Carbon particulate matter suspended in waste effluent must be either controlled or removed prior to discharge. Wastes associated with the carbon black and acetylene industries are of concern. These wastes may contain up to 1000 milligrams per liter (mg/l) carbon particles in suspension; in most cases this carbon concentration must be reduced to less than 50 mg/l suspended solids. Usually, these solids settle readily and are removed by gravity settling and/or flotation.
Individual particle sizes range from a submicron to larger than 100 micron (p). Larger particles settle, whereas smaller particles float. Transition size particles remain suspended almost indefinitely unless forced out of suspension by mechanical or chemical means. Unless a highly clarified effluent is required, suspended matter may not have to be removed as it amounts to a small proportion of total solids concentration.
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