Exploration of simulation-based optimization and impact factors in short-cut nitrification-denitrification start-up in coal pyrolysis wastewater

Phenolic compounds and nitrogen in coal pyrolysis wastewater have become limiting factors for industrial development, conflicting with principles of sustainability and environmental protection. While denitrification technology for urban sewage has matured, it still faces numerous limitations, and research on short-cut denitrification in coal pyrolysis wastewater is relatively limited. This study investigated the degradation of phenolic compounds and short-cut denitrification effects in coal pyrolysis wastewater under different pH, Dissolved Oxygen (DO), and external carbon source conditions. Under sufficient alkalinity, pH variations had no significant impact on the NO2−-N Accumulation Ratio (NAR) and Total Nitrogen (TN) removal efficiency. DO is a key control factor in short-cut nitrification-denitrification systems. Operating the reactor at low DO concentrations (0.5–1.2 mg/L) was beneficial for maintaining the stability of short-cut nitrification-denitrification. When the Chemical Oxygen Demand (COD) ratio of methanol to crude phenol was 1:1 and 1:3, the denitrification rates were 5.13 mg NO2−-N/(g vss·h) and 3.94 mg NO2−-N/(g vss·h), respectively. Using only crude phenol as an external carbon source with a C/N ratio of about 4, the TN removal rate reached 90.32 %, but the denitrification rate decreased to 1.66 mg NO2−-N/(g vss·h). Gas Chromatography-Mass Spectrometry (GC–MS) analysis revealed that phenol is the main electron donor in the system's denitrification process, and to ensure the denitrification rate, the denitrification carbon source is provided jointly by methanol and crude phenol. [Display omitted] •Methanol and crude phenol in equal proportions maximize denitrification efficiency.•Maintaining low DO levels is crucial for stable nitrification-denitrification.•Phenols were primary electron donor for denitrification.