The anaerobic fluidized bed (AFB) reactor comprises small media, such as sand or granular activated carbon, to which bacteria attach. Good mass transfer resulting from the high flow rate around the particles, less clogging and short-circuiting due to the large pore spaces formed through bed expansion and high specific surface area of the carriers due to their small size make fluidized bed reactors highly efficient. However, difficulty in developing strongly attached biofilm containing the correct blend of methanogens, detachment risks of microorganisms, negative effects of the dilution near the inlet as a result of high recycle rate and high energy costs due to the high recycle rate are the main drawbacks of this system. The expanded granular sludge bed (EGSB) reactor is a modification of the AFB reactor with a difference in the fluid’s upward flow velocity. The upflow velocity is not as high as in the fluidized bed which results in partial bed fluidization. (Rittmann and McCarty, 2001). OLR of 10-50 kg kg COD/m3-d can be applied in AFB reactors (Ozturk, 2007; Ersahin et al., 2011).

2.1 Anaerobic digestion historical

The use of anaerobic digestion for the treatment and the stabilization of solid waste is not new. It had been used in the 19th century. In rural parts of China and India, simple reactor constructions were used a long time ago to treat the manure and agricultural wastes in order to recover energy for cooking and lighting (Gijzen, 2002). In 1860s in France (McCarty, 2001), the anaerobic digestion of sludge waste was obtained from wastewater treatment plant, on a large scale, by means of an advanced technology. Furthermore, at the end of 1980s, co­digestion processes treating a mixture of different types of waste, were introduced (Ahring, 2003). Today, anaerobic digestion is one of the most environmentally friendly and suitable treatment methods for of solid organic waste. This technology is widely applied for bio­energy production, because of the increasing request for renewable energy. A consequence of the increasing implementation of this technology is the necessity to determine the ultimate biogas potential for several solid substrates (Angelidaki & al., 20096).

2.2 Anaerobic digestion principle
use organic pollution (biodegradable organic matter) as substrate to produce biogas which can be exploited according to several forms. Thus, anaerobic digestion allows a reduction of the dry matter from approximately 50% (OTV, 1997) and the production of a biogas, mainly methane (55-70%) and carbon dioxide (25-40%), with traces of hydrogen and of H2S, (Mata — Alvares, 2003). Methane can be developed in the form of energy (boiler producing of heat or electricity). At the same time the anaerobic micro-organisms consume little energy, which involves a limited production of muds limited (3 to 20 times lower than an aerobic treatment), (Bitton, 1994). Indeed, the micro-organisms use only approximately 10 to 15 % of the energy of the substrate for their growth (Trably, 2002 and Moletta, 1993), the remaining being used for the production of biogas. Finally, anaerobic digestion allows a reduction of the pathogenic micro-organisms.

Anaerobic digestion consists of sludge fermentation, under strict anaerobic conditions. It is made up of four stages: hydrolysis, acidogenesis, acetogenesis and the methanogenesis. To achieve an anaerobic digestion, it is necessary that the reaction kinetics for the consumed or produced component is balanced. The general diagram of anaerobic digestion is presented on Figure 1 (Edeline, 1997).

Bioethanol is an alcohol made by fermenting the rich sugar components of biomass which is seen as a good fuel alternative. The use of bioethanol as a biofuel has very important advantage — it is generally CO2 neutral. This is achieved because in the growing phase of the biomass plants, CO2 is absorbed and then released in the same volume during combustion of the fuel (Stephenson et al., 2010). This creates an obvious advantage over fossil fuels which only emit CO2 as well as other poisonous gasses. Bioethanol can be used as a fuel for transport in its pure form, but it is usually used as a gasoline additive to increase its octane rating and improve vehicle efficiency (Balat & Balat, 2009).

