TECHNOLOGY

Water supply

The Daugava River and moats provided water in the Middle Ages. Wells were also sunk, some like shafts by burying barrels without tops and bottoms on the top of each other in the ground, and others by lining them with oak boards.

The first pumping device in Riga was built in 1620. The water was taken from an open reservoir, the Smilsu Gravis. The plunger pumps of the device were designed to be driven by horses, and the water ran through wooden water pipes to pools and to the premises of Riga's noblemen.

The first pump-station started operating in 1863. The Daugava river water was pumped with steam engine plunger pumps. The water quality was uncertain and contamination was recorded frequently.

In 1904 a new water supply system was completed using running subsoil water from the Lake Mazais Baltezers region 20 km from Riga.

At present, the city of Riga uses a number of water sources for water supply including surface water, natural groundwater and artificially recharged groundwater. Water intakes are spread over the area around the city. Daily water consumption of drinking water is about 350 000 m³/day. Both surface and groundwater sources are used for water supply, providing a half of the total need.

Sewerage system

The first sewerage system was a combined system, and it was not after the Second World War that a separated system was operational. The oldest sewer collector, built in 1898, is still in use.

Installation of the sewerage system started in the central city areas. The second pumping station directed the central city area's waste water into the main collector outlet at Andreja Island. All sewage was discharged into water courses. In the post-war period some simple treatment plants were built. However, even in the mid 1980s as little as 7.1% of Riga's sewage was treated biologically and 22.4% mechanically.

The municipal wastewater treatment plant of Riga.

Present state

At present due to drinking water saving policies e.g. installation of water meters, lower income of the population and constant decrease of the number of inhabitants, drinking water consumption has decreased drastically during the 1990s. This lower water consumption (about 100 litres per capita per day) along with the collapse of industries, have also reduced the wastewater generated. Meanwhile with the aid of foreign investments, a number of new wastewater treatment plants have been built or reconstructed. In 1991, wastewater from Riga was directed to the newly built wastewater treatment plant Daugavgriva, containing advanced biological phosphorous and nitrogen removal systems. Until then, only 24% of the city sewerage was treated. Development of new and improved waste and wastewater treatment facilities has resulted in substantial reductions of pollutant loads to inland waters.

At present, 85% of the total sewage is biologically treated due to the implementation of a large-scale programme to install pressurised collection system, large pumping stations and a biological wastewater treatment plant. The final goal of this programme is the biological treatment of all industrial and municipal sewage. The phosphorous concentration of the purified wastewater occasionally exceeds allowed limits.

Link to Riga Water homepage.