Centrifuge or Screw Press? Where is Money Leaking Away in Sludge Dewatering?
Do you get the feeling that sludge dewatering at your wastewater treatment plant or industrial facility is “eating up” more money than it should? Do you have to constantly tweak the polymer dosing just to keep operations stable? Or would you prefer a technology you can simply switch on, leave running, and not have to stand over – even overnight?
In practice, the decision usually comes down to three technologies: the centrifuge (decanter), the screw press (VOLUTE™), and belt presses. All of them can dewater sludge. However, each does it differently, and therefore each fits a slightly different situation.
That is why it makes sense to clarify things simply: what to expect from each technology, what it can bring to your operation, and where you might hit a wall. In this article, we will focus specifically on the centrifuge (decanter) and the screw press (VOLUTE™).
Why is sludge dewatered in the first place?
On the surface, it is simple: we want to remove water from the sludge to reduce its volume and mass. This mainly means lower costs for transport and disposal, and the possibility of further sludge utilisation. However, in real operations, it is not just about what percentage of dry solids (DS) you measure at the output.
In reality, it is often more important that operations are stable, total operating costs are as low as possible, and operators do not have to solve problems every hour. So yes, the goal is to remove water, but the goal is also for the whole thing to work long-term, without stress, without fluctuations, and without dewatering becoming an endless “daily project”.
When a Centrifuge (Decanter) Makes Sense
A centrifuge is typically the choice when you need to dewater massive volumes of sludge. It is a technology that handles large flow rates very well.
At the same time, it is fair to mention the other side of the coin. A centrifuge is a high-speed machine. It commonly operates at around 3,000 rpm, which naturally brings higher demands on energy and infrastructure. In practice, this means vibrations, noise, and high maintenance requirements.
So, a centrifuge can be a great choice when you want high performance and need to manage large quantities of sludge. But if you are mainly concerned with operating costs, quiet operation, and simplicity, it becomes interesting to look at a screw press.
When a Screw Press (VOLUTE™) Makes Sense
The screw press is a technology for those who want peace of mind, stability, and predictable costs. It fits where you do not want to be constantly fine-tuning things, where you want to keep operating costs (mainly energy and often water) low long-term, and where it makes sense to minimize operator intervention.
The screw press (VOLUTE™) is a low-speed machine operating at 2–5 rpm with zero vibration, which explains very well why screw presses have lower operating costs.
And here it is important to put it simply: when technology rotates slowly, it usually means less stress on the equipment, fewer vibrations, simpler and faster servicing, lower energy intensity, and most importantly, no unplanned shutdowns or risks associated with the failure of high-speed machines like centrifuges. This is exactly the practical argument for why a screw press makes sense wherever the goal is to save energy and simplify operations.
What are the Differences in Daily Operation?
With a centrifuge, people often appreciate the performance and separation efficiency, but at the same time, they often deal with high energy consumption and more demanding maintenance. With a screw press, on the other hand, there is often talk of it being a “calm” technology with low energy consumption, often lower water requirements, and simpler operation.
However, it is fair to realize one thing: you are on a screw press website, and like every other technology manufacturer, we have a natural tendency to show our method in the best light. Centrifuge manufacturers do the same, highlighting the benefits of “their” technology in their materials while pointing out the weaknesses of the competition.
Therefore, it is good to look at such comparisons with an independent eye: every manufacturer can (without necessarily lying) select an example and operating conditions where their technology dramatically outperforms the other.
Moreover, costs are not just about energy, but also polymer, rinse water, service, and transport/disposal. That is why it pays to think of the technology as a whole, not just one parameter. And for that reason, it makes the most sense to base decisions on real data from specific operations (ideally from a pilot test or reference on similar sludge), not just marketing charts.
A Real-World Example: The Data Speaks Clearly
What does it look like in practice when you take a specific installation and put the technologies side by side?