Nowadays, the bioethanol market has continued to grow rapidly, for example, from about 46 billion L of ethanol produced worldwide in 2007 to the expected value of 100 billion L in 2015 (Balat & Balat, 2009; Sarkar et al., 2012). The USA is the world leader in the production of bioethanol with 48 billion L in 2009 (Muthaiyan & Ricke, 2010), followed by Brazil with 27,0 billion L in 2009 (Soccol et al., 2010) which determined 62% of the worldwide production (Sarkar et al., 2012). In the USA, bioethanol is mainly used as a 10% petrol additive (E10 is the standard petrol fuel, in 2011 introduced E15). In Brazil, it is offered both as a pure fuel (E100) and is blended with conventional petrol with a content of 20 to 25% (E20, E25). In Europe, with the adoption of the Biofuel Directive 2003/30/EC in 2003, the framework conditions were especially created for European bioethanol production. Today France is a leading producer of bioethanol, then Germany, Spain, Sweden and Dutch are the significant producers in Europe (Gnansounou, 2010). Current large scale production of fuel ethanol is mainly based on sugarcane (Brasil), corn (the USA), sugar beet and wheat (Europe), (Balat & Balat, 2009). The recent rise in the prices of food ethanol biomass has shifted in focus towards a possibility of deriving fuel ethanol from any type of biomass, especially cellulosic biomass (corn or wheat straw, sugarcane bagasse, wood, grass) and food waste biomass (organic waste and wastewater from food processing industries) (Sarkar et al., 2012; Soccol et al., 2010).

According to the literature, cheese whey could be a suitable substrate for bioethanol production (Kourkoutas et al., 2002; Zafar & Owais, 2006). Lewandowska & Kujawski (2007) used a solution of dried UF whey permeate as a substrate for semi-continuous ethanol fermentation. Silveira et al. (2005) fermented the solution of UF whey permeate in batch cultures. Ghaly & El-Taweel (1997) developed a kinetic model for continuous ethanol fermentation from lactose. Moreover, in 2008 there were two industrial scale whey-ethanol plants in the United States which produced 8 million gallons of fuel ethanol per year (Ling, 2008). In New Zealand there were whey-ethanol plants with an annual production of about 5 million gallons of ethanol (Ling, 2008). Industrial-scale plants producing bioethanol form whey permeate are operated in Ireland (de Glutz, 2009).

There are many reports of potential applications of yeast strains in ethanol production from UF whey permeate streams, but most of them focused on Kluyveromyces sp. due to its ability to directly ferment lactose (Kourkoutas et al., 2005; Ozmihci & Kargi, 2008; Silveira et al., 2005; ). These yeasts generally suffer from low conversion yields (0.4 kg ethanol kg-1 lactose) and are very sensitive to product (ethanol) inhibition at concentrations as low as 20 g L-1 (de Glutz, 2009). An alternative is to employ indirect fermentation yeasts, such as Saccharomyces cerevisiae, which show considerably better ethanol fermentation performance (0.520 kg ethanol kg-1 lactose) and much higher alcohol tolerance (100 — 120 g L-1) (Cote et al., 2004; de Glutz, 2009). The disadvantage of using S. cerevisiae is the inability to directly ferment lactose. It can be solved by genetic manipulation of yeasts or facilitate the process with a simultaneous lactose hydrolysis, for example by co-immobilization of yeast cells with the enzyme (Cote et al., 2004; Guimaraes et al., 2008). Moreover, higher ethanol production could be achieved by application of different stimulation processes, improving biological activity of yeasts. Many researchers have found that ultrasonic stimulation has the function of promoting the activity of enzyme, cell growth and cell membrane permeability (Chisti, 2003; Liu et al., 2003a; Liu et al., 2007; Schlafer et al., 2000). However, application of ultrasonic irradiation at improper intensity or period has destructive impact on cells by disrupting the cell membranes and deactivating biological molecules such as enzymes or DNA (Liu et al., 2007).

The objectives of the studies were: (1) to investigate bioethanol production from UF whey permeate in continuous fermentation in UASB reactors by K. marxianus 499, (2) to evaluate the effects of low intensity ultrasound (20 kHz, 1 W L-1) for ethanol production from UF whey permeate by S. cerevisiae B4.

