Microbial synergies drive simultaneous biodegradation of ethoxy and alkyl chains of Nonylphenol Ethoxylate in fluidized bed reactors

The widely-used surfactant Nonylphenol Ethoxylate (NPEO) produces endocrine-disrupting compounds during biodegradation, with these byproducts being more harmful than untreated NPEO. This study investigates the effectiveness of a Fluidized Bed Reactor (FBR) in reducing the production of 4-Nonylphenol (4-NP) during the biodegradation of NPEO. Two identical FBR filled with sand were used to assess the NPEO degradation and to enhance the microbial consortia capable of breaking down the complex byproducts, ethanol and fumarate were introduced as co-substrates. Our findings demonstrate the significant potential of the FBR, especially when coupled with fumarate, for enhancing the surfactant degradation. It outperforms the efficiency achieved with ethanol as the primary electron donor, albeit with a higher rate of byproduct production. Microbial community taxonomy and metabolic prediction revealed the high abundance of Geobacter (1.51-31.71%) and Methanobacterium (1.08-13.81%) in non-conductive sand. This may hint a new metabolic interaction and expand our understanding of Direct Interspecies Electron Transfer (DIET) in bioreactors applied to micropollutants degradation. Such an intricate relationship between facultative and anaerobes working together to simultaneously biodegrade the ethoxy and alkyl chains presents a new perspective on NPEO degradation and can potentially be extended to other micropollutants.

Broken into pieces: The challenges of determining sulfonated azo dyes in biological reactor effluents using LC-ESI-MS/MS analysis

Most studies on the biodegradation of textile azo dyes use color as parameter for measuring the efficiency of degradation. Although widely employed, spectrophotometric methods are susceptible to the interference of metabolites or degradation products from the biological treatment. We propose a method for determination of a model sulfonated azo dye (Direct Black 22, DB22) in wastewater using solid-phase extraction (SPE) and liquid chromatography - electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). MS analysis in negative electrospray ionization mode showed DB22 as the most abundant precursor ion, corresponding to [M-3Na + H]^2-, which yields two radical anions of m/z 370.1 and m/z 645 after MS/MS fragmentation by collision-induced dissociation (CID). Calibration curve presented adequate linearity and precision in the range of 120-1500 ng mL^-1, and recovery and detection limit were appropriate to the typically employed working concentrations. Nevertheless, we observed that standard heating of DB22 under alkaline conditions to simulate the production of wastewater during dye-baths resulted in loss of MS/MS signal, without affecting color. Further analysis showed that DB22 undergoes hydrolysis and does not remain unaltered in solution. Alternative methods of hydrolysis evaluated resulted in no MS/MS signal as well. SPE-LC-ESI-MS/MS analysis evidenced the structural change of DB22 in aqueous solution while the dyeing-capacity was preserved. This technique has also the potential of being tailored to consider the detection of the hydrolyzed fragments of azo dyes in wastewater for appropriate quantification, but it was not the scope of the current step of this research. Color remains as a more reliable parameter for monitoring azo compounds which are unstable in aqueous solution, while a more robust and holistic method needs to be developed for the speciation of the DB22 products of thermal hydrolysis.

Influence of organic loading rate on ciprofloxacin and sulfamethoxazole biodegradation in anaerobic fixed bed biofilm reactors

