Comparison of Degradation Efficacy and Bacterial Diversity between the A/O and O1/A/O2 Processes for Coking Wastewater Treatment

To evaluate two practical coking wastewater treatment systems, the removal efficacy of major pollutants was compared and bacterial profiles were analyzed using high-throughput sequencing. The A/O (anoxic/oxic) process (named as 1 system) used the activated sludge method, whereas the O1/A/O2 (oxic/anoxic/oxic) process (named as 2 system) adopted the biocontact oxidation method, and the latter added an oil-removal tank and a preaeration tank. The oil-removal tank removed 37.0% of the oil, and phenol and CN− were decreased to 398 and 17 mg/L, respectively. For the final effluent of the O1/A/O2 process, the concentrations of chemical oxygen demand (COD), volatile phenol, total nitrogen, and total CN− were low at 121, 0.09, 45.1, and 0.18 mg/L, respectively. The 2-O1 and 2-O2 tanks presented higher bacterial diversity and lower species richness than the 1-O tank; the most abundant phylum in five biological tanks were Proteobacteria; and Nitrospirae had high richness in the oxic tanks. The microbial diversity and principal component analysis (PCA) revealed that different biological treatment processes and operation modes have significant impacts on the microbial population and species richness. Nitrifying and denitrifying bacteria, such as Nitrosomonas, Nitrospira, Thauera, and Thiobacillus, were relatively abundant, contributing to nitrogen removal.