Stefano Bataloni, Silvia Ceracchi, Giuseppe Trinchera, Claudia Virno Lamberti,
Regasification terminals convert liquefied natural gas (LNG) transported by sea into natural gas (NG), which is subsequently injected into the national transmission network. At terminals located in the marine environment, seawater may be used in the regasification process, as it transfers heat to the liquefied gas and returns it to its gaseous state.
After use, the water is discharged back into the sea at a lower temperature, resulting in a negative temperature differential, and following treatment with chlorine as an antifouling agent. The main environmental impact potentially associated with the operation of offshore regasification terminals is therefore related to the discharge of this cold, chlorinated heat-exchange water.
The first offshore terminals to become operational in Italy, and for which historical process-water datasets suitable for assessing the environmental pressures exerted by these facilities are available, are the regasification terminals located off Porto Viro and Livorno.
For both terminals, during the 2014–2025 period, the temperature differential was closely correlated with the amount of natural gas injected into the network. Greater absolute negative values, of approximately −4°C, were recorded in years characterised by higher gas production. Nevertheless, the values always remained within the limits established by the relevant authorisation decrees.
The quantity of chlorine contained in the process water discharged into the sea also showed a strong correlation with the amount of natural gas injected into the network. At the Porto Viro terminal, active chlorine releases ranged from 10 to 50 tonnes per year, against natural gas injections ranging from 4 to 9 billion standard cubic metres (Sm³). At the Livorno terminal, chlorine releases ranged from 0.5 to 2.5 tonnes per year, against natural gas injections ranging from 1 to 4 billion Sm³.
In both cases, the release of chlorine in process water discharged into the sea consistently complied with the limits established by the applicable legislation and operating authorisations.
Natural gas is one of the most widely used energy sources worldwide. Its supply plays a crucial role in Italy’s energy system by ensuring a stable, secure and efficient energy supply for the production of electricity and heat for both domestic consumption and industrial use.
Only a small proportion of Italian gas demand is met by domestic production, while most is supplied through imports. Gas is imported through pipelines in gaseous form and by LNG carriers in liquid form.
Gas transported in liquid form is converted into gaseous form through a regasification process. In the marine environment, this process is carried out through heat exchange with seawater and results in the production and subsequent discharge of cold, chlorinated water into the sea.
Four marine regasification terminals are currently operating in Italy. Three are located offshore:
- the Adriatic Liquefied Natural Gas (ALNG) terminal, a Gravity Based Structure (GBS) located off the coast of Porto Viro, in the Province of Rovigo;
- the Offshore LNG Toscana terminal, a Floating Storage and Regasification Unit (FSRU) located off the coast of Livorno;
- the Società Nazionale Metanodotti (SNAM) FSRU terminal located off the coast of Ravenna.
The fourth terminal, also operated by SNAM and consisting of an FSRU, is located in the port of Piombino, in the Province of Livorno.
The operation of these terminals is permitted under specific authorisation decrees, including Integrated Environmental Authorisations, Environmental Impact Assessment decrees and Single Authorisations, issued pursuant to Legislative Decree No. 152/2006.
These authorisations require specific environmental monitoring activities and establish reference limits for the temperature differential of process water and the quantity of chlorine discharged into the sea.
The temperature differential is the difference between the temperature of the seawater abstracted from the marine environment and used in the regasification process and the temperature of the water subsequently discharged into the sea.
Chlorine, particularly the fraction referred to as “active chlorine”, is added to process water for antifouling purposes. Active chlorine consists of chlorine that has not yet chemically bonded with other molecules and therefore has very strong oxidising and disinfecting properties.
These two parameters are therefore useful indicators for describing the pressures exerted on the marine environment by the operation of offshore regasification terminals.
The assessment considers the ALNG terminal at Porto Viro and the OLT terminal at Livorno. Sufficient data are not yet available for the two SNAM terminals at Ravenna and Piombino, which only became operational between 2023 and 2025.
For the Porto Viro ALNG terminal, the reference limits established by the authorisation decrees are:
- −4.6°C for the annual average temperature differential;
- 0.2 mg/L for chlorine in process water, as a three-hour limit.
For the OLT terminal, the corresponding limits are:
- −6.0°C for the hourly temperature differential;
- 3.6 tonnes per year for active chlorine.
Legislative Decree 152/2006, EIA authorization decrees and AIA authorization decrees.
