Drying Out

by Howard Smallowitz, Asst. Ed.; Civil Engineering—ASCE, 345 East 47th St., New York, NY 10017,

Serial Information: Civil Engineering—ASCE, 1986, Vol. 56, Issue 4, Pg. 72-75

Document Type: Feature article

Abstract: Treatment plants are most efficient when they're treating waste, not water. Spurred on by increased fuel prices, a number of new technologies have been developed that can make sludge drier than ever. Sludge on a gravity belt thickener drains through the fabric belt it rides on as plows turn it. The City of St. Paul is using two devices to dewater its sludge. A vari-nip roll press, basically a large wringer whose design was borrowed from the pulp and paper industry is used on primary sludge, while plate and frame press dewaters secondary sludge. The sludge, which is incinerated after dewatering, is now so dry that no fuel need be added to it. Sludge freezing, an old technology is now being reexamined. Researchers for the Army Corps of Engineers have found that it may be possible to use mother nature to freeze sludge virtually anywhere in the northern United States.

Subject Headings: Dewatering | Sludge | Technology assessment |

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