Tanzania’s energy demand is characterised by a low per capita consumption of commercial energy (petroleum and electricity) and a high dependence on non-commercial energies, including biomass fuels in the form of firewood, charcoal and bio-waste. Renewable energy technologies currently in use in the country include improved wood-fuel stoves and charcoal production practices, biogas, windmills, and solar thermal and photovoltaics (PV). The applications of these technologies are at various stages of development in terms of demonstration and commercialization.

Tanzania has no renewable energy policy at the moment but only the general energy policy framework for all kinds of energy.

The National Energy Policy (2003) objectives are to ensure availability of reliable and affordable energy supplies and their use in a rational and sustainable manner in order to support national development goals. The National Energy Policy, therefore, aims to establish an efficient energy production, procurement, transportation, distribution and end — use systems in an environmentally sound and sustainable manner (URT, 2003). It also supports research and development of renewable energy and promotes the use of efficient biomass and end-use technologies. The main elements of the policy are: [21]

policy, which is the main guidance for change, backed by legislation and regulation. The ministry also facilitates mobilisation of resources into areas where market forces fail to ensure adequate energy services. The policy put guidance for licensing operators, monitoring markets and performance; and applying any other necessary regulatory measures.

Within the Ministry of Energy and Minerals there is a Rural Energy Agency (REA) for rural electrification. The policy acknowledges that around 80% of the population has very low purchasing power and depends mainly on wood-fuel for cooking and kerosene for lighting, which have negative consequences to the environment and the quality of life, especially to the rural poor. Rural electrification is a case of long-term national interest and a prerequisite for a balanced socio-economic growth for all in Tanzania through enabling rural poor accessing sustainable clean energies.

However, energy policy has attracted criticism in different ways. Stakeholders feel that consideration of improving clean energy by rural poor needs to be on the application of appropriate technologies that are affordable, environmentally sound and well adapted to local needs as explained in the Policy. Also, while gender issues have received attention at micro level in terms of technological interventions such as cookstoves, biogas, solar cookers, and wood plantations, they have yet to be addressed in macro level policies. Women’s needs for energy vary depending on whether they are in urban or rural areas, their stage of economic development and whether they are economically active. Parikh (1995) makes a plea to include gender issues in macro level energy policies such as energy investment, imports and pricing. Also there is inadequate information and data on how the ongoing and planned power sector reform can be modified to address the existing challenges, particularly with regard to electrification of the poor (Karekezi and Kimani, 2002). A study by Barnes and Floor (1996) highlights constraints towards improving clean energy in rural development and these include the widespread inefficient production and use of traditional energy sources fuelwood and charcoal which pose economic, environmental, and health threats. Also the highly uneven distribution and use of modern energy sources such as electricity, petroleum products and liquefied or compressed natural gas, pose important issues of economics, equity, and quality of life. The policy does not provide adequate strategies on overcoming these. Many developing countries including Tanzania has general energy policies pertaining to the development of electricity, oil and renewable energy sub­sectors for the benefit of the public and the economy. However, the absence of sharply focused, pro-rural energy policy and/or their policy instruments has been the major challenges towards the observed stagnation of some initiatives like the biogas (Habtetsion and Tsighe, 2002). The Energy Policy formulation in Tanzania takes place in the context of great uncertainty, due to mainly pressures exerted by conflicting interests (Mwandosya and Luhanga 1993).

Within the Energy Policy, biogas has received a low profile or recognition. There is no specific policy statement to explain and strategies for the promotion of biogas technology in rural Tanzania; rather everything is dumped in the category of renewable energy. Omer and Fadalla (2003) recommends that biogas technology must be encouraged, promoted, invested, implemented, and demonstrated, but especially for remote rural areas.

The main challenges facing biogas technology is inappropriate institutional structure and/or gaps in the structure, in addition to lack of corporate culture; poor incentives; and, poor linkages among the various stakeholders concerned in energy for rural development (Habtetsion and Tsighe, 2002). Progressive government intervention is needed to shift reform process towards a more responsible development path of renewable energy (Wamukonya, 2004). Generally speaking, the database for the context of renewable energy in Tanzania is not well documented and the renewable energy technology including biogas is still at an infant stages. So many efforts have been done by individuals of which, most of them have not been documented. The financial capital coupled with poor technology (Mwerangi, 2008) and lack of sustainable institutional framework for renewable energy developments hinders the development of biogas. This trend tallies with Uddin (1999) comment that lack of policy mechanisms, institutional development and financing exist as major barriers for Thailand

