Bio-Scru Design

At the heart of the Therma-Flite BIO-SCRU sludge drying system is proven HOLO-SCRU screw type heat exchanger technology. Screw type heat exchangers have been used in bulk processing for the agriculture, chemical, construction, and food industries for over 70 years. This versatile system is capable of processing everything from Apples to Zinc. Both reliable and customizable, HOLO-SCRU equipment is the world standard in indirect screw type heat exchange equipment.

Technology that Works


The feed hopper includes twin, intermeshed paddle mixers to keep the biosolids homogenized and break up bridging. This feature insures a consistent feed rate and material uniformity. A screw auger located in the bottom of the feed hopper conveys the biosolids to the dryer.


The thermal oil heater uses PLC control for optimal heating efficiency. The heating can be accomplished with a variety of energy sources including; waste heat, solar thermal, bio-gas, natural gas, propane, #2 fuel oil, diesel, coal, or electricity.


The dryer chamber includes twin, intermeshed HOLO-SCRU rotors. In the drying chamber, biosolids are heated under slight negative pressure in a sealed, anaerobic environment. The dehydrating heat is indirect. Thermal fluid is circulated throughout the HOLO-SCRU rotor and outer jacket of the drying chamber.


The condenser system provides the continuous removal of moisture evaporating from the biosolids. The process captures particulate and condenses the evaporated water.


The water-cooled screw rotor and jacketed housing combine to cool the dried biosolids for safe handling.

Optimum Volumetric Reduction and Efficiency

Through proprietary design, the BIO-SCRU dryer reduces biosolid volume by decreasing capacity, or pitch, at each stage of the rotor. This increases loading capacity and utilizes the maximum amount of heat transfer surface (A) through the length of the dryer. Biosolids are accumulated between each stage of the rotor in no-pitch zones allowing the mixing blades to homogenize particle size. The rotor flights use wipers to remove material adhering to the opposing screw. The self-clearing design of the rotors insures that heat transfer surfaces remain free of build-up.

Watch video below