongly agree).

5.6 Intention

Behavioural intention was measured with three items. They include make effort, intends and have plans. Participants assessed their intentions to use HEx for biogas (e.g. “I will make effort to use human excreta for biogas”, “I intend to use human excreta for biogas”, “I have plans to use human excreta for biogas”. 1 = strongly disagree, 7 = strongly agree).

6 Data analysis and descriptive analysis of variables

Although 610 participants agreed to participate in the study, 408 responses (67% response rate) were received with all items completed. This study used Statistical Package for Social Sciences (SPSS), version 21 and analysis of moment structures version 23 (AMOS 23) to analyse the collected data, and descriptive statistics as well as correlation were used. The analyses were conducted in two stages (Anderson and Gerbing, 1988). First, confirmatory factor analysis (CFA) using maximum likelihood was used to assess the underlying structure of the variables in the model as well as the adequacy of the model. Secondly, structural equation modelling (SEM) was used to find the best-fitting model and to test the causal relationships within the model. SEM is a general statistical modelling technique which uses the combination of factor analysis and regression or path analysis to analyse the structural relationship between measured variables and latent constructs (Hox & Bechger, 1999). This technique is preferred for this study because it estimates the multiple and the interrelated dependence in a single analysis. Furthermore, to know the extent or effect of education and sex (Olli et al. 2001; Wolters, 2014) on intentions, these background factors were introduced into the model (adjusted TPB model).

The study framework has three exogenous and one endogenous variables for using HEx for biogas generation. Almost all the variables of the TPB constructs had Cronbach’s alpha values above 0.60 as recommended by Hair et al. 2010. The model was assessed using normed fit index (NFI), Tucker-Lewis index (TLI), comparative fit index (CFI) and root mean square error of approximation (RMSEA). Both Cangur and Ercan (2015), and Hox and Bechger (1999) stated that NFI, TLI and CFI values of at least 0.9, and RMSEA of < 0.6 to 0.8 are required to accept a model, respectively.

7 Results

7.1 Demographic profile of respondents

The demographic characteristics of the respondents are presented in Table 2. It can be observed from the descriptive statistics of the respondents profile that majority of the respondents are male (58.3%), and about 32% of the respondents are young adults, in the 20 to 30 age category. About 45% of the respondents have tertiary education, an indication of their comprehension of the questionnaire and their ability to appreciate the benefits associated with biogas technology, especially, improvement in the environment. This high percentage of tertiary education may be due to the establishment of tertiary institutions in the study locations. Additionally, the majority of respondents earn a monthly income below GH¢ 500, equivalent to US$ 114 (34.3%) which is below the low-income group level (GSS-DHS, 2018). Majority of the respondents, 68.6% and 85.8% are Akans and Christians, respectively, a reflection of the predominant ethnic and religious groups in Ghana (GSS-PHC, 2012).

Table 2 Respondents profile
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Futhermore, we try to find out if there is a relationship between the study locations on the use of HEx for biogas. Table 3 presents the results of the study locations by their demographic profile. The results revealed that there was significant association between Cape Coast Metropolitan Assembly and Ablekuma North Municipal Assembly (Table 3).

Table 3 Respondents profile according to study locations
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It emerges that for gender, the proportions of 52.2% (male) and 47.3% (female) in CCMA are significantly different from 63.3% (male) and 35.7% (female) proportions in Ablekuma North Municipal Assembly (ANMA) on HEx use for biogas. This means that more male intend to use HEx for biogas in ANMA than their counterparts in CCMA, but it the vice versa for females in ANMA and CCMA. For age categories 20–30 and 51–60, 43.3% and 10.2% are significantly different from 18.1% and 28.6% in ANMA and CCMA, respectively, while the rest (31–40, 41–50 and above 60) do not differ significantly from each other. Thus more young adults in ANMA intend to use HEx for biogas while in CCMA, adults in the 51–60 category anticipate to use HEx for biogas. For education, 9.8% (none), 36.3% (basic) and 31.9% (tertiary) in CCMA are significantly different from 2.2% (none), 19.5% (basic) and 55.3% (tertiary) in ANMA while secondary do not differ significantly from each other. It is clear that respondents in ANMA have more formal education hence, they may have more positive intention to use HEx for biogas than respondents in CCMA.

