PHOSPHATE REMOVAL FROM WATER USING A HYBRID MATERIAL IN A FIXED-BED COLUMN
Facultad de Ciencias Básicas
Artículo publicado en: Journal of Water Process Engineering
Phosphorus (P) is a non-renewable and essential resource for life. It is one of the main nutrients for plants and in turn is primarily responsible for the eutrophication of water. The high phosphorus content in surface and groundwater is due to the uncontrolled use of fertilizers and incomplete treatment of domestic and industrial wastewater. The excess of P in waste water and the deficiency in the existing waste water treatment plant (WWTP) methods for P removal negatively affects the biodiversity of aquatic ecosystems. Although eutrophication has gained significant attention around the world, this problem is still uncontrolled. To solve the problem of increasing concentrations of phosphate in aquatic ecosystems, several methods, such as biological, physical and chemical treatment techniques have been developed for phosphate removal. Adsorption is one of the most promising methods to remove P from aqueous solutions because it is easy to implement, affordable, cost efficiency, selective and reusable; moreover, its effectiveness depends on the type of adsorbent material.
Various minerals materials and polymers have been used in phosphate removal, such as, activated carbon, zeolite, chitosan, filters, metal hydroxide and so on. Several studies have reported evidence that metal oxides have high affinity and selectivity in the P adsorption process, because metal ions have one or more empty orbitals, they act as Lewis acids by accepting an electron pair.
Among the different metal oxides, iron oxides are frequently encountered in the literature with regards to phosphorus remediation.
Iron (Fe) is an environmentally benign and inexpensive element. Owing to its hard Lewis acid property, Fe (hydr)oxides are considered as electron pair acceptors and have ultra-strong affinity toward phosphate (as Lewis base). However, metal oxides lack the properties necessary for extensive operation in WWTPs, such as mechanical strength and wear resistance. These oxides dissolve in wastewater and lose those adsorption capacity. Therefore, the need has arisen to look for Fe supports for improving the efficiency. Host materials with high specific surface area (SSA), such as activated carbon, exchange ion resins, and silica spheres can support a large amount of iron and, therefore, increase the adsorption capacity. With these materials, the process of phosphorus recovery it is easy to implement.
Therefore, several research papers have studied the performance on phosphate removal using metals immobilized on different support materials. Li et al. used sugar cane residues impregnated with MgO for the removal of P. They found an adsorption process controlled by surface electrostatic attraction with MgO; Zhou et al. modified activated carbon fibres with Fe(OH)3 and found that the presence of the metal improves the efficiency of the P adsorption process. Nur et al. studied the removal of P from aqueous solutions using the Purolite Ferr IX A33E ion exchange resin as a support material for iron oxide and found an adsorption capacity of 48 mg P/g, which remains greater than 90% after three adsorption–desorption cycles. This is because, the ion exchange resins exhibit durability and mechanical resistance. Acelas et al. immobilised three different types of metal oxides (HFeO, HZrO and HCuO) in a microporous anion exchange resin (IRA-400), finding removal capacities of 111.1 mg P/g, 91.74 mg P/g and 74.07 mg P/g, respectively. At the same time, they found high selectivity towards P in the presence of other competitive anions. For example, HFeO reduced the amount of P to 83% in a real waste water solution.
Experimental setup of the adsorption and desorption processes using a hybrid material in a fixed-bed column.
The present paper deals with the evaluation of a hybrid adsorbent, i.e. HFeO, produced in our laboratory following the methodology of Acelas et al. for phosphate removal from aqueous solution in the fixed bed column mode of operations. These continuous flow experiments are important for the design and operational improvements of large scale adsorption processes and to predict the breakthrough curve, which determines the functional longevity of the adsorbent beds. The effects of important design parameters such as, bed height and flow rate on breakthrough curves were evaluated. The Thomas, Adams–Bohart and Yoon–Nelson models were used to describe column adsorption data and predict breakthrough curves. Finally, different bases and eluting agents were evaluated to regenerate the adsorbent material for reuse.
Effect of flow rate and bed height in the breakthrough curves for the adsorption of P in HFeO. A: C0=100mgP/L;bedheightof2cm, B:C0=100mgP/L;flow1.0mL/min.
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