半个世纪的难题
半个世纪的难题-
生物固锰除锰理论经过近20年的研究已经基本成熟，困扰了人们半个多世纪的除锰难题得到了较好的解决。
Manganese removal has been a difficult problem which has puzzled water quality engineers for over half a century , but now it has been solved preferably under the theory of biological manganese fixation and removal which has been matured through the last 20 years .