Engineering Rome

Wastewater and the Tiber

By: Katrina Olson

All photos by author unless otherwise noted.


Rome is a city known for its water: magnificent fountain displays and remains of ancient aqueducts (Figure 1) reminisce of an Ancient Rome with engineering accomplishments far ahead of its time, or as one experienced Rome traveler and civil engineering professor would put it, “not to be seen again on the continent for another 1000 years” (Steve Muench, Personal Communication, Nov 15, 2019). In contrast, the Tiber River, which could be celebrated as a central part of the city, is used as a sewer (Figure 2). Even historically, the Tiber River has been abused as an outlet for untreated drainage, resulting in an unhealthy ecosystem in need of attention. This paper will begin with a brief discussion of the Tiber River’s relationship with sanitation in Ancient Rome. This will be followed by a discussion of modern Rome including theories on the Tiber’s pollution presented by two of our class’ guides, current Roman wastewater infrastructure, and case studies evaluating pollution’s impact on the Tiber’s water quality.

Figure 1. Remains of an ancient aqueduct at Parco Acquedotti
Figure 2. The Tiber River running through Rome

Sanitation in Ancient Rome

Sanitation is defined as the system by which waste, particularly sewage, is disposed of and how it relates to public health. One of the best-known elements of Ancient Rome’s sewer system is the Cloaca Maxima (Figure 3), a 4.5 by 3 meter sewer built in the 6th century B.C. initially to “drain the marsh on which Rome was later built” (Lofrano and Brown 2010). The sewer became central to Rome for sewage and storm drainage conveyance alike as branches of smaller pipes were added throughout the city, and a section of it even still functions today (Lofrano and Brown 2010). By the late third century, the Cloaco Maxima was releasing nearly 100,000 pounds of waste daily to the Tiber River (Gowers 1995).

Figure 3. The Cloaca Maxima at the Tiber River (Source: Britannica)

The Cloaca Maxima drained water directly to the Tiber River without treatment. Though the Ancient Romans did not purify wastewater, they did often find secondary uses for the water. For example, “they recycled wastewater from the spas (Figure 4) using it to flush latrines before discharging the waste into sewers and then into the Tiber River” (Lofrano and Brown 2010). Commonly, public latrines (Figure 5) would collect urine and then use it for washing clothes (T. Rankin, personal communication, Sep 10, 2019). Regardless of this recycling, the ultimate fate of the water was still the Tiber River, which conveniently diluted and flushed away waste.

Figure 4. The Baths of Caracalla, a large public bath. This large, now somewhat grassy area would have contained bathing water.
Figure 5. Public latrine in Ostia Antica. Toilet seats line the outside of the room, and the troughs at the feet of the seats would have held running water for hand washing.

Pollution in The Tiber Today: Personal Experience

Though sanitation in Rome has improved since ancient times, modern wastewater management still contributes to pollution in the Tiber. The question of what contributes to the Tiber’s pollution was raised by comments from two of our class’ tour guides and experts on Rome, architect Tom Rankin and speleologist Adriano Morabito from Roma Sotteranea. On our walking tour of Rome as we stopped to view the Cloaca Maxima, Tom told us that major contributions to the pollution include drainage through this ancient channel and a wastewater treatment plant north of Rome that, after surpassing its design life, now only treats sewage to about 50% before releasing it to the Tiber (personal communication, Aug 29, 2019). Later while touring the aqueducts, our class found ourselves adjacent to a tributary of the Tiber, the Aniene River (Figure 6). There, Adriano mentioned that though many people site dysfunctional wastewater treatment plants as the source of the Tiber’s pollution, some developing communities north of Rome lack the infrastructure to treat sewage and instead discharge directly to the Aniene, making the largest contribution to pollution downstream where the Aniene meets the Tiber (personal communication, Sep 7, 2019). Further discussion will support that both guides’ claims were at least partially true, but neither explained the full story behind the Tiber’s pollution.

Figure 6. The Aniene River, a tributary to the Tiber River north of Rome.

Sanitation in Modern Rome

Standard wastewater treatment processes can be summarized in four stages: primary, secondary, and tertiary treatment, and disinfection. Together, these treatment methods target contaminants typically measured by biological oxygen demand (BOD), total suspended solids (TSS), Nitrogen (N), Phosphorus (P), as well as pathogens (Welch and Jacoby 2004). By common practice, the treated effluent is then released to a nearby water body. That water body’s dilution capacity is a strong indicator of its sensitivity to the pollutants remaining in the effluent. European Union legislation mandates that wastewater is treated at a minimum by primary and secondary treatment (GWI 2017). Primary is the most basic form of treatment, which removes large particles by settling and screening. Secondary treatment targets fine particles by coagulation and remaining BOD by biological methods such as activated sludge and aerated lagoons. Tertiary treatment refers to any further treatment preceding disinfection, including removal of N and P. Disinfection is most commonly employed by chlorination, but can also include ultraviolet radiation or ozonation to remove pathogens (Welch and Jacoby 2004) .

