Can biogas digesters help to reduce deforestation in Africa?

Biogas digesters could help to reduce deforestation in Sub-Saharan Africa by providing a source of energy that would otherwise be provided by woodfuel. However, the link between deforestation and use of woodfuel at global level is weak because fuel is often obtained from fallen wood or from sources felled for construction or land clearance. This paper examines the link between deforestation and use of woodfuel, and evaluates whether biogas digesters are likely to help reduce deforestation in Africa. Woodfuel production and consumption in Africa are increasing over time. Of the deforestation observed in 2010, we estimated that 70(±42)% can be attributed to woodfuel demand. Uncertainties in this figure arise from uncertainty in efficiency of energy use in different designs of wood-burning stoves, and the percentage of energy obtained from woodfuel in rural and urban populations. The contribution of woodfuel demand to deforestation is predicted to increase by 2030 to up to 83(±50)%. This is due to an increasing population requiring more woodfuel and so contributing to a higher proportion of total deforestation. Biogas production has the potential to reduce deforestation due to woodfuel demand by between 6 and 36% in 2010 and between 4 and 26% in 2030. This is equivalent to 10–40% of total deforestation in 2010, and 9–35% of total deforestation in 2030. The highest contribution to biogas production is likely to be from cattle manure, and the uncertainty in the potential of biogas to reduce deforestation is mainly associated with uncertainties in the amount of biogas produced per animal.     

Prospects and challenges for urban application of biogas installations in Sub-Saharan Africa

Cities around the world generate substantial quantities of municipal solid waste, including organic residues. These organic residues can be managed productively and given value, or they can simply be wasted. Municipal solid waste management is a serious environmental and public health concern in developing countries. In addition, collecting, transporting and disposing of municipal solid wastes presents formidable challenges to many developing country cities. It is believed that the problems are likely to become even more pronounced as the level and pace of urbanization continue to grow rapidly. Moreover, cost recovery is a serious problem of municipal solid waste management in many cities in the developing world. This paper considers how anaerobic digestion can give value to organic residues and help reduce the problem of municipal waste management. Biogas technology has the potential to work for the growing urban populations of Africa as both an energy source and a waste management (minimization) tool that can be utilized both at a small or large scale. In this paper we review the potential roles of biogas in urban applications. Specifically, we review organic waste treatment methods as well as opportunities and challenges for urban application of biogas installations and identify the critical conditions for success of biogas in urban applications.     

A commentary on occupational infectious diseases due to agricultural practices in Sub-Saharan Africa

Occupational diseases associated with agricultural practices in Sub-Saharan Africa have a major health impact on farmers, farm workers and their families. This leads to reduced productivity through decreased human and livestock resource and places an additional burden on health care requirements in already poor areas. An in-depth knowledge of the various diseases and potential risks associated with farming in SSA could provide insights on effective control measures. This paper presents a review of infectious disease in farmers in Sub-Saharan Africa likely to have been contracted as a result of farming practices. The following are considered: Sources, modes of transmission, incidence, prevalence, morbidity and mortality. Infections have been classified into those of bacterial, parasitological, mycological and virological origin. The literature indicates that 80% of cases of occupational diseases due to farming with high morbidity and mortality are from helminths, protozoa and bacterial infections. More effective reporting of disease, risk awareness and appropriate intervention methods, are required to tackle the occurrence of occupational diseases amongst farmers in Sub-Saharan Africa.     

Factors determining the stability and productivity of small scale anaerobic digesters

Biogas as a technology and the factors that affect its productivity have both been well studied. Research has previously been done to look at the impact of temperature, pH, organic loading rate, carbon-to-nitrogen ratios, microbial populations and hydraulic retention time on different scales of biogas operations. Small scale biogas installations, of which many millions have been constructed and seem to be performing well, have been chosen as the area of focus for this paper. Such systems allow energy generation on site, thereby eliminating the need for energy intensive transport. This review paper explores the factors that govern the productivity and operational stability of biogas digesters, and goes on to highlight the most important factors for small scale operation.The review reveals that the key factors that govern the productivity and stability of small scale systems are feedstock variability, retention time, temperature and acidity of the system. These are the main parameters which should, therefore, be considered when looking into the potential of biogas as a widespread technology to be deployed to meet energy demands.     