Another policy issues is lack of credits. A high proportion of the respondents in this study area indicated high cost and that there were no credit facilities in the area of study. There is also an issue of awareness and culture. A study by Mwakaje (2005) show that a large number of people who have not accessed biogas technology especially from the Muslim community have a perception that biogas is a dirty thing. However, being close to Lomwe Secondary School in Kilimanjaro Region, Tanzania and observing physically the functioning of biolatrine, many neighbour households including the Muslims were motivated to adopt the technology. The challenge was the amount of waste to feed the biodigestor and of course the cost to incur. Improving credit accessibility may have significant impact on biogas adoption in Rungwe district and Tanzania at large. Factors influencing socio-political and community acceptance are increasingly recognized as being important for understanding the apparent contradictions between general public support for renewable energy innovation and the difficult realization of specific projects (Wustenhagen et al., 2007).

Section 19 of the Energy Industry Act stipulates that the operators of gas distribution networks are obliged, taking into account conditions set out in section 17 for the network connection of LNG facilities, de-centralised generation and storage facilities, other transmission or gas distribution systems and direct pipelines, to determine minimum technical requirements for design and operation, and to publish them on the Internet.

The minimum technical requirements set out according to these sections shall ensure the interoperability of the grids and shall be justified objectively and not be discriminatory. Interoperability includes in particular the technical connection requirements and conditions for grid-compatible gas properties, including gas generated from biomass or other types of gas, as far as they are technically able to be injected into the gas supply grid or transported through this grid without compromising security (Energy Industry Act, 2005). For ensuring technical security section 49 applies: energy facilities shall be constructed and operated so that technical security is guaranteed. Thereby, subject to other legislation, generally accepted technical rules are to be observed. Compliance with the generally recognized technical rules shall be presumed if, in the case of plants for the generation, transmission and distribution of gas, the technical rules of the German Association of the Gas and Water Industry have been complied with.

Conditions for gas grid access are described in the Gas Network Access Ordinance (GasNZV, 2005) in part 11a "special arrangements for injecting biogas into the natural gas grid". The Gas Network Access Ordinance regulates the conditions under which the gas network operators are obliged to grant transportation customers access to the gas networks.

There are three major types of digesters that have been in use in developing countries: Chinese fixed dome digester, the Indian floating drum digester and the more recent tube digesters. These reactors are small in size (5-10 m3) and mostly used at household level to deliver the energy demand for household cooking and lighting. The advantages of these reactors are that they are inexpensive compared to sophisticated systems, can be built with locally available material, are easy to handle and do not have moving parts which are prone to failure. The working principle of these reactors is the same although there are substantial differences between them. The substrate enters through the inlet pipe into the digester tank where the substrate has an average retention time of 10-30 days. The biogas is collected above the slurry and leaves the tank through a gas pipe into the top cover. In the fixed dome digester, the top is made of concrete or bricks as the rest of the digester below ground. The floating cover type has steel cover floating on the slurry, which is above ground, whereas the rest of the digester is also below the ground. The digested slurry leaves the digester through an outlet pipe and is collected in outlet pit. However, these digesters have several limitations. Each of the digester type does not have facilities for mixing the slurry or for maintaining a certain temperature in the digester and controlling it. There are also no facilities to remove sand, stones and other non-digestible materials, which will over the years, accumulate and decrease the volume of the digester and hence will reduce its efficiency. The accumulation of inert and non-degradable material makes it necessary to stop the process from time to time and remove the materials, thereby increasing labour and maintenance cost of the technology.

There is also lack of adequate coordinating framework as one of the most important weakness of energy institutions in Africa. Lack of coordination among institutions and conflicting interests are obstacles to good penetration of biogas technology into the African market. Rationalising functions and building institutions around them will improve the situation (Davidson, 1992). Constant persuasion and active campaigns can help reduce institutional inertia and resistance to adoption of biogas technology. Most renewable energy technologies require long development periods and dedicated stakeholders are important for building up experiences and competencies. New technologies often need to be nurtured for over decades, before sufficient socio-technical momentum emerges. Alignment between the technical, economic, regulatory and social context can provide the basis for building up momentum, until the biogas technology is able to survive on its own. Many African countries have a National programme having a three-pronged focus: sanitation, rural energy, and organic fertilizer usage, aimed at promoting domestic and agricultural based plants and this will help in promoting and implementing biogas plants. There are also now many biogas service providers in many African countries that specialize in the construction of biogas plants. The major focus of the biogas service providers is on sanitation. The service providers have used the hygiene-promoting aspect of biogas plants to market the technology.

