TOKYO, Japan, Mar. 30, 2011 -- Desalination and membrane processes could be used to help deal with radioactive contamination in seawater around the crippled Fukushima Daiichi nuclear facility, following the impact of the magnitude 9.0 earthquake.
The Tokyo Electric Power Company (TEPCO), which owns the Fukushima Daiichi facility, recently announced that radioactive materials had been detected in seawater from the discharge canal south of the nuclear power station.
While media reports and government announcements have been u-turning on whether water supplies further north in the country are safe to drink (see Water & Wastewater International story (WWi)), the impact of radioactive seawater on desalination facilities remains uncertain.
Reports last week suggested that water in downtown Tokyo was measuring 210 becquerels of iodine-131, when the acceptable level for infants under the age of one is 100 becquerels.
Industry experts have since said radioactive iodine cannot be completely removed through reverse osmosis (RO) desalination processes and that efficient removal could deteriorate with time.
Dr Graeme Pearce, a membrane technologist with 25 years experience in the membrane industry, and principal at Membrane Consultancy Associates, told WWi: “Radioactive iodine is removed quite well by RO, though it is not removed completely, and the degree of removal is dependent on the design of the RO system. The effect of radioactivity on the RO membranes and on other ionic species has not been determined, but it may be that the removal efficiency of radioactivity will deteriorate with time.”
The International Desalination Association (IDA) however said that membrane processes have been adopted by the nuclear industry for the treatment of liquid radioactive wastes (LRW).
Leon Awerbuch, the IDA programs chairman, told WWi: "Iodine is not the biggest issue with the Fukushima reactor. Radioactive iodine has a half life of approximately eight days and dissipates through natural degradation. What are potentially much more difficult to deal with are gamma rays, which are very penetrable.
"Membrane technology is clearly capable of rejecting radioactivity in the order of 93-97%, typical for what we call polyamide, thin film composite reverse osmosis membranes. Those membranes can be greatly effective in reducing the volume of the waste, obviously not perfect, but a significant reduction in radioactivity. Obviously you need to think about maximising the system of membranes which would be used for decontamination."
While desalinated water does not make up the vast majority of supply in Japan, as can be seen in many Middle Eastern countries, the Fukuoka District Waterworks Agency operates a 50,000 m3/day facility.
The Toyobo Group, which supplied RO membranes to the Fukuoka facility, said: "The impact of the earthquake on the company's consolidated performance is not clear at the present time. When timely disclosures regarding any effects on performance are necessary, we will make announcements as quickly as possible."
Awerbuch added: "Membranes have been used for radioactive radon rejection in some brackish water and other applications, so it's not unusual, but there is a need for more experience in dealing with catastrophic events, such as that in Japan. From all the options available, I would say that desalination membrane technology could be a solution. Clearly, it can remove a significant proportion of radioactivity, but there is still the problem of the concentrate reject and it depends on the volumes you have to deal with, and final disposal, which is complicated."
A report from the International Atomic Energy Agency (IAEA) has looked at the "Application of Membrane Technologies for Liquid Radioactive Waste Processing". It concluded that past processes for treating LRWs are limited by an "inability to remove all contaminants, the large operating costs involved (e.g. evaporation), or the potential to generate significant quantities of secondary solid waste".
On membranes, it concluded: "They are capable of producing high quality treated effluents with an acceptably low level of residual radioactivity for discharge, or for recycle and reuse. The concentrate waste stream containing the removed radioactivity invariably needs further processing by evaporation or other means to facilitate final conditioning to a solid waste form suitable for intermediate storage and disposal."
Meanwhile, Nitto Denko, which supplied RO technology to the 40,000 m3/day plant operating in Chatan, Okinawa, said that no significant damage was caused to the buildings and facilities of its Kanto plant, but that it's "becoming increasingly difficult to follow the normal production schedule, due to enforced power restrictions put in place".