Significance of the pathogen screening result within the REFRAME framework

The REFRAME project aims to redefine urban wastewater treatment plants by transforming them from end-of-pipe treatment facilities into resource recovery platforms and biorefineries, capable of producing high-value bio-based products such as volatile fatty acids (VFAs), polyhydroxyalkanoates (PHAs), and functional microbial biomass. This approach aligns with the broader European strategy on circular bioeconomy, where waste streams are reconceptualized as secondary raw materials through controlled biological and process-engineering solutions.

A central aspect of REFRAME is the development and validation of novel metabolic and process configurations that enable the decoupling of waste origin from product quality. In this context, recent work by Lo Coco, Pezzuto, Frison et al. on a novel closed-loop membrane contactor system has demonstrated how VFAs derived from waste-based fermentation can be transferred to microbial cultures without direct contact between the wastewater-derived matrix and the biomass itself. This configuration allows the stable production of high-quality microbial biomass with controlled composition, while effectively breaking the traditional conceptual and operational link between “waste” and “product”.

Within this technological framework, the pathogen screening of PHA-rich dried biomass represents a critical milestone. The comprehensive PCR-based analysis, performed by an independent accredited laboratory, confirmed the absence of all tested human pathogens, including high-risk viral and bacterial targets. This result is particularly significant because pathogen presence constitutes a fundamental go/no-go criterion for any downstream valorisation pathway involving feed or food-related applications. By demonstrating the absence of such pathogens, one of the most critical safety barriers associated with wastewater-derived products is effectively removed.

This finding does not merely reflect an analytical outcome, but rather validates the underlying process concept. It confirms that advanced, metabolism-driven systems, such as closed-loop membrane contactors, are not only effective in recovering carbon and producing biopolymers or microbial biomass, but can also deliver products that meet stringent sanitary expectations, independent of the waste origin of the substrate. In this sense, the result provides experimental evidence that the boundary between “waste” and “resource” can be technically and scientifically dismantled.

The absence of detectable human pathogens enables credible engagement with regulatory bodies, industrial stakeholders, and the aquaculture sector, where safety considerations are paramount. While additional analyses (e.g., nutritional profiling, and feed-specific safety assessments) are still required to progress toward formal feed certification, the pathogen screening establishes a robust foundation upon which these subsequent steps can be built.

This result represents a key milestone within REFRAME, demonstrating that wastewater-based biorefineries can generate microbial biomass and bioproducts that are not only technically functional, but also compatible with high-value and safety-sensitive applications such as animal feed. It marks a tangible shift from theoretical circularity to operational and verifiable resource recovery, reinforcing the role of advanced bioprocess engineering in redefining the future of sustainable wastewater treatment systems.