Conventional wastewater treatment combines physical and biochemical methods to reduce organic matter and pathogens from wastewater, producing sludge as a byproduct requiring disposal. Many technologies are available for wastewater treatment, and facilities are designed based on local regulations, resources, and wastewater characteristics. This creates unique infrastructures with variable processes, resulting in the production of sludge with distinct characteristics. Such variability directly impacts downstream management strategies and resource recovery opportunities. In Lawrence, Kansas, two wastewater treatment plants (WWTPs) illustrate this variability. Kansas WWTP uses traditional methods to remove contaminants, such as lime addition. In contrast, the Wakarusa River WWTP, completed in 2018, employs enhanced biological phosphorus removal (EBPR). Our research examines how these treatment routes influence sludge composition and its conversion into valuable products using hydrothermal liquefaction (HTL), a waste-to-energy technology. Results indicate that EBPR sludge contains 10% more carbon than sludge from Kansas WWTP, due to the absence of primary clarification at the Wakarusa facility. Additionally, EBPR sludge presents a wider range of phosphorus species, which is linked to the EBPR process’s tendency to accumulate polyphosphate within the microbial structures. This variability could potentially contribute to improved biochar quality, if these P compounds are bioavailable when used as a fertilizer. Conversely, sludge from the lime-added plant produces four times more biochar and yields a higher-quality biocrude, with decreased oxygen concentration as a function of the calcium present in the sludge. The inorganic matrix, particularly CaO and phosphate speciation, influences both the catalytic behavior during HTL and the partitioning of nutrients and energy-rich organics across product phases. These findings emphasize the importance of understanding local treatment processes to optimize HTL strategies for sustainable sludge management. By tailoring waste-to-energy approaches to the unique characteristics of WWTPs, the United States can lead in resource recovery, address PFAS contamination, and reduce landfill dependency.
