Fly ash based robust biocatalyst generation: a sustainable strategy towards enhanced green biosurfactant production and waste utilization.

Biosurfactants have been well recognized as an environmentally friendly alternative to chemical surfactants. However, their production remains challenging due to low productivity, short-term microbe stability and the potentially toxic by-products generated in the growth media. To overcome these challenges, the emerging biofilm-based biosynthesis was investigated in this study. A fresh insight into the biosynthesis process was provided through using waste fly ash as a carrier material. The biofilm produced by biosurfactant producer B. subtilis N3-1P attached onto the surface of fly ash acted as a robust and effective biocatalyst. Zeta potential analysis and scanning electron microscope (SEM) characterization were conducted to help unravel the biocatalyst formation. High-value biosurfactant products were then produced in an efficient and sustainable manner. Stimulation by a fly ash assisted biocatalyst on biosurfactant production was confirmed. The biosurfactant yield was boosted over ten times after 24 hours, at a fly ash dosage of 0.5%. The highest biosurfactant yield was achieved after five days, with a final productivity of 305 critical micelle dilution. The underlying mechanism of fly ash assisted biosurfactant production was tracked through it exerting an effect on the quorum sensing system. Fourier-transform infrared (FTIR) spectroscopy and matrix assisted laser desorption/ionization-time of flight (MALDI-TOF) analysis demonstrated that the final biosurfactant product belonged to the lipopeptides. This research output is expected to accelerate the development of more effective bioreactors, and make a continuous contribution to high-value product generation and waste reduction.

Design of experiment (DOE) based screening of factors affecting municipal solid waste (MSW) composting.

A design of experiment (DOE) based methodology was adopted in this study to investigate the effects of multiple factors and their interactions on the performance of a municipal solid waste (MSW) composting process. The impact of four factors, carbon/nitrogen ratio (C/N), moisture content (MC), type of bulking agent (BA) and aeration rate (AR) on the maturity, stability and toxicity of compost product was investigated. The statistically significant factors were identified using final C/N, germination index (GI) and especially the enzyme activities as responses. Experimental results validated the use of enzyme activities as proper indices during the course of composting. Maximum enzyme activities occurred during the active phase of decomposition. MC has a significant effect on dehydrogenase activity (DGH), ß-glucosidase activity (BGH), phosphodiesterase activity (PDE) and the final moisture content of the compost. C/N is statistically significant for final C/N, DGH, BGH, and GI. The results provided guidance to optimize a MSW composting system that will lead to increased decomposition rate and the production of more stable and mature compost.

Determination of five quinolone antibiotic residues in foods by micellar electrokinetic capillary chromatography with quantum dot indirect laser-induced fluorescence.

A new assay was developed for the determination of five quinolone antibiotic residues in foods, loxacin, enrofloxacin, ciprofloxacin, lomefloxacin, and norfloxacin, by micellar electrokinetic capillary chromatography with indirect laser-induced fluorescence, in which cadmium telluride quantum dots were used as a fluorescent background substance. Some factors that affected the peak height and the resolution were examined. The optimized running buffer was composed of 20 mM SDS, 7.2 mg/L quantum dots, and 10 mM borate at pH 8.8. The separation voltage was 20 kV. Under these conditions, five quinolone antibiotic residues were separated successfully within 8 min. The detection limits ranged from 0.003 to 0.008 mg/kg; the linear dynamic ranges were all 0.01 ∼ 10 mg/kg; and the average recoveries of the spiked samples were 81.4 ∼ 94.6 %. The assay can meet the requirement of maximum residue limits to these five quinolone antibiotics in the regulations of the European Union and Japan and has been applied for determining their residues in animal-derived food.

Determination of eight triazine herbicide residues in cereal and vegetable by micellar electrokinetic capillary chromatography with on-line sweeping.

A new method was developed for the determination of eight triazine herbicide residues in cereal and vegetable samples by on-line sweeping technique in micellar electrokinetic capillary chromatography (MEKC). Some factors affecting analyte enrichment and separation efficiency were examined. The optimum buffer was composed of 25 mM borate, 15 mM phosphate, 40 mM sodium dodecylsulfate (SDS) and 3% (v/v) of 1-propanol at pH 6.5. The separation voltage was 20 kV and the sample was injected at 0.5 psi for 240 s. The detection wavelength was set at 220 nm with the capillary temperature being at 25 °C. Under the optimized conditions, the enrichment factors were achieved from 479 to 610. The limits of detection (LODs, S/N = 3) ranged from 0.02 to 0.04 ng/g and the limits of quantification (LOQs) of eight triazine herbicides were all 0.1 ng/g. The average recoveries of spiked samples were 82.8-96.8%. This method has been successfully applied to the determination of the triazine herbicide residues in cereal and vegetable samples.