Simultaneous adsorptive removal of three fluoroquinolones using humic acid modified hydrogel beads.

This study elaborates the simultaneous removal of three different fluoroquinolones (FQs), i.e., Norfloxacin (NOR), Lomefloxacin (LOM), and Enrofloxacin (ENR) from water using hydrogel beads of humic acid coated biochar (HA-BC) and chitosan. In our previous study, this adsorbent has already achieved tremendous results for the removal of a single FQ, i.e., ciprofloxacin. Now, initial concentrations of all FQs were set 100 mg/L each, and the maximum adsorbed amounts were 38.08 mg/g (NOR), 25.03 mg/g (LOM), and 29.72 mg/g (ENR). Adsorption attained equilibrium after 24 h, which obeyed the pseudo-second-order kinetic model. The mutation of humic acid-biochar/chitosan hydrogel beads (HBCB) with alcoholic solvents, i.e., methanol and ethanol to replace water decreased its sorption capacities from 38.08 mg/g (NOR) to 34.91 mg/g and 32.19 mg/g, respectively. Similarly, from 25.03 mg/g (LOM) to 22.81 mg/g and 19.91 mg/g, and 29.72 mg/g (ENR) to 26.52 mg/g and 24.64 mg/g. Adsorption isotherm data for all FQs were up to both Langmuir and Freundlich, but it suited more to that of Langmuir adsorption isotherm model. Sorption capacities, for all FQs, had a minor decline due to addition of NaCl, NaNO3, and Na2SO4. However, there was a huge decline when Na3PO4 was added into the adsorption system. Adsorbent was desorbed and regenerated for consecutive removal, and it showed good adsorption in the 4th cycle, i.e., 47 mg/g net adsorption. These results prove that HBCB is not only effective for adsorption removal of ciprofloxacin but also for other FQs too.

Sonocatalytic degradation of ciprofloxacin using hydrogel beads of TiO2 incorporated biochar and chitosan.

Pharmaceuticals are necessary to be removed from environment. Herein TiO2 incorporated biochar made from pyrolysis of agricultural wastes was encapsulated into chitosan to obtain a novel hydrogel beads. This hydrogel beads executed a dual role as both adsorbent and sonocatalyst, which proved to be suitable for the removal of antibiotic ciprofloxacin (CIP) from water. The results showed that adsorption of CIP followed pseudo first order kinetics model and Langmuir adsorption isotherm model, having maximum adsorption at pH 9. Whereas the degradation was more efficient at pH 6 due to greater standard potential for •OH/H2O in acidic media. The degradation was maximum at 150 W of ultrasonic power, then decreased in presence of dissimilar electrolytes and even reduced to 0 in presence of Na3PO4. Different quenchers such as benzoquinone (BQ), Triethanolamine (TEA) and isopropyl alcohol (IPA) reduced degradation efficiency (DE) and mineralization efficiency (ME). The DE was decreased from 85.23% to 81.50% (BQ), 74.27% (TEA), and 61.77% (IPA) within 25 min. The prepared sonocatalyst was capable of regeneration with DE, remaining sufficiently high (62%) even after four regeneration steps. These results indicate that titanium-biochar/chitosan hydrogel beads (TBCB) are durable and effective for long-term CIP removal.

Characterizing stomatal attributes and photosynthetic induction in relation to biochemical changes in Coriandrum sativum L. by foliar-applied zinc oxide nanoparticles under drought conditions.

