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While Thermal and Thermochemical Hydrolysis Process (THP) systems are designed to improve digestion performance, enhance biogas production, and reduce biosolids volumes, the discussion highlighted that not all hydrolysis solutions are created equal.
In the third session of our Sludge Treatment Webcast Series, Centrisys CEO Michael Kopper and CNP President Gerhard Forstner explain how design differences, operational requirements, and integration choices can significantly influence both costs and long-term performance.
Understanding the Core THP/TCHP Technologies
The wastewater treatment industry is moving away from waste treatment to resource recovery system changes that will impact your bottom line. Plants are adopting hydrolysis to improve how biosolids are managed.
By using heat and, in some systems, pressure and/or chemicals, the process breaks down cell structures in the sludge, allowing organic material to be more easily available for digestion. While the goal is similar across technologies, the methods used to achieve these results can differ significantly.
TCHP Innovation from Germany: The PONDUS System
The PONDUS system is a Thermochemical Hydrolysis Process (TCHP) first developed in the early 2000s. It was designed to give utilities a simple, reliable solution that could be easily operated and maintained—without requiring complex or unfamiliar equipment.
The first PONDUS system was installed at a German facility and targeted three common challenges:
- Increasing biogas production
- Improving sludge dewaterability
- Reducing foaming issues
At its core, the system uses a stainless steel reactor with no moving parts, operating at atmospheric pressure and moderate temperatures around 160°F. Thickened sludge is heated, treated with caustic soda to raise pH, and held for about two hours. It is then blended with primary sludge to achieve the ideal mesophilic digestion temperature.
Over time, PONDUS has been enhanced to handle higher solids concentrations (up to 10%) if needed by integrating centrifuge thickening and optional steam injection. Despite these upgrades, it maintains its hallmark simplicity: a non-pressurized, low-maintenance design that keeps operations straightforward for plant staff.
PONDUS also plays a strategic role for facilities aiming for Class A biosolids production. By pairing hydrolysis with downstream processes like sludge drying, utilities can tailor their approach to match capacity needs while meeting compliance and sustainability goals.
PONDUS: Designed for Efficiency and Reliability
Overall, the PONDUS system keeps the focus on:
- Running efficiently with minimal operator intervention
- Simplifying ongoing management
- Making the most of existing infrastructure investments
This balance of innovation and practicality has helped PONDUS remain a trusted solution for utilities looking to enhance sludge treatment without unnecessary complexity.
Understanding the THP System
The THP system takes a different approach to sludge hydrolysis compared to TCHP. Sludge is first pre-thickened using decanter centrifuges to reach a solids content between 15% and 17%, which requires higher energy and polymer dosing.
The process then moves through a series of pressurized tanks operating at temperatures around 320°F to 360°F and pressures between 90 and 120 PSI. Hydrolysis occurs under these high-temperature, high-pressure conditions, followed by depressurization in the final tank. Because the sludge exits at a higher solids concentration and temperature, additional steps are needed, including dilution with water and cooling through heat exchangers, before the material can enter the digester.
Comparing THP and TCHP
Both THP and TCHP are forms of thermal hydrolysis, but they operate in very different ways.
How THP Works
- Relies on steam, sealed vessels, and high pressure
- Requires advanced heat exchangers and extensive cooling
- Drives up needs for polymers, water, and energy
- Often results in higher infrastructure and maintenance costs
How TCHP Differs
- Runs at atmospheric pressure and moderate heat
- Uses controlled pH adjustment and steady heating at lower temperature
- Typically eliminates post-treatment dilution steps
- Fits more easily into existing infrastructure
Key Takeaway for Facilities
When comparing the two, facilities must weigh the potential performance benefits of high-pressure systems against their added operational complexity. TCHP often proves to be a more practical and operable fit, delivering comparable results while integrating seamlessly with existing infrastructure and requiring less energy, fewer consumables, and lower long-term maintenance.
"Choosing a thermal hydrolysis system is not just about the reactor. Success depends on how well the entire process—from pre-thickening to digestion to post-dewatering—works together." - Gerhard Forstner President of CNP’s process division
Integration Matters More Than Many Expect
Choosing a thermal or thermochemical hydrolysis process (THP/TCHP) system involves considering not only the reactor itself but also how the system fits into the entire infrastructure. Even the most advanced reactor will underperform if the upstream and downstream processes—such as pre-thickening or dewatering, digestion, and post-dewatering—aren’t aligned with the chosen hydrolysis method.
