In the 1988 movie Twins, Arnold Schwarzenegger was the brother who got the looks, the brains, and the strength, while Danny DeVito wound up with the leftovers. In a similar vein, wastewater treatment plants have two main products: clean water and biosolids. Complaints rarely surface about water being too clean, but biosolids disposal frequently draws harsh criticism.

Because biosolids are the inevitable result of treating municipal wastewater, they must be dealt with. A wide range of available products and technologies advertise that they can reduce — and in some cases eliminate — waste activated sludge.

“People in our industry are always looking for ways to save money, and decreasing sludge volume or production saves money,” said Al Pincince, a senior vice president at CDM Corp. (Cambridge, Mass).

Research in France, Germany, Japan, and the United States has all resulted in the development of new physical, chemical, and biological processes with the same goals — less sludge production in activated sludge systems and better sludge digestion. Options now include bacteria dosing for selective growth, ultrasonic and mechanical destruction of cells to make material more accessible for digestion, sidestream reactors to enhance selective growth, and blasting sludge with steam to kill pathogens and rupture the cells.

Factors driving interest in minimization, Pincince said, include the need to keep costs as low as possible and the difficulty at some plants of finding local land-application or disposal options. However, he noted, sludge-disintegration systems have no long-term, large-scale experience, and the economics of sludge minimization are not well known.

Copyright © 1996-2006, VertMarkets, Inc. All rights reserved.  To subscribe or visit go to:  http://www.wateronline.com