**7. Biogas applications**

Biogas generation serves three important functions: waste removal, environmental management, and energy production [12]. The first and most direct use of biogas is for heating and domestic purposes [184]. Biogas is an excellent fuel with a numerous application [62]. Biogas that is purified and enriched in methane can be used for household applications, automobile fuel (liquefied), or electricity generation [185, 186]. The biogas is mostly utilized as a combined heat and power (CHP) application in the overall world; and apart from it, it can be used in three sides such as fuels for cars, steam generation, and electric power. Biogas obtained from renewable organic waste is counted as an alternative energy for nonrenewable fuels due to its broad applications in fuel and transportation sector [62, 104, 187].

In general, Waste-to-Energy (WtE) technologies can be defined as any waste treatment processes that create energy from a waste source in any forms of energy carrier, i.e., electricity, heat, or transportation fuels [188]. Depending on a statement by World Energy Council, restricted landfilling capacities, rise in the quantity of produced waste, high costs of energy, and rising concerns of environmental issues are the summarized major factors for the growth in WtE market in the past decades. In 2013, the international WtE market encountered a growth of 5.5% and reached a value of 25.32 billion USD with respect to its previous year [50, 188]. Biogas is a flexible energy transporter, appropriate for various applications. One of the simplest applications of biogas is the immediate utilization for lighting, and cooking, but in a lot of countries biogas is currently utilized for combining heat and power generation (CHP) or it is upgraded and fed into natural gas grids, utilized in fuel cells or as car fuel [189]. Biogas is appropriate for production of electricity in combination with heat recovery. Normally, the gas is combusted in motors with internal combustion connected to turbine. The discharged heat (being about 60% of the used energy) is utilized for heating purposes for household requirements or maintenance of the anaerobic reactor. This method is broadly used for the treatment of activated sludge, debris generated from municipal wastewater treatment plants [184, 190, 191]. Electric power generation by gas turbines can be used by biogas as a fuel, hence substituting the natural gas for small-scale applications [184]. There is a large demand to make biogas transportable. This can be simply done only after taking out impurities such as CO2, H2S, and water vapor by compressing and filling the cylinders in it after scrubbing and drying processes [185]. Elimination of carbon dioxide from the flue gas assists to get fuel of higher calorific value as well as to remove the GHG [185, 192]. Biogas is an encouraging renewable source of energy. It can be immediately transformed into electricity, e.g., in a fuel cell, or burnt, discharging

### *Recent Advances of Biogas Production and Future Perspective DOI: http://dx.doi.org/10.5772/intechopen.93231*

heat at high temperature, or burnt in a CHP for the simultaneous generation of heat and power, or fed into the natural gas network for energy rescuing purposes or it can used as fuel for cars, being sold by gas stations. Mostly, the biogas should be transported over long distances and must be purified before further utilization [18]. Biogas systems turn the cost of waste management into a revenue opportunity for farms, dairies, and industries. Converting waste into electricity, heat, or car fuel provides a renewable source of energy that can reduce dependence on foreign oil imports [189]. Biogas is mostly used in factory boilers and in engine generator sets to produce electricity and heat. In those cases, where an internal combustion engine is fuelled with biogas to produce electricity, the electricity can either be used by the facility itself or transferred to a local or national power grid [12]. The most profitable way to use biogas may be to convert it into natural gas. In reality, biogas can be utilized in all applications created for natural gas. The major difference between the two fuels is that, further to methane, natural gas consists of a variety of other hydrocarbons, like propane, butane, and ethane, which provide it a higher calorific value than pure methane. Biogas is normally burned in internal combustion motors to produce electric power. An electrical conversion efficiency of up to 25% can be obtained via small-scale internal combustion motors, with a rated capacity of less than 200 W as well as much higher electrical conversion efficiencies, of 30–35% can be provided through larger internal combustion motors (up to 1.5 MW). When biogas is utilized to generate electric power, there is the extra potential for heating water from the engine's exhaust and cooling systems. Combining hot water generation with electric power production can provide total conversion efficiency as high as 65–85%. An encouraging near-future application for electric power production is the utilization of gas turbines. Combined-cycle power stations are made up of waste heat recovery boilers, gas turbines, and steam turbines that function together to generate electric power in the larger-scale systems. Advanced gas turbine plants tend to be small, environment friendly, greatly efficient, and visually unobtrusive. Units as small as 200 kW are not uncommon, but only those greater than 800 kW have electrical conversion efficiencies that equal or surpass an internal combustion engine-based system. Gas turbines allow a greater fraction of waste heat to be recovered as steam, a critical commodity for many industries, so overall efficiency levels for gas turbines can be up to 75%. Recently, biogas applications are employed as fuel in fuel cells and as fuel for micro-CHP (combined heat and power). When connected with an organic Rankine cycle (ORC) turbine, a biogas-powered CHP can raise electrical efficiency by 8–10%, making total efficiency rate of 45–48% more than reasonable [12, 184]. Another very attractive application of biogas for electricity production is its use in fuel cells. The specialized cells for these purposes are described briefly by [193]. Identical efficiency rates are obviously being accomplished with biogas fuel cell technique. Sweden-based Acumentrics Corporation, for instance, has registered improved performances with its 5000 W fuel cells, known as solid oxide fuel cell (SOFC) systems, which work on biogas rather than hydrogen, which is difficult to handle, high cost, and difficult to store [12]. The utilization of biogas as a fuel for civil transport and road cars in place of natural gas is already widen in United States and Western Europe [194]. There are a lot of automobiles in Sweden turning on biogas in the urban public transport [184, 195]. Biogas is currently used in many developing countries as an alternative and renewable source of energy for wide spread range of applications. In contemporary times, biogas has been used most extensively in India and China. The Biogas Association in Germany, the world's largest producer country, included the three functions in its recent summary of what it called the national benefits of biogas production: 650 MW of installed electrical capacity comes from biogas, a reduction of 4 million tons per year of CO2 emissions, revenues of \$500 million for biogas farmers from electricity

