A Biosolids Management Approach that Emphasizes Environmental Sustainability

For the past fourteen years, the Greater Lawrence Sanitary District (GLSD) has relied on off-site incineration and landfills as a solution to its sludge management needs. The District owns and operates a 52 million-gallon per day (mgd) wastewater treatment plant that serves the communities of North Andover, Andover, Lawrence, and Methuen, Massachusetts and Salem, New Hampshire. The plant began operation in 1977 and currently treats an average flow of approximately 35-mgd. GLSD has recently constructed an on-site biosolids processing system that will end its reliance on disposal as a sludge management option.GLSD opted to design and build anaerobic digesters and high solids centrifuges followed by a biosolids drying and heat recovery system. As part of their solids management solution, the District selected a private company with significant prior experience in the field to build and operate the biosolids drying facility and market the resulting biosolids product. The anaerobic digestion system was placed into operation in March of 2002, and the new drying system commenced start-up in October of 2002. The construction of these facilities will save the District and its member communities approximately 1 million annually in operating costs.Cost was not the only evaluation criterion considered by the District. A significant factor in the selection of this solids management approach was that it provides environmental sustainability. The biosolids product resulting from the new biosolids processing facilities reuses nutrients from the biosolids that were formerly discarded in a landfill or incinerator. The biosolids product replaces chemical fertilizers that would otherwise be mined or manufactured industrially from irreplaceable sources. The drying facility utilizes the latest practices in direct drying technology, including exhaust gas recirculation to reduce total air emissions, two stages of particulate control, Regenerative Thermal Oxydizers (RTOs), and separate control of building air emissions.The most unique aspect of the new GLSD biosolids processing facility is the design focus on energy efficiency and resource reuse. This paper addresses the various design features that are included in the new GLSD biosolids processing facility that enable it to be considered highly "sustainable". For purposes of this paper, "sustainability" means that the process minimizes the use of the earth's finite resources, and that any finite resources that are used in the process are utilized in an efficient manner.