Can slurry biogas systems be cost effective without subsidy in Mexico?

Biogas from pig slurry in Mexico has potential to produce 21 PJ per year, equivalent to 3.5% of natural gas consumption in 2013. In this paper, three different scenarios are analysed: mono-digestion of pig slurry in a finisher farm (scenario 1); co-digestion of pig slurry and elephant grass in a finisher farm in situ (scenario 2) and co-digestion of pig slurry and elephant grass in centralised biogas plants (scenario 3). The digesters proposed are anaerobic high density polyurethane (HDPE) covered lagoons. HDPE centralised plants can have capital costs 5 times cheaper than European biogas plants. The economics of utilisation of biogas for electricity generation and as biomethane (a natural gas substitute) were investigated. Economic evaluations for on-site slurry digestion (Scenario 1) and on-site co-digestion of elephant grass and pig slurry (Scenario 2) showed potential for profitability with tariffs less than $US 0.12/kWh_e. For centralised systems (Scenario 3) tariffs of $US 0.161/kWh_e to $US 0.195/kWh_e are required. Slurry transportation, energy use and harvest and ensiling account for 65% of the operational costs in centralised plants (Scenario 3). Biomethane production could compete with natural gas if a subsidy of 4.5 c/L diesel (1 m³ of biomethane) equivalent was available.     

Biofuels development in Sub-Saharan Africa: Are the policies conducive?

This paper analyses national, regional and international biofuels policies and strategies to assess whether these policies promote or undermine the development of biofuels sector in Africa. Despite having a huge comparative advantage in land, labour and good climatic conditions favourable for the growing of energy crops, few countries in Sub-Saharan Africa have included biofuels strategies in their energy or national development policies. Further results show that while developed countries commit huge financial resources for research, technology development and the provision of tax-incentives to both producers and consumers, there is little government support for promoting biofuels in Africa. Although the consequences of biofuels on food supply remain uncertain, the mandatory blending of biofuels with fossil fuels by industrialized countries will create demand for land in Africa for the growing of energy crops for biofuels. This paper urgently calls upon national governments in Sub-Saharan Africa to develop appropriate strategies and regulatory frameworks to harness the potential economic opportunities from biofuels sector development, while protecting the environment and rural communities from the adverse effects of land alienation from the mainstream agriculture towards the growing of energy crops for biofuels at the expense of traditional food crops.     

Thermodynamic and exergoeconomic analysis of energy recovery system of biogas from a wastewater treatment plant and use in a Stirling engine

The aim of this research it is to show how the biogas biomethanisation from primary and secondary treatment of activated sludge from a wastewater treatment plant (WWTP), can be an alternative renewable energy option from fossil fuels, which offers competitive advantages and points out new horizons for the use of this fuel. This will allow to achieve some important priorities of energy plans in EU countries: to reduce the organic matter deposited in landfills and CO₂ emissions and to find viable solutions to minimize the environmental impact of sewage sludge (SS).This study analyses the biogas combustion and energy recovery processes from a thermodynamic, thermoeconomic and exergetic point of view.The results show that the boiler of the process is the main source of irreversibility and exergy destruction. Moreover, the energy and exergy economic value of exhaust gases from the combustion chamber, are significant and worthwhile to be exploited. For this reason, the present study explores the applicability and suitability of integrating a Stirling engine in such process. The study reveals that it is possible to create a small micro-cogeneration system which leads to sustainable waste management and energy savings in the treatment plant itself.     

