Enzymatic, mechanical and thermal pre-treatment of surplus sludge

The anaerobic stabilisation process depends-among other things-on the bioavailability of organic carbon. Through pre-treatment of the sludge, which leads to the destruction of microorganisms and to the liberation of cell contents (disintegration), the carbon can be microbially converted better and faster. Moreover, effects on digestion can be expected. Laboratory-scale digestion tests with thermally, enzymatically or mechanically pre-treated surplus sludge were carried out to analyse the influence of disintegration on anaerobic degradation, sludge water reload, foaming in digesters and sanitisation. The results were different, depending on the disintegration procedure used. Whereas disintegration by a high-pressure homogeniser and by enzymes only achieved low reduction of the foam phase, thermal pre-treatment at 121 degreesC resulted in effective suppression of foaming. All methods, except for enzymatic treatment, resulted in cutting up of filaments, but only beating effected a reduction in exo-cellular polymers. The improvement in gas production of thermal (121 degreesC) and mechanically pre-treated sludge was approximately 20%. (C) 2002 Elsevier Science Ltd. All rights reserved.