Comprehensive evaluation of carbon source denitrification performance using the TOPSIS method

Considering the differentiated requirements for carbon source performance and cost under diverse engineering objectives, three liquid composite carbon sources with different chemical oxygen demand (COD) equivalents (C_20, C_40, C_120), along with liquid sodium acetate (LS) and solid sodium acetate (SS), were selected as research subjects to systematically investigate their denitrification performance and economic feasibility. By comparing the differences in denitrification rate, nitrogen removal efficiency, and cost among the selected carbon sources, a multi-index comprehensive evaluation system was established based on the Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) to determine the optimal carbon source selection strategy. The results indicated that the NO₃⁻-N concentrations of all five carbon sources showed a significant linear degradation trend (R² > 0.98), which was consistent with the zero-order kinetic characteristics. Analysis of variance (ANOVA) confirmed that there were significant differences in denitrification rate, nitrogen removal efficiency, and unit nitrogen removal cost among different carbon source types. Specifically, SS, LS, and C_120 were identified as high-efficiency carbon sources, while C_40 exhibited a significantly lower nitrogen removal cost than C_20, LS, and SS, along with higher stability in unit nitrogen removal cost. The TOPSIS comprehensive evaluation results demonstrated that LS was the optimal choice for scenarios prioritizing high-efficiency nitrogen removal; when economic efficiency was the primary consideration, C_40 performed better; when equivalent consistency was regarded as the core evaluation indicator, LS and C_40 were suitable for different weight combination scenarios. To provide a theoretical basis and technical support for the scientific selection, cost control, and improvement of operational stability in wastewater treatment engineering, this study clarified the performance levels and applicable scenarios of different carbon sources.