2. The transport sector, CNG and the significance of compressed biomethane (CBM)

Traffic is one of the most significant sectors in the EU-28, with around €<sup>651</sup> billion in gross value added a year at basic prices (5% of total), with 11.2 million employees (5.2% of total), 6602 billion passenger km (on average around 12,962 km per person, of this 8.2% with buses and coaches) and about 1183 million tonnes of CO2 equivalent (30.7% of total). Private households in the EU-28 spent EUR 230 billion on transport services (e.g. bus, train, plane tickets). It should be highlighted that changing consumer attitudes from fuel to more environment-friendly way of transport may help to promote the spreading of sludge-based transport fuels, too [8].

Globally, in 2014 transport was responsible for 23% of total CO2 emissions from fuel combustion, and road transport was responsible for 20% [9].

At the same time, bus transport is one of the safest modes of transport: only 126 out of the 26,134 traffic deaths in 2015 occurred on buses.

Theoretically the existence of good public transport can deter car ownership. The paper by Cullinane and Cullinane [10] asserts, however, that once a car has been acquired, there is a tendency for it to be used irrespective of how good the public transport is.

#### The Possible Role of Large-Scale Sewage Plants in Local Transport DOI: http://dx.doi.org/10.5772/intechopen.86699

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

Conversion of biogas will always increase investment and operational costs, and

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

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

2. The transport sector, CNG and the significance of compressed

Traffic is one of the most significant sectors in the EU-28, with around €<sup>651</sup> billion in gross value added a year at basic prices (5% of total), with 11.2 million employees (5.2% of total), 6602 billion passenger km (on average around 12,962 km per person, of this 8.2% with buses and coaches) and about 1183 million tonnes of CO2 equivalent (30.7% of total). Private households in the EU-28 spent EUR 230 billion on transport services (e.g. bus, train, plane tickets). It should be highlighted that changing consumer attitudes from fuel to more environment-friendly way of transport may help to promote the spreading of sludge-based transport fuels,

Globally, in 2014 transport was responsible for 23% of total CO2 emissions from

At the same time, bus transport is one of the safest modes of transport: only 126

Theoretically the existence of good public transport can deter car ownership. The paper by Cullinane and Cullinane [10] asserts, however, that once a car has been acquired, there is a tendency for it to be used irrespective of how good the

fuel combustion, and road transport was responsible for 20% [9].

out of the 26,134 traffic deaths in 2015 occurred on buses.

the energy efficiency of the process will be reduced, but it will produce more valuable, versatile and marketable main products (electricity, biomethane).

the range is smaller than with compressed natural gas (CNG) [6].

Transportation Systems Analysis and Assessment

vehicles, the efficiency of propellant use can be increased to 33%.

find many well-functioning examples.

biomethane (CBM)

too [8].

138

public transport is.

Natural gas engine technology is already well established, and millions of vehicles 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 contribution [12].

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 biowaste [14].

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> (Sweden, 113 million m<sup>3</sup> ; Germany, 35 million m<sup>3</sup> ; Norway, 10 million m<sup>3</sup> ; Iceland, 2 million m<sup>3</sup> ; Finland, 0.2 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 is also used by taxis and sanitation companies [17].

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 Table 1.

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 terms of efficiency and environmental performance.


#### Table 1.

Biogas cleaning technology and the cost of cleaning.

We need to grow food on even less land, with less water, using less energy, fertilizer and pesticide than we use today for feeding more and more people [21], so the energy use of wastes (e.g. sewage) instead of plants can be taken as one of the most important reserves of land management; with the use of them, the net use of land declines [22].

favourable for most air pollutants, but the CO and non-methane volatile organic

Regarding the emission factors of petrol- and diesel-fuelled cars and buses, it can be stated with great certainty that bus transport is the best option, in almost any of harmful gases with respect to g/pkm (passenger km), assuming that the car is not full of passengers. The emission factors strongly depend on size and utility of the given vehicles. CO and CH4 emission is higher in petrol-fuelled cars, while NOx emission is stronger in diesel-fuelled vehicles including buses (Figure 1). It should be noted that CH4 and CO emission can reach outstanding values regarding motorcycles. Methane content also affects the emission of pollutants. Lim et al. [31] examined gases composed of 82–98% methane and found that total hydrocarbons (THC), CO, NOx and CO2 emissions increased, while volatile organic compound (VOC) emis-

Because the activation energies of high carbon-numbered hydrocarbons (HCs) (e.g. ethane or propane) are lower than those of low carbon-numbered HCs (methane), the combustion efficiencies of ethane and propane are greater than that of methane. Thus, a fuel with higher methane content has more incomplete combustion and/or poor oxidation of unburned hydrocarbons, resulting in higher emissions of HC [31]. The level of this, according to measurements taken by Subramanian

Considering biogas and natural gas, NOx emissions were lower for biogas than

Biomethane used as a biofuel produces emission savings which are 73–82% of the base values (GVA) used for the EU's sustainability legislation. Compared to biofuels

Main emission factors for passenger transport (g/pkm). Source: Own construction based on [29, 30].

compound (NMVOC) values for diesel were slightly more favourable.

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

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

sions decreased with an increased CH4 content in the fuel.

et al. [32], was 12.5%.

for the natural gases.

Figure 1.

141
