History
Early kraft pulp mills discharged black liquor to watercourses. Black liquor is quite toxic to aquatic life, and causes a very dark caramel color in the water. The invention of the recovery boiler by G.H. Tomlinson in the early 1930s, was a milestone in the advancement of the kraft process.
By 2000, the better kraft mills recovered 99.5% or more of the black liquor, and purified the remainder in biological treatment plants, reducing the environmental impact of the waste waters below the level of scientific significance, except perhaps in very small streams. Even in the 21st century, some small kraft mills remained (producing at most a few tons of pulp per day) that discharged all black liquor. However, these are rapidly disappearing. Some kraft mills, particularly in North America, still recovered under 98% of the black liquor in 2007, which can cause some environmental issues, even when biologically treated. The general trend is for such obsolete mills to modernize or shut down.
Read more about this topic: Black Liquor
Famous quotes containing the word history:
“To history therefore I must refer for answer, in which it would be an unhappy passage indeed, which should shew by what fatal indulgence of subordinate views and passions, a contest for an atom had defeated well founded prospects of giving liberty to half the globe.”
—Thomas Jefferson (1743–1826)
“We may pretend that we’re basically moral people who make mistakes, but the whole of history proves otherwise.”
—Terry Hands (b. 1941)
“The history of all hitherto existing society is the history of class struggles.”
—Karl Marx (1818–1883)