Microbial interactions and nitrogen removal performance in an intermittently rotating biological contactor treating mature landfill leachate

Achieving advanced nitrogen removal from oxytetracycline wastewater by partial nitrification-endogenous denitrification: performance, metabolic pathways, microorganism community, and potential applications

Partial nitrification-endogenous denitrification (PNED) can achieve advanced nutrient removal from wastewater. Herein, an anaerobic/oxic/anoxic/oxic-sequencing batch reactor (AOAO-SBR) was used to treat real oxytetracycline (OTC) pharmaceutical wastewater via PNED. Partial nitrification with an average nitrite accumulation ratio of 91.5 % was achieved. When the influent total nitrogen was 105 ± 10 mg/L, the effluent of it was only 5.9 mg/L, and the removal efficiency was 94.8 %. In the typical cycle, multiple nitrogen removal pathways including endogenous denitrification, simultaneous nitrification-denitrification, and denitrification contributed to 68.0 %, 20.3 %, and 7.3 %. The effluent concentration of NH4+-N was 5 mg/L, and NO2--N and NO3--N were not detected. The biodegradation pathways of OTC were proposed, 47.1 % of OTC was degraded and eight possible degradation byproducts were detected with low toxicity in the extracellular and intracellular. Moreover, Extracellular polymeric substances increased from 35.3 (mg/gVSS) to 74.4 (mg/gVSS) during 120 days, which acts as a critical role in OTC degradation. High-throughput sequencing results showed that the relative abundance of ammonia-oxidizing bacteria was 2.4 %, and nitrite-oxidizing bacteria were washed out, which was conducive to partial nitrification. Candidatus_Competibacter (13.9 %) enhanced nitrogen removal by endogenous denitrification. Thauera (13.5 %), Ottowia (9.2 %), and OLB13 (1.2 %) are the main OTC-degrading bacteria. This study provides a valuable reference to treat OTC pharmaceutical wastewater effectively.

Nitrogen removal intensification of biofilm through bioaugmentation with Methylobacterium gregans DC-1 during wastewater treatment

The increasing concern for environmental remediation has led to a search for effective methods to remove eutrophic nutrients. In this study, Methylobacterium gregans DC-1 was utilized to improve nitrogen removal in a sequencing batch biofilm reactor (SBBR) via aerobic denitrification. This bacterium has the extraordinary characteristics of strong auto-aggregation and a high ability to remove nitrogen efficiently, making it an ideal candidate for enhanced treatment of nitrogen-rich wastewater. This strain was used for the bioassessment of a test reactor (SBBRbio), which showed a shorter biofilm formation time compared to a control reactor (SBBRcon) without this strain inoculation. Moreover, the enhanced biofilm was enriched in TB-EPS and had a wider variety of protein secondary structures than SBBRcon. During the stabilization phase of SBBRbio, the EPS molecules showed the highest proportion of intermolecular hydrogen bonding. It is possible that bioaugmentation with this strain positively affects the structural stability of biofilm. At influent ammonia loadings of 100 and 150 mg. L-1, the average reduction of ammonia and nitrate-nitrogen was higher in the experimental system compared to the control system. Additionally, nitrite-N accumulation was lower and N2O production decreased compared to the control. Analysis of the microbial community structure demonstrated successful colonization in the bioreactor by a highly nitrogen-tolerant strain that efficiently removed inorganic nitrogen. These results illustrate the great potential of this type of denitrifying bacteria in the application of bioaugmentation systems.