Hidden Costs in the Complete Thermal Hydrolysis Implementation

Thermal Hydrolysis Process (THP) systems are often considered a transformative solution for improving the efficiency and effectiveness of wastewater treatment. By improving dewaterability, increasing digester capacity and performance, and supporting Class A biosolids production, THP promises higher efficiency and lower long-term costs.

But as the first of four sessions in Centrisys/CNP’s Sludge Treatment Webcast Series made clear, the real cost of THP implementation goes far beyond the initial technology investment. 

Led by Michael Kopper, CEO of Centrisys, and Gerhard Forstner, President of CNP, this first discussion in the four-part series explored the complete THP treatment train, from pre-dewatering to digestion to final solids handling. Their goal: to help operators and decision-makers understand the full scope of infrastructure, chemical, operational, and energy demands that can impact the viability of a thermal hydrolysis system.

A System, Not a Single Step

Most evaluations of thermal hydrolysis focus on the reactor itself, but the hydrolysis reactor is only one part of a much larger system. Every upstream and downstream process affects performance, cost, and complexity. When considering whether THP is a fit, facilities need to assess the entire treatment train.

The Four Interconnected Stages

THP technology is deeply interconnected with several other critical stages in the wastewater treatment process, including:

• Pre-dewatering or thickening
• Hydrolysis process
• Anaerobic digestion
• Post-dewatering and biosolids handling

Each of these stages brings its own engineering and cost implications. Ignoring them in early planning can result in oversights that delay implementation or reduce return on investment. 

High-Pressure Systems Come With High Expectations

Traditional thermal hydrolysis systems rely on high-pressure steam to break down sludge. These systems are well-established and capable of achieving significant increases in biogas production and solids reduction. However, they also introduce a new layer of complexity that affects capital budgets, staffing, and utility costs.

Infrastructure and Operating Challenges

High-pressure systems often operate at temperatures between 320 °F and 360 °F and pressures up to 150 PSI. That means adding pressure-rated tanks, control systems, steam boilers, and additional safety monitoring. The sludge must first be dewatered to about 17% total solids before hydrolysis, which requires considerable polymer dosing and high-torque pumps to move the thickened sludge through the system. Once treated, that same sludge often needs to be diluted back down to 8 or 9% solids before entering the digester. This requires either potable water or non-classified centrate, depending on the biosolids certification target.

Staff must also be trained on managing pressurized equipment and complex heating systems. Maintenance becomes more specialized, and equipment downtime can lead to bottlenecks across the treatment line.

A Lower-Cost Alternative: Thermo-Chemical Hydrolysis

To address these challenges, Dr. Andreas Dünnebeil developed the Thermo-Chemical Hydrolysis Process (TCHP), PONDUS. This approach eliminates steam boilers and pressurized vessels in favor of a lower-temperature, atmospheric-pressure system that achieves similar digestion benefits with fewer moving parts and lower costs.

How It Works

PONDUS (TCHP) uses moderate heat (typically 150 °F to 165 °F) and adds caustic soda (NaOH) to raise the pH before sludge enters the reactor. This combination breaks down cell walls, releasing organic acids that naturally neutralize the pH by the time the sludge reaches the digester. The system is capable of handling sludge that has been thickened to 6–10% total solids without requiring dilution after treatment.

Because TCHP doesn’t rely on pressure-rated vessels, the equipment design is much simpler. There are no internal moving parts in the reactor, and maintenance is limited to pumps and heat exchangers, most of which can be serviced by in-house personnel. The system also consumes less energy, avoids the need for high polymer dosing, and reduces the overall water footprint.

Dewatering and Centrate Considerations

Pre-dewatering is one of the most misunderstood cost drivers in any thermal hydrolysis implementation. For high-pressure THP systems, the requirement to reach 17% solids before treatment means high polymer usage. This is especially true with waste-activated sludge, which is notoriously hard to dewater. It also introduces pumping challenges, as the sludge becomes too thick for conventional progressive cavity pumps and may require piston or multi-stage units.

With TCHP, sludge can be thickened to 10% using much less polymer, often just one to two pounds per ton. It can be pumped using simpler equipment, and the system avoids the need to dilute the sludge after hydrolysis. This reduces both polymer and water costs, while also eliminating the need to handle hot, thickened sludge under pressure.

The benefits continue in post-dewatering. Operators using TCHP have reported clearer centrate with fewer colorization issues (less hard COD), which can otherwise cause UV disinfection complications and potentially lead to bottlenecks in the biological treatment step. Polymer addition at this stage is also more predictable and manageable compared to THP, which tends to produce more variable outcomes depending on sludge type and temperature variation.

Class A vs. Class B: Strategic Choices

Facilities as small as 5 MGD can benefit from TCHP, particularly if they already operate an anaerobic digester. The process is especially valuable for plants with limited digester capacity, high disposal costs, or existing issues with foam and gas production.

The team also addressed a common concern about upfront validation. Rather than investing in a full-scale pilot, Centrisys/CNP offers a PONDUS simulation test. Utilities send in a sludge sample, which is then used to simulate the TCHP process under lab conditions. This test reveals the potential for biogas production, solids solubilization, and polymer demand, giving operators a reliable picture of system performance without costly field trials.

Making the Right Long-Term Investment

The benefits of thermal hydrolysis are real, but so are the risks of unexpected costs. When planning for THP or TCHP, municipalities need to evaluate not just the technology, but the full lifecycle of sludge handling. That means considering energy needs, chemical inputs, staffing requirements, and infrastructure changes across the entire process.

By focusing on total system performance rather than isolated technology benefits, Centrisys/CNP helps utilities make decisions that align with budget realities, regulatory goals, and long-term sustainability. Thermal hydrolysis may be a powerful tool, but only when implemented as part of a well-designed, well-understood treatment strategy.

To explore future sessions in the Sludge Treatment Series or learn more about testing and implementation options, visit Centrisys/CNP’s webinar page.