4.3.4 Comparison of the technologies examined

The three uses of the biogas produced from the wastewater analysed above can thus be characterised by the following end parameters for a 100,000 PE (population equivalent) sewage capacity (Table 7).

to produce cheaper biomethane. For farm-sized plants, it is economical to produce and use local CBM only when using their own by-products and primarily for the

Consequently, the cost of compressed biomethane (CBM) as a propellant is typically just below or at the CNG price level (average 1.18 EUR/kg) but much

Finally, the conversion of vehicles to CNG operation and the return on the CNG

In the case of a city bus, taking into account a life expectancy of 1000,000 km, single buses use cca. 370,000 l, and articulated buses cca. 470,000 l of diesel fuel in their lifetime. The fuel cost savings during the CNG operation can be estimated at 37,000 EUR and 47,000 EUR per bus, taking into account the average reclaimed VAT and the wholesale discount. Thus, a local public transport service of county town size (e.g. Debrecen, Hungary, with 210,000 local inhabitants; a fleet 100 of single and 40 articulated buses) can save up to € <sup>5</sup>–6 million over the entire lifetime but also hundreds of thousands of EUR on a yearly basis. The expected return on the

cheaper than the diesel typically used in local transport vehicles.

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

• 60,000 km/year performance (16–17 years calculated lifetime)

• 40,000 EUR conversion cost/acquisition surplus cost

(assuming use of own money in financing)

• An average saving of 0.1 EUR/l of gas oil equivalent with CNG (gas oil

• Considering 3%/year increase in gas oil price and the same as opportunity cost

Based on CNG purchased on the basis of this data, the investment will be repaid after approximately 18 years without subsidy, so slightly beyond the useful life of the vehicle; however, with a subsidy the payback period is much shorter, and the benefits of environmental protection have not yet been taken into consideration. Increasing performance (better use of buses) and rising gas oil prices can significantly reduce the payback period. Since gas fuelling has a positive effect on engine wear, it does not endanger the potential performance; it is rather determined by the transport features. One-hundred thousand kilometre use of bus per year results in

In the case of CBM produced in its own wastewater plant, savings are much greater than with diesel; therefore, with the same technical parameters, the payback

Environmental advantages of a CNG-/CBG-fuelled bus fleet are also significant. Considering the average value of 18 kg/GJ GHG saving of CNG/CBG compared to gas oil and the bus fleet of Debrecen with the above-mentioned characteristics, the GHG saving can reach 14.4 tonnes/bus in a year, or 15,000–20,000 tonnes/bus

Therefore, in the vertical market structure (with the appropriate size and type of user), profits are generated in the current economic conditions, as well. At the same time, in the case of internal use (e.g. operation of a common sewage plant gas and local public transport system), the state loses significant tax revenue, which is, however, easily offset by the externalities present in the public finances.

fuel supply of their own vehicles.

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

premium can be estimated as follows.

conversion of a single bus is as follows.

• 37 l/100 km gas oil consumption

Basic calculation data:

wholesale price)

11-year-long repayment period.

151

period will be reduced, even without subsidy.

fleet, moreover in the city centre, mostly suffering air pollution.


#### Table 7.

Parameters of the given plant.

The above values show that introducing biomethane into the natural gas network is the least competitive compared to the other two modes of recovery both in economical and in environmental aspects. In the case of existing digesters, the gas engine is very fast—and the most efficient return on investment, if it is connected to a sufficiently large district heating network, ideally an industrial park. Although sales of biomethane for propellants can theoretically achieve the highest turnover on their own, due to the self-consumption needs of the sewage plant, and the investment cost—which is more than three times higher—it is not the most favourable alternative from the sewage plant's perspective. Since the environmental effects are near the same, it can be stated that CHP could be evaluated as the best way for biogas utilisation for the sewage plant.

#### 4.4 Economics of the use of CNG at the city level

In general, it can be stated that the long-term spread of a product market (in our case CNG/CBM) is only expected if the product is worthwhile to produce, market and use. In the event of any losses suffered by any actor in the market, in the absence of subsidies, the vertical relationship is interrupted, and so the interest of all actors must be ensured. A subsidy is justified by the macroeconomic benefits of the public finances (environmental protection, import substitution, employment). In addition, it must, of course, be cheaper and more accessible than competing fuels and must also ensure that the investment needed to operate is recovered within a reasonable period of time. Does biomethane meet all of these criteria under current economic conditions?

It can be clearly seen from the economic data listed in Table 3 that biomethane can be produced essentially at the consumer price (0.8–1.1 EUR/kg) at relatively small (250 Nm<sup>3</sup> /h) biogas plants, while the price-equivalent own costs for its substitutes, i.e. petrol and diesel (0.87–0.98 EUR/l on average), are significantly below their average consumer price (1.43–1.44 EUR/l). In the case of non-final sales (i.e. not to private individuals) but for business use (buses, machines), equivalent values for petrol and gas oil prices reduced by VAT and other price discounts must be taken into account (cca 1.08 EUR/l in both cases, with an average 25% reduction), with which the smallest agricultural biomethane plants (with a capacity of 250 Nm3 /h) are just competitive (0.8–1.1 EUR/kg), while larger farm sizes are able

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

to produce cheaper biomethane. For farm-sized plants, it is economical to produce and use local CBM only when using their own by-products and primarily for the fuel supply of their own vehicles.

