Asahi to verify system for recovery of phosphate salts

Asahi Kasei Chemicals, with the collaboration of the Japan Sewage Works Agency, completed a bench-scale trial of a new system to recover phosphate salts from sewage at sufficiently high purity for use as fertilizer materials, and plans to soon start a large-scale demonstration project at a domestic sewage treatment plant.

The system uses as an adsorbent 0.55-mm metal oxide particles with complex porous structures on their surfaces and interiors, consisting of voids that are several micrometers in diameter and pores with sub-micrometer diameters. The particles have high selectivity for phosphate salts, absorbing them efficiently. The system is capable of lowering the phosphate salt content to about 0.01 mg per liter of sewage even when the sewage is passed through 10 times faster than in a previous system developed by the company. The rate of adsorption is said to be the fastest in the world.

The recovery proceeds in three stages: the phosphate salts are absorbed by the metal oxide particles; the absorbed salts are washed off with caustic soda; and calcium hydroxide is added to the salts to form calcium phosphate while the caustic soda is recycled. The system can be run stably at low cost, even when the sewage has extremely low concentrations of phosphate salts. The purity of phosphate salts recovered in the secondary sewage treatment would still be high enough for them to be used as fertilizer materials.

The company is targeting commercialization in Japan and globally, such as in the US and China. Further R&D targets include combining the system with membrane technologies like its Microza ultrafiltration and microfiltration systems, and adapting the system to remove contaminants like boron and arsenic.