Towards low carbon demand and highly efficient nutrient removal: Establishing denitrifying phosphorus removal in a biofilm-based system

Inadvertently enriched cyanobacteria prompted bacterial phosphorus uptake without aeration in a conventional anaerobic/oxic reactor

The enhanced biological phosphorus removal (EBPR) process requires alternate anaerobic and aerobic conditions, which are regulated respectively by aeration off and on. Recently, in an ordinary EBPR reactor, an abnormal orthophosphate concentration (PO43--P) decline in the anaerobic stage (namely non-aerated phosphorus uptake) aroused attention. It was not occasionally but occurred in each cycle and lasted for 101 d and shared about 16.63 % in the total P uptake amount. After excluding bio-mineralization and surface re-aeration, indoor light conditions (180 to 260 lx) inducing non-aerated P uptake were confirmed. High-throughput sequencing analysis revealed that cyanobacteria could produce oxygen via photosynthesis and were inhabited inside wall biofilm. The cyanobacteria (Pantalinema and Leptolyngbya ANT.L52.2) were incubated in a feeding transparent silicone hose, entered the reactor along with influent, and outcompeted Chlorophyta, which existed in the inoculum. Eventually, this work deciphered the reason for non-aerated phosphorus uptake and indicated its potential application in reducing CO2 emissions and energy consumption via the cooperation of microalgal-bacterial and biofilm-sludge.

Towards low carbon demand and highly efficient nutrient removal: Establishing denitrifying phosphorus removal in anaerobic/anoxic/oxic + nitrification system

A two-sludge anaerobic/anoxic/oxic + nitrification system with simultaneous nitrogen and phosphorus removal was studied for enhanced low-strength wastewater treatment. After 158 days of operation, excellent NH4+-N, chemical oxygen demand (COD) and PO43--P removal (99.0 %, 90.0 % and 92.0 %, respectively) were attained under a low carbon/nitrogen ratio of 5, resulting in effluent NH4+-N, COD and PO43--P concentrations of 0.3, 30.0 and 0.5 mg/L, respectively. The results demonstrate that the anaerobic/anoxic/oxic sequencing batch reactor (A2-SBR) and nitrification sequencing batch reactor (N-SBR) had favorable denitrifying phosphorus removal and nitrification performance, respectively. High-throughput sequencing results indicate that the phosphate-accumulating organisms Dechloromonas (1.1 %) and Tetrasphaera (1.2 %) were enriched in the A2-SBR, while the ammonia-oxidizing bacteria Nitrosomonas (7.8 %) and the nitrite-oxidizing bacteria Nitrospira (18.1 %) showed excellent accumulation in the N-SBR. Further analysis via functional prediction revealed that denitrification is the primary pathway of nitrogen metabolism throughout the system. Overall, the system achieved low carbon and high efficiency nutrient removal.

C4-HSL-mediated quorum sensing regulates nitrogen removal in activated sludge process at Low temperatures

The activated sludge process faces challenges in achieving adequate nitrification ability under low-temperature conditions. Therefore, we investigated the effects of different concentrations of exogenous N-butyryl-homoserine lactone (C4-HSL) on nitrogen removal in lab-scale sequencing batch reactors (SBRs) at 10 °C. The results revealed that both 10 and 100 μg/L of C4-HSL could improve NH4+-N removal efficiency by 26% and reduce the effluent TN concentration to below 15 mg/L. Analysis of extracellular polymeric substances (EPS) revealed that adding C4-HSL (especially 100 μg/L) reduced the protein-like substance content while increasing the humic and fulvic acid-like substance content in EPS. Protein-like substances could serve as carbon sources for denitrifiers, thus promoting denitrification. Moreover, exogenous C4-HSL increased the abundance of bacteria and genes associated with nitrification and denitrification. Further analysis of quorum sensing (QS) of microorganisms indicated that exogenous C4-HSL (especially 100 μg/L) promoted regulation, transportation, and decomposition functions in the QS process. Furthermore, CS, sdh, fum, and mdh gene expressions involved in the tricarboxylic acid (TCA) cycle were enhanced by 100 μg/L C4-HSL. Exogenous C4-HSL promoted microbial communication, microbial energy metabolism, and nitrogen metabolism, thereby improving the nitrogen removal efficiency of activated sludge systems at low temperatures. This study provides a feasible strategy for enhancing denitrogenation performance at low temperatures through exogenous C4-HSL.