With regards to individual’s monthly income, 45.1% (below GH¢ 500), 17.6% (GH¢ 1000–2000) and 0.5% (GH¢ 2000–3000) are significantly different from 25.7% (below GH¢ 500), 28.3% (GH¢ 1000–2000) and 9.3% (GH¢ 2000–3000) in CCMA and ANMA, respectively. Monthly income groups GH¢ 500 – 1000 and Over GH¢ 3000 do not differ significantly from each other. The results show that a majority of respondents in ANMA earn between GH¢ 1000 to over GH¢ 3000 monthly, hence are more likely to use HEx for biogas than respondents in CCMA. This is because, their monthly income afford them the ability to pay for biogas installation.

For ethnicity, 74.2% (Akans) and 3.3% (Ga-Adangbe) are significantly different from 64.2 to 9.3% in CCMA and ANMA, respectively, while 90.7% (Christians) and 8.2% (Islam) are significantly different from 81.9% and 16.8% in CCMA and ANMA, respectively. The remaining demographic profile (Ewe, Northener and Traditional) do not differ significantly from each other.

8 Respondents’ knowledge on the benefits of biogas

Respondents’ knowledge on the benefits of biogas is presented in Table 4. From the descriptive statistics of the respondents knowledge on biogas, it can be seen that respondents reported strong knowledge on the benefits of biogas (M = 6.08, SD = 1.42). Generally, respondents believe that biogas has numerous benefits. A majority of the respondents strongly agree: that biogas can be an alternative fuel for cooking (62%), that biogas can be used to generate electricity (54%), that the digested sludge from biogas production can be used as bio-fertiliser on farmlands (60%), that using biogas can result in improvement in environmental sanitation (61%) and consequently using biogas can improve public health (49%). Additionally, about 60% of the respondents strongly agree that using biogas can create job opportunities while 46% strongly agree that it gives one an environmentally friendly identity. These results suggest that the positive benefits of biogas as expressed by the respondents may influence their perceptions and decision to use it.

Table 4 Respondents’ knowledge on the benefits of biogas
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9 Respondents’ perceptions concerning human excreta for biogas

A descriptive statistics of respondents’ perception concerning human excreta for biogas is presented in Table 5. Respondents reported positive perceptions towards the use of human excreta for biogas (M = 5.71, SD = 1.62). On the average, respondents strongly disagree: that using HEx for biogas is negative (49.3%), and that using HEx for biogas is dangerous (43.6%). Finally, a majority of the respondents strongly agree that they are confident of safely using HEx for biogas (36.8%). This positive perception concerning the use of HEx for biogas may positively impact on their overall intention to use HEx for biogas.

Table 5 Respondents’ perceptions concerning human excreta for biogas
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10 Descriptive statistics of TPB constructs

The descriptive statistics presented in Table 6 and indicating the overall mean score in comparison to the theoretical range showed that respondents exhibited strong intentions (M = 5.76, SD = 1.58), positive attitude (M = 10.36, SD = 8.58), high social pressure (M = 11.47, SD = 7.67) and low controllability (M = 0.44, SD = 11.10) towards the use of HEx for biogas. Additionally, the mean scores for attitudinal variables are high for environmental protection, bio-fertiliser and energy for cooking and low for health risk. The mean scores for social pressure are high for family, religion and institutions and moderate for neighbours whereas the mean scores for perceived behavioural control are low for knowledge and stigma and negatively low for subsidy and cost.

Table 6 Cronbach’s alpha, grand means, standard deviations, variable means and correlation between all variables
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The correlation matrix (see Table 6) indicates that almost all the variables have significant association with intentions. Furthermore, the results show that attitude and subjective norm are significant predictors of intentions to the use of HEx for biogas, while perceived behavioural control showed weak effect on intentions to use HEx for biogas.