What is the potential for biogas digesters to improve soil carbon sequestration in Sub-Saharan Africa? Comparison with other uses of organic residues

Using bioslurry from anaerobic digestion as an organic fertilizer has great potential to increase carbon sequestration by supplying organic matter to the soil. This paper examines this potential in Sub-Saharan Africa compared to other uses of organic residues, including burning on pyrolysis cook-stoves and composting. Measurements of loss of carbon on treatment of organic residues indicate that the proportion of carbon lost from organic residue during treatment is greater for anaerobic digestion than for aerobic composting or pyrolysis. The stability of organic residue is increased by treatment, and is similar for composted and anaerobically digested material, but is higher for material treated by pyrolysis. Simulations using the RothC model, driven by parameters based on incubations of the organic residues with soil, suggest that on the basis of decomposability alone, treated organic residues sequester significantly more carbon than untreated organic residues, and despite the differences observed in stability, unless biochar contains a high proportion of inert organic material that does not decompose at all, the potential carbon sequestration by incorporating biochar is similar to that for compost or bioslurry. However, if losses of carbon during treatment are also taken into account, incorporating bioslurry sequesters only approximately the same amount of carbon as if the organic residue had been left untreated. By contrast, incorporating compost and biochar sequesters significantly more carbon than incorporating the untreated organic residue. Therefore using bioslurry as an organic fertilizer sequesters less of the carbon in the soil from organic residue than burning on pyrolysis cook-stoves or composting.     

Resource and revenue potential of California residential load participation in ancillary services

Increasing penetrations of intermittent renewable energy resources will require additional power system services. California recently adopted an energy storage mandate to support its renewable portfolio standard, which requires 33% of delivered energy from renewables by 2020. The objective of this paper is to estimate the amount of energy storage that could be provided by residential thermostatically controlled loads, such as refrigerators and air conditioners, and the amount of revenue that could be earned by loads participating in ancillary services markets. We model load aggregations as virtual energy storage, and use simple dynamical system models and publicly available data to generate our resource and revenue estimates. We find that the resource potential is large: 10–40 GW/8–12 GWh, which is significantly more than that required by the mandate. We also find that regulation and spinning/non-spinning reserve revenues vary significantly depending upon type of load and, for heat pumps and air conditioners, climate zone. For example, mean regulation revenues for refrigerators are $11/year, for electric water heaters are $24/year, for air conditioners are $0-32/year, and for heat pumps are $22–56/year. Both consumer choices, such as appliance settings, and policy, such as the design of ancillary service compensation and appliance standards, could increase revenue potentials.     

Biomass for residential and commercial heating in a remote Canadian aboriginal community

Most residents of Canada's 300 remote communities do not have access to natural gas and must rely upon higher cost and/or less convenient heat sources such as electric heat, heating (furnace) oil, propane, and/or cord wood. This research sought to determine the techno-economic feasibility of increasing biomass utilization for space and hot water heating in remote, off-grid communities in Canada and abroad using a two-option case study approach: 1) a district energy system (DES) connected to a centralized heat generation energy centre fuelled by wood chips; and 2) a decentralized heating option with wood pellet boilers in each individual residence and commercial building. The Nuxalk First Nation Bella Coola community was selected as a case study, with GIS, ground surveys, and climate data used to design DES routes and determine heat demand. It was determined that biomass has the potential to reduce heat costs, reduce the cost of electricity subsidization for electrical utilities, reduce greenhouse gas emissions, and increase energy independence of remote communities. Although results of the analysis are site-specific, the research methodology and general findings on heat-source economic competitiveness could be utilized to support increased bioheat production in remote, off-grid communities for improved socio-economic and environmental outcomes.     