Therefore, in the vertical market structure (with the appropriate size and type of user), profits are generated in the current economic conditions, as well. At the same time, in the case of internal use (e.g. operation of a common sewage plant gas and local public transport system), the state loses significant tax revenue, which is, however, easily offset by the externalities present in the public finances.

Consequently, the cost of compressed biomethane (CBM) as a propellant is typically just below or at the CNG price level (average 1.18 EUR/kg) but much cheaper than the diesel typically used in local transport vehicles.

Finally, the conversion of vehicles to CNG operation and the return on the CNG premium can be estimated as follows.

In the case of a city bus, taking into account a life expectancy of 1000,000 km, single buses use cca. 370,000 l, and articulated buses cca. 470,000 l of diesel fuel in their lifetime. The fuel cost savings during the CNG operation can be estimated at 37,000 EUR and 47,000 EUR per bus, taking into account the average reclaimed VAT and the wholesale discount. Thus, a local public transport service of county town size (e.g. Debrecen, Hungary, with 210,000 local inhabitants; a fleet 100 of single and 40 articulated buses) can save up to € <sup>5</sup>–6 million over the entire lifetime but also hundreds of thousands of EUR on a yearly basis. The expected return on the conversion of a single bus is as follows.

Basic calculation data:

4.3.4 Comparison of the technologies examined

Transportation Systems Analysis and Assessment

tion equivalent) sewage capacity (Table 7).

Sphere of use Investment demand

Cogeneration (electricity and heat)

network)

Table 7.

Cleaning (supplying

Source: Own calculations.

Parameters of the given plant.

(thousand EUR)

way for biogas utilisation for the sewage plant.

economic conditions?

small (250 Nm<sup>3</sup>

250 Nm3

150

4.4 Economics of the use of CNG at the city level

The three uses of the biogas produced from the wastewater analysed above can thus be characterised by the following end parameters for a 100,000 PE (popula-

231 average: 243,

Expected revenue (thousand EUR/year)

max. 272

860 249 147

Emission saving (t CO2eq/yr)

762

The above values show that introducing biomethane into the natural gas network is the least competitive compared to the other two modes of recovery both in economical and in environmental aspects. In the case of existing digesters, the gas engine is very fast—and the most efficient return on investment, if it is connected to a sufficiently large district heating network, ideally an industrial park. Although sales of biomethane for propellants can theoretically achieve the highest turnover on their own, due to the self-consumption needs of the sewage plant, and the investment cost—which is more than three times higher—it is not the most

Cleaning (for fuel) 860 47 742

favourable alternative from the sewage plant's perspective. Since the environmental effects are near the same, it can be stated that CHP could be evaluated as the best

In general, it can be stated that the long-term spread of a product market (in our case CNG/CBM) is only expected if the product is worthwhile to produce, market and use. In the event of any losses suffered by any actor in the market, in the absence of subsidies, the vertical relationship is interrupted, and so the interest of all actors must be ensured. A subsidy is justified by the macroeconomic benefits of the public finances (environmental protection, import substitution, employment). In addition, it must, of course, be cheaper and more accessible than competing fuels and must also ensure that the investment needed to operate is recovered within a reasonable period of time. Does biomethane meet all of these criteria under current

It can be clearly seen from the economic data listed in Table 3 that biomethane can be produced essentially at the consumer price (0.8–1.1 EUR/kg) at relatively

stitutes, i.e. petrol and diesel (0.87–0.98 EUR/l on average), are significantly below their average consumer price (1.43–1.44 EUR/l). In the case of non-final sales (i.e. not to private individuals) but for business use (buses, machines), equivalent values for petrol and gas oil prices reduced by VAT and other price discounts must be taken into account (cca 1.08 EUR/l in both cases, with an average 25% reduction), with which the smallest agricultural biomethane plants (with a capacity of

/h) biogas plants, while the price-equivalent own costs for its sub-

/h) are just competitive (0.8–1.1 EUR/kg), while larger farm sizes are able


Based on CNG purchased on the basis of this data, the investment will be repaid after approximately 18 years without subsidy, so slightly beyond the useful life of the vehicle; however, with a subsidy the payback period is much shorter, and the benefits of environmental protection have not yet been taken into consideration. Increasing performance (better use of buses) and rising gas oil prices can significantly reduce the payback period. Since gas fuelling has a positive effect on engine wear, it does not endanger the potential performance; it is rather determined by the transport features. One-hundred thousand kilometre use of bus per year results in 11-year-long repayment period.

In the case of CBM produced in its own wastewater plant, savings are much greater than with diesel; therefore, with the same technical parameters, the payback period will be reduced, even without subsidy.

