Upgraded the Pozzilli wastewater treatment plant: a national model for environmental protection

From a small provincial treatment plant to an Italian model for water protection. This is the transformation of the Pozzilli (Isernia province) treatment plant, which has seen the completion of the upgrading works that began in June 2024, without operations ever being interrupted. Owned by the Isernia-Venafro Industrial Development Consortium and managed by Herambiente in a joint venture with Co.Ge.M. (Costruzioni Generali Molisane), the plant treats domestic wastewater from Pozzilli and Montaquila, wastewater from Pozzilli industrial hub, as well as liquid waste delivered by vehicle from various industrial sites. A total of 10 people work at the site, including both direct and indirect staff.

“With this project, Pozzilli becomes a benchmark treatment plant for the whole of central and southern Italy,” explains Andrea Ramonda, CEO of Herambiente. “It’s a benchmark for the technological standards employed, for the protection guaranteed to the surface waters of the Venafro Plain, and for the treatment capacity it can provide to numerous industrial sectors. In this sense, it can therefore be said that the investment adds value and appeal to the area from both an environmental and economic perspective.”

“The upgrade of the Pozzilli treatment plant is fully in line with the Consortium’s strategic vision” - states Pasquale Colitti, President of the Isernia-Venafro Industrial Development Consortium. “The refurbished plant, in fact, embodies the concept of sustainable and innovative development of the region to which we have been committed every day for over four years. The next step will be to maximise green spaces to contribute to CO2 reduction and climate mitigation.”

Thanks to the technologies employed, the revamp enables three key objectives to be achieved. 

Greater environmental protection in line with extremely restrictive limits

The first is a further increase in the level of environmental protection. The new Integrated Environmental Authorisation issued in November 2023 by the Molise Region imposes discharge limits that are among the lowest in the country, well below those required by national legislation (Legislative Decree 152/06, Consolidated Environmental Act). For example, for key parameters such as COD (the amount of oxygen required to chemically oxidise pollutants), BOD5 (organic pollutant load), nitrates and TSS (total suspended solids), the IEA limits are on average 40–50% lower than the already restrictive national regulations. The new configuration of the Pozzilli treatment plant will ensure full compliance with these strict parameters, regardless of the plant’s operating conditions.

Greater resilience to climate change

The second benefit of the revamp concerns the plant’s greater resilience in response to major weather events linked to climate change, such as flash floods. As is well known, these cause sudden increases in inflow, which can partially compromise the effectiveness of the treatment process. The work carried out will, however, allow for full control of this phenomenon. Consequently, even in the face of sudden high volumes of incoming wastewater, the plant will maintain full functionality much more easily, significantly reducing the risk (typical of all treatment plants) of discharging excess water directly into the environment.  

An opportunity for businesses

However, the upgrade also has significant economic value. Thanks to the expansion, the treatment plant will be able to increase its capacity for treating liquid waste from industrial activities, meeting the needs expressed by many sectors which, particularly in central and southern Italy, suffer from a structural shortage of treatment and recovery facilities – a situation that often leads to higher operating costs and a consequent loss of competitiveness. Among the sectors concerned, to name but a few, are the dairy and food processing sectors in general, ink and paint manufacturing, and the emptying and sanitisation of septic tanks. 

There are four key interventions underpinning the extensive refurbishment of the treatment plant.

The doubling of secondary sedimentation

Firstly, the new secondary sedimentation tank. This is a large circular tank with a capacity of 300 cubic metres and a diameter of 16 metres, also equipped with a foam collection system, which complements a similar tank already in operation. The effluent enters the two tanks after first undergoing a physico-chemical treatment to render non-biodegradable pollutants, such as heavy metals and toxic organic compounds, insoluble through specific reactions, and then a biological treatment, where cultures of bacteria and microorganisms break down biodegradable organic pollutants, such as, for example, phosphorus, nitrogen, surfactants and carbon-based organic substances in general. Doubling the number of sedimentation tanks ensures that, even with large volumes of incoming water, sludge settles more effectively at the bottom, thereby returning even cleaner water to the environment.

Underground first-flush tank

Another structure of great importance is the new 250-cubic-metre first-flush tank, which is completely underground. In the event of heavy rainfall, it is capable of temporarily storing excess water and then releasing it gradually, so that it undergoes the entire treatment process without any loss of efficiency or effectiveness

The sludge storage cover

An additional level of protection against the weather is provided by the full-coverage structure built for sludge storage. Here, the sludge produced during the various stages of treatment is dried to reduce its volume and thus facilitate subsequent processing (at external facilities). The large cover not only prevents contact with rain, which would cause the volume to increase again, but also accelerates the evaporation of the water contained within the sludge itself. And, of course, it acts as a significant barrier against any odour-causing emissions.

The new SBR section dedicated to liquid waste

The most technologically advanced aspect of the revamping is undoubtedly the biological treatment section known as the SBR (Sequencing Batch Reactor). The new tank enables additional biological treatment dedicated exclusively to industrial liquid waste. This means that, on the one hand, such waste can be treated with greater flexibility and effectiveness, providing businesses with a viable option for fully sustainable waste treatment. On the other hand, their treatment, even when handling significant volumes, will not impact the plant’s other functions.

The visitor trail to open the plant to the local community

The revamping of the treatment plant also includes numerous other works, including the complete refurbishment of the office building, where a conference room has been created and the analysis laboratory premises expanded. Among the civil works, the visitor trail is of particular significance: a system of nine large panels installed next to each structure that marks a stage in the treatment process. Thanks also to clear infographics, the trail illustrates how the plant operates for the benefit of schools and other visitors, confirming Herambiente’s commitment to opening this plant—as well as the nearby Pozzilli waste-to-energy plant—to the surrounding community.