The increasing share of renewable generation creates a growing need for power system flexibility. However, flexibility is often described from different physical, operational, and commercial perspectives, making it difficult to translate industrial process capabilities into market participation. This paper proposes a qualitative resource-service-product framework and audit methodology for systematically mapping physical flexibility resources to flexibility services and candidate commercialization arrangements.

The framework distinguishes between physical flexibility resources, the services those resources may provide, and the products or contractual arrangements through which flexibility may obtain economic value. The audit procedure identifies process boundaries, controllable assets, buffers, constraints, recovery requirements, service compatibility, and product access considerations. Physical feasibility, operational acceptability, product eligibility, and economic viability are treated as separate assessment layers.

The methodology is demonstrated using the aeration process of a wastewater treatment plant in Greece. Inverter-controlled aerators provide the direct electrical control action, while permissible temporary deviation of the biological process provides limited temporal buffering. Potential services include energy cost minimization, peak clipping, portfolio balance management, and balancing service provision. Day-ahead and intraday energy transactions and balancing products such as mFRR are identified as candidate commercialization routes, although eligibility is not established.

The work demonstrates that physical controllability, service compatibility, and commercial eligibility are distinct assessment stages. The qualitative audit identifies plausible flexibility pathways, exclusions, and evidence gaps, providing a structured basis for subsequent quantitative flexibility and market analyses.