Green dregs: from waste product to building material

Our Frantschach mill in Austria produces some 5,000 tonnes of green liquor sludge per year. Green dregs or green liquor sludge is a waste product of chemical pulping by the sulphate process. The green dregs are drained by filtration units at the end of the process and have historically been deposited to landfill.

However, all of this changed in 2011, when Manfred Hacker, the pulp mill manager, and Karin Morianz, head of purchasing, got together with Wietersdorfer and Peggauer (W&P) Cement Company to develop a way of using Mondi’s green dregs in the cement clinker production process. Trials were conducted in that year to see how this could be done and W&P constructed equipment to accommodate the process. The first delivery of green dregs to the cement company took place in mid-2012.

Says Elke Juri, Frantschach’s environmental manager: “Since then, we have attempted to transport sludge to W&P on a daily basis. If there is too much in any one day, we do deposit the excess. We pay for this processing of our waste, so it makes sound environmental and business sense. In just a few years the landfill area would be full and we would have to expand the deposit area.”

The mill has reduced its landfilled green liquor sludge from 9,000 tonnes in 2010 to 1,000 tonnes in 2013. The mill’s target for 2014 is for all its green liquor sludge to be utilised by the cement industry, which will make this waste product’s name most appropriate indeed.