THIN FILM DRYING WITH AUTOMATED STABILIZATION PROVIDES VOLUME REDUCTION AND ENHANCED QUALITY FOR MCUA BIOSOLIDS Session 12B
Abstract:The Middlesex County Utilities Authority (MCUA) is currently constructing improvements to its biosolids dewatering and stabilization operations at the Edward J. Patten Water Reclamation Facility located in Sayreville, New Jersey. The 40 million project includes new thin film dryers and an automated stabilization system that will allow the MCUA to process a consistent, homogeneous final product. These modifications will also provide a reduced volume of final product with minimized odor generation potential. The initial benefits include reducing the annual operating cost of the system by approximately 5.5 million per year, improving air emissions at the MCUA plant, and providing opportunities for alternative markets for the final product while eliminating current land application activities.
The MCUA treats on average 120 millions gallons per day (MGD) of wastewater from communities and industries in Middlesex County and portions of Somerset and Union Counties. The MCUA historically relied on ocean dumping for disposal of biosolids generated from the wastewater treatment processes. In 1988, the MCUA was required to abandon ocean dumping and identify an alternative method to treat and dispose of biosolids. In 1991, the Authority completed construction of Land Based Sludge Management Facilities at the WWTP, and has been generating a product called MeadowLife® using a proprietary alkaline sludge stabilization process.
The MeadowLife® product has been successfully used as landfill cover as well as for land application at various agricultural sites throughout New Jersey. The current process can generate approximately 1,100 cubic yards of Class A biosolids each day. The Authority has worked hard to make this product a success, but has been faced with the growing challenge of finding more suitable sites for an increasing quantity of materials in an area where opportunities for land application has been declining with the growth of suburban communities throughout the state. Recent pressures from the New Jersey Department of Environmental Protection (NJDEP) has resulted in the need to stop land application of the current product, necessitating modifications that would generate less quantity of a higher quality product at a lower annual cost.
The modifications are based on process technologies developed by R3 Management, Ltd and licensed to the MCUA. They will allow the MCUA to process 157 dry tons per day on average of 62% dry solids materials. All materials will be used as daily cover for the MCUA's sanitary landfill, which generates landfill gas used for cogeneration at the MCUA plant and to fire thermal fluid heaters for the new thin film dryers. On average, the system will generate approximately 480 cubic yards of Class A biosolids each day, which is significantly less than the current process.
Volume reduction is achieved by feeding filter press cake to a supplemental dewatering system consisting of five (5) indirect single pass thin film dryer units that produce approximately 50% to 55% dry solids for further mixing and treatment. The single pass thin film dryer units offer process optimization in high rate water evaporation capability while eliminating such potential operating hazards as fire and explosion risk associated with drying raw sludge at much higher dry solids levels. The design utilizes thermal fluid heaters that circulate 480°F thermal fluid through each dryer jacket for drying. This process reduces the use of alkaline additives to achieve the heat requirements of the process, and thereby a reduction on the volume of materials processed in the system.
The automated stabilization system includes three (3) continuous ploughshare mixers with tangential choppers, an admixture storage and feed system utilizing rotary discharge feed equipment, and four (4) Pasteurization units. The mixers blend dried cake with pulverized lime (CaO) to provide a consistent homogeneously mixed material that is fed into the pasteurization units. Each vessel is designed to allow the heat pulse of alkaline stabilization to be applied at a controlled rate. The materials are continuously monitored and recorded for time and temperature before discharging to a final product loading and storage area. An odor extraction system is provided to direct odorous air generated from the process through a regenerative thermal oxidizer before discharging through an existing odor control stack.
Automation and control by means of the SCADA system consisting of ten (10) remote PLCs utilizing DeviceNet communications between instruments, MCC's and equipment, will provide the MCUA with extensive monitoring and control of the new process. Construction is currently underway with planned startup of the initial drying stream by the middles of 2005, with full production capability anticipated by the end of the year.
Document Type: Research Article
Publication date: January 1, 2005
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