Solar Sludge Drying

In the summer or in a hot environment, the sludge can easily be dried completely, i. e. to 90% dry residue, which means that only 10% water remains. In autumn or spring, partial drying can be achieved (to between 50 and 75% dry residue), while in winter, with longer periods of sub-zero temperatures, plants are sometimes shut down.

With natural solar radiation alone, between 1,000 and 3,500 kg of water per square metre and year can be evaporated from sewage sludge, depending on the location. Additional heat increases this value even more; it can compensate in particular for the lower evaporation in winter.

One square metre of dryer surface is sufficient for about 10 to 35 population equivalents and "reduces" the associated dewatered sludge by 70% to dry granules.

Solar drying of sludge is suitable from a quantity of about 1,000 tonnes of dewatered sludge per year. The largest solar drying system implemented by HUBER processes 500,000 tons per year.

The largest solar sludge drying plant is located in Egypt at the Bahr el Baquar water treatment plant. With an annual throughput of almost 500,000 t/a, it is by far the largest plant in the world; 128 HUBER Sludge Turner SOLSTICE® units are in operation there.