Current State of the Practice of Sludge Reduction Technologies

The handling and disposal of wastewater sludge is an increasingly costly portion of the operation of a wastewater treatment plant and is developing into an even greater future risk given the trend of decreasing availability and increasing costs of ultimate disposal options. Recently several technologies and process innovations have been proposed to reduce or eliminate the waste activated sludge (WAS) fraction resulting from treatment, or to render it more amenable to anaerobic digestion, a common sludge stabilization step, in order to maximize biogas production and the corresponding potential for energy cogeneration. Several of these technologies are also claiming significant improvements in the dewatering characteristics of the stabilized biosolids as a result of these pre-conditioning steps. The above claims are especially relevant for industrial facilities and smaller municipal facilities which frequently have no primary sludge but generate large quantities of difficult-to-dewater waste biomass.WERF's 05-CTS-3 Evaluation of Processes to Reduce Activated Sludge Solids Generation and Disposal, which started in the Spring of 2007, seeks to establish a comprehensive evaluation methodology for WAS reduction processes based on the in-depth consideration of a select number of technologies considered to be representative of the many options currently available in the marketplace. These technologies will cover both those intended to reduce the generation of residual sludge from the liquid treatment process, as well as those designed to pre-condition whatever sludge is produced in order to make it more amenable to a subsequent stabilization process such as anaerobic digestion.This paper presents the results of a literature review task conducted in the initial stages of the project, and is intended to be the first one of a series of papers in which the results of this important project are presented to the Residuals and Biosolids community of practitioners. This literature review places into perspective the basic mechanism behind the different WAS Reduction technologies, finding applications worldwide, identifying their application point within the treatment facility (i.e., digestion pretreatment, treatment of activated sludge recycle streams), and defining its development status.