Optimized sludge dewatering removes constant manual sampling

As Ireland's national water utility, Irish Water is responsible for providing water and wastewater services throughout the country. It has sole responsibility for the cleaning and maintenance of the public sewer network and operates a network of wastewater treatment plants across Ireland.

Located at the heart of the Emerald Isle, about a two-hour drive west of Dublin, the Athlone wastewater plant treats the wastewater of 25,000 people. The dewatering process runs from eight to ten hours per day, producing 130–150 m³ of sludge per day.

Athlone Wastewater Treatment Plant has two Alfa Laval centrifuges, one on duty and the second on standby. The plant previously managed its dewatering processes manually and carried out multiple visual checks of the centrate throughout the day. There was a constant need for the operators to continuously adjust the system parameters as inlet solids vary from 3% to 0.8% during the day.

“About 25-30 hours of our caretakers’ time per week was dedicated to the centrifuge control,” points out Barry Nolan, Process Optimization Specialist at Irish Water.

While it was possible to change manually the feed rate to the centrifuge and polymer ratio, this was not possible for the centrifuge torque.

The dry cake is transported from the site by truck. The wetter the sludge is, the higher the haulage costs are.

Introducing Valmet SDO to improve centrifuge control

In mid-2021, Valmet supplied SDO and two Valmet Total Solids Measurement units (Valmet TS) for one of the two centrifuges. The pilot project was installed by RR Power Projects, Valmet’s Value-Added Reseller (VAR) partner for utility sector automation. Based in Tullamore, as per Miron Hojda (RRPP Senior Project Manager), the company has a strong position in the Irish utility market, providing turnkey solutions and maintenance.

Its role is to provide full sales and technical service for Valmet’s automation solutions in Ireland, while Valmet oversees configuration. RR Power Projects, qualified as an approved supplier for Irish Water and installation as well as customer service were highly rated during and after the installation of the system.

One Valmet TS was installed to measure the sludge feed into the centrifuge and the other one to measure the dry cake outlet. This reliable total solid measurement solution, based on microwave technology, is suitable for all wastewater sludge treatment applications in the range of 0–40% total solids.

The state-of-the-art Valmet Sludge Dewatering Optimizer (Valmet SDO) allows the Athlone Wastewater Treatment Plant to improve the control of its sludge dewatering process. With Valmet SDO the operators can minimize the amount of solids in the centrate, while maximizing the solids content in the dry cake.

Valmet SDO applies the inputs from solids and centrifuge measurements provided by Valmet Total Solids Measurement to optimize the dewatering process.  With the key data, Valmet SDO utilizes a multi-variable model predictive control (MPC) to control polymer dosing and centrifuge torque.

Less operator input, dryer cake, lower haulage costs

According to Barry Nolan, the operators have seen an immense benefit with the installation of Valmet SDO on Centrifuge 2. Thanks to its reliability, accuracy, high level of automation and low level of maintenance, less operator input and laboratory sampling are required.

“The biggest savings come from 25-30 caretaker hours per week saved on manual centrifuge operation,” he adds.  

The plant now consistently achieves cake sludge in the region of 18% dry solids as opposed to 15% dry solids during manual operation. Little operator input is necessary after the centrifuge start-up and SDO control take-over. Further savings are quantified as over 7% less energy on centrifuge and decreased haulage costs due to dryer sludge.

Jonathan Deane, Senior Engineer for Water, Environment and Climate Change at Westmeath County Council, Irish Water adds: “We have been thrilled with the solution, and it is a good value for the money spent.”

Ger McIntyre, Wastewater Process Optimization Lead, Irish Water, shares his colleagues’ positive experience with Valmet SDO: “We have been impressed by its accuracy and low maintenance.”

Based on the good experience with the Valmet SDO system, Irish Water is moving forward with integrating the second centrifuge into the system in 2023. Most importantly, the possibility to install Valmet TS and Valmet SDO in other wastewater treatment plants is currently being explored by Irish Water.