In composting municipal clarifying sludge, waste paper is used as the exclusive C-carrier for setting a C/N ratio suitable for rotting. After comminuting to irregular coarse shreds, the waste paper is added to the non-dehydrated clarifying sludge until C/N ratio is 20:1 to 25:1. The sludge obtd is then swelled 2-10 hrs., dehydrated to 30% solids content and composted. Waste paper is cheaper and more easily available than the previously used sawdust. The paper shreds and liq. sludge form an easily dehydratable mixt., yielding a higher solids content. In water-extn., the paper shreds absorb suspended materials and act as flocking auxiliaries. The dehydrated mixt can be disposed of as pellets or composted. Printers' ink on waste paper can be removed by standard flotation e.g. with 3% resin soaps and 1.5-3% cerosine. Heavy metals in sludge can be pptd mechanically, electrolytically and/or chemically. Fresh compost is pref added to the sludge before mechanical water etxn.
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