Using cassava distiller’s dried grains as carbon and microbe sources to enhance denitrification of nitrate-contaminated groundwater

Co-degradation of ofloxacin and its impact on solid phase denitrification with polycaprolactone as carbon source

Solid-phase denitrification has been applied for advanced nitrogen removal from wastewater and can co-degrade emerging pollutants. Fluoroquinolones (FQs), broad-spectral antibiotic, are frequently detected in the effluent of conventional wastewater treatment plants. However, it remains unclear whether solid-phase denitrifying bacteria can remove FQs. Thus, this study investigated the removal capacity of ofloxacin (OFX) as a representative of FQs and the microbial community structures of denitrifying sludge acclimated to polycaprolactone and OFX. The Results indicate that OFX had a negative effect on denitrification performance. OFX was degraded, and a possible pathway was revealed based on ultra-high performance liquid chromatography-quadrupole time-of-flight mass spectrometry. The dominant genera in the acclimated denitrifying sludge were Microbacterium, Simplicispira, Alicycliphilus, Reyranella, Sediminibacterium, Acidovorax and Thermomonas. Moreover, ABC transporters and cytochrome P450, related to multi-drug resistance and drug metabolism, were highly expressed in the acclimated sludge. This study provides novel insights into antibiotics control.

Effect of tetracycline on nitrogen removal in Moving Bed Biofilm Reactor (MBBR) System

The effect of tetracycline (TC) on nitrogen removal in wastewater treatment plants has become a new problem. This study investigated the effects of TC on nitrogen removal using a Moving Bed Biofilm Reactor system. The results showed that there was no significant effect on nitrogen removal performance when the concentration of TC was 5 mg/L, and that the total nitrogen (TN) removal efficiency could reach 75–77%. However, when the concentration of TC increased to 10 mg/L, the denitrification performance was affected and the TN removal efficiency decreased to 58%. The abundance of denitrifying bacteria such as those in the genus Thauera decreased, and TC-resistant bacteria gradually became dominant. At a TC concentration of 10 mg/L, there were also increases and decreases, respectively, in the abundance of resistance and denitrification functional genes. The inhibitory effect of TC on denitrification was achieved mainly by the inhibition of nitrite-reducing bacteria.

Extraction of dietary fibers from cassava pulp and cassava distiller's dried grains and assessment of their components using Fourier Transform Infrared Spectroscopy to determine on their further use as a functional feed in animal diets

Objective

The present study was to investigate the extraction conditions of dietary fiber from dried cassava pulp (DCP) and cassava distiller's dried grains (CDG) under different NaOH concentrations, and the Fourier Transform Infrared (FTIR) was used to determine the dietary fiber components.

Methods

The dried samples (DCP and CDG) were treated with various concentrations of NaOH at levels of 2, 4, 6, and 8% using a completely randomized design with 4 replications of each. After extraction, the residual DCP and CDG dietary fiber were dried in a hot air oven at 55-60 ºC. Finally, the oven dried extracted dietary fiber was powdered to a particle size of 1 mm. Both extracted dietary fibers were analyzed for their chemical composition and determined by FTIR.

Results

The DCP and CDG treated with NaOH linearly or quadratically or cubically (p<0.05) increased the total dietary fiber (TDF) and insoluble fiber (IDF). The optimal conditions for extracting dietary fiber from DCP and CDG were under treatment with 6% and 4% NaOH, respectively, as these conditions yielded the highest TDF and IDF contents. These results were associated with the FTIR spectra integration for a semi-quantitative analysis, which obtained the highest cellulose content in dietary fiber extracted from DCP and CDG with 6% and 4% NaOH solution, respectively. The Principal Component Analysis (PCA) illustrated clear separation of spectral distribution in cassava pulp extracted dietary fiber (DFCP) and cassava distiller's dried grains extracted dietary fiber (DFCDG) when treated with 6% and 4% NaOH, respectively.

Conclusion

The optimal conditions for the extraction of dietary fiber from DCP and CDG were treatment with 6% and 4% NaOH solution, respectively. In addition, FTIR spectroscopy proved itself to be a powerful tool for fiber identification.

Deciphering the toxic effects of antibiotics on denitrification: Process performance, microbial community and antibiotic resistance genes

The extensive application of antibiotics, and the occurrence and spread of antibiotic resistance genes (ARGs) shade health risks to human and animal. The long-term effects of sulfamethoxazole (SMX) and tetracycline (TC) on denitrification process were evaluated in this study, with the focus on nitrogen removal performance, microbial community and ARGs. Results showed that low-concentration SMX and TC (<0.2 mg L^-1) initially caused a deterioration in nitrogen removal performance, while higher concentrations (0.4-20 mg L^-1) of both antibiotics had no further inhibitory influences. The abundances of ARGs in both systems generally increased during the whole period, and most of them had significant correlations with intI1, especially efflux-pump genes. Castellaniella, which was the dominant genus under antibiotic pressure, might be potential resistant bacteria. These findings provide an insight into the toxic effects of different antibiotics on denitrification process, and guides future efforts to control antibiotics pollution in ecosystems.