The arrangement of the degradation period test was shown in Fig.3-1. Degradation state of film samples during degradation period was shown in Fig.3-2

Fig. 3-2. Mulching degradable process in the different time during the period of degradation test

The fibre film of biogas residue for degradation discovered that the appearance and performance of the samples changed a lot because of light, air temperature, air humidity, wind, rain and other weather factors, coupled with the soil temperature, humidity, combined effect of microorganisms. According to the observation, the degradation was divided into several stages, initially, the sample surface appeared holes or small cracks, called induction period of the film degradation; over time, holes and cracks gradually expanded, the edge glued to the soil surface, the role of soil microorganisms on the film samples increased, resulted in an increasing number of small holes, broken into fragmentation period of the film samples, the film samples effected by various types of micro-organisms would become increasingly thin, the mechanical strength decreased gradually, until the film entered into the fast degradation period of the samples. Especially, after rain, the increasing of air humidity and soil humidity would make mechanical strength of the samples decrease rapidly, so soil moisture is an important impact factor of the film degradation.

During degradation of the film, the dry tensile strengths were regularly measured, according to scatter, the trends of dry tensile strength (N) and date (d) were available, according to trend line, the time of dry tensile strength at zero of each group was estimated, which was defined degradation period. The result was shown in table 3-2.

Data were collected from both primary and secondary sources. Secondary data were collected through literature review using published documents and internet material. There was also a review of policies related to energy in Tanzania. Secondary data helped to establish what has been done in the subject and to read what were the remained gaps for field work were. Institutions supporting biogas development were consulted for

understanding their performance and constraining factors they are facing. Primary data were collected in areas related to investment cost, awareness, household energy demand, technology service providers, and expertise. In addition, there were consultations with service providers to get information on cost, demand as well as factors constraining the spread of the biogas technology in the District. Furthermore, there was a consultation with local and district institutions and authorities for detailed information on biogas use in the district and whether there has been any efforts to facilitate the adoption of biogas.

The sample frame for this study involved respondents with dairy cattle/biogas use and those with dairy cattle but have not installed biogas plants. Also respondents with access to electricity and other clean energy sources such as LPG were included in the sample. A total of 3 villages were selected for the household sample. These were Isagilo, Kyimo and Mpandapanda. The selection of the villages based on the availability of dairy cows, adoption of biogas technology, availability of other energy sources, socio-economic status and accessibility. The households were selected purposively for those with biogas as well as those with access to electricity as they are few but random for the rest of the dairy keepers.

The total number of households (n) to be surveyed was estimated using the formula below:

A sample size of about 10% was selected making a total sample of 120 households. Out of this, 35 had biogas facilities and the remaining 85 had dairy cattle without biogas facility (Table 1). Village roster were used to select the sample households. Data were collected using structured and semi-structured questionnaires and analysed using Statistical Package for Social Sciences (SPSS) as well as livelihoods models. Results have been presented in tables and figures.

If the fermenters are filled regularly with biomass which is air-tight heated and regularly stirred, the biogas will be formed within a matter of days where the formation of biogas is a complex and delicate process. The organic fats which cover high rates contained in the substrates are digested by various kinds of bacteria, this is a starting point for the development of the gas, the contents are continuously stirred, the gas drives slowly to the top of the container and it consists of approximately 50 to 70% methane, carbon dioxide, water vapor, hydrogen, and hydrogen sulfide. As water vapor and hydrogen sulfide are problematic for the utilization of the gas maker, it is necessary to purify the biogas.

The gas is first cleaned from water vapor. The condensed water is collected and a condensation shaft pumps it out. On the other hand, the aggressive trace gas hydrogen sulfide is now extracted from the biogas in a biological desulfurization unit, by introducing air to the container certain bacteria culture which is able to establish colonies on chains. The bacteria decompose the hydrogen sulfide to harmless sulfa and water. The almost unpressurized biogas is then fed into a compressor where it is watered up to 70 mbar pressure later required for burning. In order to completely condense any reaming water vapor freeing biogas of any suspending matters, the biogas is subjected to a washing brine process, this is carried out at almost a freezing point, so that the gas is cooled down to a temperature of 5 degrees. In order to control the purification of the gas, the biogas is constantly tested with an online measuring system which records the amount of methane, hydrogen sulfide, and carbon dioxide. This guarantees a high degree of efficiency and security. In case of any over production of biogas, it is necessary to operate a gas flame for the unburned methane gas that escapes to the atmosphere which is harmful for the environment.

Using 15,000 tons of biomass per year, the plant produces a total of 500 kW of electricity and heat. The optimal gas processing engines can run several years with the minimum of maintenance costs. Up to 30% of the waste heats from the water cooling the engine is used in the heat exchanger and the fermenter so that no additional heat is required, the remaining heat can also be used profitably to heat industrial plants and houses. The electric power generated by the Combined Heat and Power Plant (CHP) is converted to high voltage and then the electricity can be fed into the grid who meets the annual requirement of around 1000 households.

