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Three Reasons For Choosing Direct Steam Injection (DSI) Heaters For Your Anaerobic Digested Sludge

The goal of wastewater treatment is to return clean water to the local water supply. This involves removing any solids in the waste stream and breaking down any microorganisms present by heating and circulating the waste. Hydro-Thermal's Direct Steam Injection (DSI) heaters (especially the Non-Obstructing Heater [NOH]) are ideal for heating and maintaining the digester's sludge temperature for break down. Compared to other heating systems, they utilize a smaller footprint and precise temperature control (+/- 1°F). NOH's straight through design reduces maintenance by operating continuously without plugging or fouling.

Waste streams are generally made up of all residential and industrial systems in which organic or inorganic waste is discharged. The wastewater treatment process begins by screening, settling, and filtering inorganic solids and percolating the remaining waste in aerated tanks or ponds to allow bacteria to reduce a significant quantity of the organic material (the remaining organic material is known as sludge). Bacteria further break down this sludge in equipment known as digesters. The liquid waste is agitated and circulated to maintain a uniform temperature, and the process is very temperature sensitive. Optimum biological action occurs between 85°F and 140°F (25-60°C), depending on what digestion process is chosen, and the entire process can take between 10 and 22 days to break down the organic material completely.

TWastewater NOH Install 01he Hydro-Thermal Solution: Precise Heating with Flexibility

An increase in biological activity can be seen when maintaining a tight temperature band and eliminating hot or cold spots in the digester, as consistent digester temperature improves methane production and sludge stabilization. Less digestion time is possible due to the sludge maintaining its temperature more consistently throughout the digester. Energy costs are reduced due to the DSI heater's high efficiency, compared to a heat exchanger.

Realizing significant cost savings is possible through optimizing the anaerobic digestion process by keeping microorganisms at the required temperature to optimize effectiveness and increase methane gas production to power the boilers. The ideal temperatures is 85-100°F (29-38°C) for mesophilic digestion or 120-140°F (49-60°C) for thermophilic digestion to optimize biogas generation.

The Hydro-Thermal Solution: Reduce Maintenance 

No special tools are required to maintain the rugged, flow-through NOH design, helping minimize downtime caused by wipes or rags collecting and plugging the heater. If material gathers and plugs other heating devices (like a heat exchanger), then these units must be opened up and manually cleaned to remove the solids plugging the system. Solids in the sludge can also burn onto a surface that is hotter than 150°F (10°C), like in a tube/shell or tube/tube heat exchanger.Wastewater clog 01

On the other hand, most DSI heaters have no hot surfaces where burn-on can begin to occur. As a result, there is generally no maintenance required to keep them clean. The NOH is produced using wear and corrosion-resistant metallurgies to withstand grit and highly abrasive materials. Its straight through design ensures that rags do not get caught in the heater.

The Hydro-Thermal Solution: Smaller Footprint

Whether a tube/shell, tube/tube, spiral, or any other type of heat exchanger, they will all result in a larger footprint than Hydro-Thermal's Direct Steam Technology.

DSI heaters require little, if any, floor space because of their small size and direct installation into the existing system piping.

For installations using a heat exchanger, there is also a need for a condensate return system, which requires a steam trap, collection well, condensate return pump, and the associated piping to return the condensate to the boiler. Some of this equipment is not required for a DSI heater, reducing the installation cost.


DSI heaters offer significant advantages over competing heating systems. DSI heaters precisely control process fluids to +/- 1°, minimizing the potential for disrupting the anaerobic digestion process, all while requiring less floor space than other options.

DSI heaters are also much easier to clean and require minimal access due to their compact design, showcasing how they produce better results and lead to a reduced cost of ownership

Click here to learn more about our application experience in anaerobic digestion, industrial pre-treatment and tank heating

Contact us at 800-952-0121 or This email address is being protected from spambots. You need JavaScript enabled to view it. today to get a free evaluation from our application experts. We can provide tips on how to optimize heating systems in wastewater treatment plants.


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Hydro-Thermal is the global leader in the development and manufacturing of Hydroheaters. Through our vast global channel partners, we support hydro heating in six continents and all industrialized areas. We create heating systems for a variety of industries including: pulp, paper, chemical, ethanol, food & beverage, metal, & more!

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