Challenge of High Water Hardness and Elevated Temperature: MBR Pilot Trials in the Paper Industry under Mesophilic and Thermophilic Conditions

The results of two MBR pilot trials conducted in paper mills are discussed. In the first trial it was possible to operate a MBR pilot plant under the challenges of extremely high water hardness and a mean calcium concentration of 770 mg/L that caused massive scaling problems. An upstream lime softening pilot plant was designed and constructed. As a result, the flux increased again and the cleaning intervals could be extended significantly. With the help of lime softening, 50-80 % of the calcium was removed upstream of the MBR pilot plant. The second part of the paper describes trials using a thermophilic aerobic MBR (TMBR) at 50?°C. A new and innovative use of submerged flat-sheet MBR-modules to treat paper industry circuit wastewater was studied. The elimination rates of the TMBR regarding COD and BOD5 were 83 % and 99 %, respectively. A pilot trial was conducted at a flux of 4.5 to 8.5 L/m²/h. Lab experiments with a smaller membrane module had shown a higher flux of 8 to 13 L/m²/h.