B. Amigun1,*, W. Parawira2, J. K. Musango3, A. O. Aboyade4 and A. S. Badmos1

1Renewable Energy Group, National Biotechnology Development Agency (NABDA)- an Agency Under the Federal Ministry of Science and Technology, Abuja,

2Department of Applied Biology, Kigali Institute of Science and Technology (KIST), Kigali, 3Gauteng City-Region Observatory, a Partnership Between University of Johannesburg, University of Witwatersrand and Gauteng Provincial Government, Wits, 4Process Engineering Department, Stellenbosch University, Stellenbosch,

1Nigeria 2Rwanda 3,4South Africa

1. Introduction

1.1 Energy overview in Africa

Energy plays a central role in national development process as a domestic necessity and major factor of production, whose cost directly affects price of other goods and services (Amigun and von Blottnitz, 2008). It affects all aspects of development, such as social, economic, political and environmental, including access to health, water, agricultural productivity, industrial productivity, education and other vital services that improve the quality of life. Currently, many African countries experience frequent blackouts and the cost of electricity blackouts is not known. The continent’s energy consumption and demand is expected to continue to grow as development progresses at rates faster than those of developed countries. The desire for improved quality of life and rises in population together with energy demands from the transport, industrial and domestic sectors will continue to drive this growth. Ensuring the provision of adequate, affordable, efficient and reliable high-quality energy services with minimum adverse effect on the environment in sustainable way is not only pivotal for development, but crucial for African countries most of which are struggling to meet present energy demands (Amigun et al., 2008). African countries need sustainable energy supplies to be in a position to improve their overall net productivity and become major players in global technological and economic progress. Unreliable energy supply may account for the low levels of private investment the African continent attracts and the poor economic productivity of its limited industries. Improvement

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in the quality and magnitude of energy services in developing countries is required for them to meet developmental objectives including the Millennium Development Goals (MDGs). Africa is not only the poorest continent in the world but it was the only major developing region with negative growth in income per capita during 1980-2000 (World Bank, 2003).

Although reliable regional energy statistics are not readily available, existing estimates of energy use in Eastern and Southern Africa indicate a significant and persistent dependence on traditional biomass energy technologies and limited use of modern, sustainable energy technologies (Karekezi, 1994a). Biomass in the form of mainly wood-fuel and charcoal is the dominant energy source used in sub-Saharan Africa

Because of the shortage in commercial modern energy and current economic situation in most African countries, the fuel substitution away from biomass is less likely because of declining disposable incomes for both urban and rural population. There is fuel-switch back to traditional fuels as modern fuels become scarce in some areas but the wood fuels are also becoming scarce in some countries. Biomass is cheap but when used in an unplanned (unsustainable) manner leads to consumption beyond regenerative limits with serious environmental consequences. On average, about 40% of total commercial energy is consumed in six countries in the Northern sub-region and a similar share in Southern Africa with over 80% by South Africa. The other 45 or more countries share the remaining 20%. Similarly, the major oil and gas producers are limited to about ten countries in the North and West regions while about 95% coal (anthracite in nature) is produced in South Africa. This uneven distribution of the fossil energy resources (crude oil and natural gas) on the African continent is reflected in the energy production and consumption patterns (Table 1). As a result, 70% of countries on the continent depend on imported energy resources, which support the need to harness the available abundant renewable energy resources (Amigun, 2008).

