The water utility in Ardea, a booming seaside getaway near Rome, chose a Wedeco ozone solution from Xylem to tackle its growing need for purification. But it found that the system also cut the treatment plant’s sludge output nearly in half, resulting in hefty savings on disposal costs.
The vast coastal area between Anzio and Pomezia, near Rome, has long been a popular vacation destination for residents of the capital. Thanks to the availabilty of low-cost land, the region has also seen a boom in construction of second homes in recent decades. As often happens though, the rapid development outpaced the growth of local infrastructure and, until 15 years ago, most of the area’s buildings weren’t even connected to sewer systems.
Eventually, however, the town of Ardea took the initiative, launching a dramatic redevelopment plan that included the creation of an extensive water treatment service. The municipality entrusted that task to Idrica, a utility provider that gradually took over the management of the entire integrated water service, building a sewage treatment plant capable of serving the equivalent of 72 thousand year-round residents.
Idrica needed to maximize efficiency both in terms of service and energy consumption, a task made all the more complex by the fact that, due to population growth, the load on the plant was 25 percent higher than expected. The plant’s technical manager began looking for a new technical solution, one that would limit the impact on the environment – a key consideration when the slurry outflow into the sea could affect the town’s vital tourism sector – and at the same time reduce the costs borne by the public.
A lingering problem, a new solution
With the growth in the number of households and businesses connected to the system, Idrica found itself increasingly faced with another difficulty: sludge. Centrifugal dewatering was able to eliminate most of the moisture, but the purification plant was still producing three thousand tons of sludge per year, refuse that had to be disposed of at a cost of over €130 per ton. Given this heavy weight on the company’s bottom line, Idrica decided to look into switching to an ozone-based waste treatment system to cut down the sludge output.
From the theoretical point of view, the production and use of ozone is relatively simple. Oxygen molecules (O2) are broken into individual atoms by passing them through two electrodes of varying potentials. These atoms then re-form as triatomic molecules (O3), or ozone. When ozone comes into contact with other molecules, it can cut their chemical bonds, breaking them down and facilitating treatment. For this process to reach maximum effectiveness for sewage treatment, the ozone has to be introduced in the form of very fine bubbles, which increases contact between the gas and the water. After this oxidation process, most of the ozone breaks down naturally and regroups in the form of common oxygen. Any residual ozone gas still present can be collected and reused in the process, thereby preventing any risk of atmospheric contamination.
But the systems for mixing and contact have to be able to handle specific adjustments for microbubble size, pressure and tank depth. Very few companies on the international market can provide the necessary competence and technical support. That’s why Idrica turned to its long-time supplier of pumping systems, Xylem, to discuss testing one of its Wedeco ozone treatment systems.
Seeing is believing
After studying Idrica’s needs, Xylem specialists set up a preconfigured test unit that operated at the plant for six months, the time period needed to assess its effectiveness at different periods of the seasonal cycle. But the positive results were apparent right from the start and the plant’s technical manager was able to convince his company’s management to go forward. The Wedeco SMO evo ozone system that was later delivered came preprepared, which minimized down time and reduced the time needed for certifications.
One year after installation, Idrica was able to verify that the amount of sludge the plant has to dispose of in landfills has decreased by 43 percent, or almost 1,300 tons, at a savings of more than €170,000 per year.
There have been other cost benefits as well, in addition to a drastic reduction of filamentous bacteria. Whereas in the past the plant workers had to spend a full 10 hours per day on sludge removal, now they spend only 16 hours per week, allowing Idrica to free up its resources for other activities.
The most telling result of the entire implementation is based on the accounts in hand. A look at the numbers shows that the entire investment will pay for itself in just two years, with significant advantages in both economic and environmental terms.