4.3.1 Expected revenue from cogeneration

Electricity generation

• E85 conversion, EUR 300; extra consumption 20–25% [11]

Transportation Systems Analysis and Assessment

counterparts of the same brand and with the same parameters.

offset by the more favourable price of the alternative fuel.

the sale of surplus heat energy)

• Gas engine loss: 15%

Source: [49–51].

146

(average) technological characteristics:

• 13,000 m3 \* 0.37 kWh/m3 = 1860 Nm3

• Amount of treated wastewater: 13,000 m<sup>3</sup>

the aqueous phase through microorganisms)

plants

• Vegetable oil conversion, from 1500 to 5000 EUR; excess consumption 10% [47]

• 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

It is clear that all alternatives to CNG involve increased consumption, ideally

4.3 Comparison of energy self-supply and biomethane production of sewage

In our case study, in order to quantify energy possibilities, we conducted our calculations for a nutrient-containing wastewater treatment plant using a anaerobic fermentation technology for a population equivalent of 100,000 inhabitants (equivalent to an adult inhabitant's wastewater), which was considered as average in Hungary. Based on our conception and data collection - which were partly promoted by the Higher Education Institutional Excellence Programme of the Ministry of Human Capacities in Hungary (No. 20428-3/2018/FEKUTSTRAT) - for the use of biogas produced during fermentation, we present two possibilities in this section:

• Cogeneration energy production and then own consumption (and, if possible,

• Biomethane production and sales: supply to the natural gas network or use as fuel

• Biological oxygen demand (BOD) content: 6000 kg BOD/day (BOD, biological oxygen demand; oxygen demand for aerobic removal of organic matter from

/day

)

Basic data of the 100,000 household equivalent wastewater plants:

• Specific biogas yield (per m<sup>3</sup> treated wastewater): 0.93 kWh/m<sup>3</sup>

• Heat energy/electricity ratio for power generation: 60%/40%

• Non-residential natural gas price in EU-28: 0.0078 EUR/MJ

• Non-residential electricity average price in EU-28: 0.112 EUR/kWh

The amount of biogas generated by anaerobic technology, using the above

/day.

• CH4 content of biogas: 65% (heating value: 6.5 kWh/m<sup>3</sup>


Thermal power generation


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

Average value of savings: 34.411 MJ/day \* 0.0078 EUR/MJ natural gas \* 0.6 = 122 EUR/day = 45,000 EUR/year.

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 insecure.

In the case of district heat sales, together with the electricity, revenue is 198,000 + 45,000 = 243,000 EUR/year.

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