sales annually, and use by the AD process of biomass material that would otherwise end up in landfills. Economic production of biogas can be economically achieved for both large- and small-scale applications. Hence, it can be designed to fit into rural, urban, as well as regional and nationwide energy needs making it a versatile source of energy [12, 96, 107]. All over the world, Europe has registered the highest growth of biogas utilization with a notable 18% raise registered between 2006 and 2007. Sweden and Germany have registered the highest growth levels with Germany leading to brag over 4000 biogas plants, most of them are established on farms for electric power and heat co-generation [21, 96].

In Sweden, there is currently great interest in the biogas process, since it can stabilize and reduce various types of organic waste while producing renewable and environmentally friendly energy in the form of biogas. There is also increasing interest in both the production of biogas from municipal sewage treatment plants and on-farm biogas production within agriculture [196]. Biogas is also burned in boilers to produce hot water and steam in a variety of settings, including hotels, warehouses, factories, schools, prisons, and other public buildings. The forestproduct segment is perhaps the largest user of biomass (combustion) energy in the industrial sector. In addition, in many countries, biogas is viewed as an environmentally attractive alternative to diesel and petrol for operating busses and other local transport vehicles [12]. The food and drinks industries are the largest users of AD for wastewater pretreatment. In 2006, 3400 GW of biogas power was generated in Germany, equivalent to 0.6% of the country's total energy consumption, reducing carbon dioxide emissions by 2.5 million tons. Countries such as Sweden is considered pioneered in the utilization of upgrading biogas as a light duty car fuel, and the use of biogas in the country has already exceeded natural gas [12, 197]. Identical attempts are also being made in Germany which presently turns on roughly 5000 anaerobic reactors for generation of bioenergy [198]. In the UK, fears over the utilization of biogas as fuel stem from an insufficiency of quality standards and infrastructure, as well as contest with other utilizes of biogas [199, 200]. At the moment, close to 50 biogas plants, mainly small, farm-scale ones, are in operation in Austria, Currently, around 25 biogas plants operate in Denmark, with capacities ranging from 50 to 500 tons of biomass feedstock per day. The resulting biogas is mainly used in heat and power generation applications, while the digested biomass is redistributed to farms as fertilizer. Swedish company Svensk Biogas has developed a passenger train that runs exclusively on biogas. The train has a range of 600 km and can attain speeds of 130 kph. There are also up to 100 municipal busses running on biogas. The Swedish agricultural sector is also increasingly using the residues from the anaerobic digestion of crops and clean organic waste in order to return nutrients to the soil and reduce its dependence on mineral fertilizers. Biogas can also be used to generate electricity alone or with heat (co-generation). Biogas can also be used, like pure methane, as a fuel for motor vehicles [12, 201]. Biogas can be considered as alternative green energy carrier for harnessing electricity, heat, and as a transport fuel [62, 202]. Biogas is a renewable source of energy that can be used as a substitute for natural gas or liquefied petroleum gas. Biogas is a clean, efficient, and renewable green source of energy, which can be used as a substitute for other fuels in order to save energy in rural areas [86, 203, 204]. A series of zero-waste technologies are presented. They are similar to the "five zeros" of the Olympic logo which are zero waste in the product life cycle, zero emissions, zero waste in activities, zero use of toxics, and zero resource waste. This design, firstly invented by Lakhal and H'Mida [205] was titled the Olympic Green Chain model. Lately, Khan and Islam [206] suggested a method for zero-waste (mass) utilization for an ideal urban setting, involving processing and regeneration of gas, liquid, and solid. In this process, kitchen sewage waste and waste are used for diverse purposes, involving generation

of biogas, water heating from flue gas, good fertilizer for agricultural production and desalination. The carbon dioxide produced from biogas burning is used for the desalination plant. This process gets zero-waste in mass utilization. The technology development in this line has no negative impact on global warming. It is estimated that biogas usage in the world will be doubled in the coming years, increasing from 14.5 GW in 2012 to 29.5 GW in 2022 [37, 189, 207].
