Tuesday, May 22, 2007

Tampere's Water!

I was inspired by the architecture Valle (the scholarship program that’s funding me) students’ abilities to connect their work to the non-architects. So I’m giving it a try with my own work in Tampere. While my project in the lab is involves molecular biology, nucleotides, polymerase, statistical significance, and sampling plans, it also involves water. Civilizations are formed around convenient water supplies. We all swim, wash, transport ourselves and our things, and most of all, we drink water. The architects have the fancy interiors, exteriors, and photographically artistic presentation, but I have the substance that makes up more than half of your body and 70% of your planet’s surface. Tampere has its history, present, and future which, in order for it to survive, has been centered around water.

Tampere’s Water System

Tampere is geographically sandwiched between two large lakes, Näsijärvi (the largest lake in the Tampere area**, 257 km²) and Pyhäjärvi. The city was originally established on the Pispala ridge, around the Tammerkoski Rapids. These rapids run from north to south, out of Näsijärvi and into Pyhäjärvi. Since there is an elevation difference of 18 meters between the two lakes, the rapids can produce energy. Power plants from Finlayson, Tampella and Liljeroos were able to use the rapids as Tampere’s sole energy source until 1916. If you look down the Tampere Rapids today, the view is dominated by historical industrial buildings that were once used to produce cotton, wood, shoes and textiles. In spite of the drive for industrial development, Koskipuisto Park was deliberately left undeveloped for the public to enjoy. Tampere is the largest inland Nordic city and the third largest city in Finland, currently with 200,000 residents.

Tampere’s Water History

From 1835 to 1921, just after the industrial revolution, Tampere grew from approximately 1,600 to over 40,000 residents. At the beginning of this period, the major objective of a water system was to provide fire-fighting protection, but simultaneously led to improved hygienic conditions. Throughout history, Tampere’s water has been provided by both ground and surface water sources. The first municipal pumping station was installed in 1835 and was used to fill buckets for household distribution. Free-flowing ditches were later used to direct wastewater into lake Pyhäjärvi. In 1866 a municipal committee was formed to control drainage, as a measure to address the Typhoid problem that was worst in the least drained areas of Tampere (Germ Theory and microbes had not yet been discovered). This committee proposed a sewer network to separate sewage from drinking water. In 1876, the sewer construction began. The city’s first health official, A. Ahlberg- a civil engineer (like me!)- proposed the first modern drinking water distribution and sewage system in Tampere. He recommended charging for water by the household. He also suggested constructing a robust and sustainable system, rather than quickly solving the short-term water shortage problems. The city constructed the first waterworks in 1882, without using Ahlberg’s recommendations. Unfortunately, the system lacked the pressure necessary to provide water to everyone, did not resolve water quality issues, and did not meter water usage to equitably charge consumers. The sewer system was completed in various parts of the city between 1883 and 1894. A second drinking water system was constructed in 1898 with higher pressure, but still no water treatment. There was a serious Typhoid problem that was said to have spread along the water pipe network.

In the early 1900s, Lake Näsijärvi was considered polluted and Typhoid outbreaks were common. It wasn’t until 1917, when Tampere began to chlorinate its drinking water, that the Typhoid problem was contained. There have been no Typhoid epidemics since this time. To address taste and turbidity problems, the city opened a new treatment plant in Kaupinoja, which used both chlorination and sand filters to treat the Lake Näsijärvi’s water. A second plant was built in 1931 in Mältinranta to serve the western part of the city. In 1972 the water source was changed to Lake Roinejärvi, which currently provides 70% of Tampere’s water, while the other 30% comes from various groundwater sources. In comparison, Finland receives about 50% of its water from surface sources and 50% from groundwater sources.

It seems like Tampere is unusual with such a water centered history, but you'd be surprised. Do you know where your water comes from? Do you know why your city was founded where it is?

Warning: the following section contains more science than usual!

Artificial Groundwater Recharge (AGR)

Reija, one of my collegues at the lab, is focusing on AGR for her PhD work. The main idea of AGR is to load up aquifers with untreated water. The natural microbial processes in groundwater are capable of removing certain contaminants that are currently removed at the treatment plant. Her results may help the City of Tampere decide on its best future water treatment option.

She has two sets of reactors installed at the local water treatment plant. She varies temperature and oxygen with time in one set. Some people worry that the CO32- in the system will turn to organic matter instead of CO2 and cause the AGR system to clog and shut down. She has some smaller fluidized bed reactors that provide a small, but perfectly porous material to simulate ideal aquifer conditions. In the fluidized bed reactors, Reija studies the effects of varying the hydraulic retention time, fluidization rate, temperature, and phosphorus and nitrogen concentrations on the microbial communities. She’s currently using stable carbon isotopes to measure the biodegradation rate. She’s getting approximately 30 to 50% biodegredation, based on the 12C:13C ratio.

Tampere’s Water Treatment Plant

The present-day treatment plant was built in the end of the 1970s and is located in Rusko, approximately 2 km from the Tampere University of Technology (TUT). It’s time for a renovation, but there is a hot political debate over whether to switch to artificial groundwater recharge (AGR) that is holding up plans for renovation. AGR is (not coincidentally) also a hot research topic in our lab at TUT. The city doesn’t want to renovate or build a new treatment plant if it is going to switch to AGR, which requires much less water treatment. AGR consists of pumping surface (or whatever type of) water into the ground and letting the microbes in the soil do the treatment. It would still require chlorination, but almost entirely eliminates the need for a water treatment plant. However, we need some science to tell us if it’s a viable option for Tampere.

The current treatment plant consists of 720 km of pipelines and five steps of treatment, with a flow rate of 1800 to 2200 m3/hr. These are the five treatment steps:

  1. Calcium carbonate addition. This prevents corrosion
  2. Hypochlorite addition. This prevents biofilm from forming on the sand filters.
    1. It may also unfortunately cause disinfection byproducts to form, which cause cancer in lab animals at high doses
  3. Rapid sand filtration. There is a one meter deep sand bed that is backwashed once per day. This process removes natural organic matter and iron. Some people think the rapid sand filtration should go before the hypochlorite addition to reduce the formation of disinfection byproducts.
  4. Air flotation. This treatment process is considered advanced and efficient. Ferric sulfide sticks to the organic matter and forms flocs. These flocs adhere to bubbles that are diffused through the water column, bringing the organic matter to surface where it can be scraped off.
  5. Activated carbon filtration. Water is filtered, the pH is raised to 8.5, and the final chlorination takes place before the treated water is stored in one of Tampere’s five water towers.

So wow! Before I drink that water, it sure goes through a lot! It's pretty nice that we don't get Typhoid here anymore. That's not the case everywhere!

By the way, there’s a new policy to keep the door shut at the water treatment plant in Rusko. Since you need an appointment to get into our water treatment plants in Seattle, and you have to go drive past intimidating signage that makes you think you have to go to prison if you make a wrong turn, I really noticed the cultural difference.

**Näsijärvi is nowhere near the largest lake in Finland, that was a mistake (see Sannamari's comment)!


Anonymous said...

Hi there,

I just noticed that you write in your blog about the largest lake in Finland. I would also like to say that Näsijärvi is the largest lake in Finland with its 257 km2 but unfortunately that is not the case :(
In southeastern Finland we have a lake called Saimaa. At approximately 4,400 km², it is the largest lake in Finland, and the fourth largest in Europe. And guess what, the Saimaa Canal from Lappeenranta to Vyborg binds Saimaa to the Gulf of Finland!

Just to let you know :)


laurita said...

Oh my goodness! I'll have to check my sources. I guess everything on wikipedia isn't necessarily true! Thanks for you comment!