Antibiotic compounds, notably sulfamethoxazole (SMX) and ciprofloxacin (CIP), are ubiquitous emerging contaminants (ECs), which are often found in domestic sewage. They are associated with the development of antimicrobial resistance. Operational parameters, e.g. organic loading rate (OLR), hydraulic retention time (HRT) and sludge retention time, may influence EC biodegradation in wastewater treatment plants. This study assessed the impact of the OLR variation on the biodegradation of CIP and SMX, applying two configurations of anaerobic fixed bed reactors: anaerobic packed bed biofilm reactor (APBBR) and anaerobic structured bed biofilm reactor (ASBBR). A significant reduction in the biodegradation of SMX (APBBR: 93-69%; ASBBR: 94-81%) and CIP (APBBR: 85-66%; ASBBR: 85-64%) was observed increasing OLR from 0.6 to 2.0 kgCOD m^-3 d^-1. The decrease in the HRT from 12 to 4 h resulted in higher liquid-phase mass transfer coefficient (APBBR: k_s from 0.01 to 0.05 cm h^-1; ASBBR: k_s from 0.07 to 0.24 cm h^-1), but this was not enough to overcome the decrease in the antibiotic-biomass contact time on biofilm, thus reducing the bioreactors' performance. The ASBBR favored biomethane production (from 7 to 17 mLCH₄ g^-1VSS L^-1 d^-1) and biodegradation kinetics (k_bio from 1.7 to 4.2 and for SMX and from 2.1 to 4.8 L g^-1VSS d^-1 for CIP) due to the higher relative abundance of the archaea community in the biofilm and the lower liquid-phase mass transfer resistance in the structured bed. CIP and SMX cometabolic biodegradation was associated to the hydrogenotrophic methanogenesis (mainly Methanobacterium genus) in co-culture with fermentative bacteria (notably the genera Clostridium, Bacillus, Lactivibrio, Syntrophobacter and Syntrophorhabdus). The anaerobic fixed bed biofilm reactors proved to be highly efficient in biodegrading the antibiotics, preventing them from spreading to the environment.

Feasibility of anaerobic packed and structured-bed reactors for sulfamethoxazole and ciprofloxacin removal from domestic sewage

This study assessed the applicability of fixed bed bioreactors in two configurations - anaerobic structured bed reactor (ASBR) and anaerobic packed bed reactor (APBR) - in the removal of Sulfamethoxazole (SMX) and Ciprofloxacin (CIP), two antibiotics frequently detected in sanitary sewage. The problem of these pharmaceuticals as emerging contaminants in conventional sewage treatment systems is mainly because they encourage the development and spread of resistance genes in bacteria. Both reactors had similar performances, and the antibiotics were highly removed - APBR: 85 ± 10% for SMX and 81 ± 16% for CIP; ASBR: 83 ± 12% for SMX and 81 ± 15% for CIP. The ASBR showed to be potentially more feasible in operating and economic terms compared to the APBR, as the former presents a smaller amount of support material in the bed. SMX was completely biotransformed, while the influence of the sorption mechanism was observed for CIP, as its presence was detected sorbed onto biomass throughout the reaction bed of the reactors, with a partition coefficient (log K_D) of around 2.8 L·kg^-1TSS. The degradation kinetics of the pharmaceuticals were fitted using a first-order kinetic model, whereby the reactors behaved as plug flow ones, indicating the possibility of optimizing the operation for a hydraulic retention time of 6 h. The removal kinetics was more favorable for CIP (higher apparent constant kinetic - k_CIP^app > k_SMX^app), since its biodegradation is linked to the biomass, which is more concentrated in the bed bottom layer. The experimental results showed the potential of anaerobic fixed bed reactors in removing environmentally relevant concentrations of SMX and CIP found in sewage.

Fluorescence Modulation of Acridine and Coumarin Dyes by Silver Nanoparticles

Silver nanoparticles were synthesized by chemical reduction of silver ions by sodium borohydride in the presence of poly-(N)-vinyl-2-pyrrolidone in solution of short chain alcohols. The nanoparticles are stable in 2-propanol, and the average diameter of the Ag colloid obtained in this solvent is about 6 nm. The photophysical properties of acridinium and coumarin dyes in 2-propanol are affected by the presence of silver nanoparticles. The interaction of silver nanoparticles with acridinium derivative leads to a spectral change of its intramolecular charge transfer (ICT) absorption band. The dye emission increases suddenly with the initial addition of the Ag metal nanoparticles, but at a high concentration of the colloid, static fluorescence quenching occurs with a progressive decrease of the fluorescence efficiency. Amino coumarin fluorescence is only quenched by the silver nanoparticles in solution.