There is need for continuous improvement of the biogas technology because its implementation is intrinsically the exploitation of the technical advantages. In some instances biogas plants have not worked effectively because of lack of support, lack of repairs and poor design. Lack of knowledge about biogas technology is often cited as a reason for non-adoption of biogas in some countries in Africa. Where people have installed biogas reactors, problems arising from the bad quality of the installed units and the poor operations and maintenance capacity of users have led to poor performance and even abandonment of biogas digesters. In some instance, the demonstration effect has been one of failure and has served to deter rather than enhance biogas adoption. A survey in Kenya of about 21 existing plants in 1986 found only 8 out of 21 functional and 13 out of 21 not functional or never finished (Day et al., 1990). According to the authors, the major problems associated with existing biogas plants in Kenya include inadequate design and construction, poor maintenance, and poor social acceptance. The effect of individual economic status is also important to consider in the assessments of biogas technology. Ni and Nyns (1996) reported that most surveys have revealed that biogas is more accepted by upper and middle-income farmers. The obvious effect of the income of individuals is the ability of investment to install a digester system and above all to maintain it operational. The regular operation of a biogas plant is more difficult to achieve than its initial installation. The routine operation and maintenance of the digester system need much physical work that is usually laborious and messy, making the biogas benefits less attractive.

The following parameters were determined: total and soluble COD, pH, total solids, mineral solids, volatile solids, total suspended solids, mineral suspended solids, volatile suspended solids, total volatile fatty acids (TVFA), alkalinity and total phenolic compounds. All analyses were carried out according to the recommendations of the Standard Methods of American Public Health Association (APHA, 1989).

In each steady-state experiment, samples were collected and the above parameters analysed. The pH and gas volume were determined daily, whilst the remaining parameters were measured at least five times per week on five different samples taken on different days to ensure that representative data were obtained.

2. Results and discussion

2.1 Influence of substrate concentration and OLR on the COD removal efficiency and operational parameters

The anaerobic degradability studies were carried out using two different two-phase OMSWs with COD concentrations of 35 g COD/L (OMSW 1) and 150 g COD/L (OMSW 2). The experiments were performed using progressive influent substrate concentrations, those corresponding to the OMSW 1 being the first ones and those corresponding to the OMSW 2 carried out at the end of the study.

Tables 2 and 3 summarize the steady-state operating results including HRT, OLR, methane production rates (rcm), total and soluble CODs, VS, TVFA, alkalinity and TVFA/alkalinity ratio for the OMSW 1 and OMSW 2, respectively (Borja et al., 2002).

OLR (g COD/(L d))

Fig. 1. Variation of the percentage of COD removed with the OLR for the two OMSWs used (■: OMSW 1; •: OMSW 2).

Values are the averages of 5 determinations taken over 5 days after the steady-state conditions had been reached. The differences between the observed values were less than 3 % in all cases. (* rCH4: methane production rates)

Table 2. Steady-state results under different experimental conditions for the OMSW 1 with a COD of 35 g/L.

Table 3. Steady-state results under different experimental conditions for the OMSW 2 with a COD of 150 g/L.

As can be seen in Figure 1 the percentage of COD removed decreased with increased OLR for the two influent substrate concentrations studied. The percentage of COD removal decreased from 93.3% to 83.2% when OLR increased from 0.86 to 4.14 g COD/(L d) for the most diluted substrate (OMSW 1). For the most concentrated influent (OMSW 2) OLRs were varied from 3.00 to 15.03 g COD/ (L d) and COD removal efficiencies higher than 88% were obtained at an OLR of 12.02 g COD/ (L d). Even under a higher OLR of 15.03 g COD/(L d), corresponding to an HRT of 10 days, COD removal was 82.9%.

The total effluent CODs of the anaerobic reactor increased with increased OLR for the two influent substrate concentrations studied, as summarized in Tables 2 and 3. Such an increase in the effluent COD was paralleled by a similar increase in the effluent total volatile fatty acids (TVFA). This seems to indicate that, at higher OLR, the effluent total COD and mainly soluble COD is largely composed of the unused volatile acids produced in the reactor.

Given that the buffering capacity of the experimental system was found to be at favourable levels with excessive total alkalinity present at virtually all loadings, the efficiency of the process and the rate of methanogenesis was not very affected. The experimental data obtained in this work indicate that a total alkalinity of about 1.7 g/L as CaCO3 is sufficient to prevent the pH from dropping to below 7.0 at an OLR of 9.05 g COD/(L d) for the most concentrated substrate used (OMSW 2).