11 Measurement model

The CFA results, as shown in Fig. 3 indicated that the model fits the data well (RMSEA = 0.075, NFI = 0.901, TLI = 0.911 and CFI = 0.933). All items loaded were significantly associated with their respective latent variables as shown in Table 7, except health risk (β =—0.092, p = 0.085). Nonetheless, it was not excluded because, it was important to assess respondents beliefs as far the use of human excreta, and health risk are concerned. Composite reliability of study constructs indicating the internal consistency of multiple indicators for each construct, ranged from 0.71 to 0.86, exceeding the recommended threshold suggested by Bagozzi and Yi (1988).

Fig. 3
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Results of confirmatory factor analysis

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Table 7 Results of measurement model
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12 The TPB model

The SEM results showed an adequate fit to the data (RMSEA = 0.075, NFI = 0.901, TLI = 0.911 and CFI = 0.933), presented in Fig. 4. The structural model explained 30% of the total variance in respondents’ intentions to use human excreta for biogas, and two constructs (attitude and subjective norms) were significantly related to intentions to use HEx for biogas based on their path coefficients. Furthermore, based on Cohen (2013) classification, it was revealed that attitude (β = 0.256, p < 0.001) had a significantly moderate effect on intentions to use HEx for biogas, subjective norm (β = 0.315, p < 0.001) had a strong and significant effect on intentions to use HEx for biogas whereas perceived behavioural control (β = 0.100, p = 0.064) had non-significantly small effect on intentions to use HEx for biogas. In comparing the path coefficients of the three latent variables, it can be observed that effect from social pressure including family, neighbours, religion and institutions was important factor to motivate people’s intentions to use HEx for biogas generation.

Fig. 4
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Human excreta for biogas

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Finally, the direct association between the three latent variables showed significant paths between attitude and subjective norms (β = 0.578, p < 0.001), attitude and perceived behavioural control (β = 0.302, p < 0.001), and subjective norms and perceived behavioural control (β = 0.269, p < 0.001).

13 Adjusted TPB model

An adjusted model was developed by introducing gender and education into the TPB model. This is consistent with previous studies (Botetzegias et al. 2015; Christian et al. 2007; Lopez-Mosquera, 2016). Thus, the TPB model was compared to the adjusted model. The SEM results (RMSEA = 0.072, NFI = 0.906, TLI = 0.902 and CFI = 0.942) showed adequate fit to the data (Fig. 5). Compared to the TPB, the adjusted model showed similar explained variance of intentions to use HEx for biogas (adjusted TPB = 31% vs standard TPB = 30%), and marginally better fit (adjusted TPB: RMSEA = 0.072, NFI = 0.906, TLI = 0.902, CFI = 0.942 vs standard TPB: RMSEA = 0.075, NFI = 0.901, TLI = 0.911 and CFI = 0.933). However, with the adjusted model, all the three constructs (attitude: β = 0.261, p < 0.001, subjective norms: β = 0.318, p < 0.001, and perceived behavioural control: β = 0.107, p = 0.045) were significantly related to intentions to use HEx for biogas. This implies that the adjusted TPB model could well predict individuals’ intentions to use HEx for biogas production.

Fig. 5
figure 5

Human excreta for biogas with background factors. Note: to avoid overloading the figure, some arrows between the background factors and the predictor variables are not depicted. Only significant paths are displayed.

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Furthermore, the results indicated that both gender and education had no direct impact on intentions to use HEx for biogas. However, gender mediated through attitude (health risk and bio-fertiliser) and perceived behavioural (HEx knowledge and stigma) control, while education mediated through all three constructs (attitude: environmental protection and bio-fertiliser, subjective norms: family, religion and institution, and perceived behavioural control: stigma) displayed in Table 8. This implies that for gender, although bio-fertiliser could be obtained for agricultural purposes, health risk associated with the use of HEx cannot be overlooked. Furthermore, gender considers HEx knowledge and stigma important since they have not received any biogas technology training or campaign. For education, environmental protection and bio-fertiliser are key are far as HEx use for biogas is concerned. This is evident with high percentage of respondents (45%) reporting tertiary education. Moreover, education does not down play important referents such as family, religion and institution, however, stigma is of concern irrespective of the level of education. Additionally, a cross tabulation of gender and education showed that more females as compared to males have no education as well less tertiary education, as presented in Table 9.

