Environmental assessment of three different utilization paths of waste cooking oil from households

• Paper analyzes different treatment and utilization concepts of WCO.
• Conversion to biodiesel, thermal and electric energy and biogas were evaluated.
• Totals of CO2-equivalent emissions were compared to illustrate variations.
• Esterification of waste cooking oil showed highest savings of CO2eq/ton.
• Sensitivities were assessed with perturbation and scenario analysis.

Inadequate disposal of waste cooking oil (WCO) through sewage systems causes economic and environmental problems, e.g., hindering sewage treatment at wastewater treatment plants (WWTP). Additionally, it leads to the loss of a valuable resource with high energy content. In this work, the greenhouse gas balances of three different utilization concepts for WCO were investigated. The utilization options assessed were (1) the conversion of WCO to biodiesel, (2) direct combustion in a cogeneration plant and (3) the production of biogas within an agricultural biogas plant. The scope of the study was limited to the treatment of WCO originating from a separate collection system for private households.The results show that all three options contribute to a reduction of greenhouse gas emissions with esterification of the WCO (scenario 1) being the best environmental option with savings of 3089 kg CO2eq t−1 WCO. The utilization of WCO in a cogeneration plant (scenario 2) results in a similar range of environmental benefits with 2967 kg CO2eq t−1 WCO. When using WCO as a co-substrate in an agricultural biogas plant (scenario 3), an environmental saving of 1459 kg CO2eq t−1 WCO was achieved. Parameter uncertainties were assessed by perturbation analysis and model and scenario uncertainties by scenario analysis. A special focus was put on the substitution potential of the resulting energy outputs concerning primary production of fossil energy carriers. The results confirm that the definition of reference systems in the course of an environmental assessment has a major influence on the overall results.