Combined Effects of Alkalinity Limitation and Chlortetracycline Addition on Ammonia Removal in Sequencing Batch Reactors

摘要

Livestock wastewater is characterized by chlortetracycline (CTC) contamination and alkalinity insufficiency, and ammonia is difficult to remove from this type of wastewater. This study explores the combined effects of alkalinity limitation and CTC addition on the ammonia removal process in sequencing batch reactors. CTC concentrations in the inflow of four bench-scale reactors were 0, 5, 20, and 100mg/L, and the operation phase was divided into five stages by alkalinityitrogen (ALK/N) ratios (7.14, 4.76, 3.56, 2.38, and 0). As the ratio of ALK/N decreased from 7.14 to 0, the ammonia removal efficiency dropped from 98.2% to 28% and the ammonia oxidation rate dropped gradually from 3.713 to 1.416mg/g VSSh. Existence of CTC has an inhibitory effect on ammonia oxidation, ammonia removal efficiency decreased with CTC concentration increases, the same goes for the ammonia oxidation rate. With a decrease in alkalinity, inhibition difference of ammonia removal caused by CTC is narrowed, indicating that alkalinity becomes a limiting factor. CTC had an obvious effect on nitrite accumulation, because nitrite-oxidizing bacteria was more vulnerable to CTC than ammonia-oxidizing bacteria. By considering the use of pH and DO as ammonia removal online detection parameters, only under sufficient alkalinity conditions can pH and DO be used to mark the end of nitrification. CTC does not influence the emergence of the pH and DO inflection points.