1. Introduction

The EU-28 2016 energy use was 1147 million tonnes of oil equivalent (MTOE), 17% of which was from renewable energy sources; the proportion of renewable fuels was 7.1% [1]. The proportion of renewables was 9.5% in 2006, so renewable energies have cca. 8% growth per year in average during the last decade in the process of energy production [2].

However, the average levelized cost of electricity (LCOE) of fuel generation and biogas electrical power generation is still much higher than the reference [3], and therefore without financial support, it is not competitive with oil and other highly renewable electricity generation technologies (solar panels, geothermal energy, hydropower, solid-fired biomass power plants).

Biogas production is also a remarkable process in terms of the environment and energy production, but its efficiency, with new raw materials, technologies and markets, can be significantly increased. Due to the capital requirements and the uncertainty of innovative solutions, the establishment of biogas plants and their

operation and the research conducted in this area are significantly supported by all EU member states. The dominant product of current biogas plants is green electricity, which is supported by competent power suppliers at a subsidised price and is acquired as a compulsory purchase by the relevant electricity suppliers, details of which are given for the EU-27, the EFTA countries and countries waiting to join in [4]. The feeding of biomethane purified with biogas to the natural gas pipeline is regulated by stringent standards in the EU member states, according to Szunyog [5]. However, gas with a lower methane content than natural gas may also be utilised as a propellant, although its compression and transport costs are larger, and the range is smaller than with compressed natural gas (CNG) [6].

Natural gas engine technology is already well established, and millions of vehi-

The spread of biogas plants in the EU has been very rapid over the past decade: rising from 6227 to 17,662 between 2009 and 2013. Growth in farms was primarily significant (12,496 plants), the number of sewage plants was 2838 and the remainder were landfill waste plants. The number of plants has stagnated since 2015, but the installed electric capacity has increased further; currently it is 9985 MW [13]. Anaerobic digestion is a key technology for the treatment of large volumes of

The energy significance of biogas is underlined by the fact that in the EU, the amount of biogas produced in 2015 reached 18.4 billion normal cubic metre (Nm<sup>3</sup>

replacing 4% of natural gas consumption [15]. The amount of biomethane fed to the natural gas pipeline reached 1.5 Mrd m<sup>3</sup> (mainly the Netherlands), while the amount of biomethane used as propellant is considerably less, at 160 M m<sup>3</sup>

; Norway, 10 million m<sup>3</sup>

; Germany, 35 million m<sup>3</sup>

) [16]. However, the use of purified biogas for transport in some countries is rapidly expanding: over 30 cities in Sweden power their municipal buses with biogas, which

There are 247 biomethane plants around the world and around 80 in the EU. Their technology and the biomethane produced are characterised by the data in

Regarding environmental performance, methane loss is of great importance, as methane is a greenhouse gas 21 times stronger than CO2 [19]. As clarified by Beil and Beyrich [20], pressurised water scrubbing (PWS) is one of the best solutions in

content (%)

),

; Iceland,

Specific operating costs (USD/Nm<sup>3</sup> biomethane)

cles using natural gas are in operation worldwide and suitable for using CBM. While at the turn of the millennium, a million registered vehicles around the world were powered by CNG; by 2015 this figure had already increased to 22.3 million, an average annual increase of 22%, well above the growth in the total fleet of cars. Typically, most of the gas-fuelled vehicles (Iran, 4 million; Pakistan, 3.7 million; Argentina, 2.5 million; India, 1.8 million) [11] are found in low-income countries with a high population density. In the EU, 3345 refuelling stations provide for the operation of about 1.3 million gas-powered vehicles with an annual gas consumption of around 5 billion cubic metres. For the operation and further spread of this existing transport infrastructure, CBM could make a significant

The Possible Role of Large-Scale Sewage Plants in Local Transport

DOI: http://dx.doi.org/10.5772/intechopen.86699

contribution [12].

biowaste [14].

2 million m<sup>3</sup>

Table 1.

\*Hydrolysis purification.

Table 1.

139

Source: Own construction based on Yang et al. [18].

Biogas cleaning technology and the cost of cleaning.

(Sweden, 113 million m<sup>3</sup>

; Finland, 0.2 million m<sup>3</sup>

is also used by taxis and sanitation companies [17].

terms of efficiency and environmental performance.

Cleaning technology Number of plants Biomethane CH4

Water wash 107 96.1 0.18 Pressure change adsorption 55 95.8 0.34 Chemical (amino) absorption 53 94.6 0.23/0.38\* Membrane 22 90.3 0.16/0.30\* Genosorb© 12 96 n.a. Cryogen 1 88 0.59

Conversion of biogas will always increase investment and operational costs, and the energy efficiency of the process will be reduced, but it will produce more valuable, versatile and marketable main products (electricity, biomethane). According to Hakawatia et al. [7], on the basis of 49 different biogas transformation technology studies, the overall efficiency of the process ranges from 16 to 83% in the case of direct burning of biogas and 8 to 54% for cogeneration (for electricity and waste heat coupled production), while when producing biomethane for fuel, it varied from 4 to 18%. If the electricity generated by cogeneration is used in electric vehicles, the efficiency of propellant use can be increased to 33%.

Most of the wastewater plants produce electricity and waste heat from biogas. The reason for this is clear from direct heat utilisation: it is almost impossible to use biogas exclusively for heating purposes in larger-sized plants and during summer time. On a large scale, however, the summer utilisation of waste heat generated during the cogeneration process is also problematic. In order to avoid the problems of heat utilisation, in the case of large plants, biomethane can be considered as an alternative to biogas purification and the utilisation of by-product carbon dioxide in the algae sewage system. In our chapter, we would like to point out that the inclusion of biogas from wastewater treatment plants in large cities in vehicles involved in local transport (buses, taxis, public utility vehicles) can also be an environmentally and economically promising alternative, of which we can already find many well-functioning examples.