Abiotic stress, particularly drought, will remain an alarming challenge for sustainable agriculture. New approaches have been opted, such as nanoparticles (NPs), to reduce the negative impact of drought stress and lessen the use of synthetic fertilizers and pesticides that are an inevitable problem these days. The application of zinc oxide nanoparticles (ZnO NPs) has been recognized as an effective strategy to enhance plant growth and crop production during abiotic stress. The aim of the current study was to investigate the role of ZnO NPs in drought stress management of drought-susceptible Coriandrum sativum L. (C. sativum) in two consecutive seasons. Drought regimes (moderate drought regime-MDR and intensive drought regime-IDR) were developed based on replenishment method with respect to 50% field capacity of fully irrigated (control) plants. The results showed that foliar application of 100 ppm ZnO NPs improved the net photosynthesis (Pn), stomatal conductance (C), and transpiration rate (E) and boosted up the photosynthetic capacity associated with photosynthetic active radiation in MDR. Similarly, 48% to 30% improvement of chlorophyll b content was observed in MDR and onefold to 41% in IDR during both seasons in ZnO NP-supplemented plants. The amount of abscisic acid in leaves showed a decreasing trend in MDR and IDR in the first season (40% and 30%) and the second season (49% and 33%) compared with untreated ZnO NP plants. The ZnO NP-treated plants showed an increment in total soluble sugars, total phenolic content, and total flavonoid content in both drought regimes, whereas the abaxial surface showed high stomatal density and stomatal index than the adaxial surface in foliar-supplied NP plants. Furthermore, ZnO NPs improve the magnitude of stomata ultrastructures like stomatal length, stomatal width, and pore length for better adaptation against drought. Principal component analysis revealed the efficacy of ZnO NPs in inducing drought tolerance in moderate and intensive stress regimes. These results suggest that 100 ppm ZnO NPs can be used to ameliorate drought tolerance in C. sativum plants.

Membrane biofouling retardation by zwitterionic peptide and its impact on the bacterial adhesion.

Nanofiltration polyamide membranes naturally tend towards biofouling, due to their surface physicochemistries. Nisin, a type of short cationic amphiphilic peptide with antimicrobial properties, has been recognized as a safe antimicrobial for food biopreservation and biomedical applications. This study investigates the impact of nisin on the initial bacterial attachment to membranes, its anti-biofouling properties, and characterizes a non-monotonic correlation between nisin concentration and biofilm inhibition. Nisin was found to inhibit B. subtilis (G+) and P. aeruginosa (G-) attachment to both the nanofiltration membrane and the PES membrane. To determine the mechanism of action, we investigated the polysaccharides, protein, and eDNA as target components. We found that the quantities of polysaccharides and eDNA were significantly changed, resulting in bacterial death and anti-adhesion to membrane. However, there were no discernable impacts on protein. We postulated that nisin could prevent irreversible biofouling by decreasing adhesion, killing bacteria, and reducing biofilm formation. We examined membrane flux behavior through bench-scale cross-flow experiments at a set concentration of nisin (100 µg mL-1), with membrane behavior being confirmed using CLSM images. Results showed that nisin could enhance anti-biofouling properties through both anti-adhesive and anti-bacterial effects, and therefore could be a novel strategy against biofouling of membranes.

Enhanced removal of ciprofloxacin using humic acid modified hydrogel beads.

In this study, humic acid coated biochar (HA-BC) and chitosan were combined to prepare an adsorbent with enhanced reactivity for the removal of ciprofloxacin (CIP). With initial CIP concentrations of 250 mg/L, the maximum adsorbed amount was 154.89 mg/g. Removal rates reached equilibrium after 12 h, obeying the pseudo second-order kinetic model. Adsorption isotherm data was better fitted to the Langmuir isotherm model. The sorption capacity of humic acid-biochar/chitosan hydrogel beads (HBCB) decreased by 11.42%, 6.66%, 9.32%, and 23.92% in the presence of NaCl, NaNO3, Na2SO4, and Na3PO4, respectively. A complex mechanism was found to be responsible for the adsorptive removal of CIP including, hydrogen bonding, π-π electron donor-acceptor (EDA) interactions and hydrophobic interactions. After four regeneration steps, sorption capacity remained sufficient (61.23 mg/g). These removal results indicate that HBCB is durable and effective for long term CIP removal.

Qualitatively and quantitatively assessing the aggregation ability of sludge during aerobic granulation process combined XDLVO theory with physicochemical properties.

Inexact mechanism of aerobic granulation still impedes optimization and application of aerobic granules. In this study, the extended Derjaguin, Landau, Verwey, and Overbeek (XDLVO) theory and physicochemical properties were combined to assess the aggregation ability of sludge during aerobic granulation process qualitatively and quantitatively. Results show that relative hydrophobicity of sludge and polysaccharide content of extracellular polymeric substances (EPS) increased, while electronegativity of sludge decreased during acclimation phase. After 20days' acclimation, small granules began to form due to high aggregation ability of sludge. Since then, coexisted flocs and granules possessed distinct physicochemical properties during granulation and maturation phase. The relative hydrophobicity decreased while electronegativity increased for flocs, whereas that for granules presented reverse trend. Through analyzing the interaction energy using the XDLVO theory, small granules tended to self-grow rather than self-aggregate or attach of flocs due to poor aggregation ability between flocs and granules during the granulation phase. Besides, remaining flocs were unlikely to self-aggregate owing to poor aggregation ability, low hydrophobicity and high electronegativity.

