4. Economic characteristics of production and use

Large-scale sewage plants in large cities are suitable for the production of large quantities of biogas, using economically viable biogas upgrading technologies and generally available public transport fleets of a sufficient number of local buses, as well as municipal vehicles. The conditions for the sale of locally produced CNGs do not depend on gas suppliers, they can be very well integrated with local waste management and the local emission reductions occur in the inner city where air pollution is the most serious problem.

At the same time, it is not clear from the point of view of sewage plants whether it is the production of biomethane or the cogeneration solution—which is currently more important—which is more viable economically and in terms of harmful emissions. Here, it must be taken into account that the consumption of heat and electricity by these plants is significant, and this must be purchased when producing biomethane.

The economic and environmental approach should take into account not only the substituted energy source but also the cost and emissions of fossil fuels bought because there is no cogeneration (including the electricity and heat needed for self-consumption at sewage plants).

In this section we present the investment and operating costs of CBM production and the specific aspects of economic evaluation.

#### 4.1 Investment and operating costs

The expected level of the biomethane plant's investment costs is greatly influenced by technology and size. Goulding and Power [34] provide the following equation for the average of the investment costs of biomethane plants operating with agricultural raw materials, with a 95.6% probability:

$$\mathbf{C} = 1066.2 \mathbf{x}^{0.8455}$$

where C is the investment cost (€/t yearly raw material) and x is the processed raw material quantity (t/year).

The equation—with a 91% degree of confidence (C = 21080x0.5367)—also shows that, in the case of larger dimensions, from an economies of scale perspective, it is advisable to use biomethane instead of cogeneration technologies. At the same time, at bigger dimensions cogeneration technology also has economies of scale. According to Patrizio et al. [37], the proportion of available heat and electricity between an operating capacity of 300 and 200 kWe increases from 58 to 70%,

considering a value of 25 and 11% for plant self-consumption of electricity and for heat to maintain the mesophilic process.

Patrizio et al. [37] examining the influence of the low market value of CO2 found that starting from a carbon price of 15 EUR/tCO2, the cogeneration option is preferable if plants are located in the proximity of existing district heating infrastructure. CNG plants are only competitive starting at a carbon price of 70 EUR/tCO2 in areas with high feedstock availability, when the first upgrading plant for CNG

Finally, it should be noted that the consumption of diesel oils tested by Farkas et al. [43] in Hungary showed a 5% difference in the same vehicles. This is important because the substitution value of the biomethane and its environmental savings

Market prices are examined for the most important biomethane-producing countries and for Hungary. Including this latter country is justified by the fact that the case study we presented is also Hungarian. CNG is cheaper than its competitors —petrol and diesel—in all countries, not only in terms of unit price but also petrol and gas oil equivalents, with a typical price difference of between 33–57% and 25–48%. Interestingly, there is a large difference between the two most widely regarded model countries in the EU—Italy and Sweden; in the former it is consumed for reasons of economy, and in the latter because of the environmental consciousness there. CNG prices in the countries surveyed show that differences can be more than double, but petrol and gas oil prices are much more balanced

Rebuilding of passenger cars to use alternative fuels involves additional costs

Country Fuel consumer price CNG price as

Petrol EUR/l

Bulgaria 0.71 0.52 1.2 0.59 1.23 43 48 Finland 1.34 0.98 1.54 1.11 1.47 64 75 Germany 1.07 0.79 1.53 0.88 1.4 51 63 Hungary 1.12 0.82 1.22 0.92 1.34 67 69 Italy 0.99 0.73 1.66 0.82 1.56 44 52 Sweden 1.87 1.37 1.48 1.54 1.58 93 98 Average 1.18 0.87 1.44 0.98 1.43 60 68

CNG, gasoline and diesel prices for key EU countries and two Central and Eastern European countries

EUR/l diesel equivalents

1.08 1.07

Diesel EUR/l

percentage (%) of other propellants

Petrol Diesel

• CNG conversion, approx. 1.600 EUR; extra consumption 0–10% [11]

• LPG conversion, approx. 1.000 EUR; extra consumption 5–20% [11]

production is introduced into the optimum mix.

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

4.2 The European market

(Table 4).

Relating to buses

Source: [44–46].

(October 2018).

