Short-term effects of monoethanolamine and copper on the activities of Anammox bacteria

Organic solvents and heavy metals are commonly found in industrial wastewater. These compounds may affect or inhibit the activities of microbes involved in biological wastewater treatment process. Monoethanolamine (MEA) is an organic nitrogen containing solvent used in thin-film transistor liquid crystal display industry as stripper. MEA is usually recognized as slowly biodegradable organic solvent. Copper is the most common heavy metals found in swine wastewater. The presence of copper in wastewater can stimulate or inhibit the microbial processes involved in the biological treatment process. In this study, the effects of MEA and copper on the activities of Anammox (anaerobic ammonium oxidation) bacteria were investigated in batch tests. Synthetic wastewaters containing NH₄ ⁺-N (70 mg L⁻¹) and NO₂ ⁻-N (70 mg L⁻¹) were spiked with either MEA (0 to 500 mg L⁻¹) or copper (0 to 10 mg L⁻¹) at different concentrations and used as media for batch tests. Results of batch tests revealed that MEA, at all concentrations inhibited the activity of Anammox bacteria. The IC₅₀ value of MEA was calculated to be 175 mg L⁻¹. The noncompetitive inhibition model (R² = 0.81) and linear inhibition model (R² = 0.87) were fitted well with the experimental data of Anammox inhibition at different MEA concentrations. On the other hand, activity of Anammox bacteria was strongly inhibited by the presence of copper at mixed liquor volatile suspended solids (MLVSS) of < 2000 mg L⁻¹. The IC₅₀ value of copper was calculated to be 4.2 mg L⁻¹. Under the experimental conditions, inhibition of Anammox bacterial activity increased with concentration of copper (1 to 10 mg L⁻¹) and exposure time (3 to 24 h) at lower biomass concentration (< 2000 mg L⁻¹ VSS). However, the specific Anammox activity is positively affected by copper at higher biomass concentration (> 2500 mg L⁻¹ of VSS) and longer exposure time. The inhibition of Anammox bacterial activity by copper was found to be higher at 25 °C compared to at 35 °C. Overall, the results suggested that effect of copper on specific Anammox activity was influenced by concentrations of copper and biomass, exposure time and temperature.