Energy-saving Sludge Drying
Drying for more Sustainability
by Anke Geipel-Kern
The technology to dry sludge resulting from production processes captured the market 30 years back. The issue at that time was to reduce disposal cost. Why sustainability, recycling and new markets play an even more important role today.
Time is money – most of us are familiar with this saying. That water may also cost money only those of us know who have ever had to pay the cost for sludge combustion or disposal. Thin sludge, after all, has a water content of between 60 and 80 percent even after pre-dewatering.
According to the Federal Statistical Office of Germany, disposal costs a neat sum of money – between 25 and 50 Euros per cubic metre. And this is only true for “normal” sludge. Some types of sludge from plating, chemical, textile, leather or paper industry processes are considered hazardous waste and have to be disposed of in hazardous waste combustion plants – at higher cost commensurate with the effort involved.
The waste management market is changing, too. The cost of energy, discussion about closed-loop economy, shortage of rare earths, the environmentally hazardous mining of copper, nickel and cobalt, regulations concerning phosphorus recovery, recycling quotas for electronic scrap and batteries – all this whips on the recycling market and companies to find new solutions. Thin sludge formed in recycling processes must undergo intense drying in order to extract the coveted metals.
To recover zinc, for example, a residual humidity of eight percent is required. Much the same applies to nickel, cobalt and copper – an effort that requires much energy and makes recycling expensive.