The urban solid wastes (USW) that, defined as biomass, can be considered as renew­able energy sources include all the green biodegradable fractions, which can be divided into those made of lignocellulose wastes component and an humid organic component. The residuals coming from the garden management and public or private boulevards of the habited centres belong to the lignocellulose wastes. Although the urban rubbish is generally used for composing, it can be applied after an appropriate conditioning for heat and/or electricity production through combustion.

The organic part with a higher humidity content can, however, be applied to the bio-gas through anaerobic digestion production. Fermentation in anaerobic condi­tions processes also happen in the dumps with a high level of material compaction. In these cases, through appropriate catchment systems (we talk about controlled dumps), it is possible that the cargo and the storage of bio-gas can be applied for energy purposes (Fig. 9) [2].