Evolution of nanoscale zero-valent iron (nZVI) in water: Microscopic and spectroscopic evidence on the formation of nano- and micro-structured iron oxides.

Knowledge on the transformation of nanoscale zero-valent iron (nZVI) in water is essential to predict its surface chemistry including surface charge, colloidal stability and aggregation, reduction and sorption of organic contaminants, heavy metal ions and other pollutants in the environment. In this work, transmission electronic microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy are applied to study the compositional and structural evolution of nZVI under oxic and anoxic conditions. Under anoxic conditions, the core-shell structure of nZVI is well maintained even after 72h, and the corrosion products usually contain a mixture of wustite (FeO), goethite (α-FeOOH) and akaganeite (ß-FeOOH). Under oxic conditions, the core-shell structure quickly collapses to flakes or acicular-shaped structures with crystalline lepidocrocite (γ-FeOOH) as the primary end product. This work provides detailed information and fills an important knowledge gap on the physicochemical characteristics and structural evolution of engineered nanomaterials in the environment.

Modeling optimization and evaluation of tightly bound extracellular polymeric substances extraction by sonication.

Tightly bound extracellular polymeric substances (TB-EPS) are important components of sludge, playing a crucial role in the behavior of activated sludge. They are located in the innermost layer of EPS which closely combine with the cell surface and are difficult to be extracted. To fully understand the role of TB-EPS, it is extremely important to find an appropriate TB-EPS extraction protocol, which provides maximum yields of TB-EPS under the premise of minimal contribution of cell lysis. Ultrasonic method has been widely applied for TB-EPS extraction due to its unique advantages, but no one has developed a systematic and scientifically optimized method for this protocol. In this study, a novel method based on response surface methodology (RSM) was successfully developed to optimize the conditions of TB-EPS extraction. The optimal conditions were determined at an ultrasound time of 1.00 min, ultrasonic density of 5.59 W/mL and a mixed liquor suspended solid (MLSS) of around 1700-1800 mg/L. Furthermore, combined analysis of microscopy, particle size, and excitation-emission matrix (EEM) was successfully applied to evaluate the optimal conditions. The result indicates that the optimal conditions are efficient, reliable, and reproducible which effectively solves the bottleneck problem of the conflict between cell viability and TB-EPS yield, and little effect on its chemical structure.

Continuous-flow combined process of nitritation and ANAMMOX for treatment of landfill leachate.

Due to the difficulty in removing nitrogen from landfill leachate, a combined continuous-flow process of nitritation and anammox was applied to process mature leachate. The transformation rate of ammonia and nitrite accumulation ratio in A/O reactor were kept above 95% and 92% respectively through associated inhibition of free ammonia (FA) and free nitrous acid (FNA) to NOB. The total nitrogen volumetric load of anammox in an UASB reactor was brought up from 0.5kg/(m(3)·d) to 1.2kg/(m(3)·d) by gradually increasing influent substrate concentration and reducing hydraulic retention time (HRT). The results show that COD from mature leachate did not bring obvious inhibition effects to anammox. Under concentrations of influent ammonia and COD which were respectively 1330mg/L and 2250mg/L, the removal efficiencies of TN and COD reached 94% and 62% respectively. In the quantitative PCR reactions, the proportions occupied by AOB, NOB and anammox in A/O were 11.39%, 1.76% and 0.05% respectively; and proportions of those in UASB were 0.35%, 4.01% and 7.78% respectively.