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Data Entry: June 2011
Name of Technology Production of biosolid fuel from sewage sludge
Technology Owner Hitachi Zosen Corporation
General Description This technology aims to make efficient use of the heating value of sewage sludge by drying to a low moisture content, and making further beneficial use of sewage sludge by producing a pelletized, easy-to-handle biosolid fuel as a substitute for coal.  A further aim is to help reduce greenhouse gas emissions, using carbon-neutral sewage sludge as fuel. Selling the resultant biosolid fuel as a valuable product is a more cost-effective way of recycling dewatered sludge than disposal.

Conceptual diagram of newly developed technology

Components of Technology The technology features a treatment system comprising the following three main equipment components.
  • (1) Thermal oil heater: Heats thermal oil and also takes in sludge dryer-pelletizer venting for thermal oxidation and deodorization.
    (2) Sludge dryer-pelletizer: Simultaneously dries and pelletizes dewatered sludge, incorporating an indirect heating system.
    (3) Scrubber: Cools and dehumidifies sludge dryer-pelletizer venting.

Equipment 1 generates heat required for drying. Equipment 2 dries and pelletizes sludge to produce biosolid fuel.
Heat of the venting from equipment 2 is recovered by equipment 3, a scrubber, to heat sludge, thereby improving the overall thermal energy balance of the wastewater treatment plant.

Note 1. If the wastewater treatment plant has a digestion tank or other sludge digestion facilities, digestion gas can be used as fuel for the thermal oil heater and scrubber wastewater can be used to heat thickened sludge.

Schematic Diagram of the Technology System

Mechanism of sludge drier-pelletizer

Features of Technology This technology has the following features:
  • Recycles dewatered sludge more cheaply than disposal.
  • Produces easy-to-handle fuel through the sludge drying and pelletizing process.
  • Reduces carbon dioxide emissions through the use of dry sludge pellets as biosolid fuel.
  • Uses a highly safe drying technique incorporating an indirect heating system.
  • Uses the thermal oil heater also on the sludge dryer-pelletizer venting for thermal oxidation and deodorization.
The sludge dryer-pelletizer has the following features:
  • Produces dry sludge pellets (biosolid fuel) with a low water content (5% to 10%).
  • Is simple to maintain since the equipment dries and pelletizes sludge simultaneously.
  • Enables stable operation by circulating dry sludge pellets to reduce variations in the water content of the dewatered sludge.
  • Discharges dryer venting at a lower rate than a flash type or direct air type drying system, so the venting treatment system can be made compact since the equipment dries dewatered sludge indirectly via the thermal oil.
  • Free from concerns about piping corrosion or scale deposits since the equipment uses thermal oil.
  • Dust is minimized because the dryer lets dry sludge pellets roll slowly on the heat transfer disks while allowing dewatered sludge to deposit on the surfaces of the sludge pellets. (No bag filter is needed.)
  • No odor emissions since the sludge dryer-pelletizer is closed and maintains a negative inside pressure during operation.
  • The coating process prevents dewatered sludge from depositing on the drier, reducing the dryer’s power requirements.
  • Use of thermal oil eliminates the need for water treatment equipment or addition of chemicals unlike steam-based systems.
  • Reduces fuel consumption since the thermal oil heater also serves as a deodorization furnace.
  • Treated water produced in the plant can be used to meet all water requirements of the drying and pelletizing processes.
The sludge dryer-pelletizer also offers the following safety features to minimize the risk of ignition or explosion.
  • (1) Avoids extended retention of sludge. (Minimized risk of ignition)
  • (2) Low thermal oil temperature (Minimized risk of ignition)
  • (3) Low oxygen concentration (Reduced spontaneous ignition and other risks)
  • (4) Low level of dust (Reduced risk of dust explosion)
Evaluation of Technology This technology was developed in the LOTUS Project (Lead to Outstanding technology for Utilization of Sludge Project) and evaluated and reviewed by the Sewerage Technology Development Project Committee under the Ministry of Land, Infrastructure and Transport in Japan in 2007.

[Link to the technology evaluation report]
Contact Information Osaka Environmental Systems Sales Department, Sales Unit, Environmental Systems & Solutions Division, Engineering Headquarters
Hitachi Zosen Corporation

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