Exogenous phytohormone-assisted rotating algal biofilm reactor for enhanced polyacrylamide wastewater treatment and bioresource recovery.

Polyacrylamide (PAM) is a refractory pollutant with a stable molecular structure and low bioavailability, which severely limits the efficiency of conventional biological treatment processes. This study established a rotating algal biofilm (RAB) system for PAM-laden wastewater treatment and investigated the regulatory effects of exogenous indole-3-acetic acid (IAA) and salicylic acid (SA) on treatment performance, carbon metabolism, and microbial communities. Single-dose tests identified 15 mg L-1 IAA and 3 mg L-1 SA as the optimal concentrations under laboratory conditions. The combined IAA + SA treatment outperformed single-hormone and control groups, achieving higher PAM and total organic carbon removal efficiencies, accelerated inorganic carbon turnover, and significantly improved biofilm biomass, chlorophyll-a content, and intracellular lipid accumulation. This approach achieved synchronous wastewater treatment and biomass enrichment within the experimental cycle, and lipid-rich biofilms have potential for subsequent resource utilization. Specifically, IAA promoted the enrichment of typical heterotrophic genera including Persicitalea, Arenimonas and Lewinella, which were positively correlated with PAM removal. Meanwhile, SA facilitated photoautotrophic growth to maintain metabolic stability. Combined phytohormone regulation reshaped prokaryotic and eukaryotic community structures, balanced trophic relationships, and supported PAM transformation and carbon metabolic coupling during operation. Overall, this strategy optimized carbon metabolic patterns and microbial assembly, and simultaneously enhanced pollutant removal and high-value biomass accumulation at the laboratory scale. The findings provide a theoretical reference for PAM wastewater bioremediation and biomass resource recovery in phototrophic biofilm systems.