TABLE OF CONTENTS All biological treatment systems generate excess sludge or biosolids that must be removed (eventually) from the system to maintain optimum treatment efficiency. Some high rate activated sludge systems produce excess biosolids at the rate of 0.5 lb sludge per 1.0 lb of BOD removed. A plant removing 120,000 lbs per day of BOD could generate as much as 60,000 lbs of biosolids per day requiring treatment and disposal. While not all of the biosolids produced are the result of cellular synthesis (a significant portion is influent suspended and colloidal matter), it still requires disposal.
Sludge disposal is a major problem for many wastewater treatment facilities, especially industrial facilities. Sludge management and disposal can cost up to one-third of the cost of BOD removal in some systems, more if the sludge is considered to be a hazardous waste.
Biosolids quality is becoming more and more important as the range of disposal alternatives continues to diminish. Landfills are increasingly refusing to accept waste biosolids for disposal or are demanding additional treatment prior to acceptance. Regulatory agencies are imposing more and increasingly strict regulations on sludge quality for land application, composting, and other uses. The safe disposal or recycling of biosolids remains a major issue in the field of wastewater management.
Most of the treatment processes employed in industrial water pollution control yield a sludge from a solids/liquids separation step (sedimentation, flotation, etc.) or produce a sludge as a result of a chemical coagulation or a biological reaction.
Sludges usually undergo a...
