Improved centrate water quality and higher DS sludge cake at Amersfoort WWTP

The challenge: Optimise the sludge dewatering process

The annual increase of wastewater production puts pressure on Amersfoort Wastewater Treatment Plant (WWTP). The processing of sludge is becoming an increasing challenge, and costs approximately 40% of the total treatment cost. In addition, the sludge line requires a lot of time and attention from the operators. Meanwhile, the water sector is dealing with an aging workforce. Waterschap Vallei en Veluwe was looking for a solution to reduce the cost of sludge dewatering and sludge final processing, by improving the PE dosage and sludge flow rate, and optimising the existing digestion and dewatering infrastructure.

The solution: Training operators with Aqua Suite Mine

In 2017, we jointly started developing Aqua Suite Mine for Amersfoort WWTP, and this was fully rolled out in 2020. Through close collaboration and the knowledge that the operators had built up, the use of the software was fully embraced. However, when the original operators were redeployed, that Mine knowledge was lost, and the software was no longer always enabled. Following a joint cost-benefit analysis, the qualitative and quantitative benefits of Mine quickly became clear, and the use of the software was revived. Using a project-based approach, the existing software configuration was upgraded to the latest technical standards. Furthermore, we invested in educating and training the operators to increase local knowledge and support. And that has produced excellent results.

The result: <1000 mg/l suspended solids and an estimated cost saving of €91,466 in 2024

Results from May to October clearly shows that the hours required to operate the centrifuges and Mine decreased over the longer term, and the results of the sludge dewatering do not suffer from this. On the contrary, the results show an improvement in sludge dewatering and thus a saving in sludge final processing. In principle, Mine requires time and attention to adjust, but after a period of two months it becomes increasingly stable. It demonstrably requires less effort from the operator, making more time available for the operators to focus on their specific expertise. Aqua Suite Mine has also contributed to a significant reduction in costs and chemical consumption.

Centrate quality: < 1000 mg/l suspended solids measured by Aqualysis
A lot of data from the centrate was collected over a six-month period. The graph below makes it clear that performance has visibly improved over time and has also come within the levels required. The centrate water quality is important, among other things, for a positive impact on struvite production.

The dry solids content (DS) of the sludge cake > 25%
In standard sampling, following the final sludge process, the DS content of the sludge cake is included in the analysis. From this data, which is supplied as a combined value from both centrifuges, it can be concluded that an exceptionally high DS content is achieved in the discharged sludge cake.

Total savings of €36,131 incl. VAT in six months
Through the process automation of Aqua Suite Mine, the operator can spend more time on their specific expertise. The costs during final sludge processing are also significantly reduced. The combination of more efficient polymer consumption and the higher DS content, which leads to lower sludge final processing, results in a saving of €17.47 per tonne of sludge cake. During the test period, 2,068 tons of sludge cake were removed, resulting in a saving of €36,131 in six months.

Because Mine still had to optimise in the first months, the results were less good in the beginning than at the end of the test period. Using the polymer consumption and the dry solid content achieved at the end of the test period, an estimate can be made of the savings for 2024. For this year it is assumed that 4,150 tons of sludge cake will be removed from Amersfoort WWTP, which could potentially result in a total savings of €91,466 with Mine.

“It's nice to see that what we develop really contributes to tangible results for the customer. More optimal and sustainable business operations with impressive savings. That's what we do it for.” Otto Icke, Product Manager & Developer Twinn Wastewater