The turbidity of raw water entering a sedimentation tank is \(120\) NTU. After sedimentation, the turbidity is reduced to \(30\) NTU. What is the turbidity removal efficiency of the sedimentation process?
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Removal efficiency:
\[
\boxed{
\eta=
\frac{C_i-C_f}{C_i}\times100
}
\]
where \(C_i\) = initial value and \(C_f\) = final value.