Wastewater treatment plant (WWTP) utilization of combined heat and power (CHP) systems allows for the efficient use of on-site biogas production, as well as increased annual savings in utility costs. In this paper, a review of biogas energy recovery options, CHP prime mover technologies, and the costs associated with biogas cleaning give a broad summary of the current state of CHP technology in WWTPs. Even though there are six different prime mover technologies, the main ones currently being implemented in WWTPs are micro turbines, fuel cells and reciprocating engines. Different prime movers offer varying efficiencies, installation costs, and biogas impurity (H2S, siloxanes, HCl) tolerances. To evaluate the long-term savings capabilities, a techno-economic assessment of a CHP installation at a case study WWTP shows the payback, annual savings, and initial costs associated with the installation of a CHP system. In this case, a study a payback of 5.7 years and a net present value of USD 709,000 can be achieved when the WWTP generates over 2,000,000 m3 of biogas per year and utilizes over 36,000 GJ of natural gas per year.

In this study, the degradation of the solid-oxide fuel cell (SOFC) nickel-yttria stabilized zirconia anode under decamethyltetra-siloxane (L4) contamination is examined. A model is developed for the polarization losses based on the charge transfer coefficient, α, and diffusion layer thickness, į, and fitted to the experimental data to understand how the siloxane degrades the SOFC performance with time. Ohmic losses are dominant in the anode due to much higher anode thickness (380 µm) compared to electrolyte thickness (13 µm). Activation losses vary with α, which decreases from 0.31 to 0.25. Mass transport losses vary with both į and α, with įincreasing from 28 µm to 45 µm. The results of the model indicate that the total polarization losses increase for each subsequent time interval, with a total increase of approximately 45% from 0 to 180 min. Activation losses dominate the polarization losses initially but decrease in their total contribution while mass transport losses increase.