Modelling and optimization of the smart hybrid renewable energy for communities (SHREC)

The future energy system in community level should be more ‘smart’ to secure reliability, enhance market service, minimize environmental impact, reduce costs and improve the use of renewable energy source (RES). Therefore, this paper proposes an energy integration system – smart hybrid renewable energy for communities (SHREC). It considers both thermal (heating and cooling) and electricity market in a large community level and highlight the interactions between them through utilizing RES, combined heat and power (CHP) and energy storages. A planning model based on CHP modelling is developed for the SHREC system. A linear programming (LP) algorithm is developed to optimize the SHREC system in a weekly period and the results are compared with an existing energy optimization software. We also demonstrate the model in a sample SHREC system during three typical weeks with cold, warm and mid-season weather in the year 2011. The results indicate that the developed modelling and optimization method is more efficient and flexible for the smart hybrid renewable energy systems.     

Environmental assessment of electricity generation from an Italian anaerobic digestion plant

A standard ISO Life Cycle Assessment study was carried out to evaluate the environmental sustainability of electricity production from an anaerobic digestion (AD) plant using a mixture of dedicated energy crops, agricultural residues and livestock effluents as input materials. The functional unit was 1 MJ of electricity. System boundaries were from cradle to grave and covered all the phases from energy crops cultivation to the production of biogas and its use in a Combined Heat and Power plant to produce electricity. Liquid and solid digestate storage and spreading on agricultural land were included. Primary data were collected from the AD plant for all the above phases. Since heat produced is used only internally, no allocation was applied in the study. As regards digestate management, CH₄ emissions were calculated from literature, whereas four literature methods were applied for calculation of nitrogen emissions with the goal to perform a sensitivity analysis on LCA results. ILCD Handbook impact assessment methodologies were used. Results show that the main hotspots are energy crops cultivation and the management of digestate, mainly because of both nitrogen and methane emissions, affecting Global Warming, Acidification, Marine and Freshwater Eutrophication. Finally, a detailed Monte Carlo analysis, was carried out to evaluate the results uncertainty. The study represents the state of the art about the environmental performance of the AD plant with the use of sensitivity and uncertainty analysis, which both improve the reliability of results, and allows drawing general conclusions on how to mitigate the environmental impacts of AD process.     

Simulation study of a large scale line-focus trough collector solar power plant in Greece

This paper deals with the technical feasibility and economic viability of a solar thermal power plant using parabolic trough collectors in Greece. The power plant is to be installed in the island of Rhodes and its power output will be 8.55 MW. Power plant simulation is carried out using TRNSYS software (STEC library) and economic issues of the project such as initial cost of investment, operation and maintenance (O&M) and energy costs will be analyzed. It was found that for the particular investment, considering a 75% of initial investment cost loan (with a 10-year period), the payback period will be approximately 13 years.     

Optimization of mechanical pre-treatment of Laminariaceae spp. biomass-derived biogas

Macroalgae have not met their full potential to date as biomass for the production of energy. One reason is the high cost associated with the pretreatment which breaks the biomass's crystalline structure and better exposes the fermentable sugars to anaerobes. In the attempt to overcome this technological barrier, the performance of a Hollander beater mechanical pretreatment is assessed in this paper. This pretreatment has been applied to a batch of Laminariaceae biomass and inoculated with sludge from a wastewater treatment plant. The derived biogas and methane yields were used as the responses of a complex system in order to identify the optimal system input variables by using the response surface methodology (RSM). The system's inputs considered are the mechanical pretreatment time (5–15 min range), the machine's chopping gap (76–836 μm) and the mesophilic to thermophilic range of temperatures (30–50 °C). The mechanical pretreatment was carried out with the purpose of enhancing the biodegradability of the macroalgal feedstock by increasing the specific surface area available during the anaerobic co-digestion. The pretreatment effects on the two considered responses are estimated, discussed and optimized using the tools provided by the statistical software Design-Expert v.8. The best biogas yield of treated macroalgae was found at 50 °C after 10 min of treatment, providing 52% extra biogas and 53% extra methane yield when compared to untreated samples at the same temperature conditions. The highest biogas rate achieved by treating the biomass was 685 cc gTS⁻¹, which is 430 cc gTS⁻¹ in terms of CH₄ yield.     

