It was Sumitomo Osaka Cement Company, the 3rd largest cement manufacturer in Japan after Taiheiyo Cement and Ube-Mitsubishi Cement, who unknowingly bought the radioactive sewage sludge from Koriyama City's treatment center.
From Yomiuri Shinbun (11:06PM JST 5/3/2011):
928 tons? So it is almost double of what was initially reported (500 tons).
Regarding the high level of radioactive materials detected in the sewage sludge at a sewage treatment center in Koriyama City in Fukushima Prefecture, tt was revealed on May 3 that the cement made from the sludge had been shipped to Tochigi Prefecture and other places.
According to Sumitomo Osaka Cement (headquartered in Tokyo), the sewage sludge was recycled as cement material at its plant in Sano City in Tochigi Prefecture. The company has stopped production and shipment of the cement from the plant.
928 tons of the sewage sludge [from Koriyama facility?] have been used since the Fukushima I Nuke Plant accident, and the cement has been shipped to Tochigi, Gunma, and Ibaraki Prefectures and other locations. [The article doesn't say where.]
汚泥から放射性セシウムが１キロ・グラムあたり２万６４００ベクレル検出されている。Radioactive cesium of 26,400 becquerels per 1 kilogram has been detected from the sewage sludge.
Additional info from the cement company's press release on May 2:
The company received sewage sludge from the treatment center in Koriyama since the Fukushima accident from March 12 to April 30. [So, total of 50 days.]
The total amount of the sewage sludge received: 928 tons. [18.56 tons per day, NOT 10 TONS per day as initially reported.]
Understate everything by half. At this point, nothing surprises anyone, does it?
There are 22 other treatment centers in Fukushima that sell sewage sludge. No news on them yet.