Table 8 Results of background factors and constructs
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Table 9 Gender and education cross tabulation
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14 Hypotheses testing

Standardised coefficient estimates indicate that the association between attitude and behavioural intentions (attitude: β = 0.261, p < 0.001) supports hypothesis 1, association between subjective norms and behvioral intention (β = 0.318, p < 0.001) supports hypothesis 2, and association between perceived behavioural control and behavioural intentions (β = 0.107, p = 0.045) also supports hypothesis 3. Thus the SEM results indicate that all the paths were significant and positive. Therefore, hypotheses 1 – 3 are confirmed.

Furthermore, it can be observed in Fig. 4 that the standardised coefficients indicate that the direct effect of subjective norms on behavioural intentions was greater than behavioural attitude and perceived behavioural control. Also, subjective norms indirectly influenced behavioural intentions through attitude (β = 0.564, p < 0.001). This suggests that attitude plays a mediating role in the relationship between subjective norms and behavioural intentions to use HEx for biogas generation.

15 Discussion

The results of this study confirm to a large extent that TPB can be used in explaining people’s perceptions on the use HEx for biogas generation in Ghana. The TPB provided useful insight into the perceptions people have about the use of HEx for biogas, although not all the theory tenets were supported (Galaviz et al. 2015) in the standard TPB. The modelling comparison revealed that the adjusted model including gender and education has a relatively but modestly better explained variance or explanatory power towards the use of HEx for biogas than the standard TPB. Thus the adjusted model provides a useful and effective framework for analysing the interrelationships between socio-demographic variables (education and gender) and TPB constructs than the standard TPB. While the results revealed that for the standard TPB, attitude and subjective norms were the only factors that significantly influenced intentions to use HEx for biogas, the adjusted model showed that all the three constructs (attitude, subjective norms and perceived behavioural control) have significant effect on people’s intentions to use HEx for biogas and are valid predictors of intentions.

In line with this, Ghana’s Strategic National Energy Plan (SNEP) (2006/2020) seeks to achieve 2% penetration of biogas for cooking by 2020. However, this goal may not be achieved considering low or no implementation of policies such as Strategic Environmental Sanitation Investment Plan (SESIP) and SNEP.

Generally, people’s attitudes are considered important determining factor to using HEx for biogas, and its importance has been supported by previous studies (Boehmer-Christiansen, 1995; Petts et al. 1998; Zhang et al. 2013). With reference to attitude, although four items were measured, three of them (energy for cooking, bio-fertiliser, environmental protection) significantly influenced intentions to use HEx for biogas while health risk had a negative and non-significant impact to intentions to use HEx for biogas. This suggests that individuals have perceived belief that the use of HEx for biogas has no significant health implications. This is supported by a study in Rwanda and Uganda where individuals with high benefit and low risk judgement will engage in HEx use regardless of the actual risks involved (Ekane et al, 2015). Additionally, this was confirmed by individuals’ direct evaluation of perceptions concerning HEx for biogas. Specifically, a minority of the people regarded HEx as dangerous and negative. These outcomes suggest that people have a positive attitude towards the use of HEx for biogas generation in Ghana and that interventions designed to promote HEx for biogas could highlight these four factors.

The results revealed that subjective norms were a major factor to influence people’s intentions to use HEx for biogas. For subjective norms, all four important referents (family, neighbours, religion and institution) had a significantly positive influence towards the use of HEx for biogas generation. This finding demonstrates that the judgement of significant others is important (Leeuw et al., 2015) with regards to the use of HEx for biogas generation. Of particular importance is religion (religious leaders), where a majority of people in Ghana consider their religious leaders as very important. For example, in Mthatha, in the Eastern Cape of South Africa, respondents were asked what they thought might work to change peoples’ perception towards using HEx as fertiliser and soil conditioner in their gardens. The response was, leading by example by people with high standing seen using HEx and educational workshops by institutions, would be the best way to inform and change peoples’ perception towards HEx use (Vuuren, 2008). For norm-based interventions to be effective, behaviour of important others should be a focus, especially religious leaders.