Achieving synchronous and highly efficient removal of nitrogen and phosphorus by rapid enrichment and cultivation denitrifying phosphorus accumulating organisms in anaerobic-oxic-anoxic operation mode

Realizing the quick enrichment and development of denitrifying phosphorus accumulating organisms (DPAOs) in actual household wastewater and industrial nitrate wastewater has significant research significance. In this study, a novel operation mode of anaerobic-oxic-anoxic (AOA) was adopted to successfully realize the enrichment and cultivation of DPAOs in urban domestic wastewater. Adjusting influent COD to PO43--P ratio, shortening the aerobic time and decreasing the aeration volume were conducive to select DPAOs in microbial populations. The system was operated for 180 days and the DPAOs were well enriched during the stable operation with the percentage of Dechloromonas increased to 5.1 %. Accordingly, the effluent PO43--P was < 0.3 mg P/L, the removal efficiency of phosphorus was 96.9 % and the removal efficiency of nitrate was 92.5 %. Above all, DPR can be successfully applied to AOA systems with good phosphorus removal performance.

Epiphytic microorganisms of submerged macrophytes effectively contribute to nitrogen removal

Submerged macrophytes play important roles in nutrient cycling and are widely used in ecological restoration to alleviate eutrophication and improve water quality in lakes. Epiphytic microbial communities on leaves of submerged macrophytes might promote nitrogen cycling, but the mechanisms and quantification of their contributions remain unclear. Here, four types of field zones with different nutrient levels and submerged macrophytes, eutrophic + Vallisneria natans (EV), eutrophic + V. natans + Hydrilla verticillata, mesotrophic + V. natans + H. verticillata, and eutrophic without macrophytes were selected to investigate the microbial communities that involved in nitrification and denitrification. The alpha diversity of bacterial community was higher in the phyllosphere than in the water, and that of H. verticillata was higher compared to V. natans. Bacterial community structures differed significantly between the four zones. The highest relative abundance of dominant bacterioplankton genera involved in nitrification and denitrification was observed in the EV zone. Similarly, the alpha diversity of the epiphytic ammonia-oxidizing archaea and nosZI-type denitrifiers were highest in the EV zone. Consist with the diversity patterns, the potential denitrification rates were higher in the phyllosphere than those in the water. Higher potential denitrification rates in the phyllosphere were also found in H. verticillata than those in V. natans. Anammox was not detected in all samples. Nutrient loads, especially nitrogen concentrations were important factors influencing potential nitrification, denitrification rates, and bacterial communities, especially for the epiphytic nosZI-type taxa. Overall, we observed that the phyllosphere harbors more microbes and promotes higher denitrification rates compared to water, and epiphytic bacterial communities are shaped by nitrogen nutrients and macrophyte species, indicating that epiphytic microorganisms of submerged macrophytes can effectively contribute to the N removal in shallow lakes.

Responses of the microbial community and the production of extracellular polymeric substances to sulfamethazine shocks in a novel two-stage biological contact oxidation system

Introduction

The biological contact oxidation reactor is an effective technology for the treatment of antibiotic wastewater, but there has been little research investigating its performance on the sulfamethazine wastewater treatment.

Methods

In this study, a novel two-stage biological contact oxidation reactor was used for the first time to explore the impact of sulfamethazine (SMZ) on the performance, microbial community, extracellular polymeric substances (EPS), and antibiotic-resistant genes (ARGs).

Results

The chemical oxygen demand (COD) and ammonia nitrogen (NH 4 + -N) removal efficiencies kept stable at 86.93% and 83.97% with 0.1-1 mg/L SMZ addition and were inhibited at 3 mg/L SMZ. The presence of SMZ could affect the production and chemical composition of EPS in the biofilm, especially for the pronounced increase in TB-PN yield in response against the threat of SMZ. Metagenomics sequencing demonstrated that SMZ could impact on the microbial community, a high abundance of Candidatus_Promineofilum, unclassified_c__Anaerolineae, and unclassified_c__Betaproteobacteria were positively correlated to SMZ, especially for Candidatus_Promineofilum.

Discussion

Candidatus_Promineofilum not only had the ability of EPS secretion, but also was significantly associated with the primary SMZ resistance genes of sul1 and sul2, which developed resistance against SMZ pressure through the mechanism of targeted gene changes, further provided a useful and easy-implement technology for sulfamethazine wastewater treatment.