Diana López

Selective removal of phosphate from wastewater using hydrated metal oxides dispersed within anionic exchange media.

Hydrated ferric oxide (HFeO), hydrated zirconium oxide (HZrO) and hydrated copper oxide (HCuO) were immobilized within a microporous anion exchange resin (IRA-400), forming hybrid media for enhanced phosphate removal from aqueous systems. Empirical data from batch kinetic trials fitted the pseudo second order mechanism for chemical adsorption and each media was rate limited by intraparticle diffusion overall. These models were also used to predict the adsorption rate constants and the equilibrium adsorption capacities, which ranged from 26.51 to 30.44 mgP g(-1), and from 24.15 to 27.90 mgP g(-1) of media for the calculated and experimental capacities, respectively. The phosphate adsorption behavior by the hybrid materials fit both the Langmuir and Freundlich adsorption isotherms (R(2)>0.94), and the maximum adsorption capacities were 111.1 mgP g(-1) for HFeO, 91.74 mgP g(-1) for HZrO and 74.07 mgP g(-1) for HCuO. The effect of competing ions such as sulfate reduced these capacities to 18.52 mgP g(-1) for HFeO and 18.97 mgP g(-1) for HZrO. Despite this decrease, HFeO was capable of reducing the phosphate in a real wastewater matrix by 83%, and the HZrO media was able to reduce it by 86%, suggesting that such hybrid media have the potential for application at full scale.

Phosphorus recovery through struvite precipitation from wastewater: effect of the competitive ions

AbstractIn wastewater treatment plants (WWTP), struvite precipitation occurs spontaneously under conditions which are influenced by factors such as: concentration of Mg2+, and , pH, temperature, and competitive ions. These parameters are often difficult to control and, spontaneous precipitation of struvite creates operational problems in WWTP. Struvite is also a potentially marketable product as a fertilizer alternative. For these two reasons it is important to study the principles of struvite precipitation, and evaluate the parameters that control this process. In this study, the influence of the ions Ca2+ and Al3+ in struvite precipitation process was evaluated using three different molar ratios of Mg2+:Ca2+ and Mg2+:Al3+. The products were characterized by thermogravimetric analysis, X-ray diffraction, and scanning electron micrograph. The results showed that calcium interfered in struvite precipitation only when this is in equal or greater molar ratios to magnesium, while aluminum inhibited completely...