Hammer mills (crushing) and knife mills (chopping) have been usually used as a mechanical pretreatment. ... Electromagnetic mill: Municipal solid waste: Applying 120 Hz frequency of the magnetic field rotation for 0.5, 1.0, 2.0, and 4.0 min ... Manure (M), potato waste (PW) and mixed organic waste (MOW) 5–10-30 gO 3 /g TS: Increase by …