Phosphates and ammonia recovery from secondary effluents by selective ion exchange with production of a slow-release fertilizer

A process for the reduction of eutrophic potential in urban secondary effluents. which comprises the selective exchange of phosphates on a weak anion resin and of ammonia on clinoptilolite, is described. Sodium chloride is used to regenerate both resins, with some Ca(OH)₂ added for clinoptilolite. By adding Mg(OH)₂, eventually precipitated with lime from sea water, the premium quality, slow-release fertilizer MgNH₄PO₄-6H₂O is recovered from the concentrated regeneration streams, which can then be recycled. Laboratory evaluations of the hydrolysis extent of the weak anion resin in the presence of bicarbonates showed that a steady-state is attained with resin exchange capacity reproducibly averaging about 80 mmol phosphates 1,⁻. The preliminary runs on a pilot plant for the tertiary treatment of urban sewage are also presented.