4.5.3 United Kingdom

At the beginning of the 2000s, the largest wastewater-based power plant in the United Kingdom was operating at Minworth. During the operation of the plant, several technological developments were introduced, resulting in an increasing amount of biogas production.

The total investment cost of the plant was €8,150,000, which allowed the production of 3400 Nm3 /h of biogas (nearly half of which is upgraded to biomethane) with 16 digesters, totalling 80,000 m<sup>3</sup> /day. The type of raw material is sewage sludge (4000 m<sup>3</sup> /h). The development of biomethanic purification is due to two important factors: (1) simultaneously with the increase in the quantity of biogas produced—due to the variable amount of energy—the amount of electricity that can be supplied to the electricity grid was limited; (2) a significant amount (40%) of heat loss was also a serious problem. All of this led to the construction of biomethane purification capacity, which keeps the energy produced from sewage well stored and also avoids heat loss. The unit uses absorption, which provides a high-pressure water scrubbing process to clean biogas and to increase the methane concentration [67]. With an annual biomethane production of 63,000,000 kWh, Minworth is the first connection of unconventional gas into the local transmission system, with a significant impact on reducing CO2 emissions [68].

#### 4.5.4 Other examples of good practice

In the following we present other international examples, and cases of good practice of use as a fuel and for supply to the natural gas grid, using as a source the Bin2GRID (2016) project [69]:

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

Good practice for usage of biomethane and CNG vehicles:


cleaning system, while the cost of the filling station was HUF 20 million. Daily

Zalaegerszeg wastewater treatment plant with biomethane filling station. Source: Own photo.

[64]. Although this value is slightly higher than the consumer price of natural gas, it is just about half as much as the price of diesel oil. Since the substituted buses typically run on diesel oil, the use of CBG should result positive economic effect. The composition of the biogas is 65% methane, 30% carbon dioxide and 5% other gases, including hydrogen sulphide. Raw biogas significantly reduces the lifetime of machines because of its hydrogen sulphide content. For a safe and efficient use, a multistage cleaning process is initiated: gas is pressurised through an activated carbon filter, which reduces sulphur content, other gas content and humidity. Subsequently, 75% methane and 25% carbon dioxide gas is subjected to an aqueous wash, whereby the carbon dioxide is converted to carbonic acid and transferred from the biogas to the aqueous solution. During the production of biomethane, the purified biogas is pressed at a pressure of about 6 bars into the washer, in which the chemical transmission process occurs. After aqueous washing, a 99.7% methane gas is produced, which is excellent for use in CNG vehicles. The biofuel produced fuels for municipal vehicles (12 vans and 3 buses). The CO2 saving can be estimated 22

At the beginning of the 2000s, the largest wastewater-based power plant in the United Kingdom was operating at Minworth. During the operation of the plant, several technological developments were introduced, resulting in an increasing

The total investment cost of the plant was €8,150,000, which allowed the pro-

important factors: (1) simultaneously with the increase in the quantity of biogas produced—due to the variable amount of energy—the amount of electricity that can be supplied to the electricity grid was limited; (2) a significant amount (40%) of heat loss was also a serious problem. All of this led to the construction of biomethane purification capacity, which keeps the energy produced from sewage well stored and also avoids heat loss. The unit uses absorption, which provides a high-pressure water scrubbing process to clean biogas and to increase the methane concentration [67]. With an annual biomethane production of 63,000,000 kWh, Minworth is the first connection of unconventional gas into the local transmission

In the following we present other international examples, and cases of good practice of use as a fuel and for supply to the natural gas grid, using as a source the

system, with a significant impact on reducing CO2 emissions [68].

/h of biogas (nearly half of which is upgraded to biomethane)

/h). The development of biomethanic purification is due to two

/day. The type of raw material is sewage

, while the biomethane's unit cost is 0.52 EUR/m<sup>3</sup>

biomethane production is 3600 m<sup>3</sup>

Transportation Systems Analysis and Assessment

Figure 3.

tonnes/year [65, 66].

4.5.3 United Kingdom

duction of 3400 Nm3

sludge (4000 m<sup>3</sup>

amount of biogas production.

with 16 digesters, totalling 80,000 m<sup>3</sup>

4.5.4 Other examples of good practice

Bin2GRID (2016) project [69]:

154


Good practice of biomethane injection into the natural gas grid:


#### 5. Conclusions

Public transport, sewage treatment and district heating are mostly operated by local authorities and can therefore be influenced by local decisions, so biomethane can be well integrated into local transport systems, and the terms of sale are not dependent on gas suppliers, either. The latter may be significant in the event of potential future gas price rises, which does not affect the cost of locally produced biomethane. At the same time, it should be noted that the economic interests of biomethane-producing wastewater plants are rather geared towards traditional cogeneration technologies rather than biomethane production because of the significant electricity and heat demand of sewage treatment technologies.

From an environmental point of view, it is also noteworthy that the reduction of the emissions of cadmium due to the use of local public transport with CNG occurs right in the city centre, where air pollution is the most serious problem. From the operation point of view, it is essential that in the case of local transport, there is no danger of emptying fuel tanks, since the filling station is available locally, unlike with long-distance transport. The public education objective of technology is not negligible as many people (those travelling by public transport) are affected by the use of environmentally friendly fuel.

Midterm proliferation is expected to take place, given that in October 2014 the European Parliament and the Commission adopted the "Clean Fuel for Transport" package, which obliges member states to take the first steps by 2020 in cities and suburbs and by 2025 on motorways, to make CNG fuelling stations for cars and then allow transport by LNG trucks on Europe's main transport lanes.

Due to the above, the production of biomethane at metropolitan wastewater plants for transport purposes can serve the interests of residents in an efficient way, both economically and environmentally, also enabling them to enjoy a kind of energy self-sufficiency.

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