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As the finale of our four-part Sludge Treatment Webcast Series, we explored one of the most overlooked yet costly stages of biosolids management: post- dewatering. Inconsistencies in post- dewatering can lead to hidden costs that offset future gains.
In this session, Centrisys CEO Michael Kopper and CNP President Gerhard Forstner, not only reviewed different aspects of post-dewatering, but also tied the series together, showing how total-system thinking (not “hydrolysis-only” thinking) protects performance and budget.
Looking Beyond the Hydrolysis Process— Tip of the Iceberg
A key takeaway from this series is the need to look at the whole process rather than focusing on individual pieces of the process. An “iceberg” comparison captures this idea: The upfront capital costs are the visible tip, while the larger, hidden long-term expenses below the surface actually determine ROI.
Key drivers below the waterline:
- Polymer — demand, where/when it’s dosed, preparation strategy, mixing and retention time
- Centratequality — turbidity/colloids raise UV dose, raised nutrient levels complicate nutrient removal processes
- Sidestreams — higher N/P loads often impact deammonification and phosphorus removal
- Maintenance & staffing — certifications, cleaning intervals, and downtime impact overall cost
- Disposal — cake dryness and hauled tonnage drive fees
Post-dewatering brings these factors into sharp focus: higher polymer demand, less clean centrate, or added maintenance can quickly erode upstream gains. These drivers make scrutinizing this stage critical to sustaining performance and protecting long-term returns.
Pilot Insights: THP vs. TCHP Performance
Drawing from a recent pilot test in Texas, Centrisys/CNP shared real-world data comparing THP and TCHP digestates. As discussed, the two; thermal and thermochemical hydrolysis process (THP) systems offer different options for the sludge treatment:
- THP (Thermal Hydrolysis Process) — high-temperature, steam/pressure-based hydrolysis that cooks sludge at elevated temperatures to rupture cells and increase bioavailability. In practice, it runs hot and pressurized (e.g., ~212–336°F ), and typically requires pre-dewatering to ~15–20% to size reactors reasonably.
- TCHP (Thermochemical Hydrolysis Process) — low-temperature, pressureless hydrolysis that uses caustic soda (NaOH) plus low heat to achieve cell lysis. It operates around ~160°F with a pressureless reactor and heat exchanger, and commonly handles feed around ~6% solids (with options to go higher if preferred with steam injection as an option).
Centrisys dewatering can adjust their performance to handle different sludge types. In one of our recent pilot tests using THP digestate, we could achieve high capture rates (98–99%) and planned cake solids in the 30–32% range. However, THP sludges usually produces darker, more colored centrate, creating downstream challenges for denitrification, UV disinfection, and sidestream treatment.
In contrast, TCHP centrate remains relatively more clear, requiring less corrective treatment and offering simpler long-term management. The tests confirm that with optimized polymer conditioning and centrifuge adjustments, polymer demand in post-dewatering could be reduced even with THP digestate using our specialized dewatering machines, narrowing the performance gap but not fully eliminating the quality concerns.
Learn more about how THP and TSHP technologies compare from Centrisys/CNP’s experts.
Efficiency Gains and Hidden Costs
THP’s higher operating temperature and pressure can produce a modest boost in energy generation during digestion, but the advantage is often balanced out by increased polymer use and greater energy demand during pre- and post-dewatering.
In comparison, TCHP systems have shown clear cost benefits—saving an estimated $350,000 per year for a 50 MGD facility targeting class B—while also simplifying operations by minimizing the need for specialized staff, frequent shutdowns, and additional certification requirements.
Looking at the whole picture, TCHP offers a straightforward and dependable option for plants aiming to keep operating costs low, maintain flexibility, and avoid unexpected expenses or complexities.
TCHP Offers Savings over THP
Post-dewatering is where projected savings from upstream processes of biosolids treatment are either realized or quietly eroded. Polymer strategy, centrate quality, and day-to-day O&M ultimately determine ROI, not the reactor (hydrolysis) process alone. If your goals include lower lifecycle cost, less specialized staffing, and fewer downstream penalties, TCHP is a strong path. It’s been shown to offer up to $350,000/year savings at 50 MGD-class B (similar but not necessarily the same for other scenarios) when you account for polymer and energy across pre-reactor and post-dewatering stages.
THP & TCHP FAQs
Watch the full webcast here to see the side-by-side THP vs. TCHP results and learn how your plant can improve centrate quality and lower lifecycle costs.