T-RFLP biomolecular indicator for partial nitritation under saline conditions and machine learning application

Abstract

This study introduces the smart development of a cost-effective biomolecular indicator using terminal restriction fragment length polymorphism (T-RFLP) based on the 16S rRNA gene database obtained from operating the partial nitritation (PN) process under saline conditions. As a result of next-generation sequencing (NGS) on the 16S rRNA gene, ammonia-oxidizing bacteria (AOB) of Nitrosomonas sp. OTU0 (N. OTU0) favored higher salinity of 20-35 g-NaCl/L, while Nitrosomonas sp. OTU8 (N. OTU8) and Nitrosomonas sp. OTU11 (N. OTU11) were predominant under 20 g-NaCl/L. The T-RFLP system with the restriction enzymes of TaiI and FnuDII, which was thoroughly simulated based on the NGS data of the 16S rRNA gene, effectively differentiates N. OTU0 against N. OTU8 and N. OTU11. In addition, together with AOB's signals, the signals of nitrite-oxidizing and heterotrophic bacteria were obtained as biomolecular indicators of successful PN under saline conditions. These findings suggest that T-RFLP can serve as an economically viable monitoring approach for the sensitive PN process under saline conditions to achieve more sustainable nitrogen removal. For further application, the designated T-RFLP signals of this study were applied to the regression of ammonia conversion rate through machine learning modeling. The regression showed R2 values of 0.9446 and 0.9458 for the training and test sets, respectively. The contribution of T-RFLP for the regression was quantified by a shapley additive explanation (SHAP).