Evaluating a novel permeable reactive bio-barrier to remediate PAH-contaminated groundwater

Permeable reactive barriers (PRBs) are an environmentally-friendly, cost-effective in-situ technology that can be used to remediate polycyclic aromatic hydrocarbons (PAHs)-contaminated groundwater. In this study, PRBs of two different materials (A and B) that relied on microbes self-domestication mechanism were designed and tested. The materials A and B were the same apart from their carbon source: A was based on wheat straw and B was based on coconut shell biochar. We used laboratory batch experiments followed by long-term column tests to assess the capacity of these two materials to remediate PAHs. The results showed that both A and B removed almost 100% of the phenanthrene. More carbon was released from A (80-500 mg/L) than from B (72-195 mg/L), and slightly more oxygen was released from B (7.31-10.31 mg/L) than A (7.15-9.64 mg/L). The release of organic carbon from material B was more stable than that from material A. The bacterial communities of both columns comprised members of the Mycobacterium, Pseudomonas, and Sphingomonas genera that are known to degrade phenanthrene, and Pseudomonas and Sphingomonas were 7 times more abundant in column B than in column A. Material B is more promising for treating PAH-contaminated groundwater than material A.

Characterizations of dissolved organic matter and bacterial community structures in rice washing drainage (RWD)-based synthetic groundwater denitrification

In this study, characteristics of dissolved organic matter (DOM) and bacterial community structure in rice washing drainage (RWD)-based groundwater denitrification systems inoculated with and without seeding sludge were investigated. Complete nitrate removal was achieved with a maximum denitrification rate of 64.1 mg NO₃^--N·(gVSS·h)^-1. Analysis of three-dimension fluorescence excitation-emission matrix (FEEM) identified three main compositions of DOM associated with tryptophan protein-like, aromatic protein-like, and polycarboxylate humic acid-like substances in the inoculated system, while one composition associated with tryptophan protein-like substance in the un-inoculated system. Illumina sequencing analysis revealed a distinguished bacterial community structure in two systems over time. Notably, the microbial diversity was significant lower in the un-inoculated system than that in the system inoculated with seeding sludge. The predominant phyla shifted from Proteobacteria (49.2%), Bacteroidetes (20.5%) and Chloroflexi (14.8%) in the seeding sludge to Bacteroidetes (56.3%) and Proteobacteria (37.7%) after the RWD addition in the inoculated system. With RWD as sole microbe source, temporal changes in the bacterial structure from Proteobacteria (99.4%) and Bacteroidetes (5.3%) to Proteobacteria (88.8%) and Bacteroidetes (10.3%) were observed in the un-inoculated system. Specific comparison down to the genus level showed the dominant denitrifying bacteria of Thiobacillus, Anaerolineaceae and Methylophilaceae in the seeding sludge. Ideonella, Cloacibacterium and Enterobacter were dominant after the RWD addition in the inoculated system, while Stenotrophomonas and Enterobacter were dominant genera when RWD as sole bacteria source in the un-inoculated system. This finding indicates that both RWD addition and inoculation had strong impacts on bacterial community structure.

Minimization of nitrous oxide emission from CASS process treating low carbon source domestic wastewater: Effect of feeding strategy and aeration rate

Nitrous oxide (N2O) emission during wastewater treatment can be mitigated by improving operational conditions, e.g., organic carbon supply and dissolved oxygen. To evaluate the control parameters for N2O emission in the low carbon source domestic wastewater treatment process, N2O emissions from Cyclic Activated Sludge System (CASS) under different feeding strategies and aeration rates were investigated. Results showed that continuous feeding enhanced nitrogen removal and reduced N2O emission compared to batch feeding, while a higher aeration rate led to less N2O emission. N2O was mainly produced during non-aeration phases in batch feeding CASS and the amount of N2O generated from denitrification decreased under continuous feeding, indicating that carbon source in the continuous influent relieved the electron competition between denitrification reductases during non-aeration phase. Moreover, taxonomic analysis based on high-throughput 16S rRNA gene sequencing revealed higher abundance of denitrifying bacteria, especially N2O-reducing bacteria in continuous feeding CASS.