Abundance and distribution of microorganisms involved in denitrification in sediments of a Myriophyllum elatinoides purification system for treating swine wastewater

Environmental pollution from livestock production, particularly swine production, is often managed by the use of constructed wetlands, which incorporate plants such as Myriophyllum elatinoides as a means of treating wastewater. The M. elatinoides purification system has been shown to effectively remove, via nitrification and denitrification, more than 90 % of the total nitrogen (TN) and 84 % of the NH₄ ⁺-N produced in swine wastewater. However, the mechanisms of variation in aquatic environmental factors and how the interaction of these factors affects denitrification by microorganisms in sediments remain poorly understood. In this study, the impacts of dissolved oxygen (DO), TN, NH₄ ⁺-N, and NO₃ ⁻-N on the abundance, diversity, and community distribution of denitrifiers in the sediments from different concentrations and types of wastewater including tap water (CK), two strengths of synthetic wastewater: 200 mg NH₄ ⁺-N L⁻¹ (T1) and 400 mg NH₄ ⁺-N L⁻¹ (T2), swine wastewater diluted 50 % (T3), and swine wastewater (T4) were investigated in a microcosm experiment. A significant improvement was observed in the abundance of denitrification genes (nirK and nirS) in response to increased NO₃ ⁻-N and DO in the swine wastewater sediments. The abundance of these denitrification genes was highest in the T4 sediments compared with other treatments. Terminal restriction fragment length polymorphism (T-RFLP) analysis revealed that the DO, TN, and NH₄ ⁺-N positively impacted the richness index (S) of the nirK denitrifiers in T1, whereas the NO₃ ⁻-N negatively affected the Simpson diversity index (D) of nirK and nirS denitrifiers in T3 and T4. However, the NO₃ ⁻-N positively affected the nirK and nirS denitrifier community distribution, whereas the DO negatively affected the nirK and nirS denitrifier distribution in T3 and T4. These findings will be helpful in that they allow us to recognize the effects of environmental factors on the formation of the denitrifiers in the sediments in a M. elatinoides purification system.