(556c) Resource and Techno-Economic Analysis of Biogas from WWTP (WasteWater Treatment Plants) Biosolids Using Anaerobic Digestion

Authors: 
Tao, L., National Renewable Energy Laboratory
Han, J., Argonne National Laboratory
Markham, J., National Renewable Energy Laboratory
Zhang, Y., National Renewable Energy Laboratory

Waste is an under-utilized biomass resource and is high-impact renewable feedstock with collection infrastructure already in place. Thus, Waste-to-energy (WTE) technologies can position at near-term market entry point with wide spectrum of end products (fuels, chemicals and power) while mitigating methane emissions from current waste treatment. Among various wastes, municipal solid waste (MSW) and biosolids have potential to produce about 590 TBtu (equivalent to 5 billion gallons of gasoline or 1/3 of current biofuel production) per year. In the other hand, the United State of environmental protection agency (EPA) has recognized the benefits of promoting net low-carbon fuels derived from biogas, and in a recent rulemaking, EPA classified many sources of biogas from cellulosic feedstock for transportation fuels as part of the Renewable Fuel Standard (RFS) 1. Use of biogas-derived fuels in the transportation sector can substantially reduce GHG emissions and can serve to promote effective organic waste management, as well as efficient biogas production, recovery, and utilization. There are many existing treatment processes for converting municipal sludge into biosolids, which are most landfilled but can be applied to land typically as a soil amendment (US EPA, 40 C.F.R. § 503. 10, 2008). According to EPA 2008 data and the EPA Clean Watersheds Needs Survey 2, 3, 16,675 WWTPs are treating 34,211 million gallons per day (MGD) of wastewater. Economic viability and environmental sustainability, however, have yet to be addressed for widespread deployment of WTE pathways for better utilization of biosolids. Thus, for economic viability and environmental sustainability, the techno-economic analysis (TEA) of WTE pathways are performed for converting biosolids anaerobic digestion then upgrading the biogas to various energy products, such as power and liquid fuel.

This work is to determine whether waste resources are large enough to justify the economies of scale and whether WTE pathways can increase the value proposition of the waste feedstocks. The criteria are whether waste resources within a practical transportation radius are large enough for, at a minimum, a small-scale biorefinery (e.g., 10–100 million gallons per year) and whether the investigated WTE pathways have the potential to increase the value proposition. Several alternative process concepts are defined and studied for TEA. Due to uncertainties in the data available for WTE, it is difficult to support a single economic target/potential. Reasonable cost ranges are established for base case as well as process alternatives. In addition to further investigate and update key TEA assumptions and to examine process sensitivity and alternatives to increase waste value proposition. Other more advanced technologies should be considered in the future to understand the economic viability of the conversion technologies using biogas from biosolids of WWTPs, particularly for pathways to make transportation fuels. For instance, methanol-to-gasoline, methanol-to-olefins, syngas catalytic upgrading pathways (syngas-to-oxygenates, syngas-to-mixed alcohols, syngas to triptyls), and methane biological pathways could have promising potential to meet cost and sustainability criteria set by this study. To meet production criteria, more feedstocks would be needed, either by increasing biosolids using centralized options or by blending biosolids with other types of waste, such as food waste.

References:

1.           EPA Regulatory Announcement. EPA Issues Final Rule for Renewable Fuel Standard (RFS) Pathways II and Modifications to the RFS Program, Ultra Low Sulfur Diesel Requirements, and E15 Misfueling Mitigation Requirements. 2014.

2.           EPA. Clean Watersheds Needs Survey (CWNS) 2008 Report to Congress. 2008.

3.           USEPA. Clean Watersheds Needs Survey 2008 - Report to Congress. Washington, DC: US Environmental Protection Agency, 2010.