Biosolids Pyrolysis and Gasification - Lessons Learned from Early Adopters

Traditionally, biosolids in the United States (US) have been managed through land application, disposed in landfills, or incinerated. These biosolids management approaches are experiencing significant challenges due to rising costs associated with transport and landfill disposal, reduced availability of land to beneficially land apply biosolids, operational challenges during biosolids management (e.g. odors) and landfill disposal, and risks due to emerging regulations related to contaminants of emerging concern (CECs) such as PFAS. Utilities are experiencing a significant increase in annual budgets to manage biosolids, resulting in an increased cost burden for rate payers, and a constant risk of disruption to their biosolids management approach due to market, regulatory and social factors e.g. utilities in the State of Maine experienced significant challenges, disruption to their operations and cost increases when the State banned land application of all biosolids and biosolids containing products in April 2022. Also, more informed communities across the US are demanding sustainable approaches to manage biosolids to address potential concerns due to odors, pollution risks (real or perceived) to the environment due to CECs, and due to increased focus on sustainability and resource recovery. The above-described market, regulatory and community factors are driving a renewed interest in sustainable thermal treatment technologies such as pyrolysis and gasification. Pyrolysis or gasification include high temperature treatment of biosolids in an oxygen starved environment (pyrolysis) or sub-stochiometric oxygen environment (gasification) to produce a value derived product referred to as biosolids-biochar (biochar). These processes offer promise to address biosolids management challenges discussed above and provide a sustainable solution to create resilient and lasting community benefits. Figure 1 provides a typical process flow diagram of commercially viable pyrolysis and gasification processes for biosolids. Figure 1 - Pyrolysis and Gasification Process Flow Diagram Gasification and pyrolysis processes, although considered proven and have been successfully used for decades by the energy and biomass industry, are new and considered innovative for the wastewater industry. Commercial scale experience with implementation of pyrolysis and gasification for biosolids is limited. The presence of high ash content and metals in biosolids as compared to woody biomass also result in unique treatment and operational challenges. This paper will examine the challenges faced by the wastewater industry in the adoption of these technologies, and provide recommendations to accelerate its adoption, manage implementation risks and chart a path to success. Challenges faced by some of the early adopters described below range from lack of technology readiness, commercial viability, procurement and supply chain challenges, compliance with US codes and standards, limited experience that the technology providers have working with public utilities and risks associated with the financial strength/maturity of the technology providers. Operational facilities in the United States, Europe and Australia will be used as case studies to assimilate key learnings related to the planning, design, construction and operation of these facilities, and provide recommendations to incorporate into future projects. The following is a list of facilities that will be evaluated and presented as case studies: 1.Biosolids pyrolysis facility at the Ephrata Borough WWTP # 1 in Ephrata, Pennsylvania, USA. The facility is under construction and is expected to be operational by mid-2024. 2.Biosolids gasification facility at the Edmonds WWTP in Edmonds, Washington, USA. This biosolids gasification facility became operational in October 2023. 3.Biosolids pyrolysis facility at the Silicon Valley Clean Water WWTP located in Redwood City, California. This facility has been operational for more than five years. 4.Biosolids gasification facility in Bethel, Pennsylvania, USA. The facility is under construction. 5.Operational biosolids pyrolysis facility located at the Farevejle WWTP in Denmark, Europe. 6.Biosolids gasification facility located at Logan Water's Loganholme WWTP near Brisbane, Australia. The case study summaries will provide an understanding of the drivers behind selection of pyrolysis and gasification for biosolids treatment, considerations and key questions addressed during the planning phase to proceed forward with this approach, design criteria and approach, lessons learned during procurement and construction, operational and maintenance requirements and how is biochar beneficially used. Operating and performance data from operational facilities, biochar characterization/quality data including PFAS, will be presented to demonstrate the differences between technologies and the inter-relationship between the various process components. The marketability of biochar produced will be compared to other common biosolids end products. The authors are currently working on the construction of the biosolids pyrolysis facility at the Ephrata Borough WWTP # 1. Figure 2 is a construction progress photograph that shows the air pollution control equipment in the foreground, and the biosolids dryers and ancillary equipment in the background. Figure 2 - Ephrata Borough WWTP #1 Biosolids Pyrolysis Facility (construction progress photograph) For the Ephrata Borough WWTP # 1 biosolids pyrolysis facility, the design of a complete pyrolysis treatment process will be evaluated, including the selection and sizing of dewatering equipment, drying equipment, dried biosolids storage, pyrolysis reactor and heat recovery, biochar handling equipment, and air pollution control equipment. Presentation Learning Objective: This paper and presentation will provide Utility Owners, Engineers and Operators a fundamental understanding of biosolids pyrolysis and gasification facility planning, design, construction and operational considerations, including lessons learned by early adopters that will be valuable for the implementation of future projects. Attendees will learn about biochar, including its current uses and emerging beneficial use trends. Attendees will also learn how thermal technologies like pyrolysis and gasification offer promise to destroy PFAS compounds, rendering it a resilient biosolids stabilization solution in the face of PFAS risks to water and resource recovery facilities (WRRFs). The paper will demonstrate how innovative thermal treatment technologies can help address pressing challenges faced by current biosolids management practices e.g. land application, and result in a value-added solution to realize long-lasting community benefits.