Sewage in Venice: how does it work?

Feb 28, 2020 | architecture, environment, history, preservation | 0 comments

 

Sewage treatment is one of those subjects that visitors in Venice inquire most about. Surely, they are curious about the history of Venice and its amazing heritage, but not just. Building a city on marshland has its challenges and they regard construction issues, too, even everyday utilities. So, why not asking what happens when you go to the toilet?

While as for other utilities Venice has become a modern town, sewage treatment has proved to be a challenge to face with a different attitude.

Till the 1960s, human waste was slowly delivered through brick tunnels called “gatoli” into the canals, an indeed very ingenious system designed in the 16th century. The “gatoli” connected toilets and streets’ manholes for rainwater finally to the canals.

A typical “gatolo” allowing sewage to reach the canal in Venice

A typical “gatolo” allowing sewage to reach the canal in Venice

These tunnels were built in clay bricks and stone and ran under the streets of the city till they connected to a waterway. The heavy sediment would lie at the bottom of the tunnel, while the liquid part slowly reached the canal. Septic tanks today work similarly. The “gatoli” were constantly dredged.

Thus, the city streets were clean. The lagoon’s brackish water had a powerful disinfecting effect, too. Moreover, canals would be constantly dredged also thanks to the tide exchange.

This went on till the 1960s when Italy’s economic boom took place in Venice, too. Washing machines, dish washers moved into Venetian homes. Chemical detergents and toilet paper started get heavily used while the aqueduct allowed people to use a lot more fresh water than before. The city “gatoli” started receiving more than they used to. Too bad that at the same time the City Council considered regular maintenance an extraordinary intervention. So till the 1990s not much was made to clean the city canals and the “gatoli”.

In order not to let the holes along the canals connected to the “gatoli” get clogged, these same holes were moved higher. When low tide arrived then, these holes were no longer below water level as they used to. Bad smell, unbearable hygienic situations, rats… and bugs. I remember when I learnt the word “chironomid” as I saw the windows of the vaporetto stops all covered with these dark mosquitoes that didn’t bite. It was in the late 1980s. The lagoon was literally invaded by these bugs generated from water’s eutrophication.

A few years later a solution was studied. Mapping the “gatoli” network was helpful, even if it partially failed due to the fact that the system had been modified throughout the centuries: sometimes it was not clear which canals the toilets in the old homes were connected to.

Abandoning the plan to create a modern sewer in Venice, as it would have implied to rebuild the whole city, a compromise was found in the creation of septic tanks, maintenance of the existing “gatoli” as well as cleaning the canals.

A drawing illustrating what happens under the streets in Venice while cleaning the canals; from a publication edited by Insula

A drawing illustrating what happens under the streets in Venice while cleaning the canals; from a publication edited by Insula

 

A “gatolo” and its hole by the canal during maintenance in Venice; ph. by Michela Scibilia

A “gatolo” and its hole by the canal during maintenance in Venice; ph. by Michela Scibilia

You may remember visiting Venice and finding canals with no water. This project run by the company Insula went on till 2010. A couple of gates and pumps at the sides and a canal would be dredged from dirt that had been deposited for years. I considered those workers true heroes.

Maintenance of canals in Venice, including taking care of the underground utilities and septic tanks; from a publication edited by Insula

Maintenance of canals in Venice, including taking care of the underground utilities and septic tanks; from a publication edited by Insula

On the other hands, septic tanks were built whenever it was possible. Nowadays, over 7,000 septic tanks collect the city’s sewage. Septic tanks allow for sewage treatment so that liquid waste will not pollute the water when reaching a canal. There are also special boats designed to empty septic tanks of solid and fat sediments. These “honey suckers” boats can be seen in the city pretty much everywhere.

This happens with hotels, restaurants, museums, cafes, hospitals… and partially with private homes.

As a matter of fact, the solution of the septic tank in Venice is not always practicable. A septic tank require space and you cannot build it on public ground or close to the main walls of your house. The volume of the tank is calculated in proportion to the number of inhabitants potentially expected in a building. Sometimes it simply does not fit in.

Even when room is available, digging in the ground uncovers the petrified wooden pilings supporting the building. Obviously, a septic tank must not affect the stability of the construction itself, threatening its foundations. In this latter case, a compromise needs to be found and you get back to the ancient “gatoli” turning them waterproof and placing the holes by the canals at a height which guarantees they are under water even during low tide.

A “gatolo” in a canal in Venice by Campo Santa Maria Formosa during a very low tide

A “gatolo” in a canal in Venice by Campo Santa Maria Formosa during a very low tide

Living in Venice also means to accept its uniqueness and diversity. Organic detergents or special toilet papers help a lot. Surely, we would all love Venice to be a modern town, with no sewage ever delivered into the city’s canals.

But are we sure Venice is such a little innovative town? Even in modern towns where there is a sewer, some waste water still reaches rivers or the sea. Just, you do not see it. This is the paradox of Venice, as in the end what happens here, happens everywhere. With just one difference: we get more aware of the impact of our waste on the environment than the inhabitants of other towns.

Luisella Romeo
Best Venice Guides
www.seevenice.it

Translations: deDeutsch itItaliano