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  • Continuous plug flow process 
  • Guaranteed Class A biosolids 
  • Utilizes existing facilities
  • No chemicals, dust, off gas or odor
  • Can increase digester capacity   

Ashbrook® ECO-THERM™ technology is a continuous pasteurization process for the on-site production of exceptional quality, neutral pH, Class A biosolids. When comparing the options available for sludge disposal, the beneficial use associated with land application is much preferred over other options such as land filling or incineration.  The current trend is toward both land application and the use of Class A biosolids, as Class A biosolids are ideal for usage as a soil amendment as these biosolids contain a relatively high total nitrogen and phosphorus nutrient content.

The system can run on a continuous basis without operator attention or in low flow scenarios, the system may run on shifts.  By using methane from anaerobic digestion as the energy source for heating the sludge, energy consumption is very low. In most cases the heated pasteurized sludge will provide the digester heating requirements.  

A progressive cavity pump moves the sludge through the Heat Recovery Exchanger where it is heated to approximately 90 deg. F. The Heat Recovery Exchanger runs counter current to the final product, allowing both heat recovery from the final stream and the reduction of heat of the final product which enters the mesophilic anaerobic digester.  The Primary Heat Exchanger then heats the flow to just above the mandatory temperature of 158 deg. F. The sludge runs countercurrent to hot water from low pressure hot water boilers.

A second pump moves the sludge through the Plug Flow Reactor to provide the required 30-minute detention time at temperature. The ECO-THERM™ produces Class “A” sludge that is completely in accordance with U.S. EPA 503 regulations. The patented continuous process plug flow reactor positively ensures the sludge is exposed to the critical time and temperature conditions. A third pump moves the sludge through a Cooling Heat Exchanger, which maintains the proper temperature of the anaerobic digester. The anaerobic digester reduces volatile solids and provides for vector attraction reduction, resulting in Class A biosolids.  
The benefits of biosolids for both soil and vegetation are numerous and well recognized.  Biosolids provide primary nutrients (nitrogen and phosphorous) and secondary nutrients such as calcium, iron, magnesium and zinc. Also, the use of biosolids increases crop yields and maintains nutrients in the root zone and unlike chemical fertilizers, biosolids provide nitrogen that is released slowly over the growing season as the nutrient is mineralized and made available for plant uptake.  Land application of biosolids can also offer net greenhouse gas benefits by recycling carbon to the soil and fertilizing vegetation for further carbon dioxide capture.

With the higher level of pathogens (< 2,000,000 MPN/g TS) present in Class B biosolids, land application is highly restricted and not attractive to the public in general. Conversely, Class A biosolids substantially lower pathogen levels (< 1,000 MPN/g TS), enabling it to be used with few restrictions
The PLC continuously monitors the temperature and time of pasteurization.  If either parameter falls below a setpoint, the system automatically goes into a recirculation loop and alarms the operator. The process will not begin to discharge pasteurized sludge until the time and temperature requirement is met.