Tunnelling miles for wastewater to give the Baltic Sea a chance

The completion of the NIB-cofinanced 12-kilometre Northern Tunnel Collector crowns the city’s decades-long efforts to eliminate discharges of untreated effluent into the Baltic Sea. The head of the St Petersburg water utility believes it rehabilitates the city’s name and gives it a new sound—the sound of clean water.

From now on, the city is treating, cleaning and removing nutrients from more than 98% of its wastewater, which is a huge leap from a few years ago. The Northern Tunnel Collector closes up about 400 points of direct discharge of untreated effluent. Before the collector was built, about 334,000 cubic metres of untreated sewage ended up in the River Neva and the Gulf of Finland every day.

“This is a huge investment, a very challenging endeavour from an engineering point of view, and a matter of prestige for the city and our company,” says Felix Karmazinov, Director General of the city’s water utility Vodokanal St Petersburg.

St Petersburg has been slowly but steadily growing its wastewater treatment capacity since the mid-1970s, when the then four-million-strong metropolis had no sewage cleaning at all. It is no wonder that this made St Petersburg the largest single point source polluter in the Baltic Sea area for many decades.

In 2005, the city launched the state-of-the-art South-Western Wastewater Treatment Plant (SWTP) with a treatment capacity of 330,000 cubic metres a day. That allowed the total volume of effluent cleaning to increase to 85%. Modern technologies in its treatment plants now allow the city to remove about 90% of all phosphorus in wastewater. It has helped to decrease the annual load of phosphorus into the sea by 1,700 tonnes during the past decade.

NIB was a lead bank to structure the packages of international financing for both projects. NIB loans for the SWTP and the Northern Tunnel Collector totalled EUR 45 million and EUR 25 million respectively.

“We are already witnessing small changes in the amount of blue-green algae which perhaps are the most visible sign of the eutrophication of the seawater,” says Seppo Knuuttila, Senior Research Scientist at the Finnish Environment Institute SYKE.

In the summer months, the average amounts of algae in the eastern part of the Gulf of Finland are now significantly lower than they were approximately a decade ago. Please see the graph of the changes in the amount of algae. The level of chlorophyll-a indicates the amount of algae in the sea water.

“Although this is mainly due to the better oxygen situation during recent years, we cannot exclude the effect of decreased external loading of nutrients in the eastern—closest to St Petersburg—part of the gulf. We are very likely to see more obvious effects from closing the discharges of untreated effluent from St Petersburg in a couple of years,” says Mr Knuuttila.

The effect of closing untreated discharges is not immediate. A large part of the phosphorus that has entered the sea from the catchment area stays in the sediment on the seabed. Phosphorus can be stored in this way for years.

“We cannot stop the sea from releasing nutrient from its storage as long as the oxygen depletion area in the Baltic Sea’s main basin is very extensice as it is nowadays. We can only stop releasing more untreated wastewater from the catchment area. Russia is investing and making good progress in cutting its loading. All the countries around the Baltic Sea should continue decreasing their discharges,” says Mr Knuuttila.

“Today, we are cleaning 98% of our wastewater, and we are already working on the remaining points of discharge. We are also giving a new sound to the city’s name—the sound of clean water,” says Mr Karmazinov.

In 2014, Vodokanal is planning to close up some six remaining discharge points in the oldest part of the city, a few hundred metres away from the Winter Palace. Another collector needs to be built along the river Ohta, where more than a hundred discharge points emit about 50,000 cubic metres of untreated wastewater a day.