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:

Kenya has population of 40.6 million people, of which 77.8% reside in the rural areas (United Nations, 2007). Kenya similarly has a programme for promoting domestic biogas development, in which the Kenya National Federation of Agricultural Producer is the implementing agency[10]. The programme targets to install 8000 domestic biogas plants of between 6m3 — 12 m3 capacity by 2013, and prioritizes the high agricultural potential regions. A number of demonstration plants have currently been constructed and launched.

1.1.5 Ethiopia

Ethiopia has a population of 89.6 million people, of which 82.4% live in the rural areas (United Nations, 2007). Through the Ethiopia Rural Energy Development and Promotion Centre (EREDPC) the National Biogas Program (NBP) was also launched. The aim of the programme is to establish 14000 biogas plants between 2008 and 2012, in four regions of Ethiopia (EREDPC, 2008). The NBP utilises cattle manure as the feedstock for biogas production (EREDPC, 2008). In 2009, some households had already started experiencing the benefits of the project such as: use of clean cooking fuel; income savings made in terms of time and money to search for fuel and purchase other traditional fuels (wood, charcoal and kerosene) respectively; and income generation from the sale of biogas to the neighbouring towns (Hivos, 2009b).

There are only a limited number of studies found specifically focused on the effects of mixing on the treatment efficiency and biogas production using various types of agro­industrial wastewater including palm oil mill effluent, wash water of animal waste, lixiviate of municipal waste and fruit and vegetable wastes (Kaparaju et al., 2007; Sulaiman et al., 2009). Adequate mixing is very important in order to achieve successful anaerobic treatment of organic rich wastewater. In another word, it enhances the anaerobic process rate by preventing stratification of substrate, preventing the formation of surface crust, ensuring the remaining of solid particles in suspension, transferring heat throughout the digester, reducing particle size during the digestion process and releasing the biogas from the digester content (Kaparaju et al., 2007; Sulaiman et al., 2009).

Prior to 1950s, anaerobic digesters treating sewage sludge were not equipped with mechanical mixing and thus caused the formation of scum layer at the surface (Fannin, 1987). To overcome this problem, mixing was employed to disrupt scum formation and enhance contact between microorganisms and substrates. It has been reported that the acetate-forming bacteria and methane-forming bacteria are required to be in close contact to achieve continuous degradation of organic materials (Tabatabaei et al., 2011). In addition to the mentioned advantages, mixing also helps to eliminate thermal stratification inside the digesters, maintain digester sludge chemical and physical uniformity, rapid dispersion of metabolic products and toxic materials and prevent deposition of grit (Gerardi, 2003).

2.8 Features of available simulation programs, short overview

2.9 IT-systems requirements

The simulation programs can be executed already on a powerful PC; for big networks which have more than 100,000 pipes a powerful server type of computer with fast and large storage capacity is recommended. Computing time for static simulation ranges from seconds to few minutes (10,000 pipes about 20 s, 200,000 pipes about 150 s); dynamic simulations will take time according to the length of the period to be simulated.

Marta Kisielewska

University of Warmia and Mazury in Olsztyn,

Poland

1. Introduction

Cheese whey is a by-product generated during cheese manufacturing. The disposal of whey is problematic because of its high COD (Chemical Oxygen Demand) (about 50,000 mg L-1 — 80,000 mg L-1), low solids content (5% DM), low bicarbonate alkalinity and its tendency to get acidified very rapidly (Akta§ et al., 2006; Gonzalez Siso, 1996; Venetsaneas et al., 2009). In 2008, Poland produced almost 1123 thousand tonnes of whey (Agricultural Market Agency [ARR], 2009). Traditionally, cheese whey has been used to feed animals, but redistribution of whey to farmers is very expensive. Moreover, lactose intolerance of farm animals also limits the use of whey in feeding (de Glutz, 2009). Since large quantities of whey are produced (about 9 kg of whey in the production of 1 kg cheese) (Zafar & Owais, 2006), there is an increasing concern as how it can be efficiently and cost-efficiently processed without adversely effecting the environment.

Proteins from cheese whey have a high nutritional value. For this reason cheese manufacturers have explored the possibilities of valorisation of whey. They recover proteins by membrane ultrafiltration (UF) process (Silveira et al., 2005). This method of separation has the main advantage — in does not denature proteins, so they save their original nutritional value (de Glutz, 2009). The residual protein-free material is called whey permeate. Permeate streams have very high COD value (about 50,000 — 70,000 mg L-1) (own studies), which represents an important environmental problem, similarly to whey. The chemical and biological instability of the UF whey permeate resulting in difficulties and high cost in its transport and storage. Proper management of this liquid is important due to strict legislation and economic reasons. Because of those there is a strong need to efficiently treat UF whey permeate.

UF whey permeate is composed mainly of lactose. Lactose concentration is about 50,000 mg L-1, so more than 90% of COD is due to lactose (de Glutz, 2009). Moreover, valuable compounds (proteins, vitamins) can be found in its composition. Since UF whey permeate contains significant quantities of lactose, the way to use this waste product could be as a substrate for fermentation to produce biofuels.

potatoes, wheat, followed by distillation and drying. The production of bioethanol from corn or sugarcane is a mature technology. For example, in Brazil there are 448 bioethanol production units installed and according to a report of the Brazilian Ministry of Mines and Energy, ethanol production was 25 billion liters in 2008 (Soccol et al., 2010). Biogas is produced by anaerobic digestion of organic materials by anaerobic microorganisms. It can be used to produce thermal energy (heating), electricity, or if compressed — it can be used in vehicles. The current operation of biogas plants is relatively large in Europe, especially in Germany. According to Poschl et al. (2010), the estimated biogas production potential in Germany is 417 PJ per year and 80% of which derived from agricultural resources, including farm waste (96.5 PJ per year), crop residues (13.7 PJ per year), and dedicated energy crops (236 PJ per year).

