Fermentation-derived carbon sources for enhanced biological phosphorus removal (EBPR) in dairy-processing wastewater: Pathways, control and process integration

Enhanced biological phosphorus removal (EBPR) in dairy-processing wastewater is often constrained not by total chemical oxygen demand (COD), but by whether dairy-derived carbon is converted into substrates that are available to polyphosphate-accumulating organisms (PAOs). Lactose, proteins, fats and sludge-derived organics follow different hydrolysis and fermentation pathways, producing variable mixtures of acetate, propionate, lactate, branched-chain volatile fatty acids and long-chain fatty acids. This review specifically examines this upstream carbon-transformation problem and its integration with downstream EBPR, rather than revisiting the broader EBPR mechanisms and operational constraints. Evidence is synthesised across dairy COD fractionation, fermentation pathway and intermediate speciation, and downstream microbial and phosphorus removal responses. The review identifies composition-specific failure modes, evaluates how pH, hydraulic retention time, loading, biomass retention and stream management influence fermentate quality, and develops a process-selection framework linking feed characteristics to fermentation, pretreatment and side-stream options. The synthesis indicates that reliable EBPR requires control of not only total VFA production, but also fermentate speciation, inhibitory carryover and the timing and location of carbon delivery. These findings provide practical guidance for designing and monitoring fermentation-assisted EBPR under variable conditions in dairy-processing wastewater treatment.