Table 4.

145

depend greatly on the quality of the substituted oil product.

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

and changes in consumption, the values of which are:

EUR/l petrol equivalent

Units used: CNG, 43.6 MJ/kg; petrol, 32 MJ/l; diesel, 36 MJ/l [46].

CNG EUR/kg

Yang et al. [18] also explored the cost of investment in various cleaning technologies at various farm sizes, which support the economies of scale of large plants:


The distribution of investment costs by the same source can be characterised by the following average numbers:


Most of the investment costs are related to distribution, the proportion of which is largely dependent on the method used to transport methane [25]:


The cost price of methane produced is also largely dependent on the size of the wastewater treatment plant, primarily because of the significant proportion of fixed costs (Table 3).

Regarding the economic indicators of the wastewater plants, it can be said that the existing rotting equipment and the larger size of the plant typically offer more favourable costs, thus allowing faster returns.

It should be noted that a reduction in the cost of biomethane can also be achieved by using carbon dioxide resulting from purification (in some cases in pure form), which has a significant increase in yields in greenhouses or algae plants. Algae can also be easily integrated into sewage treatment or can be used in bioenergy production and are capable of doubling their yield (up to 400 t/ha/year) with inorganic nutrients in wastewater and carbon dioxide [39, 40]. With the use of digested effluent Paulownia tomentosa [41] or Sida hermaphrodita [42], plantations may support the aim to meet the growing needs for site remediation and biomass production.


#### Table 3.

Cost of biomethane based on farm size and raw material (EUR/kg).

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

Patrizio et al. [37] examining the influence of the low market value of CO2 found that starting from a carbon price of 15 EUR/tCO2, the cogeneration option is preferable if plants are located in the proximity of existing district heating infrastructure. CNG plants are only competitive starting at a carbon price of 70 EUR/tCO2 in areas with high feedstock availability, when the first upgrading plant for CNG production is introduced into the optimum mix.

Finally, it should be noted that the consumption of diesel oils tested by Farkas et al. [43] in Hungary showed a 5% difference in the same vehicles. This is important because the substitution value of the biomethane and its environmental savings depend greatly on the quality of the substituted oil product.

#### 4.2 The European market

considering a value of 25 and 11% for plant self-consumption of electricity and for

Yang et al. [18] also explored the cost of investment in various cleaning technologies at various farm sizes, which support the economies of scale of large plants:

/h in crude (input) biogas capacity: 1.6–2 million USD

/h in crude (input) biogas capacity: 0.7–1.1 million USD

The distribution of investment costs by the same source can be characterised by

Most of the investment costs are related to distribution, the proportion of which

The cost price of methane produced is also largely dependent on the size of the wastewater treatment plant, primarily because of the significant proportion of fixed

Regarding the economic indicators of the wastewater plants, it can be said that the existing rotting equipment and the larger size of the plant typically offer more

It should be noted that a reduction in the cost of biomethane can also be achieved by using carbon dioxide resulting from purification (in some cases in pure form), which has a significant increase in yields in greenhouses or algae plants. Algae can also be easily integrated into sewage treatment or can be used in

bioenergy production and are capable of doubling their yield (up to 400 t/ha/year) with inorganic nutrients in wastewater and carbon dioxide [39, 40]. With the use of digested effluent Paulownia tomentosa [41] or Sida hermaphrodita [42], plantations may support the aim to meet the growing needs for site remediation and biomass

> Medium-sized plant (500 Nm<sup>3</sup>

[25] 1.1 0.8 0.7 [38] 0.8–1\* 0.7–0.9\* 0.6–0.7\*

/h)

Large operation (1000 Nm<sup>3</sup>

/h)

is largely dependent on the method used to transport methane [25]:

• CNG lorry transport: 12 €/GJ biomethane

• LNG lorry transport: 7 €/GJ biomethane

• CNG pipeline delivery: 5 €/GJ biomethane

favourable costs, thus allowing faster returns.

heat to maintain the mesophilic process.

Transportation Systems Analysis and Assessment

• 1000 Nm3

• 250 Nm3

costs (Table 3).

production.

Table 3.

144

Source Farm-sized plant

(250 Nm<sup>3</sup>

\*Assuming 0–100% of purchased raw material.

