Treatment of wastewater with high carbon-to-nitrogen ratio using a waterfall aeration biofilm reactor combined with sequencing batch reactor: Microbial community structure and metabolism analysis

Different in root exudates and rhizosphere microorganisms effect on nitrogen removal between three emergent aquatic plants in surface flow constructed wetlands

Swine wastewater contains high concentration of nitrogen (N), causing pollution of surrounding water bodies. Constructed wetlands (CWs) are considered as an effective ecological treatment measure to remove nitrogen. Some emergent aquatic plants could tolerate high ammonia, and play a crucial part in CWs to treat high concentration N wastewater. However, the mechanism of root exudates and rhizosphere microorganisms of emergent plants on nitrogen removal is still unclear. Effects of organic and amino acids on rhizosphere N cycle microorganisms and environmental factors across three emergent plants were investigated in this study. The highest TN removal efficiency were 81.20% in surface flow constructed wetlands (SFCWs) plant with Pontederia cordata. The root exudation rates results showed that organic and amino acids were higher in 56 d than that in 0 d in SFCWs plants with Iris pseudacorus and P. cordata. The highest ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) gene copy numbers were found in I. pseudacorus rhizosphere soil, while the highest nirS, nirK, hzsB and 16S rRNA gene copy numbers were detected in P. cordata rhizosphere soil. Regression analysis results demonstrated that organic and amino acids exudation rates were positive related to rhizosphere microorganisms. These results indicated that organic and amino acids secretion could stimulate growth of emergent plants rhizosphere microorganisms in SFCWs for swine wastewater treatment. In addition, the EC, TN, NH4+-N and NO3--N were negatively correlated with organic and amino acids exudation rates, and abundances of rhizosphere microorganisms via Pearson correlation analysis. These results imply that organic and amino acids, and rhizosphere microorganisms synergically affected on the nitrogen removal in SFCWs.

Denitrification efficiency, microbial communities and metabolic mechanisms of corn cob hydrolysate as denitrifying carbon source

In this study, the denitrification efficacy of corn cob hydrolysate (CCH) was compared and analyzed with that of glucose and acetate to determine its feasibility as an additional carbon source, and its metabolic mechanism as a denitrification carbon source was investigated in depth. By constructing a denitrification reactor, it was found that the TN removal rate exceeded 97% and the effluent COD remained below 70 mg/L during the stable operation with CCH as the carbon source, and the denitrification effect was comparable to that of the glucose stage (GS) and the acetate stage (AS). The analysis of the microbial community showed that the dominant phylum was Proteobacteria and Bacteroidota, where the abundance of Bacteroidota in the hydrolysate stage (HS) (24.37%) was significantly higher than that of GS (4.89%) and AS (11.93%). And the analysis at the genus level showed the presence of a large number of genera of organic matter hydrolysis and acid production in HS that were almost absent in other stages, such as Paludibacter (12.83%), Gracilibacteria (4.27%), f__Prolixibacteraceae_Unclassified (2.94%). In addition, the higher fatty acid metabolism and lower sugar metabolism of HS during carbon metabolism were similar to the ratio of AS, suggesting that CCH was mainly fermented to acids and then involved in the tricarboxylic acid (TCA) cycle. During nitrogen metabolism, the high relative abundance of narG, nirS, and nosZ ensured the denitrification process. The results of this study were expected to provide a theoretical basis and data support for promoting denitrification from novel carbon sources.

Biodegradation and optimization of bilge water in a sequencing batch reactor using response surface methodology

Bilge water is a significant source of pollution in the marine environment and has captured widespread international attention. In this study, a sequencing batch reactor (SBR) combined with strain S2 identified as Bacillus licheniformis was employed to assess the biodegradation of Chemical Oxygen Demand (COD) from bilge water. The influencing variables such as temperature, pH level and inoculum concentration on the performance SBR system were optimized by utilizing response surface methodology (RSM). The experimental results showed that the maximum COD removal of 77.81% was reached at the optimal SBR operation conditions of temperature 35.44 °C pH 8.13, and inoculum concentration 31.47 mL. In the practical application of SBR, it was found that the decrease in hydraulic retention time (HRT) was accompanied by a decrease in COD degradation rate. The biodegradation kinetics of COD in bilge water were well fitted with the first-order equation with a higher R² value of 0.98106. In conclusion, COD in bilge water can be efficiently biodegraded by SBR under the optimization of RSM.

High-concentration COD wastewater treatment with simultaneous removal of nitrogen and phosphorus by a novel Candida tropicalis strain: Removal capability and mechanism

Aerobic and anaerobic continuous stirred-tank reactor (CSTR), up-flow anaerobic sludge blanket (UASB) were set up and inoculated with newly isolated Candida tropicalis. Reactors were operated at high concentrations of chemical oxygen demand (COD) (8000 mg/L), the modified UASB expressed better COD removal rate simultaneously removal of nitrogen and phosphate than other two reactors. Notably, under both aerobic or anaerobic conditions, large amounts of organic acids and alcohol were generated. Transcriptomic analysis showed that carbon metabolism under anaerobic conditions shared the same pathway with aerobic conditions by regulating and inhibiting some functional genes. Experiments utilizing different carbon sources proved that our strain has excellent performances in utilizing organic materials, which were verified by transcriptomic analysis. Finally, the strain was applied to treat four types of sugar-containing wastewaters. Among them, our strain exerts the best removal capability of COD (90%), nitrogen (89%), and phosphate (82%) for brewery wastewater.

A Study of a Composite Biofilm Reactor for the Treatment of Mariculture Wastewater: Performance and Microbial Communities

Mariculture wastewater is one of the main sources of saline wastewater. This study used a waterfall aeration biofilm reactor combined with a sequencing batch reactor (WABR-SBR) to treat simulated mariculture sewage. Despite the high inhibition by salinity, the reactor maintained a high removal efficiency for organic matter and ammonium nitrogen. The ammonia nitrogen removal rate was greater than 99%, while that for nitrite, which is extremely toxic to farmed animals, was greater than 80%. Fourier transform infrared spectroscopy and scanning electron microscopy showed that salinity affected the surface structure and composition of biofilms, which became compact and secreted more solute to resist the impact of salinity. High throughput 16S rRNA sequencing revealed that the main phyla in the biofilms were Actinobacteria, Proteobacteria, Firmicutes, and Bacteroidetes. Metagenomic annotation of genes further indicated nitrogen metabolism pathways under high salinity. The conclusions of this study can provide a theoretical foundation for the biological treatment of high-salt wastewater and provide a technical reference for further application of the WABR-SBR composite system.