Africa is a net energy exporter, but the majority of its population lacks access to modern fuels, and many countries rely on imported energy. More than 500 million people living in sub-Saharan Africa do not have electricity in their homes and rely on solid forms of biomass (firewood, agricultural residues, animal wastes, etc) to meet basic energy needs for cooking, heating and lighting. The disadvantages of these traditional fuels are many: they are inefficient energy carriers and their heat is difficult to control, they produce dangerous emissions and their current rate of extraction is not sustainable. The unsustainable use of fuel wood biomass can accelerate deforestation and lead to soil erosion, desertification and increased risk of flooding and biodiversity loss. The low levels of modern (commercial) energy consumption prevalent in Africa besides the heavy usage of traditional (non­commercial) biofuels- primarily biomass is also due to largely underdeveloped energy resources, poorly developed commercial energy infrastructure, widespread and severe poverty which makes it impossible for people to pay for conventional energy resources and the landlocked status of some African countries that make the cost of importing commercial energy more expensive (World Bank, 2003; Amigun et al., 2008). The existing aging and neglected facilities for thermal and hydro energy production need rehabilitation and expansion for the efficient delivery of useful energy services. Upgrading the abundant biomass in Africa to higher-quality energy carriers could help change the energy situation in the continent. The problems arising from non-sustainable use of fossil fuels and traditional biomass fuels have led to increased awareness and widespread research on the accessibility of new and renewable energy resources, such as biogas. The development of renewable energy technologies and in particular biogas technology can help reduce the dependence on non-renewable resources and minimise the social impacts and environmental degradation problems associated with fossil fuel (Amigun and von Blottnitz, 2008).

The failure to develop a suitable and economical effluent wastewater treatment technology for OMW has lead manufacturers of technology to develop the "ecological" two-phase process, which delivers oil as the liquid phase and a very wet olive cake (two-phase olive mill solid waste — OMSW-) as the solid residue. This technology has attracted special interest where water supplies are restricted and/or aqueous effluent must be reduced (Borja et al., 2006).

In the two-phase process a horizontally mounted centrifuge is used for primary separation of the olive oil fraction from the vegetable solid material and vegetation water. The resultant olive oil is further washed to remove residual impurities before finally being separated from this wash water in a vertical centrifuge. Therefore, the two-phase olive mills produce three identifiable and separate waste streams. These are:

1. The wash waters generated during the initial cleansing of the fruit.

2. The aqueous solid residues generated during the primary centrifugation (two-phase OMSW).

3. The wash waters from the secondary centrifuge generated during the washing and purification of virgin olive oil.

Spain was the first country where the two-phase system was used and from there this new technology was installed around the world. The two-phase decanting reduces the water requirements. Nevertheless it has created a new solid residue, two-phase OMSW, which requires further investigation to find out how it must be handled.

The two-phase olive oil extraction process has several advantages over the three-phase centrifugation process (Alba et al., 2001; Di Giovacchino et al., 2001 and 2002): [11]

• The throughput of the two-phase centrifuge in relation to the oil quantity is higher because no additional water is required to produce the pulp. Energy consumption is also reduced as a result of the lower processing quantity.

• Oil produced by the two-phase centrifuge is of higher quality; in particular, it has higher oxidation stability and better organoleptic characteristics.

• The operating costs are lower. Water utilization in the olive mill decreases considerably.

In addition, the disadvantages of two-phase manufacturing process are:

• The two-phase process, although it produces no olive mill wastewater as such, generates the wash waters derived from the initial cleansing of the fruit and from the purification of virgin olive oil. In addition, it combines the olive vegetation water that is generated with the solid waste to produce a single effluent stream in semi-solid form. This doubles the amount of "solid" waste (OMSW or ‘alperujo’) requiring disposal, and it cannot be composted or burned without some form of expensive pre-treatment.

• Two-phase OMSW has a moisture content significantly higher than that of traditional cake from three-phase centrifuges. This increased amount of moisture, together with the sugars and fine solids that in the three-phase system were contained in OMW give two-phase OMSW a doughy consistency and makes transport, storage and handling difficult -it can not be piled and must be kept in large ponds.

• Two-phase OMSW is characterized by higher values of the pulp/stone ratio, as well as the greater weight produced.

• This two-phase technology transfers the problem of disposing of the olive-mill waste from the mill to the seed-oil refineries. Two-phase OMSW, prior to oil solvent extraction, must be dried with considerably higher energy requirements than in the three-phase continuous oil production process, making the industrial recovery of the residual oil difficult and expensive.

A characterization of the three potential biofilter packing materials was performed. The highest water retention capacity (WRC) was found in vermiculite (65%), while the WRC for lava rock was 15%. Although vermiculite showed a higher WRC, lava rock favored water irrigation, which ensured that the desired moisture level was maintained and avoided sulfate accumulation at the same time.