Each contaminant type can adversely affect the receiving ecosystem and public health if not properly treated. Of primary concern for public health are pathogens, which are removed by attachment to other particles in primary and secondary treatment and killed or deactivated with the final disinfection step (Welch and Jacoby 2004). As we walked along the Tiber on our tour, Tom Rankin advised us to report to the nearest hospital if we contacted the Tiber’s water. This claim is not unprecedented: for example, in 1979 a man died of an infection caused by a brief swim in the river (Giacomini and Hinrichsen 1981). BOD additions to a water body use up available oxygen, leading to fish kills while excess nutrients (N and P) can lead to the dominance of nuisance phytoplankton blooms, which can also be toxic to humans. Additional pollutants, such as toxins from industrial waste, can devastate ecosystems, as in the case of a large-scale fish kill in the Tiber in 2002 (Caroll 2002). Other sources, such as the illegal dump found in March of 2017 along a rural area of the Aniene River’s shore (Figure 7) also contribute to pollution (Marevivo 2017).

Figure 7: An illegal dump along the Aniene river. Waste ranges from old refrigerators to plastic containers.  (Source: Marevivo)

A 2017 study partnered with high schools in Rome to sample from eight sites on the Tiber and Aniene rivers to measure temperature, conductivity, pH, BOD, ammonia, N, and P content (Legambiente 2017). The study found ammonia concentrations of up to 0.53 and 0.28 mg/L and BOD of up to 16.2  and 10.2 mg/L in the Aniene and Tiber, respectively, which classifies both rivers as poor water quality (Legambiente 2017). The higher concentrations in the Aniene River would support Adriano’s claim that the Aniene is a major contributor to the Tibers pollution. The president of the environmental organization leading the study, Robert Scacchi, stated, “The quality of the water of Tiber and Aniene is poor due to the ineffective purification … and untreated waste” (Legambiente 2017). High ammonia concentrations, as in this case, typically indicate the presence of domestic wastewater, which undiluted commonly contains 15mg/L of nitrogen in the ammonia phase (Welch and Jacoby 2004).

Today, four wastewater treatment plants (WWTPs) surround Rome (Figure 8). The North, West, and South Plants release effluent to the Tiber River while the East Plant releases to the Aniene River. The East Plant, designed by Studio Pietrangeli Consulting Engineers, treats using activated sludge that is later disposed of by incineration (Pietrangeli, 2017). The plant has the capacity for 600m^3/day to serve a future population of 1.2 million, an increase from the 0.4 million it currently serves (Pietrangeli, 2017). Though only a small amount of information was available on this plant, its excess treatment capacity suggests that it is insignificant to pollution in the Tiber. The South Plant is operated by Acea AT02, an Italian Environmental and Water Resources firm, and has a design capacity of  820.8 m^3/day using activated sludge and biofiltration (GWI, 2017). In both of these cases, the methods meet the EU’s requirement for secondary treatment. Similar information was unavailable for the North and West Plants.

Figure 8. Map of Wastewater Treatment Plants surrounding Rome (Source: Google Maps)

Italy is not blind to the need for improvements in its wastewater sector. In fact, it “has received two final sentences by the European Court of Justice because 151 urban settlements are not complying with the EU Urban Wastewater Treatment Directive, which requires wastewater collection systems and wastewater treatment systems [to comply] with secondary or better treatment level in all urban conglomerates” (GWI 2017). In 2018, the EU fined Italy €25 million and imposed a continuing fine of €30 million for every 6 months that the country continues releasing insufficiently treated urban waste (AFP 2018).

The EU’s complaints rise from some communities in Italy having only primary treatment or no treatment (Figure 9).

Figure 9. Italian Wastewater Treatment plants categorized by most advanced level of treatment. Data specific to Rome’s four treatment plants was unavailable. (Source: GWI 2017)

Below are some statistics on the issue:

According to Utilitalia, improvements for conveyance alone require installing 21,000 km and replacing 45,000 km of pipe (GWI, 2017).

According to Istat, in 2012 3.8% of the total Italian population had no wastewater treatment (2015). 

According to a European Bathing Water Quality Report, Italy is among the three worst countries for greatest percent poor quality bathing water sites (European Environmental Agency, 2019). Here, “bathing water sites” are defined as water areas officially designated for swimming, such as parks and beaches. In 2017, Rome’s mayor announced a public beach to open on the Tiber’s shore by summer of 2018, but the project has since been delayed pending clean-up efforts (The Local Italy 2018).

To meet the EU’s standards, Italy will require an immense investment to improve its wastewater infrastructure, but the recently imposed fines should motivate improvements. However, public information on Italy’s plan to improve its wastewater infrastructure since these fines were imposed is scarce.