The pH in the reactor was always higher that 7.0 for all the HRTs and OLRs studied corresponding to the most diluted OMSW studied. In addition, pH values equal or higher than 6.9 were observed for OLRs lower than 12.02 g COD/(L d) and HRTs higher than 12.5 d when the most concentrated influent was processed, with pH of 7.2 as a maximum value achieved. This high stability can be attributed to carbonate/bicarbonate buffering. This is produced by the generation of CO2 in the digestion process which is not completely removed from the reactor as gas. Buffering in anaerobic digestion is normally due to bicarbonate, as carbonate is, generally, negligible if compared to the bicarbonate (carbonate/bicarbonate ratio is equal to 0.01 for pH 8.2) (Speece, 1983). The buffering guards against possible acidification of the reactor giving a pH of the same order as the optimal for methanogenic bacteria (Wheatley, 1990).

The TVFA/ Alkalinity ratio can be used as a measure of process stability (Wheatley, 1990): when this ratio is less than 0.3-0.4 the process is considered to be operating favourably without acidification risk. As was observed in Tables 2 and 3 the ratio values were lower than the suggested limit value for OLRs lower than 9.05 g COD/ (L d) in the experiments corresponding to the highest influent substrate concentrations studied (OMSW 2). For this substrate, between HRTs of 50.0 and 16.6 days, the TVFA/Alkalinity ratio was always lower than the above-mentioned failure limit and the TVFA values were always lower than 1,08 g/L (as acetic acid). However, at a HRT of 10.0 days, a considerable increase of the TVFA/ Alkalinity ratio until a value of 0.95 was observed in the reactor, which was mainly due to a considerable increase in the TVFA concentration (1.57 g/L as acetic acid) with simultaneous decrease in alkalinity (1.32 g/L, as CaCO3).

Gas mixing occurs when streams of different gas qualities are united to a single stream. In pipeline systems this means that different gas sources meet in a T-type or Y-type of pipeline. A simple example of two streams of volume (V) with two calorific values (H) is given below (see figure 3). The resultant value depends on the product of volumes or flow (Q) and the amount of each calorific value according to:

V1*H1 + V2 * H2

Hi,2= v:+v

H Zi(V, * Hi) Zi(Qi * Hi)

Hs ZiVi ZiQi

H1,2 , Hs = resulting calorific value V1 , V2 = volume of stream #1, #2 H1 , H2 = calorific value of stream #1, #2 Qi = flow of stream i ( = dV/dt)

The mixing of the flows and thus the resulting value is not perfect in the vicinity of the mixing point. This is due to the pipe dimensions which may be large or different and the flow characteristic: laminar or turbulent. The mixing process is better and faster if the flow is turbulent. If the flow is laminar mixing may take a long way and time as even a layering effect may occur. In order to speed up mixing in such cases static mixer pipes, which have small obstacles inside to provoke little turbulence, will be built in the line.

Process Network Synthesis (PNS) was used as a tool for economic decisions to get an optimal technology solution for biogas production with particular consideration of feedstock which is not in competition with food or feed production. Ecological evaluation of the resulting optimal PNS solution through footprint calculation was based on the Sustainable Process Index (SPI). These calculations are based on the data, which was gathered in three field tests, and the practical experiences, that were gained in the growing and harvesting of intercrops on more than 50 hectares of arable land. Besides the determination of dry matter yields of different kinds of intercrops and intercrop mixtures the effects on ground water, soil and nutrient management were investigated in the field experiments with time-domain-reflectometry, soil water and mineral nitrogen content measurement. Additionally, the potential biogas production was measured by means of biogas fermenter lab scale experiments.

Krystyna Seifert, Roman Zagrodnik, Mikofaj Stodolny and Marek Laniecki

Faculty of Chemistry. A. Mickiewicz University, Poznan,

Poland

1. Introduction

Constantly increasing demand for energy has created extensive consumption of fossil fuels and the thread of their exhaustion has became a serious concern. At the same time it has been an inspiration for search for new, environmental friendly energy sources, out of which hydrogen seems to be one of the most promising. It is easily accessible, harmless, renewable and effective (high heat of combustion) energy carrier (Ball, 2009). Within the numerous methods of hydrogen production, biological methods (so called "green technology") have gained substantial importance. These methods consist of fermentative decomposition of organic substances, biophotolysis of water by algae and cyanobacteria, decomposition of organic compounds by photosynthetic bacteria and two-stage hybrid systems with fermentative and photosynthetic bacteria (Waligorska, 2006, Koku, 2002, Su,

2009) .

