Implementing Supercritical Water Oxidation to Overcome Biosolids Challenges

Presentation Description: Growing concerns associated with contaminants of emerging concerns (CECs) (especially PFAS), greenhouse gas emissions, and regulations have begun to limit the end-use alternatives for biosolids. In response to these pressures, biosolids producers are considering new and innovative treatment options that require a new perspective to the historical understanding of biosolids treatment and end-use. Orange County Sanitation District (OC San) has embarked to seek a new technology, Supercritical Water Oxidation (SCWO) to diversify their end products from water reclamation facilities (WRRFs). OC San teamed with 374Water that is collaborated Hazen and Sawyer, and Merrell Brothers to demonstrate this technology at their site. SCWO is a promising technology that converts organic material (biosolids) to inert gases, minerals and water. Water above 374°C and 22.1 MPa becomes supercritical, a special state where organic solubility increases, and oxidation processes are accelerated.
SCWO has been recently shown to destroy hazardous substances such as halogenated compounds including poly-fluoroalkyl substances (PFAS). Studies showed a greater than 99% reduction of the total PFAS identified in a targeted compound analysis, including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) (Krause et al, 2022). As a destructive technology, SCWO is proposed as an alternative to incineration and other combustion processes and could be a permanent solution for PFAS-laden biosolids or solid matrices. However, additional investigation of reaction byproducts: water, solids and air emissions need to be conducted for a complete assessment of SCWO’s potential as a safe and effective technology.
OC San is located in South Coast Air Quality Management District (SCAQMD) and an air permit is required for this demonstration project. The research team, including OC San (a Utility), 374Water (a private firm-technology provider), Hazen and Sawyer (a consulting firm), Yorke Engineering (permitting support), Alliance Testing (a source testing firm) worked together to develop a rigorous test plan and granted a research permit to implement SCWO at Plant 1. This presentation will focus on the technology and design details, and provide the steps taken to implement this technology at OC San. The information will benefit utilities that seeks sustainable solution for their biosolids management considering recent end-use restrictions.