**4. Conclusions**

Biowaste separate collection and its subsequent treatment by composting or fermentation are considered a sustainable way of handling this waste stream. First, an inventory of GHG for a composting process and fermentation process was carried out. The modelled cases suited current European conditions and are mainly focused on the Czech Republic's conditions. The net GWP value of biowaste treatment by composting, including transport and collection, was equal to −57.1 kg(CO2)eq.twaste<sup>−</sup>1. Positive effect resulting in GWP credits, which result mainly from the substitution of primary resources such as fertilisers or substrates, are burdens from the collection, transport, and treatment itself. Much positive effect can be achieved through fermentation, where net GWP of −206.1 kg(CO2)eq.twaste<sup>−</sup><sup>1</sup> can be achieved. In comparison with composting and fermentation, WtE processes biowaste present in residual waste. Therefore, the effect of biowaste incineration as a component of residual MSW was investigated next. A simulation model based on a marginal change concept was proposed for this purpose. Since net GHG emissions (burdens plus credits) are, in the case of WtE, dependent on heat utilisation rate (district heating systems), the primary goal of the case study was to carry out an energy production-related analysis. In the case of high heat delivery (75% of the thermal output of the boiler), the effect is comparable with the impact of fermentation/composting. In the case of missing heat demand (electricity generation), separate collection and fermentation is preferred.

**Author Contributions:** Conceptualization, M.P.; Investigation, J.D., T.P. and R.P.; Methodology, M.P., J.D. and T.P.; Software: J.D.; Supervision: M.P.; Visualization, M.P. and J.D.; Writing—original draft preparation, J.D. and M.P.; Writing—review and editing, T.P. All authors have read and agreed to the published version of the manuscript.

**Funding:** The authors gratefully acknowledge the financial support provided by the project Sustainable Process Integration Laboratory—SPIL, funded as Project No. CZ.02.1.01/0.0/0.0/15\_003/0000456, by Czech Republic Operational Programme Research and Development, Education, Priority 1: Strengthening capacity for quality research.

**Conflicts of Interest:** The authors declare no conflict of interest.