Sickle bush (Dichrostachys cinerea L.) field performance and physical–chemical property assessment for energy purposes

The sickle bush (Dichrostachys cinerea (L.) Wight & Arn.) comprises a woody legume shrub which is widely distributed throughout of the tropical areas of Africa, Asia and Oceania, being found as well in Cuba where it represents a difficult to control invasive plant. It holds great silvopasture and energy crop potentials. In southwestern Spain a two year field trial was conducted contemplating also another six hardwood taxa commonly used as energy crops. The sickle bush above ground dry biomass fraction was 60.4%; sickle bush displayed a high transpiration rate during hot days (3.02 kg m⁻² d⁻¹ to 6.82 kg m⁻² d⁻¹); cold winter temperatures (<−2 °C) together with hot and dry summer air (<20% relative humidity) committed survival and growth. The physical-chemical wood properties and the pellets thereof derived were analyzed and compared to those of the other energy crop taxa. The within other woody species normal chemical composition range coupled to a high wood density and energetic use properties (19.2 MJ kg⁻¹ higher heating value, 29 g kg⁻¹ ash content) all allow for an industrial use. Pellets evidenced also good physical and mechanical properties (690 kg m⁻³ bulk density, 42 g kg⁻¹ moisture content). However, the mechanical durability (93.9%) was slightly less than that required by the non-industrial use standards, therefore further improvements should be studied. All of the above could encourage scrubland cuts in Cuba as a mechanical control method, in addition to the expansion of plantations within of their tropical climate based natural habitats.     

Fuelwood: The “other” renewable energy source for Africa?

In recent years, increasing concerns over rising oil prices, supply shortfalls and the environmental impacts of fossil fuel use have fed growing interest in renewable energy sources for Sub-Saharan Africa. Although traditional biofuels already enjoy widespread popularity, their use has often been actively discouraged due to the lingering influence of “fuelwood crisis” era narratives. In particular, urban fuelwood consumption is frequently portrayed as a cause of environmental degradation leading to energy insecurity among low-income households, especially where the resource is commercialized. Such views have had significant influence among policy makers, often resulting in repressive forestry legislation. In contrast, however, a number of researchers have demonstrated that wood energy dependence is often not a significant cause of deforestation and can provide important livelihood opportunities. This article reassesses urban fuelwood sourcing and its impacts using a recent case study conducted by the authors in Maun, Botswana and results previously reported in the literature. Findings indicate that although harvesting is unregulated, its impacts are significantly mitigated by collectors' strong preferences for source sites with abundant dead wood, low competition and recognized access rights. As well, fuelwood vending is found to provide critical support to rural incomes and a key source of low-cost urban energy. As such, the benefits of fuelwood use and avoidance of negative effects will most effectively be achieved by decentralised management approaches that build on local institutions and understandings of the resource.     

Anaerobic digestion of maize and cellulose under thermophilic and mesophilic conditions – A comparative study

The aim of this study was to advance in understanding of digestion process of energy crops. Cellulose and maize silage were fermented in batch mode at mesophilic (38 °C) and thermophilic (55 °C) conditions and corresponding organic loads of 5.5 ± 0.2 kgVS/m³, 11.2 ± 0.3 kgVS/m³ and 16.7 ± 0.4 kgVS/m³.For both substrates more stable and faster digestion took place at 38 °C. Due to complex structure maize degradation was characterized by varying digestion rate and longer total digestion time resulting form breakdown of hard-degradable fractions. The digestion retard at increased OLRs of cellulose and lower degradation level obtained for all cellulose series confirm a higher overloading potential for systems dealing with single-component-substrates but also the enhanced sensitivity of such systems to any inconvenient digestion conditions.Based on observed patterns of volatile fatty acids and oxidation-reduction potential, different fermentation mechanisms can be concluded for cellulose and maize, but also for different temperature modes. Conversion of maize at highly reductive conditions with increased concentrations of butyric acid was accompanied by much higher activity of hydrogenotrophic methanogens than for cellulose digestion.Two factors showed a strong potential to influence test results: an insufficient VS content of inoculum, which caused reduced biogas yields, and a high natural biodiversity of maize silage, resulting in higher biogas yields than calculated based on the maize composition.     