- SNPA Guidelines 53/2024. Guidelines for verifying any impacts on the marine environment of regasification terminals and connecting gas pipelines. IBN 978-88-448-1230-0, October 2024.
- Virno Lamberti C., Gabellini M., Maggi C., Nonnis O., Manfra L., Ceracchi S., Trabucco B., Moltedo G., Onorati F., Franceschini G., Di Mento R., 2013. An environmental monitoring plan for the construction and operation of a marine terminal for regasifying Liquefied Natural Gas (LNG) in the North Adriatic Sea C. Book: “Mediterranean Sea: Ecosystems, Economic Importance and Environmental Threats”, Ed. Terrence B. Hughes, 2013, Nova Science Publisher, Inc.
- Virno Lamberti C., Tomassetti P., Ceracchi S. And Gabellini M, 2020. Water Column Study in the Monitoring Plan of the First Italian Offshore LNG Terminal. Int. J. Environ. Sci. Nat. Res. 2020; 26 (3): 556187. DOI:10.19080/IJESNR.2020.26.556187.
At present, the indicator does not provide information for all four marine regasification terminals operating in Italy. It covers only the two terminals for which consolidated datasets are available, based on the date on which their operational phase began.
Following the start of operations at the Piombino and Ravenna FSRU terminals, data from these energy infrastructures will also be incorporated, thereby expanding the spatial coverage of the indicator.
- Companies owning and operating the regasification terminals: Adriatic LNG and Offshore LNG Toscana.
- Ministry of the Environment and Energy Security — MASE.
- ISPRA — Italian Institute for Environmental Protection and Research.
The data are held by the respective terminal-owning companies, MASE and ISPRA.
Regional (Adriatic Sea and Tyrrhenian Sea)
2014-2025
For each year in the period considered, annual average process-water temperature differentials were calculated using the monthly average data supplied by the companies operating the regasification terminals.
The temperature differential is expressed in degrees Celsius and is calculated in relation to the temperature of the seawater abstracted by the terminal before being used in the regasification process.
The annual cumulative quantities of natural gas injected into the network, expressed in billions of standard cubic metres, and active chlorine contained in process water, expressed in tonnes, were obtained from the operating companies and presented without further processing.
In 2025, the Porto Viro terminal injected 8.18 billion Sm³ of natural gas into the network (Table 1), representing a slight decrease compared with the previous year.
The average temperature differential of the process water discharged into the sea was −3.8°C, lower in absolute terms than in 2024 and within the reference limit of −4.6°C.
In line with the contraction in regasification activity, the quantity of active chlorine also declined compared with the previous reporting year, reaching 47.9 tonnes in 2025.
The Livorno terminal returned to full regasification operations in 2025. It injected 4.09 billion Sm³ of natural gas into the network (Table 2), representing a substantial increase compared with the previous year.
Consequently, the average temperature differential of the process water discharged into the sea reached −4.38°C, increasing in absolute terms compared with 2024. The quantity of active chlorine also increased, reaching 2.45 tonnes in 2025.
Based on the most recent data, the pressures exerted on the marine environment by both regasification terminals remained within the limits established by their operating authorisation decrees.
Natural gas production at the Porto Viro terminal increased considerably between 2014 and 2025, rising from 4.3 to 8.18 billion Sm³ and reaching a maximum of 8.72 billion Sm³ in 2024.
In parallel, the average temperature differential of the process water increased in absolute terms from −2.67°C to −3.75°C, with a peak of −3.93°C in 2024 (Figure 1). The parameter therefore remained within the reference limit of −4.6°C as an annual average throughout the period.
The quantity of chlorine discharged into the sea (Figure 2) declined markedly from 43.04 tonnes in 2014 to 15.43 tonnes in 2015. It subsequently increased, although with some fluctuations, reaching a maximum of 48.37 tonnes in 2024 before decreasing slightly to 47.86 tonnes in 2025.
At the Livorno terminal, natural gas production increased moderately during the initial operating period from 2015 to 2018. It then increased sharply in 2019, reaching 3.51 billion Sm³, before declining to 3.14 billion Sm³ in 2020.
Activity decreased in 2021 and subsequently rose to 3.67 billion Sm³ in 2023, the highest value recorded up to that time. This was followed by another decline in 2024, associated with an extraordinary shutdown for maintenance of the FSRU mooring system.
In 2025, production reached the maximum value for the period, with 4.09 billion Sm³ injected into the network.
The temperature differential of the water discharged into the sea followed the trend in natural gas production (Figure 3). Positive annual average values, ranging from 0.96°C to 2.17°C, were recorded between 2015 and 2018, while negative annual average values were recorded from 2019 onwards.
The lowest value, −4.38°C, was reached in 2025, coinciding with the peak quantity of natural gas injected into the network.
The quantity of active chlorine released into the sea also generally followed the trend in natural gas production, except during the initial operating period (Figure 4). It reached a maximum of 2.56 tonnes in 2019, remaining below the reference limit of 3.6 tonnes per year.
Overall, the trend in the pressures exerted on the marine environment by both regasification terminals remained stable and within the limits established by their operating authorisation decrees.
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Table 1: Amount of GN released into the sea, thermal delta, and active chlorine levels in the process waters discharged into the sea from the ALNG regasification terminal in Porto Viro (RO) Data source
ALNG data Note
(*) The annual amount of active free chlorine discharged into the sea is an estimate based on the project data, the operating hours of the chlorination plant, and the three-hour concentration limit. |
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Table 2: Volumes of NG injected into the network, thermal delta and active chlorine in the process water discharged into the sea from the OLT regasification terminal in Livorno Data source
OLT data
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Figure 1: NG injected into the network and thermal delta of the process water discharged into the sea (ALNG Porto Viro) Data source
ISPRA processing on ALNG data
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Figure 2: NG injected into the network and active chlorine in the process water discharged into the sea (ALNG Porto Viro) Data source
ISPRA processing on ALNG data |
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Figure 3: NG fed into the network and thermal delta of the process water discharged into the sea (OLT Livorno) Data source
ISPRA processing on OLT data |
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Figure 4: NG injected into the network and active chlorine in the process water discharged into the sea (OLT Livorno) Data source
ISPRA processing on OLT data |
For both regasification terminals, an increase in the quantity of natural gas injected into the network is associated with a decrease in the average temperature of the heat-exchange water discharged into the sea and, despite some fluctuations, an increase in the quantity of chlorine released into the marine environment.
The general reduction in natural gas consumption associated with the COVID-19 emergency between 2020 and 2021 resulted in a downturn in the natural gas production curves of both facilities and, consequently, in the temperature differential and quantity of chlorine discharged into the sea.
At the OLT terminal, the substantial decline in natural gas production recorded in 2024 was associated with extraordinary maintenance work that made the terminal non-operational between 22 February and 24 November 2024.
The temperature differential of the process water discharged into the sea may also be influenced by the natural interannual variability of the seawater temperature. Seawater is abstracted from the marine environment and used for heat exchange with LNG.
From an environmental perspective, discharge from a regasification terminal may generate a mass of cold water, or cold plume, with potential effects on the marine environment.
With regard to chlorine in the heat-exchange water discharged into the sea, active chlorine is highly reactive and unstable. It readily reacts with organic matter to form organohalogenated by-products, which may be toxic to marine organisms and persistent in the marine ecosystem.
Both process-water parameters are continuously monitored by the terminal-owning companies to verify that the environmental pressure generated by the discharge remains within the statutory limits, regardless of annual fluctuations.
Legislative Decree No. 152/2006 and the relevant authorisation decrees establish hourly or three-hour limits for these parameters. The operating companies report that these limits have never been exceeded.
Overall, for both terminals and throughout the period analysed, the pressure exerted on the marine environment by regasification activities remained within the limits established by the environmental authorisations.
From a technical and methodological perspective, the Italian National System for Environmental Protection (SNPA) developed and approved the Guidelines for Assessing Potential Impacts on the Marine Environment from Regasification Terminals and Connecting Gas Pipelines (SNPA 53/2024).
These guidelines define the principles to be followed by ISPRA and regional environmental protection agencies when assessing the potential impacts associated with the construction and operation of LNG regasification terminals and connecting gas pipelines.
The guidelines should be taken into account when designing marine environmental monitoring programmes and assessing environmental impacts. In addition to identifying the parameters to be monitored, including physical, chemical and biological parameters, they define monitoring methods, frequencies and sampling plans.
Their purpose is to ensure the consistent and comparable analysis of data and an accurate assessment of the potential environmental effects of regasification activities.