The study revealed that all the four perceived behavioural control factors (cost, subsidy, stigma and HEx knowledge) significantly influenced HEx use intentions, and this is consistent with previous study (Osei-Marfo et al, 2018). The mean score suggests that the participants perceive low controllability over HEx use. Thus an individual may be having positive attitude and normative disposition towards HEx use due to its significant benefit yet their volitional control would ultimately moderate their behavioural intentions and consequent behaviour. However, it appears that in spite of the significant benefits associated with HEx use, the high costs and maintenance coupled with lack of subsidy could contribute to low controllability to use HEx for biogas (Osei-Marfo et al, 2018). Per the Environmental Sanitation Policy (MLGRD 2010), households are responsible for financing their own household facilities, hence currently, there is no government subsidy on household biogas installations for HEx use. Nonetheless, the SESIP proposes the establishment of a national sanitation fund for addressing financing challenges. Furthermore, the SESIP encourages microfinance institutions to support government acquire more public financing for HEx management especially at the household level. For stigma and HEx knowledge, it could be mitigated when people with high societal standing are seen using HEx coupled with HEx use campaigns by relevant institutions.

Therefore for perceived behavioural control to be effective, intervention designed in promoting the use of HEx for biogas generation should include financing and/or subsidies to reduce the cost implications, important persons in society leading HEx use campaigns to deal stigma and relevant institutions educating the society on HEx use for biogas.

It was revealed that generally, there was a significant association between the study locations (CCMA and ANMA) which could be attributed to the unique demographic characteristics of these locations.

Additionally, it was shown that gender had no direct significant influence on intentions, but its effect is, however, significantly mediated through attitude (health risk and bio-fertiliser) and perceived behavioural control (stigma and HEx knowledge). This suggests that people believe that bio-fertiliser could be obtained for agricultural purposes, however, there appears to be some health concerns associated with using HEx for biogas. This is supported by previous study by Mariwah and Drangert (2011), that handling HEx is not a taboo but is rather perceived as an act of uncleanliness that may pose a health risk. Additionally, people were of the view that HEx knowledge and stigma could hinder individuals’ intentions to use HEx for biogas. These results may provide indications for gender-specific intervention elements because, it was revealed that more female respondents had no education and few had tertiary education as compared to their male counterparts (see Table 5). This could influence their perceptions on the use of HEx for biogas generation, and this is supported in previous studies (Jan & Akram, 2018; Shane et al. 2015); higher education enhances one’s ability to analyse and understand information.

For education, the results showed that there was no direct significant impact on intentions, rather, it was mediated through all the three predictors of intentions towards the use of HEx for biogas. In this study, effects of education on the positive outcomes of environmental protection and bio-fertiliser were significant. This suggests that ones’ level of education is related to beliefs they form on HEx use for biogas, as it was observed that majority of the respondents had tertiary level of education. Again, the views of important others were key in the use of HEx for biogas and education had a significant effect on the perceived social pressure of the two most important referent, religion and institutions. It is worth noting that these two factors may play an important role in intervention designs. Furthermore, education had a significant link with stigma. This is an indication that stigma could prevent people from using HEx for biogas irrespective of their level of education.

Finally, the study revealed that participants showed strong positive perceptions about the use of HEx for biogas and as well, showed strong positive knowledge on the benefits that come with biogas in general. This might be due to advertisements on local radio stations and the display of posters about biogas technology.

These findings provide useful insight for designing appropriate interventions towards the use of HEx for biogas generation.

16 Conclusion

This study applied TPB in explaining people’s perceptions on the use of HEx for biogas generation. Understanding people’s perception on the use of HEx for biogas is important to promote the implementation of HEx use strategies. This study concludes that the adjusted model has better explanatory power and is a valid predictor of peoples’ intentions to use HEx for biogas generation which is influenced by demographic profile (education and gender). This is an indication that there is the need for a critical look at the effect of socio-demographic characteristics in terms of promoting HEx use for biogas. Though attitude and subjective norm were positive, perceived behavioural control was low. This situation should inform authorities/policy-makers that interventions aimed at promoting HEx use for biogas should address low controllability and that should include government subsidy and financial support to deal with cost and subsidy, as well as education to address stigma and HEx knowledge. The intervention should also bring on board important persons such as religious leaders and persons from relevant institutions to lead more open discussions on HEx use for biogas.