More recently, hydrogen is playing more important role as a fuel used for heating, lighting and as a motor fuel. The main advantage of hydrogen as a future alternative energy carrier is the absence of polluting emissions when combusted, results in pure water. Today, most hydrogen gas is obtained from fossil fuels which generate greenhouse gas (GHG) that contribute to global warming. The biological hydrogen production is an attractive method because it can be produced from renewable raw materials such as organic wastes. Wastewater from food processing industries show great potential for economical production of hydrogen (Van Ginkel et al., 2005), but today no strategies for industrial-scale productions have been found.

The ability to produce biofuels from low-cost biomass such as agricultural waste and by­products (including for example crop residues, sugar cane waste, wood, grass and wastewater from food processing industries) will be the key to making them competitive with other fuels, for example gasoline. Only biofuels derived from waste products show low environmental effects, such as reduction of GHG emission, small land demand and damage the environment. As a result, since UF whey permeate disposal represent a real problem for the dairy industry, biofuels production offers an ideal alternative to its valorization (de Glutz, 2009; Silveira et al., 2005).

The objectives of this work were to study the applicability of fermentation processes for the production of biogas (methane), fuel bioethanol and biohydrogen in Upflow Anaerobic Sludge Blanket (UASB) reactors fed with raw UF whey permeate. To optimize and enhance the biofuels production, the different processes were used (ultrasonic stimulation of microbial cells, anaerobic steel corrosion process) and the different operational parameters (pH, hydraulic retention times — HRTs regimes, organic loading rates — OLRs) were applied.

1.2 The physical components of biogas residue

The determination of physical components of biogas residue was shown in table2-1.

Table 2-1 showed that biogas residue was composed of three parts, fibre proportion was maximum, mineral proportion was minimum. There were mainly plastic, hair and grass seeds in the non-mineral impurities

1.2.1 Each component fibre and mineral content of biogas residue

Table 2-2 showed that fibre quality percentage of 0.25 mm to 0.5 mm was maximum; fibre quality percentage of more than 0.5 mm was min; minerals quality percentage of 0.5 to 1 mm was maximum, minerals quality percentage of more than 5 mm was min.

1.2.2 Fibre morphology

Fig. 2-1 showed the fibre morphology of each group.

Beside the fertilizer or amendment properties of digestate, nowadays there are some other ways to utilize it. These new methods are very creative and make the possibility of proper utilization of digestates with different quality.

A new promising alternative of the digestate utilization is its use as solid fuel after drying. Kratzeisen et al. (2010) used liquid digestate originated from silage maize co-digestion with different field crops and animal residues. After drying the digestate, the water content of pellets made was 9.2-9.9%. Their mechanical durability fulfilled the requirements of standards for pellets. Moreover, the calorific value of these pellets was similar to the calorific value of wood. Therefore digestate fuel pellet seems to be a good alternative fuel for wood.

Another interesting possibility of digestate utilization is the using of digestate effluent to replace freshwater and nutrients for bioethanol production. Gao & Li (2011) found that ethanol production was enhanced with digestate effluent by as much as 18% comparing to the freshwater utilization.

Digestate can be separated to liquid and solid fraction. Liquid fraction is suitable for irrigation and it has high N and K content. Solid fraction contains a great amount of volatile solid and P (Liedl, et al., 2006) and — by its fertilizer effect — has also high biogas and methane potential, therefore it could be used as a co-ferment for anaerobic digestion (Balsari et al., 2009)

2. Conclusion

The use of anaerobic digestion for treatment of solid and liquid organic wastes has vastly increased world-wide. The by-product of this process is the digestate, a liquid or solid material with high nutrient and organic matter content. These properties of the digestate make possible to use it as plant nutrients and to characterize it as a fertilizer. On the other hand, a biomass, reach in recalcitrant molecules is characterized by a high biological stability degree which is suitable for soil improving. The utilization of digestate as fertilizer provides economic and environmental benefits because of its higher stabile organic matter content, the hygienization effect of anaerobic digestion process and the reduced quantity of the artificial fertilizers needs for plant production. Moreover, the alkaline pH of digestate could contribute to the decrease of soil acidification, which is a serious problem of the world. Using digestate in place of artificial fertilizers could contribute to maintain the fertility of soil.

As the results show, the digestate application in solid or liquid form could result significant improvement of the quantity and quality of foods through the even nutrient supply harmonizing with the necessity of plants and through its microelement content in the available forms for plants. In this way, digestate application in agriculture could contribute to the healthy life of humans.

Microbiological activity of soil could be increased by application of digestate which is also an important condition of soil fertility.

Beyond these "classical" application possibilities of digestate, there are new promising alternatives for its utilization which means more opportunities to use this valuable matter for making better our environment and our life.

3. Acknowledgment

Our thanks to Dr. Judit Dobranszki at the University of Debrecen, Research Institute of Nyiregyhaza and Prof. Gyorgy Fuleky at the Szent Istvan University, Department of Soil Sciences and Agrochemistry for their enthusiastic checking of the English and for their valuable comments on improvements of the manuscript.