Auto-Thermal Gasification and Biosolids Drying: Achievements and Lessons Learned from a Three-Year Pilot at a Pennsylvania WWTF (>1.3 wet metric tons/hr)

Introduction
The Morrisville Biosolids Gasification Pilot Project (the Project) demonstrated that Ecoremedy's Fluid Lift Gasification technology can reliably dry and gasify industrial volumes of dewatered biosolids without bulking agents or fossil fuel. The Project garnered international interest and was lauded by industry experts during tours.

This case study explores how a public-private partnership enabled piloting of this innovative technology. After briefly reviewing design, construction, permitting, and commissioning, this presentation will summarize key accomplishments, including a summary of "lessons learned" during this historic project.

Design and Construction
The Morrisville Municipal Authority (MMA) is developing a new wastewater treatment facility (WWTF) at a nearby industrial park to replace the existing WWTF. The goal of the Project was to demonstrate Ecoremedy's FLG technology at the existing WWTF for potential inclusion at the new WWTF.

The MMA provided a greenfield site and waste supply to the Project through a pilot agreement signed in July 2018. Within one year, Ecoremedy completed design, construction, and Phase I permitting. The Project was self-financed by Ecoremedy under a Build-Own-Operate-Maintain model and operated on a tip-fee basis. Startup extended from July 2019 through February 2020, after delays from COVID-19. After commissioning, the Project operated until August 2021.

Ecoremedy completed engineering design in only three months. This was possible by leveraging decades of past success with high-ash, high-moisture manure-based feedstocks, including a week-long demonstration with composted biosolids. The Project was a 7x scale-up from past commercial projects.

A single process train was designed to operate for both Phase I loading (up to 4,536 wet metric tons/yr of undigested cake at 18-22% solids from the MMA's filter belt press) and Phase II loading (18,144 wet metric tons/yr of regional merchant capacity, with 22,680 wet metric tons/yr of total system capacity). It was designed to convert cake to three end-products without shutting down or retooling: concentrated minerals (ash fraction), carbon-rich biochar, and dried Class A product (permitted as an EPA recognized "Alternative Fuel").

The Project was housed in a single-story post and beam, metal-clad building (30 m long x 15 m wide with an eave height of 8 m) adjacent to the MMA's dewatering building. Pumping was not possible, so a receiving building was added to accept roll-off containers from MMA and cake hauled in from off-site. The building was selected for easy deconstruction due to the temporary nature of the pilot location.

Permitting
For Phase I, Ecoremedy submitted a Request for Determination of eligibility for a Permit By Rule (PBR) as a captive waste processer with de minimis air emissions. The PA Department of Environmental Protection (PA DEP) granted the PBR permit, with additional flexibility for R&D activities. Without previous biosolids gasification air data, air emissions were modeled using stack data from Ecoremedy poultry litter gasification projects. The elemental analysis of biosolids is similar to poultry litter for energy comparison.

Phase II air permitting required stack testing to validate emissions modeling as a minor source status, or potential de minimis source.

PA DEP granted a general waste permit for Phases I and II, as well as a Phase III expansion to multiple process trains (99,790 wet metric tons/yr). Following precedent from past FLG projects and similar technologies, the Project was deemed a non-incineration technology in PA, and later by the United States Environmental Protection Agency.

Operations
The Project was designed for continuous round-the-clock operation. Due to site-specific conditions and circumstances caused by COVID-19, Ecoremedy operated the facility with daily startup and shutdown on a five-day work week for two years. Automated operations were overseen by two operators per shift.

Project Results and Lessons Learned

Major successes of the Project include:
• Autothermal gasification of biosolids with temperatures across the gasifier and oxidizer ranging from 815 C - 1093 C and natural gas used only during start-up
• Fully automated biosolids drying with temperature drop across of 400 C across the dryer
• Sustained throughput of over 1.4 wet metric tons per hour with two-shift operations and daily shutdown
• Incoming PFAS levels ranged from 1 - 400 ppb per compound in pressed biosolids. 36 PFAS compounds were each reduced to non-detect (<2 ppb) in concentrated minerals after gasification.
• Non-detect odors from Ecoremedy process discharge during steady-state operations
• Consistent production of granular Class A biosolids > 90% TS with low-dust, suitable for land application and use as an EPA-recognized Alternative Fuel
• Consistent production of concentrated minerals suitable for land application or landfill
• Technology-wide determination from US EPA that FLG is not subject to the Sewage Sludge Incineration (SSI) Rule

Lessons learned include:
• Upgrades were needed for the mixer, material handling, bucket elevator, and odor control systems
• When possible, excess thermal energy recovered from the biosolids should be used to preheat the stack for plume abatement due to negative public perception of steam
• To prevent overnight freezing of a carbon filter, 24-hour operations and a condensing venturi scrubber are preferred with a targeted RH of 60%
• Direct pumping of dewatered biosolids to the mixer is preferred to avoid overworking the cake during material handling

Project Completion
On August 23, 2021, when the plant was offline for the weekend, a fire started in the receiving building. No one was injured. The fire marshal's official report ruled the cause of the fire as accidental. There was insufficient time left in the pilot agreement to rebuild and resume operations. Ecoremedy and the MMA agreed to conclude the pilot.

Next Steps and Conclusion
As a result of the Project's successes, the MMA remains interested in the potential of Ecoremedy's gasification technology to halt the rising costs and environmental hazards associated with biosolids disposal. The industrial park where the new MMA WWTF is being constructed has changed ownership and now requires the new WWTF to be completed (estimated 2026) before Ecoremedy can begin construction. At the time of this writing, Ecoremedy is evaluating project sites near Philadelphia for a regional merchant facility, with a general waste permit already granted for 99,790 wet metric tons/yr.

Knowledge gained from the Project, including the Lessons Learned above, were applied to the design of the Edmonds Project near Seattle, WA. The Edmonds Project has a design capacity of 12,927 wet metric tons/yr of dewatered biosolids, with co-gasification of all grit and screenings, and will be installed in 2022.

This paper will present the challenges overcome and advancements made by this historic project, including the operations data in the figures and tables following this abstract.