A Study on Rome’s South Plant

One 2001 study performed a series of experiments to evaluate water quality surrounding Rome’s southernmost wastewater treatment plant along the Tiber River. The study used a common strategy for water quality evaluation, choosing to observe daphnia due to their sensitivity as an indicator species. The toxicity of the water was measured by daphnia mortality and fertility when exposed to water samples taken upstream, downstream, and at the outfall of the WWTP (Figure 10).

Figure 10. Map of study on Rome’s South WWTP (Source: Google Maps & Mattei et al. 2006)

Results of this study combined with samples of macroinvertebrate benthic communities (organisms living at the bottom of the river) in the soil upstream and downstream indicated seasonally varying levels of pollution at each site. Upstream of the WWTP, pollution was attributed to ditches discharging directly into the river, but the study noted that “it [was] very difficult to charge the toxic effects [in a river ecosystem] to a specific source of contamination” (Mattei et al. 2006). The strongest toxicity was found at the outfall during summer months, which was attributed to chlorine residue left over from the plant’s disinfectant process. The researchers came to this attribution because “no significant differences from the other seasons were observed in water chemistry, such as pH, oxygen, [and] conductivity” (Mattei et al. 2006). Downstream of the plant, the river had diluted pollutants enough to lessen the impact on daphnia, but soil samples still showed negative effects on the macroinvertebrate population (Mattei et at. 2006).  Chlorine is also known to react with organic matter to form disinfectant byproducts that are harmful if consumed by humans, though this is a lower concern since the Tiber is not a source of drinking water (EPA 2019).

The observation that disinfectants from the plant harm the river ecosystem may seem counter-intuitive when compared to Tom Rankin’s earlier commentary about Rome’s North Plant: the North Plant may under-treat its sewage, but this South Plant over-disinfects. However, both cases reflect dysfunctions of the treatment plants and result in pollution to the river. Furthermore, the background section of the same research paper also found similar contributions to the river’s pollution as our tour guides:

“[The Tiber River] collects several different sources of contaminations passing through the city of Rome such as the highly polluted Aniene River, several still not depurated ditches, agricultural and industrial wastes, including sewage treatment plants (Sanna and Floccia 1993).”

Still, this study suggests that the improvements needed to the South Plant may differ than those needed at the North Plant. For example, efforts at the South Plant may require improvements to pathogen removal with less chlorination, whereas North Plant improvements would include capacity increases to all stages of treatment. At the time of the study, the South Plant increased the use of disinfectants in the summer months to counteract higher amount of microbes due to warmer temperatures (Mattei et al. 2006), which explains the highest toxicity at the outfall in these months. Further information would be needed to evaluate the need for this level of disinfection. If the over-dosage were not needed for killing excess microbes in the effluent, the plant could reduce the chlorine dosage to no longer release toxic concentrations. But more likely, if the dosage were reduced without adjusting any other stages of the treatment process, the effluent water would then contain dangerous levels of microbes, only creating a different but potentially worse pollution problem. Further research on the plant could determine if it is possible to reduce the need for disinfection by improving removal of pathogens earlier stages of treatment, such as by lengthening biological treatment or adding a coagulation step (Welch and Jacoby 2004). Other non-residual forms of disinfection such as ultraviolet radiation or ozonation could also be explored.

This study began in 2001 and its paper was published in 2006, but information is not publicly available on if Rome has since found funding to improve the plant.


Italy’s Tiber River is currently facing the consequences of improper wastewater management, and the country will need to focus funding and efforts on resolving this issue. Future developments, such as a beach along the Tiber have been proposed, but cannot be realized without major improvements to the river’s health. Ideally, new infrastructure will be added to bring all communities access to wastewater treatment, and existing infrastructure will be brought up to modern standards. However, not all this can be done at once, so further studies on the Tiber will be valuable to identifying which pollutant sources are the most detrimental and therefore indicate where efforts will be most valuable for improving the river’s ecosystem.


AFP. (2018, May 31). EU’s top court fines Italy for failure to treat sewage. Retrieved December 4, 2019, from

Carroll, R. (2002, July 17). Something about Rome’s river smells fishy. Retrieved from

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Marevivo. (2017, Dec 20). On the Tiber an island of waste transported by an illegal dump on the Aniene.

Mattei, D., Cataudella, S., Mancini, L., Tancioni, L., & Migliore, L. (2006). Tiber River Quality in the Stretch of a Sewage Treatment Plant: Effects of River Water or Disinfectants to Daphnia and Structure of Benthic Macroinvertebrates Community. Water, Air, and Soil Pollution, 177(1-4), 441–455. doi: 10.1007/s11270-006-9183-1

Pietrangeli. (2017, November 7). Roma Est Sewage Plant (Italy). Retrieved from

Welch, E. B., & Jacoby, J. M. (2004). Pollutant Effects in Freshwater (3rd ed.). Cambridge University Press.

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