Photofermentation represents the process where heterotrophic bacteria in the presence of light decompose organic substances and produce hydrogen and CO2. It has been already shown that purple non-sulphur bacteria Rhodobacter sphaeroides act as efficient biocatalyst in the process of hydrogen production from the wastes coming from breweries and dairy industry. Brewery wastes carry high concentration of organic compounds (COD 0.8- 2.5kg/hl of beer) and represent high volumes (1.3-1.8 hl/hl of beer). The amount of waste during beer production is enormous and equals the amount of water applied for production diminished with water present in beer (usually 3-4 hl of waste per 1 hl of beer). A chemical composition of waste strongly depends on the kind of beer produced and fermentation degree. Such waste can contain aminoacids, proteins, organic acids, sugers, alcohols, as well as vitamins of the B group. (Wojnowska-Baryla, 2002, Srikanth, 2009, Cui, 2009) As far as dairy wastes are concerned, they contain an average of 5-50 g O2 /l. These wastes are mainly composed of remaining of milk, fats and whey. Typical Polish dairy produces 450-600 m3 of wastes per day, half of which goes directly to rivers, lakes and to the ground. These wastes easily undergo fermentation, which causes acidification, intense oxygen consumption, bottom sedimentation and growth of fungi. The organics in both dairy and brewery wastes represent the efficient substrate for Rhodobacter sphaeroides and seem to be a promising source for energy production. The efficient use of food wastes in hydrogen generation with

simultaneous degradation of these laborious wastes seems to be a very environmentally friendly solution. The US Department of Energy Hydrogen Program in United States estimates that contribution of hydrogen to total energy market will be 8-10% by 2025 (National Hydrogen Energy Roapmap, 2002). It is predicted that hydrogen will become the main carrier of energy in the near future due to environmental and universal applications reasons. It is clean, highly energetic energy carrier (142.35 kJ/ g), with almost tripled gravimetric energy density compared to ordinary hydrocarbons. Although the described method is relatively simple and cheap it still requires optimization due to the obtained unsatisfied yields.

The quality of a digestate is determined by the digestion process used and the composition of ingestates therefore the agricultural use and efficacy of the nascent materials could be different. Nevertheless, some common rules can be found in the course of the digestion process which allow us to evaluate the results of a digestion process.

1.1 pH of digestate

Generally, the pH of digestate is alkaline (Table 1). Increases in pH values in the course of the AD may have been caused by the formation of (NH4)2CC>3 (Georgacakis et al., 1992).

The alkaline pH of digestate is a useful property because of the worldwide problem of soil acidification.

M. Samer

Cairo University, Faculty of Agriculture, Department of Agricultural Engineering,

Egypt;

1. Introduction

The chapter concerns with the constructions of the commercial biogas plants as well as the small and household units. Furthermore, the chapter aims at providing a clear description of the structures and constructions of the anaerobic digesters and the used building materials. Ultimately, the chapter answers an important question: how to build a commercial biogas plant and a household unit, and what are the construction steps?

2. Chapter description and contents overview

The chapter describes the construction steps and operation of biogas plant, which include:

a. Planning the biogas plant layout and designing the digesters, where the rules of thumb for planning the layout of a commercial biogas plant are elucidated and a methodology for specifying the dimensions of both digester(s) and residue storage tank(s) is illustrated, and they are: internal and external diameters of the tanks, wall thickness of the tank, height…etc.

b. Undertaking the project, i. e. carrying out the excavation (digging) works, preparation of the bottom plate of the digester, integrating the heating tubes, building the fermenter, installing the insulation, and technology installation.

c. Running the biogas plant including the mechanization of the biogas plant such as: solids feeder, gas processing unit, mixing technology. etc.

d. System control, i. e. how the individual facility components are monitored by computer technology even from afar as well as on-site using a computer system.

3. Overview

3.1 Components of the biogas unit

The components of a biogas unit are:

1. Reception tank

2. Digester or fermenter

3. Gas holder

4. Overflow tank

All experiments were done in 20 L anaerobic sequencing batch reactor followed by 10 L fixed bed reactor with gas outlet (Fig. 1). All the reactors were seeded with anaerobic acclimatized banana stem sludge. The anaerobic digestion system was varied at different reaction temperatures using water bath. The HRT and OLR for this system were 9 d and 4 g TS/l. d respectively. The process was conducted at ambient temperature for the first stage and thermophilic temperature for the second stage. Daily withdrawal of an appropriate volume from the reactor corresponding to the determined HRT or OLR was done by a draw-and-fill method. Biogas evolved from the fixed bed reactor was measured and collected in a gas holder by water displacement. Samples were collected and analyzed for performance evaluation.

1.2 Two-stages biogas production system description

1.2.1 Bioreactor description

This system consists of 4 components which are hydrolysis reactor, liquid-solid separator, storage tank and methanogenesis reactor. The dimensions of those four components are listed in Table 1. Detailed of each component are as follows: