The Iren Group, a multi-utility operating in the energy sector, wanted to restructure its own wastewater treatment system for urban sewage waste. Dating from 1982, the current system has served a population of 45,000 across the municipalities of Rubiera and Scandiano across Italy's Reggio Emilia Province. However, the system's air production system is oversized for the treated load making it inefficient in terms of both energy and costs. A greener and leaner solution was essential and Iren Group turned for help to the advanced technology and skills of Robuschi.
The Rubiera water system comprises four parallel lines, each supplied by its own compressor for generating air in the oxidisation/nitrification compartment. Renovating this part of the system highlighted some problems. Loris Canovi is Head of Waste Water Treatment in the Emilia area at Ireti, part of the Iren Group. He reflects, “The original system was found to be oversized given the tank's actual oxygen demand. The tank must hold enough oxygen to support biomass respiration as well as the oxidation of the organic components and ammonia nitrogen inside it. However, it became clear that actual air consumption varied significantly throughout the 24-hour cycle, meaning that the system was both wasting energy and creating high residue levels. Essentially, the set-up didn't have the flexibility to lower the machines' production below a certain threshold. As a result, for much of each day the excessive air supply was generating more oxygen than the lines needed.
Rebalancing the system
Iren Group designed and built a system for controlling air production which, when combined with Robuschi's innovative new compressor, made it possible to dramatically improve the Rubiera system's performance. The first step was to change the set-up, linking all the machines together. The Iren team knew that provided it could handle wide variations in capacity, only one compressor was needed. With demand fluctuating between 600m3/h and 3000m3/h, the Rubiera system needed a compressor with immense flexibility, and this is where Robuschi technology, with the new permanent magnet screw ROBOX energy WS 85, came into its own.
Iren and Robuschi technicians worked side by side during the project to refurbish the Emilia waste water treatment system. Loris Canovi explains, “We began with a prototype, the WS 65, and then moved on to a solution with dimensions that matched the Rubiera system requirements The WS 85 was the ideal solution.” During the test phases, the system was aligned to the operating logic implemented by the Iren Group. The WS 85 was then calibrated for the specific working conditions.
The Robuschi technology immediately demonstrated the operating flexibility it needed for sewage plant and unlike its competitors, the WS 85 can be switched on and off as needed. The flexibility and versatility of the new ROBOX compressor also communicated smoothly with the Iren PLC which transforms it into a controller that adjusts the process parameters as required. Alternatively, the ROBOX energy WS 85 analyses and applies the oxygen data received directly from the process. Canovi comments, “This flexibility supports the process and feedback without disrupting them. It's a unique feature that sets our system apart from other technologies and delivers excellent energy savings.”
As Canovi explains, the next step is to combine the new logic with the air production unit. “In order to the system at times of higher demand, we'll probably need another unit with a power rating lower than the WS 85. This will guarantee maximum flexibility across all system load demands.”
The new and enhanced Rubiera system has now been operating for nearly six months and, while it may yet be too soon to detail the specific advantages of the new configuration, initial data has already been evaluated. Loris Canovi explains, “Thanks to the electricity measurement units that we'd installed to measure the energy consumption of the tank in its original system configuration, we've been able to monitor the electricity consumption as the project proceeded. As a result, we can report that the new logic resulting from the Iren control system has delivered a 30% reduction in the tank's electricity consumption. Furthermore, by installing the WS 85 we've secured a further reduction of 20% in air generation and a total of total energy saving of 50%.”
Given the significant cost of energy, this remarkable reduction in consumption is itself a praiseworthy achievement. However, Iren and Robuschi believe they can go even further: “The excellent level already reached can be increased by a few percentage points more if we refine certain system components, such as the size and efficiency of the permeable mat for the air supply. These are just simple operational measures, but they raise the remarkable savings that we've achieved with this refurbishment to even higher levels!”
The Rubiera case study demonstrates how the Robox screw compressor technology delivers greater efficiency compared with other solutions available on the market, thanks to its special permanent magnet motor. Able to maintain its operating capacity when operating at a lower speed, the technology allows the machine to reach an efficiency level which surpasses the IE4 standard. This fundamental feature means the Rubiera solutions will add value to the Iren Group's wider mission to improve energy efficiency and reduce operating costs. In addition, the Robuschi technology has no moving parts, thus eliminating deterioration of the product due to wear as well as reducing maintenance costs and ensuring a safer, more robust compressor. These advantages are particularly important in managing systems such as wastewater treatment of sewage flows, where reliability is key. “It's a big plus,” comments Canovi “Highly innovative technologies rarely offer durability and dependability, but this solution wins at every level.”
Iren Group's successful work in Reggio Emilia Province represented a pilot project that has helped them to assess whether the solution can be adopted in other Group sites. “We have various systems with parallel lines each served by a separate machine, just the same as the Rubiera sewer plant. We're therefore evaluating the possibility of replicating this configuration in other locations, reproducing the same functional pattern but adapting it to the different system dimensions and sizes. The installation of a control system and the modularity of the Robuschi system will be crucial in allowing us to achieve this. With the excellent energy efficiency improvement embedded in their operations, Iren Group can request TEE recognition (energy efficiency (or 'white') certificates, both for the logic and for the machines introduced.
Ireti is the operational company of Iren Group, and manages gas and electricity distribution and integrated water services. Together with the three other operational companies it forms a multi-utility based in Reggio Emilia, from where the strategic development and control activities for the entire Group are coordinated. Iren Group operates in the sectors of electricity, thermal energy for district heating, gas, integrated water services management, environmental services such as the collection and disposal of waste and services for public administration bodies. Other operating sites of the industrial holding are located in Genoa, Parma, Piacenza and Turin.