How? By switching around the order in which the contaminated water is treated at Kurion's system and adjusting the amount of water.
To review the whole process, the water first goes to Toshiba's oil separation system. Then it goes to Kurion's system for oil/technetium removal, then cesium removal, then iodine removal. Then it goes to Areva's system for further decontamination, and finally arrives at Hitachi's desalination system.
From Yomiuri Shinbun (9:56PM JST 6/20/2011):
TEPCO announced on June 20 that the radiation level at the water treatment system at Fukushima I Nuclear Power Plant rose sharply because the level of contamination of the water to be treated was more than they had expected.
TEPCO said the radiation level [at the system] would go down if they changed the sequence of the water flow [Kurion's system uses 3 types of zeolites for 3 different radioactive materials] and adjust the amount of water. TEPCO will continue the testing on June 20 evening, and the company hopes to resume the full run on June 21.
Initially, TEPCO thought the high radiation at the system was due to the larger than expected amount of radioactive materials absorbed by the zeolite, but when they removed the zeolite and injected the highly contaminated water through the system, the radiation level on the surface of the system jumped to 11.55 millisieverts/hour.東電の松本純一・原子力立地本部長代理は記者会見で「放射線量がここまで高いとは思わなかった」と話し、今後、汚染水を浄化するゼオライトやシリカなどの吸着剤の順序を入れ替えるなどして線量が急上昇しないよう調整し、運転再開を急ぐ
TEPCO's Junichi Matsumoto said in the press conference that they hadn't expected the radiation to be that high. The company will adjust the system so that the radiation level would not rise rapidly, and resume the full operation.