/h)

Cost of biomethane based on farm size and raw material (EUR/kg).

the following average numbers:

• Cleaning: 40–45%

• Distribution: 50–55%

• Compression: approx. 5%

Market prices are examined for the most important biomethane-producing countries and for Hungary. Including this latter country is justified by the fact that the case study we presented is also Hungarian. CNG is cheaper than its competitors —petrol and diesel—in all countries, not only in terms of unit price but also petrol and gas oil equivalents, with a typical price difference of between 33–57% and 25–48%. Interestingly, there is a large difference between the two most widely regarded model countries in the EU—Italy and Sweden; in the former it is consumed for reasons of economy, and in the latter because of the environmental consciousness there. CNG prices in the countries surveyed show that differences can be more than double, but petrol and gas oil prices are much more balanced (Table 4).

Rebuilding of passenger cars to use alternative fuels involves additional costs and changes in consumption, the values of which are:



Units used: CNG, 43.6 MJ/kg; petrol, 32 MJ/l; diesel, 36 MJ/l [46]. Source: [44–46].

#### Table 4.

CNG, gasoline and diesel prices for key EU countries and two Central and Eastern European countries (October 2018).


Allowing for a 15% loss of biogas above, a biogas calorific value of 6.5 kWh/m3 and the energy consumed in energy production, and calculating using 60% heat and 40% electricity ratios, the quantity of the final product with the two technologies

• Quantity of electrical energy that can be produced: 0.37 kWh/m3 \*

• Consumption of electricity at the plant (Kárpáti [52] and authors' own calculations, allowing for 0.59 kWh/m<sup>3</sup> sewage sludge): 13,000 m<sup>3</sup> sewage \*

• Electricity balance: 2872 kWh/day (electricity self-sufficiency: 63%)

• Quantity and value of heat energy to be produced: 0,558 kWh/m3 \*

13,000 m<sup>3</sup> = 7254 kWh/day = 26,114 MJ/day

): 5140 kWh/day = 18,500 MJ/day

• The amount of heat energy self-supply: in principle 91%

can be utilised. In the following we calculate on an assumption of 60%:

• Savings: 4837 kWh/day \* 0.112 EUR/kWh = 542 EUR/day = 197,745 EUR/year

• The heat energy consumption of the plant (assuming a heat demand of 0.40

However, in practice, heat utilisation beyond the plant's own heat demand is problematic, especially in the summer, and in addition, the heat energy consumption is also lower. For district heating purposes, depending on the length and insulation of the piping system, 10–15% heat loss can be expected. If the remainder of the winter heat surplus is fully utilised by the district heating system and the summer hot water demand is considered, then about 55–70% of the heat generated

Average value of savings: 34.411 MJ/day \* 0.0078 EUR/MJ natural gas \* 0.6 = 122

It should be noted that if total heat energy could be sold, the revenue and savings would reach EUR 203/day and EUR 74,000/year. This would be possible if sales were not for the heat-variable demands of the district heating system, but for the sufficiently high constant heat demand of an industrial consumer in a nearby industrial park (e.g. a bioethanol plant or a slaughterhouse) when the heat would be bought at the natural gas price. However, the latter is in practice much more

In the case of district heat sales, together with the electricity, revenue is

The investment cost of CHP technology (with 266–280 kWe capacity) (with existing rotting equipment) following our own calculations is 231,000 EUR.

examined is shown below.

Electricity generation

4.3.1 Expected revenue from cogeneration

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

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

13,000 m<sup>3</sup> = 4837 kWh/day

0.59 kWh/m<sup>3</sup> = 7709 kWh/day

• Heat energy surplus: 7614 MJ/day

EUR/day = 45,000 EUR/year.

198,000 + 45,000 = 243,000 EUR/year.

insecure.

147

Thermal power generation

kWh/m<sup>3</sup>

• Biodiesel conversion, from 1000 to 4000 EUR; surplus consumption 10% [48]

For buses, conversion to CNG operation costs € 30,000–€ 50,000. CNGpowered cars are about € 3000 to 5000 more expensive than their petrol and gas oil counterparts of the same brand and with the same parameters.

It is clear that all alternatives to CNG involve increased consumption, ideally offset by the more favourable price of the alternative fuel.
