Pyrolysis and gasification at water resource recovery facilities: Status of the industry

Abstract

Wastewater treatment generates solids requiring subsequent processing. Costs and contaminant concerns (e.g., per‐ and polyfluoroalkyl substances [PFAS]) are challenging widely used landfilling and land application practices. These circumstances are partly driving the re‐emergence of pyrolysis and gasification technologies along with beneficial reuse prospects of the char solid residual. Previously, technologies experienced operational challenges leading to revised configurations, such as directly coupling a thermal oxidizer to the reactor to destroy tar forming compounds. This paper provides an overview of pyrolysis and gasification technologies, characteristics of the char product, air emission considerations, and potential fate of PFAS and other pollutants through the systems. Results from a survey of viable suppliers illustrate differences in commercially available options. Additional research is required to validate performance over the long‐term operation and confirm contaminant fate, which will help determine whether resurging interest in pyrolysis and gasification warrants widespread adoption. Practitioner Points Pyrolysis and gasification systems are re‐emerging in the wastewater industry. Direct coupling of thermal oxidizers and other modifications offered by contemporary systems aim to overcome past failures. Process conditions when coupled with a thermal oxidizer will likely destroy most organic contaminants, including PFAS, but requires additional research. Three full‐scale facilities recently operated, several in construction or design that will provide operating experience for widespread technology adoption consideration.

High‐temperature technology survey and comparison among incineration, pyrolysis, and gasification systems for water resource recovery facilities

“…The long‐term durability of components subjected to high temperatures and the potentially abrasive nature of the materials being processed can lead to significant maintenance requirements anecdotally supported by the authors' experience with incineration systems. Winchell, Ross, et al (2022) also discussed some of the challenges experienced by past versions of the pyrolysis and gasification technologies including material handling difficulties. Contemporary systems need to prove the equipment employed reliably handles sludge or biosolids and the resulting residuals.…”

“…Particulates emitted with the flue gas require removal to meet air emissions regulations. In FBFs, all the ash flows out of the furnace with the flue gas requiring a robust APC system that removes PM (Winchell, Ross, et al, 2022). Conversely, pyrolysis and gasification systems generally remove the char from the thermal reactor mechanically, reducing the potential particulate load in the flue gas.…”

“…The fate of emerging pollutants has been discussed for pyrolysis systems (Winchell, Ross, et al, 2022) in detail. For example, Mercl et al (2021) tested 69 pharmaceuticals from 27 drug classes in biosolids finding undetectable levels in the char after pyrolysis at 420°C.…”

“…A parallel and similar track of research shall include the drying process critical to the success of pyrolysis and gasification systems. Winchell, Ross, et al (2022) discussed the importance of drying for these high‐temperature systems and the lack of a reliable technology to dry sludge compared with digested biosolids. Overcoming this hurdle would broaden the applicability of these pyrolysis and gasification technologies.…”

“…In addition, five technology suppliers known to the authors are in the process of designing or constructing several facilities across North America. See Winchell, Ross, et al (2022) for a more in depth discussion on these topics.…”