Organic Waste as a Secondary Carbon and Nutrient Resource: A Systematic Review of Microbial Recovery Routes, Technology Readiness and the Determinants of Resource Accessibility

Organic waste is society’s largest under-exploited secondary carbon and nutrient resource, and what limits access to it is not microbiology. Existing reviews are organized along a single axis, one feedstock, one organism, or one product, and so cannot say which routes are closest to deployment. This review is organized instead around resource accessibility, classifying streams by the macromolecular class dominating their fermentable fraction rather than by industrial origin; no single product is its subject. Under PRISMA 2020, 19 PubMed/MEDLINE queries returned 7104 records; 81 sources were synthesized into a matrix of eight waste-stream classes, four microbial platforms and eight non-energy product families, scored on the European Commission technology readiness level scale. Reported performance is high, peaking at 27.4 g L−1 h−1 of lactic acid from cheese whey permeate, yet readiness tracks none of product value, resource abundance, or research volume. It tracks three determinants: feedstock variability, downstream cost share, and regulatory status. Industrial enzymes and organic acids reach TRL 7–9, natural pigments and biosurfactants only TRL 3–6, and life-cycle evidence shows that waste-derived does not imply low impact. Research effort, indexed by records retrieved under the study queries rather than total literature, is inversely related to reported feedstock availability. We propose a resource-side decision framework and a minimum reporting set for recovery accounting.