| http://www.w3.org/ns/prov#value | - Tank unit 20 is preferably the same as tank unit 16 and includes a treatment tank 58 having compartments 2A, 2B, 2C and 2D and including means, for example, skimming means and sludge dredging means for removing surface debris 60 and sludge or activated sludge 62 from compartment 2A. The compartments 2A-2D are preferably the same as compartments 1A-1D and have respective openings 64, 66, and 68 joi
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