The acetic, propionic, butyric and valeric acid could also be present in the biogas stream, their assimilation was determined in batch experiments. The biodegradation of different loadings of acetic and propionic acids as individual substrates were also evaluated in the lava rock biofilter as it as previously described elsewhere (Ramirez-Saenz et al., 2009).

As the MR proportion increased in the ADS, the H2S concentration in the biogas stream also increased. The biodegradation of H2S was determined in the lava rock biofilter under two different empty-bed residence times (EBRT). Results for H2S elimination capacity as a function of H2S inlet loading in the lava rock biofilter, operated at 85 sec and 31 sec EBRT, are depicted in Figure 2. As shown in Figure 2A, at an EBRT of 85 sec, the relationship between the inlet loading and the elimination capacity was linear, and the critical H2S elimination capacity defined by Devinny et al., 1999 (i. e., deviation from the 100% removal capacity) was not yet reached at an inlet loading of 144 g/ m3h. Under these operation conditions, the removal efficiency of H2S for loadings between 36 and 144 g/ m3h was always above 98 %. Furthermore, the EC reached a maximum of 142 g/ m3h when the H2S loading was 144 g/m3h.

For an EBRT of 31 sec (Figure 2B), the H2S elimination capacity was found to be linear with respect to H2S inlet loading up to 200 g/ m3h (100% removal efficiency). A higher inlet loading of 300 g/ m3h reduced the removal efficiency in the system to 85 %. An inlet loading of 400 g/ m3h (corresponding to 3000 ppmv) caused the removal efficiency to drop to 75%, which suggested inhibition of biological activity and/or insufficient mass transfer. In this case, the critical H2S EC was 200 g/ m3h, whereas a maximum H2S EC value of 232 g/ m3h was achieved in the biofilter. At the same time, however, the removal of VFAs present in the gaseous stream (approximately 10 ppmv) reached 99%.

For long operation times, the biofilter nearly eliminated all the H2S from the biogas stream. The H2S concentrations of the AD gas stream were previously diluted to maintain an inlet concentration of 1500 ppmv and to allow complete elimination (99% removal efficiency), but the high removal efficiency was maintained over 90 days and complete biodegradation of VFAs was also observed. Fifty days after the start-up period, a technical failure in the AD system blocked the feeding of the biofilter, no data was obtained during that time. After operation conditions were restored, an inlet H2S concentration was maintained at approximately 1500 ppmv from day 103 to 194 at an EBRT of 31 sec. Under these conditions, a removal efficiency of 95% was maintained for 90 days. Higher concentrations, around 3000 ppmv, caused a drop in the biofilter efficiency to 50% (Ramirez-Saenz et al., 2009). The biofilter was fed with the ADS gas stream every two weeks, which corresponded to the HRT of the AD system.

According to the stoichiometry of aerobic biological H2S oxidation (Eq. 1 and 2) and the sulfate determinations obtained between days 103 and 194 of the operational period of the biofilter, 51 to 60% of the H2S was completely oxidized to sulfate. These data are correlated with those reported by Fortuny et al., 2008 with respect to the H2S conversion to sulfate. The elimination of these compounds allowed the potential use of the biogas while maintaining the methane (CH4) content throughout the process.

There are many industrial applications in which the principal goal of anaerobic digestion is the organic treatment of waste instead of the production of gas. On this subject, the elimination of the difference between the organic matter contained before and after treatment, is a significant parameter that it is necessary to control. This is measured in term of Total solid (TS), volatile solid (VS), total organic carbon (TOC), COD or BOD (Boe & al., 2005). These parameters are appropriate for the control of the anaerobic digestion applied to several types of waste.

2.5 Carbon monoxide

The carbon monoxide is a possible intermediate in the metabolic route of the acetogens and the methanogens (Moletta, 1993); Carbon monoxide was found in a great quantity during toxic inhibition by heavy metals (Liu & al., 2003). According to Moletta (Moletta, 2002) the presence of carbon monoxide is directly related to the acetate concentration, and conversely related to that of methane (Batstone & al., 2002).

N. B: there are other process control parameters of the production of biogas during anaerobic digestion, but they do not find any wide application in practice. However, the hydrogen gas is controlled in the gas phase and its measure in the liquid phase enables the identification of the existing different types of bacterial populations which may influence the process of the anaerobic digestion.