Environmental advantages of a CNG-/CBG-fuelled bus fleet are also significant. Considering the average value of 18 kg/GJ GHG saving of CNG/CBG compared to gas oil and the bus fleet of Debrecen with the above-mentioned characteristics, the GHG saving can reach 14.4 tonnes/bus in a year, or 15,000–20,000 tonnes/bus fleet, moreover in the city centre, mostly suffering air pollution.

Average data used for calculation of passenger cars:


ratio of sewage and sewage sludge, thereby achieving higher biogas and

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

In what follows we present a few examples of biogas or biomethane production

In Linköping, Sweden, biomethane is used in urban transport, not only for buses and heavy and light motor vehicles but also for trains [56]. The total cost of EUR 14,000,000 invested in 1996 can be mentioned as one of the successful examples of the integration of fuel supply for agriculture, the community and individual transportation. In the Linköping waste-to-energy plant, biogas production was initially based on the by-products and wastes of the crop and livestock (slaughterhouse) sector, while in the framework of a development programme, from 2001, they have also produced renewable propellants from organic waste from public institutions and restaurants [57]. Since 2002, there are only biogas buses in the urban transport fleet, and the CO2 emissions have been reduced by more than 9000 tonnes per

Another Swedish example is the Nordvästra Skånes Renhållning AB (NSR) biomethane plant in Helsingborg, which generates 80 GWh of biomethane per year from 160,000 tonnes of separated food waste. The methane produced is supplied to

Another interesting example is the Swedish city of Uppsala. As early as 1996, animal manure and slaughterhouse waste were used for biogas production, and then for biomethane production after purification, which was used for the operation of buses. Thereafter, developments in two stages up to 2010 resulted in the production of biomethane from significant quantities of organic waste from their own city and other settlements; annual production has reached 3000,000 Nm3 [60]. Overall 71 of the city buses were fuelled by biomethane, which amounts for 35% of fuel used in

Considering the Swedish examples, it is not surprising that in Swedish house-

Sewage water-based biomethane production was implemented in Hammarby Sjöstad (Stockholm), Sweden. Within the framework of the project, an integrated closed wastewater-energy system has been implemented based on local authority/ municipal sewage. After the sewage is purified in the system, propellant biogas and biomethane are also produced, as well as heat and electricity. Hammarby Sjöstad is located in one of the most progressive cities in the world with regard to sustainability. The city has reduced carbon emissions by 25% per resident since 1990 and has established a target of reducing emissions to 3 tonnes of CO2 per capita in 2015. This value is extremely low for developed countries, considering the entire country of Sweden has an average emission rate of 4.5 tonnes of CO2 per capita, while the average for Europe is approx. 6.5 tonnes per capita, and the average for the United

Sewage-based, biomethane propellant production was also implemented in Zalaegerszeg (Hungary) (Figure 3). The investment began in 2011 and cost 140 million HUF (about 444,000 EUR), of which HUF 120 million was for the biogas

holds 60% of organic waste is collected separately and utilised.

the grid and is used for the operation of trucks, taxis and private cars. From 160,000 tonnes of digested food waste in the biogas plant, approximately 490 tonnes of N, 90 tonnes of P and 170 tonnes of K are available for recirculation as

biomethane yields.

4.5.1 Sweden

year [58].

fertilizer each year [59].

public transport in Uppsala in 2014 [61].

States is 16.5 tonnes per capita [62, 63].

4.5.2 Hungary

153

plants based on organic waste or sewage.

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


In the case of the above parameters, the conversion is expected to take place within 2–3 years, while the purchase price of the new car would be repayable in 5–6 years, mainly depending on the mileage and current petrol prices, if there was no problem with refuelling. In the case of a local public CNG filling station, gasfuelled cars can be recommended primarily to those private individuals who are involved in local transport and travel long distances in a year (e.g. local taxi drivers) or those that are more environmentally sensitive and thus appreciate the benefits of using gas-fuelled cars.

#### 4.5 Reference plants

Biomethane production based on various types of waste and its use as a propellant can be found in several places. At this point, we will introduce some international examples, focusing in more detail on wastewater-based biomethane production.

As the study by Barisa et al. [55] shows, there are many potential waste-based raw materials available to a settlement that are suitable for biogas and biomethane production:


With regard to their available volume, it can be said in general that in a given settlement the municipal solid waste, separated green waste and sewage sludge produced in the sewage plant make up the largest amount. However, considering the costs of collecting and separating these three types of raw materials, there may be significant differences. The utilisation of sewage sludge in the sewage plant continuously and, in a relatively homogeneous amount, free of charge—can be considered cost-effective in this respect. In addition, other waste materials can be used safely for biogas production and its subsequent purification in sewage plants.

In practice, wastewater treatment plants in many cases include organic food waste/by-products that contribute to improving the carbon-nitrogen

ratio of sewage and sewage sludge, thereby achieving higher biogas and biomethane yields.

In what follows we present a few examples of biogas or biomethane production plants based on organic waste or sewage.
