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 andDisposal, 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.

WERF's 05-CTS-3 Evaluation of Processes to Reduce Activated Solids Generation and Disposal aims to establish a comprehensive evaluation methodology for waste activated solids (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 cover both those intended to reduce the generation of wastewater treatment residuals from the liquid process, as well as those designed to pre-condition solids in order to make it more susceptible to subsequent stabilization processes such as anaerobic digestion.In conjunction with the previous paper titled "CURRENT STATE OF THE PRACTICE OF SLUDGE REDUCTION TECHNOLOGIES" (Sandino et al, 2008), this paper is intended to focus on the evaluation of the performance data collected from full-scale facilities. Laboratory analyses conducted at Virginia Polytechnic Institute from samples collected from these same facilities are included. This paper will discuss the mechanisms behind the technologies, present performance data, and discuss the operational considerations influencing the observed performance (e.g. wastewater characteristics, activated solids operational practice, solids reduction technology design basis and operation).

Sludge reduction technologies have gained popularity as solids handling and disposal become an increasingly costly portion of a wastewater treatment plant. The technologies are implemented within the liquid processes for waste activated sludge minimization, or as pre-treatment to anaerobic digestion to enhance digestion and reduce biosolids. Biological, chemical, and/or physical procedures are used and achieve varying level of success, but the underlying mechanisms are not well understood and modeled. The paper presents a general framework -via the WERF project 05-CTS-3, Evaluation of Processes to Reduce Activated Solids Generation and Disposal -for simulating representative sludge reduction technologies, including Cyclic Metabolic Environments (e.g. Siemens' Cannibal (biological)) and Ozonation (chemical), as well as the Thermal Hydrolysis (Cambi, Veolia) and Pressure Release (Siemens' Crown (physical)) digestion pre-treatment technologies. Non-proprietary ASM 2d model was implemented for activated sludge processes and ADM1 model for anaerobic digestion, with modifications to reflect potential solids reduction mechanisms. The models were calibrated to existing installations where adequate process data are available, or compared with reported performances otherwise. The modeling framework generally resulted in predictions consistent with plant records or reported performance for selected sludge reduction technologies, suggesting successful capture of key mechanisms and parameters.

A biogas utilization study identified both internal combustion engines and microturbines as competitive alternatives for retrofit of the existing cogeneration system at the Oceanside Water Pollution Control Plant, San Francisco, California. To select a single preferred alternative to be carried forward into the conceptual design phase of the project, a multi-attribute evaluation of the alternatives was performed. Key criteria developed by the project team, force ranking of the criterion to establish weighting of the criteria, and detailed evaluation of the alternatives is presented. Ultimately, the internal combustion engine alternative was recommended, driven largely by the ability of the internal combustion engines to be able to more fully utilize the average and the maximum month biogas production at the Oceanside plant and physically fit within the existing facility. In addition, for this particular evaluation, the internal combustion engine alternative resulted in a higher net present value due to higher conversion efficiency of fuel to electrical power, while providing a higher product maturity ranking with equipment available from multiple equipment suppliers.

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