Asahi Kasei Chemicals, the core operating company for chemical-related operations of the Asahi Kasei Group, has developed the world's fastest phosphorus adsorbent, together with an efficient water treatment system using this adsorbent for the selective, high-level removal and high-purity recovery of phosphorus from treated water. Commercial development of the adsorbent and system will be performed as part of the water processing business of Asahi Kasei Chemicals.
Occurring in effluent water, phosphorus has been identified as a cause of eutrophication, in which an excess of nutrients in enclosed bodies of water such as lakes and harbors fosters the growth of an algal bloom, disrupting the local ecosystem and rendering the water unsuitable for many purposes. The concentration of phosphorus in effluent water has therefore become subject to increasingly stringent regulation in many locations throughout the world.
Each of the conventional methods of large-scale dephosphorization has its drawbacks: Using biological treatment, it is difficult to maintain consistently low phosphorus concentrations; coagulation-sedimentation produces a large amount of sludge which requires costly treatment and disposal. While it is possible to reduce phosphorus concentration to the order of 0.01 ppm using adsorbents, the slow speed of adsorption has made large-scale application impractical.
Phosphorus is also an important resource, particularly for the production of fertilizer. With studies forecasting the depletion of phosphate mineral deposits in as little as a few decades, recovery from effluent water is potentially a valuable complementary source of phosphorus. Conventional methods of dephosphorization, however, generally recover phosphorus in the form of a mixture with many impurities. There is thus great latent demand for practical technology to remove phosphorus from effluent water and recover it for use.
The phosphorus adsorbent developed by Asahi Kasei Chemicals is highly selective for the phosphate ion, and is formed into small beads featuring a novel structure of surface micropores with an internal network of submicron pores, resulting in an extremely high effective surface area. This structure gives the adsorbent a very high adsorption capacity and enables phosphate concentration to be reduced to 0.01 ppm or less at a flow rate some ten times higher than with previously available adsorbents. The new adsorbent also readily desorbs phosphate ions in an alkaline solution, enabling repeated use.
The phosphorus removal and recovery system using this adsorbent comprises three stages. In the adsorption stage, water is fed through a column charged with the adsorbent and phosphorus is removed. In the desorption stage, an alkaline solution is passed through the column and the phosphate ions are desorbed. The adsorbent can then be used again in the adsorption stage. In the recovery stage, desorbed phosphate ions are separated as solid phosphate salt. The alkaline solution can then be used again in the desorption stage, while the recovered phosphate salt, of high purity, can be used as precursor for fertilizer.
Operation of a pilot facility is underway jointly with the Japan Sewage Works Agency to verify the performance of this adsorbent and system in the removal of phosphorus from secondary effluent from municipal wastewater treatment. The trial is scheduled for completion in fiscal 2008.
The high rate of adsorption enables the system to be applied at low cost and with a small space requirement, making it suitable not only for the treatment of municipal wastewater but also the treatment of industrial wastewater from foods and chemicals plants and the remediation of polluted bodies of water. Market development of the adsorbent and system will target Japan, the US, China, and other regions of Asia which face water pollution problems and shortages of clean water.
The water processing business of Asahi Kasei Chemicals is led by Microza(TM) hollow-fiber membranes and systems for large-scale production of potable water, for preparation of process water in the electronics, automotive, food, and medical industries, and for environmentally sound wastewater treatment, including treatment with membrane bioreactor (MBR) systems. Microza systems are in operation in Japan, the US, Europe, China, and other major markets in Asia.
The adsorbent and system will not only be developed as an independently viable business, but will also be incorporated with Microza filtration systems to enable the provision of comprehensive water treatment solutions. Further development of adsorption technology will extend to substances other than phosphorus, forming a core technology and a key driver for the expansion and growth of operations in water treatment products and systems.