The Challenges with High-Pressure Systems
High-pressure THP systems typically require sludge to be thickened to 15–17% total solids before treatment. Achieving this level of thickening often demands higher polymer usage and greater pumping energy, adding both cost and operational complexity. After hydrolysis, many systems also require the sludge to be diluted before entering the digester, introducing yet another step that increases water consumption and overall system complexity.
The Advantage of TCHP
Thermochemical Hydrolysis Processes (TCHP) simplify this integration challenge. TCHP systems operate effectively with sludge in the 6–10% solids range, which significantly reduces the need for polymers and pumping energy. Just as importantly, TCHP generally eliminates the need for post-treatment dilution. The result is a streamlined process that integrates more smoothly with digestion and dewatering, helping facilities realize performance gains without unnecessary complexity.
Operational Demands and Maintenance Needs
High-pressure steam-based systems of THP require ongoing attention:
- Maintenance of pumps, valves, heat exchangers, and safety systems
- Operators with specialized training
- Higher risk of unexpected downtime if teams aren’t prepared
TCHP avoids many of these challenges. Its reactors have no moving parts, run at lower pressures and temperatures, and only require maintenance of external pumps and heat exchangers—equipment most facilities already know well. For plants with limited staff, this is a clear operational advantage.
Energy Consumption and Cost Implications
Energy requirements are one of the most significant cost drivers in any THP implementation. High-pressure systems depend on steam generation, which can dramatically increase utility costs if waste heat recovery systems are not optimized. Facilities that fail to account for these energy demands during planning often face operational budgets that exceed expectations.
TCHP reduces energy consumption by eliminating the need for steam boilers and using moderate heat. Because the process does not require significant sludge dilution, the system uses less water overall, further lowering operational expenses. While both systems improve digester performance, understanding the true lifecycle costs of each approach is critical for making an informed investment.
Centrisys/CNP works with clients to recommend the best fit for their needs.
"Energy demands are one of the most underestimated costs of high-pressure THP systems. Without careful planning, operational budgets can climb quickly." - Michael Kopper, CEO and Founder of Centrisys
Performance Beyond the Reactor
Many benefits attributed to THP/TCHP (better dewaterability, improved centrate quality, and higher biogas production) depend heavily on how well the entire system is designed. For example, dewatering performance after hydrolysis is influenced by the polymer strategy, digester configuration, and downstream solids handling equipment.
When aiming for Class A biosolids certification, operators also need to pay close attention to centrate quality. High-pressure THP systems can sometimes produce colloidal filtrate, which makes UV disinfection more challenging and can increase the need for chemicals to stay compliant. Facilities using TCHP often report a clearer centrate, which can reduce downstream complications and help maintain post-treatment requirements more easily.
Matching Technology to Facility Goals
Choosing the right THP/TCHP system requires more than just comparing advertised performance numbers. Facilities need to assess:
- How much digester capacity is available and whether expansion is planned
- The balance between Class A biosolids goals and overall energy efficiency
- Existing infrastructure that can be leveraged to minimize capital costs
- Staffing levels and training resources to manage operational complexity
For smaller plants or facilities with limited personnel, TCHP often provides a more manageable solution. Larger facilities that already have strong steam systems and energy recovery infrastructure in place may find that both high-pressure THP or low temperature/ pressure TCHP systems better match their long-term goals.
Testing Before Investing
Testing sludge characteristics before proceeding with a full-scale installation is highly recommended. Centrisys/CNP offers a specialized test that analyzes a facility’s sludge sample under TCHP conditions, giving operators a clear picture of potential gains in dewaterability, biogas production, and polymer use. This small-scale, low-cost assessment helps utilities confirm performance expectations early, avoiding the significant expense of piloting an entire system.
Final Thoughts
Thermal & Thermochemical hydrolysis technologies can offer significant operational advantages, but the best fit depends on a facility’s goals, available budget, and existing infrastructure.
THPs with high-pressure steam-based systems are capable of strong performance, yet often require greater upfront investment and higher ongoing operational support. TCHP offers a simpler, lower-energy alternative that integrates more easily into existing treatment trains and reduces ongoing maintenance needs.
FAQS
Watch the full webinar here to learn more about THP technologies.
