Nitrogen purification from blasted rock

As part of the E16 Bjørum - Skaret expansion, a full-scale purification plant has been established to cleanse nitrogen runoff from a blasted rock fill in Nordlandsdalen in Hole municipality. The facility comprises a forechamber, a sedimentation pond, and two purification filters. There is also a system of wells, overflow channels, and valves. The amount of water directed to the purification filters can be adjusted, and the filters are designed to purify up to 130 m3 per day.

The facility has been operational since late 2021. So far, the results are promising – at least for relatively dry periods.

"From January to September 2022, the average purification effectiveness was just above 80 percent," says Roger Roseth, project leader at NIBIO.

Autumn 2022 saw intense rain and floods, along with several subsequent precipitation events. With increased water flow during that autumn and winter, the purification rate in the nitrogen filters decreased to between 20 and 60 percent.

He says they are now exploring options to improve purification results in wet periods, including controlled leaching of nitrogen from the fill during the summer to match the filters' purification capacity. This can be done for example by irrigating purified water back onto the top surface of the landfill.

"The results and experiences provide new and valuable knowledge that can be used to optimise an enhanced nitrogen purification solution. We are well underway in developing the concept to achieve more efficient nitrogen purification while minimizing the leaching of organic matter and phosphorus from the filter."