Physicochemical characterization and enzymatic digestibility of Chinese pennisetum pretreated with 1-ethyl-3-methylimidazolium acetate at moderate temperatures

1-ethyl-3-methylimidazolium acetate ([EMIM] AC) pretreatment at moderate temperatures (60 °C and 75 °C) was evaluated for improving hydrolysability of Chinese pennisetum, a leading candidate as an energy crop, for bioethanol production. The pretreatment caused slight carbohydrate and lignin loss but significantly changed the material physicochemical characters, such as crystallinity and surface structure. Both changes exhibited positive effects on improving the enzymatic digestibility of the Chinese pennisetum. It was observed that approximately 90% of the cellulose and 50% of the xylan in the Chinese pennisetum after pretreatment at 75 °C were converted to fermentable monosaccharides by the combined cellulases and endo-xylanase. The results suggested that Chinese pennisetum could be effectively pretreated with ([EMIM] AC) pretreatment at moderate temperatures, and the high hydrolysis yield of fermentable sugars from pretreated Chinese pennisetum could be achieved by the synergistic action of accessory xylanase in enzymatic hydrolysis by cellulases.     

Smart metering for residential energy efficiency: The use of community based social marketing for behavioural change and smart grid introduction

Community-based social marketing (CBSM) has shown to be very effective at inducing behavioural change due to its pragmatic approach. It has been found that nonintegrated intensive approaches towards changing individual's behaviour, such as education and economic self-interest are not successful.This paper will explain how a large urban electricity meter replacement program can achieve a reduction in peak demand and overall energy consumption through the use of advanced metering infrastructure (AMI or ‘smart meters’) coupled with CBSM, which in turn enables the progression towards a ‘smart grid’. In order to measure success the following targets were set:

• •Peak demand reduction (peak lopping) of 20% from the households participating in the Behaviour Change Programs (BCPs).
• •Peak demand shifting (load shifting) to reduce energy consumption during ‘super peak’ by 10% in BCP participating households.
• •Average total energy use reduction of 10% in BCP participating households.

The energy efficiency actions discussed with householders during eco-coaching, and other feedback communications, are identified by utilising the information regarding barriers and benefits generated from the research phase prior to coaching. These actions can include referral to other initiatives such as the provision of reduced cost solar PV power systems, direct load control devices for domestic air-conditioners, the time-of-use pricing product, the provision of in-home-displays (IHD) and other devices necessary for development of a ‘smart grid’.     

Anaerobic digestion of corn silage on a commercial scale: Differential utilization of its chemical constituents and characterization of the solid digestate

The utilization of different chemical constituents of corn silage during industrial-scale anaerobic digestion was determined. Corn silage together with the resulting solid digestate generated during biogas production were collected from an industrial plant during a regular operating period. Moisture, water and ethanol extractives, ash, total nitrogen, starch, cellulose, the monomeric composition of hemicellulose, acid soluble and acid insoluble lignin were measured in both corn silage and corn silage solid digestate. The relative consumption of each component of corn silage during its anaerobic digestion was estimated with reference to acid insoluble lignin. It was assumed that lignin was not digested throughout the process. Starch and large fractions of extractives and acid soluble lignin were digested. In contrast, the digestion of cellulose and particularly hemicellulose were limited (40% and 29% respectively). Of the hemicellulose monomers, xylose was the least digested (20%). The present work shows that the digestate produced by commercial corn-silage anaerobic digestion contains a notable quantity of cell wall polymers. These could potentially be used in biorefinery processes, e.g. ethanol and xylo-oligosaccharide production.