Decarburization, denitrification characteristics and microbial community analysis of a full-scale two-stage anoxic–oxic process for treating refractory coking wastewater

Coking wastewater is a representative intractable industrial wastewater, which contains plenty of organic pollutants and nutrient nitrogen and needs to be treated effectively. The decarburization, denitrification characteristics and microbial community composition and structure of coking wastewater treated by a full-scale two-stage anoxic-oxic (A/O) process were systematically investigated. The results showed that the full-scale two-stage A/O process exhibited outstanding decarburization and denitrification capability with a removal efficiency above 90% for chemical oxygen demand (COD), ammonium nitrogen (NH₄ ⁺-N), and total nitrogen (TN) in coking wastewater. Different biological reaction tanks in the two-stage A/O process played various roles in coking wastewater treatment. COD was mainly removed in the first stage anoxic tank (A1), TN was mainly removed in A1 and the second stage anoxic tank (A2), and NH₄ ⁺-N was mainly removed in the first stage oxic tank (O1). The function of different biological reaction tanks was highly associated with the composition and structure of the microbial community. The differential microorganisms in different biological reaction tanks were determined by multidimensional analysis. <i>Thiobacillus</i>, <i>Thauera</i>, <i>Thioalkalispira</i>, <i>Pedomicrobium</i>, <i>Azoarcus</i>, <i>etc</i>, were the key differential microorganisms in A1. <i>Mycobacterium</i>, <i>Nitrospira</i>, <i>Acinetobacter</i>, <i>Pseudomonas</i>, <i>Nitrosomonas</i>, <i>etc</i>, were the key differential microorganisms in O1. <i>Bacillus</i>, <i>Thiobacillus</i>, <i>Mesorhizobium</i>, <i>Pusillimonas</i>, <i>etc</i>, were the key differential microorganisms in A2. <i>Truepera</i>, <i>Legionella</i>, <i>Sphingobium</i>, <i>Pseudomonas</i>, <i>etc</i>, were the key differential microorganisms in the second stage oxic tank (O2). Augmenting the key microorganisms in different biological reaction tanks is crucial for boosting the treatment effect of actual coking wastewater.