Study on the synergistic mechanism of proline in the treatment of high-salt phenolic wastewater by short-time aerobic digestion process

Abstract

High salt concentrations pose a significant challenge to the efficiency of activated sludge (AS) in phenolic wastewater treatment. As a cellular osmoprotectant, proline (Pro) has the capacity to increase the salt tolerance of microbes in AS, hence improving the efficiency of phenolic wastewater degradation. Nevertheless, the precise mechanism behind this enhancement remains ambiguous. This study utilized short-time aerobic digestion (STAD) to examine the kinetics of phenol degradation (250–750 mg/L) by AS under high-salinity stress (2–8%), with the inclusion of Pro (115–575 mg/L) as an auxiliary agent. The process was optimized via response surface methodology (RSM), and the mitigating effect of Pro on microorganisms in AS subjected to salt stress was evaluated. The results demonstrated that the addition of 468 mg/L Pro substantially improved the ability of AS to withstand high-salinity wastewater with high phenol concentrations, which had a salinity of 5.1% and a phenol concentration of 531 mg/L. The addition led to a mitigation rate of the phenol degradation constant k₀ of 38.59 ± 1.54%, resulting in enhanced degradation of chemical oxygen demand (COD), NH₄⁺-N, and NO₃⁻-N. In addition, the prolonged presence of Pro increased AS dehydrogenase activity (DHA) by 24.82% after 30 days. Microbial community analysis demonstrated that Pro promoted the proliferation of functional microorganisms such as Proteobacteria, Firmicutes, Acinetobacter, and Comamonas. These bacteria have essential functions in the elimination of phenol and organic matter, as well as the absorption of nitrogen. This study emphasizes the impact of Pro as a compatible solute in the treatment of high-salinity and high-phenol wastewater in the STAD process.