Conventional methods of wastewater treatment have been developed primarily to overcome public health hazards, and nuisances such as odors and unsightliness, caused by disease organisms and organic matter in the wastes. Advances in method have been typically in the direction of more sophisticated and more energy intensive processes. The most common form of secondary treatment, after removal of coarse solids and floatables in primary treatment, is currently the activated sludge process using air or oxygen introduced into the wastewater in the presence of concentrated bacteria.