We are comparing a VOLUTE DUO™ RVP-601 against a currently used centrifuge (Alfa Laval). Based on our calculations and client data for this reference, the following annual comparison emerges:
Energy Usage (10-Year Cumulative) [MWh]
CO₂ Emissions (10-Year Cumulative) [t]
Annual Energy Consumption
- Screw Press (VOLUTE™): 25,1 MWh/year
- Centrifuge: 254,1 MWh/year
- Difference: Approximately ~10× lower consumption (approx. −90%)
Annual CO₂ Emissions (derived from energy consumption)
- Screw Press (VOLUTE™): 6,0 t CO₂/year
- Centrifuge: 60,2 t CO₂/year
- Difference: Again roughly −90%, as CO₂ in this approach is directly linked to electricity consumption.
Cumulative Electricity Costs
- Year 1: €5,023 vs. €50,820
- Over time, the difference only accumulates.
To ensure this isn’t just one example from one location, a similar trend is shown by an extensive case study [1], which results in specific energy of 31.1 kWh/tDS for centrifuges vs. 3.51–3.76 kWh/tDS for VOLUTE, concluding with savings of up to 84%.
Not only based on the example above but also based on experience from other installations, we have observed that centrifuge energy consumption is typically about 10x higher than that of a screw press.
Electricity Costs (10-Year Cumulative) [€]
Every Sludge is Different: You Cannot Decide Without a Pilot
It is important to add one thing: similar comparisons must always be read very carefully.
For example, in a documented case study by GEA [2] for digested sludge with 3% DS and a flow of 8 m³/h, the decanter comes out “more advantageous” in their setup compared to a competitor’s screw press. However, these conclusions are extremely sensitive to specific input parameters (actual dry solids and fluctuations, sludge type, required cake dry solids, polymer dosing and type, required capture rate, operating mode, energy prices, disposal costs, etc.).
Conversely, on a very similar type of sludge in reference [3], we see that with the correct design and settings, the screw press (VOLUTE™) can achieve significantly better results in both cake dryness and energy efficiency.
Therefore, a simple rule applies: when deciding between technologies, a pilot test directly on your sludge always pays off. It is the fastest way to get real data for your conditions and avoid a decision based solely on a “table from a presentation”.
What to Watch Out For When Choosing
Before you draw a conclusion, try switching your selection criteria from catalogue parameters to operational reality. It is not just about how much the machine handles per hour, but what it will cost you every day.
- Do you primarily want maximum throughput, or are low operating costs your priority?
- What sludge are you dealing with, and how much does it change during the day?
- Do you need continuous 24-hour operation?
- Do you prefer to operate it manually, or automate it to run quietly without constant supervision?
At that moment, the total operating costs come into play, not just electricity. Energy is important, but the sum often decides: polymer + rinse water + service + labour costs, and finally transport/disposal depending on the dry solids you actually achieve.
That is why it pays to look at technology “per tonne of dry solids” and at operational stability. In references, you can see that results vary, and not everything can be answered from behind a computer. That is why a pilot test is always needed, where you fine-tune the process and find out all the operating costs, and only then can you decide.
And one more practical thing that often gets lost in tables: comfort and “peace” of operation. Low-speed technology is typically significantly quieter and vibrates less than high-speed machines, which simplifies the operating regime and helps where you truly want to “let the machine do the work” even outside of shifts.
Conclusion
If your key goals are to reduce energy consumption and CO₂, simplify operation, and lower operating costs, the screw press (VOLUTE™) is a very strong choice in most real-world operations. And the mentioned references show this clearly—the difference is not cosmetic, but exponential.
On the other hand, centrifuges cannot be effectively replaced in WWTPs with capacities of hundreds of thousands of PE, where their energy and operational intensity are compensated by high throughput.
In this article, we mainly wanted to highlight one thing: manufacturers’ claims must always be taken with a grain of salt, whether it is references we show or those presented by other manufacturers. At the same time, we believe that in many plants, there is a significantly more advantageous alternative to centrifuges. However, this itself is just another claim until verified under specific conditions.
That is why our approach relies not on promises, but on proof in practice: on your sludge, at your site, in real operation. If a pilot test makes sense, we are ready to arrange it and base the results on measurable data, fairly and transparently.
Sources:
- [1] Case Study – VOLUTE vs Centrifuge (Davyhulme WwTW, UK)
- [2] GEA report – Screw press vs Decanter comparison (2022)
- [3] Reference – AMCON Europe (ES-302, Tranås, Sweden)