Sludge is a major challenge in sewage treatment. There’s a lot of it, it stinks, and handling it is costly. Thanks to Kemira’s KemiCond, Swedish Käppala is now one of the world’s most effective wastewater treatment plants.
On the island of Lidingö just north of the Swedish capital is the Käppala wastewater treatment plant. Serving 11 municipalities in the greater Stockholm area, the plant treats about 50 million cubic meters of wastewater a year.
“We did a major renovation from 1994 to 2000, but left the sludge treatment as is because at the time, regulations were not clear,” says Per Manhem, Managing Director at Käppala.
Since 2000, sludge handling has been their focus.
“We needed to upgrade our dewatering system and had prepared a proposal for new dewatering centrifuges,” recalls Manhem. “Right about this time I was contacted by Kemira. They asked to use our plant as a testing ground for a new sludge treatment idea. We pulled the handbrake on the centrifuge investment and began following the trials.”
“Even though KemiCond was totally new, we thought it was wrong not to proceed,” continues Manhem. After successful testing, development was quick, spurred on by the addition of Andreas Thunberg, a process engineer hired by Käppala and Kemira to optimize the KemiCond process. Currently, he works as a Process Manager for Käppala.
Less sludge
KemiCond was taken into full-scale use during 2006. After dewatering, they used to average 20 percent dry solid content. At present, with the last of four new Bucher Drytech presses being installed, they easily average 40 percent.
Although the investment in KemiCond has been more than estimated, there are no regrets.
“We gain other advantages because of the method,” says Manhem.
“The main one is that sludge volume is reduced dramatically,” adds Thunberg. “We see an approximately 50 percent reduction, which means instead of transporting 40,000 tons of sludge a year, we transport around 20,000.”
The process also reduces foul smell.
Cleaning it up
Because the plant is situated in a highly populated residential area, fewer transports and a neutral odor are very important. In addition, the process can be modified on the fly.
“Sludge composition changes; sometimes it is very hard to dewater. Now we have a tool to change the treatment of the sludge by changing the chemical recipe,” says Thunberg.
Looking to the future, Manhem sees recycling as the hot topic. In Sweden, the ReVAQ certification allows sludge to be used on farmland. Käppala is already certified, but currently they have to store the sludge for several months to get rid of harmful bacteria.
“We know KemiCond kills most of the pathogens,” says Thunberg.“ The challenge is the machinery which recontaminates the sludge.”
The company is now working on cleaning up the plant to get KemiCond certified. Once certified, sludge can be sent to farms without delay, further improving the efficiency and sustainability of the Käppala wastewater treatment plant.
Text: Randel Wells
Original article published in Kemira’s stakeholder magazine Waterlink 1/2010