To Do Class A or Not? What To Do To Enhance Sludge Processing?

The Metropolitan Water Reclamation District of Greater Chicago
Chicago, Illinois

Recently, more and more wastewater treatment plants (WWTPs) are upgrading their conventional solids treatment systems which produce Class B biosolids to produce Class A biosolids. This trend has triggered rapid growth of not only new sludge treatment technologies but also conventional treatment modification technologies. The main focus of this paper is on anaerobic digestion process modification techniques to produce Class A biosolids or enhanced digestion to achieve multiple solids processing objectives. The paper is based on information collected from various WWTPs throughout the US on practices and trends to enhance sludge digestion, worldwide literature review, and from technology vendors. A systematic analysis (case studies) of 4 WWTPs to evaluate and shortlist alternatives to enhance the existing solids thickening-anaerobic digestion-dewatering complex into either Class A or enhanced solids processing system as well as estimation of the operational carbon footprint (OCF) of each of the alternatives are presented in this work. Carbon footprint analysis of all the recommended options showed that Class B systems have smaller footprint than Class A or enhanced digestion systems mainly due to the higher heat and power requirements. Class B conventional anaerobic digestion ratio of OCF footprint to volatile solids loading to digesters (OCF/VSL) for solids processing part of plants is in the range of 0.45-0.55 [mass of CO2/mass of volatile solids]. Class A and enhanced digestion systems OCF/VSL do not vary greatly from each other, being in the range of lowest 0.52 for TPAD in continuous operation mode to 0.6-0.7 for the other modifications. Further heat and energy requirement analysis demonstrated that although all enhanced digestion systems result almost in the same carbon footprint, TPAD and OpenCEL require less electricity and natural gas supply from the outside sources due to higher biogas production and further heat recovery. More detailed analysis of heat and power requirements for each system at each of the plants should be performed in order to identify the most suitable option. This analysis should also include calculations of capital cost, carbon footprint associated with installations and maintenance, estimation of social factors and economic benefits of each of the systems. Source: WEFTEC 2009 Proceedings

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Posted: July 6th, 2010 | Filed under: Waste Water Treatment, Water Treatment | Tags: Biosolids Management, Reduced Carbon Footprint | No Comments »

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