Electricity and substitute natural gas generation from the conversion of wastewater treatment plant sludge

The results were presented by using supply-cost curves and then integrated into a geographical information system (GIS), the latter of which shows the distribution of energy potential nationwide. A comparison with a reference market price of the corresponding secondary energy type, electricity or natural gas, was conducted to elucidate the economic attractiveness of the two assessed options. From the assessment, it was concluded that the economic potential for the injection of Bio-SNG into the grid is 19 MM Nm3 y−1 at a representative generation cost of approximately 43 € MMBTU−1, whereas biogas for the electricity generation pathway has an economic potential of 75 GW he y−1 at a representative generation cost of 21.5ct€kWhe-1. In view of these results, it can be observed that the electricity generation pathway may offer more major economic and environmental benefits than the Bio-SNG pathway, despite both options being hardly competitive without subsidies. Additionally, it can be observed that the Bio-SNG route is not competitive in most cases, and it is economically attractive solely under restricted conditions, principally those established by plant capacity. Furthermore, steadily increasing electricity prices over time suggests that the biogas-to-electricity option will become progressively more competitive. These results can be considered as outcomes to elaborate a national macro-policy to tackle the sludge issue under a waste-to-energy approach.