Sludge Minimization Technologies-Doing More to Get Less
Sludge minimization technologies have been available for several decades; however recent developments have brought some sludge minimization technologies to the forefront. All of the technologies utilize one or more of three basic approaches to minimize the amount of waste activated sludge produced by an activated sludge process: cell lysis, cyclic oxic environments, and long solids retention time. This paper will discuss the three basic mechanisms, will review the development of several sludge minimization technologies, and will report on the current viability of each technology as well as current research needs for each.
Sludge minimization refers generally to the optimum reduction of the mass of sludge or biosolids produced at a wastewater treatment facility. The sludge minimization technologies that have emerged perform their main solids reduction mechanisms within the activated sludge process, prior to sludge stabilization and conversion to a biosolid. These are the technologies that are of interest in this paper. A fundamental understanding of the basic mechanisms available to minimize sludge production is needed prior to evaluating the various sludge minimization technologies that are emerging onto the market. From that understanding, each technology can be evaluated.
Early attempts at sludge minimization focused on long solids retention times within the activated sludge process, and the reduced sludge production was seen as a benefit of extended aeration plants. Ultrasonic cell lysis was first developed through laboratory-scale research in the 1960s, but was initially uneconomical due to limitations of the ultrasound equipment available at that time. Advances in ultrasound technology in the last decade have enabled commercial
application of the technology for wastewater applications. Ultrasound can be used for sludge minimization in the activated sludge process or in digestion. The CannibalTM process has shown recent success, and is marketed by Siemens USFilter. IDI has developed a competing process, know as Biolysis® ‘O’. Both of these technologies emphasize cyclic alternation between aerobic, anoxic and anaerobic environments. The MicroSludgeTM homogenization process is another recent development for sludge minimization, relying on chemical pretreatment and mechanical shear forces to lyse bacterial cells.