Evaluation of phosphate and ammonium removal and valorization from urban waste waters by impregnated metal hydrated oxides inorganic natural zeolites

Resumo

Phosphate and ammonium removal from waste water by adsorption using inorganic natural sorbents has been identified as a promising technology. The advantages of this methodology are associated with its availability and effective low cost. Some natural and synthetic zeolite materials have been used for the individual phosphate and ammonium removal from aqueous solutions. The zeolites revealed high affinity for ammonium removal. However, some modifications stages are indispensable to enhance their oxyanionic sorption capacity to achieve high phosphate removal ratios. So, it is highly desirable to obtain a single sorbent for both cation and anion removal capacity from aqueous solutions. For this purpose, a natural zeolite with clinoptilolite as major mineral phase, was impregnated with metallic oxyhydroxides after conversion to the sodium form. As a result, hydrated metal oxides (HMO) of Al, Fe and Mn were immobilized on the zeolite surface structure. The efficiency of aluminium, iron and manganese hydrated metal oxides was individually evaluated for the simultaneous phosphate and ammonium removal from aqueous solutions through batch and continuous mode assays using a granular natural zeolite sample. High selectivity was developed by modified zeolites towards these species in the presence of competing ions commonly present in urban and industrial waste waters. The regeneration assays demonstrated the limited use of modified zeolites in operational cycles as losses of the hydrated metal oxide along within the operation cycles will require re-impregnation stages. Then, an alternative option for final valorization of ammonium and phosphate is the use of the loaded zeolites as soil amendment for agricultural and forestry purposes or for environmental rehabilitation of degraded soils. Therefore, a second approach could be to use the impregnated zeolites as nutrients carriers, improving their fertilizing properties by including potassium. For this purpose, powder samples of the natural zeolite in the potassium form were impregnated with the metallic oxyhydroxides and were enriched on nutrients (N,P,K) by using treated waters from the secondary effluent from ¿El Prat¿ Waste Water Treatment Plant using batch mode assays. The N-P-K release rates of the enriched zeolite samples were determined by column test using mixtures with three different types of agricultural soils.