Guidance to Selecting and Delivering the Optimal Bioenergy Project at WRRFs

Many water resource recovery facilities (WRRFs) are motivated to beneficially utilize biogas for Renewable Natural Gas (RNG) or cogeneration due to a combination of environmental, economic, and regulatory factors. WRRFs are increasingly recognizing the potential of biogas as a valuable resource that can be upgraded to RNG for pipeline injection for vehicle fuel or used in cogeneration systems to produce electricity and heat. RNG projects typically focus on upgrading biogas to pipeline-quality gas, while cogeneration projects aim to simultaneously produce electricity and useful heat from the biogas. This shift is motivated by the desire to reduce greenhouse gas emissions, comply with stringent environmental regulations, and capitalize on financial incentives such as Renewable Identification Numbers (RINs), and tax credits from recent legislation like the Inflation Reduction Act. Additionally, the economic benefits of biogas utilization, including reduced energy costs and potential revenue from selling RNG or producing electricity, make it an attractive option for WRRFs aiming to enhance their sustainability and financial performance.

Selection and delivery of bioenergy projects involve three major evaluation decisions to ensure that the correct, most economically favorable project is selected and the WRRF is set up for a successful operation. The three major decisions are project lifecycle analyses, delivery model, and technology selection. These phases involve distinct components including feasibility studies, design, procurement, construction, commissioning, ownership, operation, and market credit administration. Table 1 outlines the consideration of project impacts depending on WRRF's extent of ownership of the system, which is impacted by project delivery type. This manuscript will provide guidance on each step of the decision-making process to align the right bioenergy project for an individual WRRF through the experience demonstrated in three case studies.

WRRF 1 — RNG Upgrading Facility Under Construction
In the case of WRRF 1, the facility is currently undergoing a major infrastructure improvement project and the agency's primary driver was cost reduction. In assessing biogas utilization alternatives, RNG pipeline injection was projected to reduce capital costs, yield the highest value for the biogas and provide a revenue source, and reduce onsite air emissions by eliminating cogeneration combustion at a utility already reliant on GHG free electricity. This project will upgrade up to 2300 scfm of digester gas to natural gas quality and inject it into the local utility's natural gas pipeline for use as vehicle fuel to participate in the EPA RFS program. This case study will primarily focus on the questions and considerations that led WRRF 1 to a selected delivery model with multiple iterations that would aim to reduce capital cost investments and transfer performance and financial risk.

WRRF 2 — Cogeneration Facility Under Construction
In the case of WRRF 2, the project was initiated in response to a quickly expiring biogas commodity agreement with the local utility, which stipulates that the utility provide reliable power and backup power, steam for digester heating, and revenue in exchange for biogas delivery. To determine whether to extend terms with the utility or pursue an alternative use for its biogas, WRRF 2 developed feasible and complete project alternatives that included energy and financial modeling, project schedules and delivery method options, and the applicability of OSHA process safety management program. The selected bioenergy project will exempt the WRRF from 'covered' process regulations via onsite biogas use via combined heat and power (CHP) generation. The project is being delivered through a design-build approach. This delivery method was selected to streamline the project and ensure better coordinate between design and construction teams because time is of the essence. This case study will focus primarily on determining the best fit project and delivery method for implementing a bioenergy project.

WRRF 3 — Operational RNG Facility Purchasing and Selling RINs
WRRF 3 is currently operating an energy recovery facility where HSW is co-digested with municipal sludge to produce biogas that is upgraded to RNG vehicle fuel quality and utilized as vehicle fuel for the city's solid waste collection fleet. The facility is currently registered with the RFS program as a closed-loop RNG facility and is producing D5 RINs under the previous RFS program regulations. This case study will focus primarily on the hurdles associated with registering for the RFS program and the financial commitment during the registration process and ongoing management of the RFS program that is often overlooked when considering participating in the RFS program.
In summary, selection, delivery, and ongoing success of the best fit bioenergy project involves multiple phases and requires careful consideration of economic factors, delivery models, and technology selection. By addressing these objectives, stakeholders can ensure the successful implementation and operation of these projects, ultimately contributing to sustainable energy production and environmental benefits.