Enhancement of ciprofloxacin sorption on chitosan/biochar hydrogel beads.

Biochar is effective in water treatment but it is hard to retrieve or separate biochar powder from aqueous solutions. In this study, the removal of ciprofloxacin from aqueous solutions was investigated using chitosan/biochar hydrogel beads (CBHB). The results showed that the adsorption rate was almost independent of the temperature and occurred at the homogeneous sites of adsorbent thus obeying the Langmuir model. The equilibrium time was varying for different initial concentrations and found to be 48 h for maximum one. The maximum sorption was found to be >76 mg/g of adsorbent out of 160 mg/L as initial concentration. Adsorption obeyed the second-order mechanism with leading role of intra-particle diffusion and outer diffusion. Adsorption capacity decreased from 34.90 mg/g to 15.77 mg/g in the presence of 0.01 N Na3PO4 whereas other electrolytes such as NaCl, Na2SO4, NaNO3 with same concentration did not affect the sorption capacity. However, increased concentration of NaCl reduced the sorption capacity to some extent. CBHB showed a mixed mechanism by removing CIP through π-π electron donor-acceptor (EDA) interaction, hydrogen bonding and hydrophobic interaction. The reformation of CBHB with methanol and ethanol instead of water decreased its sorption capacity to 32.69 mg/g and 29.29 mg/g. Adsorption decreased by little after every regeneration of CBHB and was still >64 ±â€¯0.68% (25.73 mg/g) after 6th regeneration. The efficacy of CBHB for CIP removal proved that CBHB is an economical and sustainable adsorbent.

Electronic-property dependent interactions between tetracycline and graphene nanomaterials in aqueous solution.

Understanding the interactions between graphene nanomaterials (GNMs) and antibiotics in aqueous solution is critical to both the engineering applications of GNMs and the assessment of their potential impact on the fate and transport of antibiotics in the aquatic environment. In this study, adsorption of one common antibiotic, tetracycline, by graphene oxide (GO) and reduced graphene oxide (RGO) was examined with multi-walled carbon nanotubes (MWCNTs) and graphite as comparison. The results showed that the tetracycline adsorption capacity by the four selected carbonaceous materials on the unit mass basis followed an order of GO>RGO>MWCNTs>graphite. Upon normalization by surface area, graphite, RGO and MWCNTs had almost the same high tetracycline adsorption affinity while GO exhibited the lowest. We proposed π-electron-property dependent interaction mechanisms to explain the observed different adsorption behaviors. Density functional theory (DFT) calculations suggested that the oxygen-containing functional groups on GO surface reduced its π-electron-donating ability, and thus decreased the π-based interactions between tetracycline and GO surface. Comparison of adsorption efficiency at different pH indicated that electrostatic interaction also played an important role in tetracycline-GO interactions. Site energy analysis confirmed a highly heterogeneous distribution of the binding sites and strong tetracycline binding affinity of GO surface.

Mitigation of membrane biofouling by d-amino acids: Effect of bacterial cell-wall property and d-amino acid type.

Development of novel approaches for biofouling mitigation is of crucial importance for membrane-based technologies. d-amino acids (d-AAs) have been proposed as a potential strategy to mitigate biofouling. However, the effect of bacterial cell-wall properties and d-AAs type on biofouling mitigation remains unclear. This study assesses the effect of d-AAs type on membrane biofouling control, towards Gram positive (G+) and Gram negative (G-) bacteria. Three kinds of d-AAs were found to inhibit both G+ and G- bacterial attachment in short-term attachment and dead-end filtration experiments. The existence of d-AAs reduces extracellular polysaccharides and proteins on the membrane, which may decrease membrane biofouling. Cross-flow filtration tests further indicated that d-AAs could effectively reduce membrane biofouling. The permeate flux recovery post chemical cleaning, improved for both P. aeruginosa and B. subtilis treated with d-AAs. The results obtained from this study enable better understanding of the role of d-AAs species on bacterial adhesion and biofilm formation. This may provide a new way to regulate biofilm formation by manipulating the species of d-AAs membrane systems.