Preparation of chitosan/citral forward osmosis membrane via Schiff base reaction with enhanced anti-bacterial properties.

In this study, hydrogels generated by the Schiff base reaction between citral and chitosan (CS) were used for the first time to improve the anti-bacterial property of forward osmosis (FO) membranes. The composite membranes were characterized by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), Water contact angle (WCA), Zeta potential and confocal laser scanning microscopic (CLSM). In the FO filtration experiment, the membrane performance of TFC-1 with 1 M sodium chloride solution as the draw solution and deionized water as the feed solution was the best, with the water flux of 25.54 ± 0.7 L m-2 h-1 and the reverse salt flux of 4.7 ± 0.4 g m-2 h-1. Although the hydrogel coating produced a certain hydraulic resistance, the flux of the modified membrane was only reduced by about 8%, compared with the unmodified membrane. However, the anti-bacterial property (Pseudomonas aeruginosa) and anti-fouling properties (bovine serum protein and lysozyme protein) of the modified membranes were improved, showing good antibacterial properties (99%) and flux recovery rate (over 90%). The modified method has the advantages of easy access to raw materials, simple operation and no risk of secondary pollution, which can effectively reduce the cost of chemical cleaning and extend the service life of the membrane. The modification of membrane by chitosan-based hydrogel is a promising option in the field of membrane anti-bacteria.

Nitrogen removal from dewatering liquid of landfill sludge by partial nitrification and denitrification.

Two pilot-scale two-stage anoxic/oxic membrane bioreactors were operated at different dissolved oxygen (DO) levels to evaluate nitrogen removal performances for treating landfill sludge dewatering liquid. Under either high (5.0-6.0 mg/L) or conventional DO (2.0-3.0 mg/L) conditions, partial nitrification (PN)-denitrification was both achieved, and high-concentration free ammonia (FA) ensured stable PN. The high DO system exhibited higher nitrite accumulation (98.5 %) and nitrogen removal (98.0 %), and its nitrogen removal was mainly ascribed to PN-denitrification (53.8 %). Kinetic inhibition tests and microbial sequencing results demonstrated that high DO condition improved the abundance and ability of ammonia-oxidizing bacteria (AOB) rather than nitrite-oxidizing bacteria under the FA inhibition. Pseudomonas, Thauera, and Soehngenia were characteristic genus in the high DO system, and Nitrosomonas was only AOB. Metagenomic analysis confirmed the important role of PN on nitrogen removal in high DO system. This provides valuable references for the efficient and economic treatment of ammonia-rich wastewater.

Synthesis of ZnFe2O4/SiO2 composites derived from a diatomite template.

A novel porous ZnFe2O4/SiO2 composite product has been generated with a template-directed assembly method from porous diatomite under different synthesis conditions, such as precursor concentrations (metallic nitrates), calcination temperature and diatomite type. The phase composition and morphology of all the materials were examined by x-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The results indicated that an inherited hierarchical porous structure from the diatomite template can be obtained, and the synthesis conditions were found to have clear effects on the formation of the ZnFe2O4/SiO2 composite. The ideal composite of ZnFe2O4/SiO2 can be obtained through optimization of diatomite template type, precursor solution and calcination temperature. Furthermore, the adsorption abilities of two types of diatomites were analyzed in detail using FTIR spectra and nitrogen adsorption measurements etc, which proved that A-diatomite (Shengzhou-diatomite) is better than B-diatomite (Changbai-diatomite) on the aspect of adsorbing Zn and Fe ions, and of forming the ZnFe2O4.