Nanostructured faujasite zeolite as metal ion adsorbent: kinetics, equilibrium adsorption and metal recovery studies.

The hydrothermal synthesis of nano-faujasite has been successfully performed and the effects of some crystallization parameters were investigated, along with the use of this material as a heavy-metal ion adsorbent. X-ray diffraction patterns have shown that the structure of the nano-faujasite is strongly dependent on both the crystallization time and the alkalinity of the synthesis medium. According to N2 physisorption, X-ray fluorescence, SEM/EDS, and solid state 29Si and 27Al NMR data, the produced nano-faujasite consists of a solid with low molar Si/Al ratio (1.7), with high availability of ion exchange sites and high surface area/small particle size, allowing easy diffusion of metal ions to adsorbent active sites. As a consequence, an excellent performance on removal of Cd2+, Zn2+ and Cu2+ ions was found for this solid. The adsorption capacity followed the order Cd2+ (133 mg·g-1) > Zn2+ (115 mg·g-1) > Cu2+ (99 mg·g-1), which agrees with the order of increasing absolute values of the hydration energy of the metal ions. Kinetic studies and adsorption isotherms showed that the metal ion removal takes place by ion exchange on the monolayer surface of the nano-faujasite. The electrochemical recovery of copper in metallic form exhibited an efficiency of 80.2% after 120 min, which suggests that this process can be adequately implemented for full-scale metal removal.

Long-term performance and acute toxicity assessment of scaled-up air-cathode microbial fuel cell fed by dairy wastewater.

Long-term performance of a scaled-up air-cathode microbial fuel cell (MFC) and toxicity removal were studied with dairy wastewater (DW) used as the substrate. The MFC in a semi-continuous flow was strategically inoculated with consortium of Shewanella oneidensis and Clostridium butyricum. The scaled-up approach delivered a maximum power density of 0.48 W/m3 (internal resistance of 73 Ω) removing 93% of total chemical oxygen demand and 95% of total biochemical oxygen demand at organic loading rate (OLR) of 0.9 kg COD/m3/d and hydraulic retention time (HRT) of 21 days. It also achieved high removal efficiency of nitrate (100%), organic nitrogen (57%), sulfate (90%) and organic phosphorus (90%). The power generation and DW degradation performance decreased with OLR of 1.8 kg COD/m3/d and HRT of 10.5 days. Furthermore, testing of acute toxicity with the microcrustacean, Daphnia similis, revealed high toxic effect of the raw DW, but no toxic effects of the MFC effluent during 95 days of operation. These outcomes demonstrated that scaled-up MFC fed with high-strength DW should be an effective system for pollutants removal and simultaneously energy recovery.