Comparing the effects of three pre-treatment disintegration techniques on aerobic sludge digestion: biodegradability enhancement and microbial community monitoring by PCR–DGGE

Abstract

The objectives of this work were to compare and investigate the effect of three activated sludge disintegration processes before aerobic sludge digestion on 1) aerobic biodegradability enhancement and 2) microbial community evolution using the polymerase chain reaction–denaturant gel gradient electrophoresis (PCR–DGGE) technique. The comparison of three disintegration processes: thermal treatment (95 °C, 2 h), sonication (100,000 kJ/kg TS) and ozonation (0.108 g O₃/g TS) showed that the disintegration processes acted differently according to the composition of the soluble phase and to the DNA damage. Thermal treatment led to significant protein solubilization and to DNA modification. Sonication and ozonation resulted in similar soluble phase compositions and did not lead to any DNA modifications. During activated sludge aerobic digestion, intrinsic biodegradability enhancement was observed for thermal and ozone activated sludge pre-treatments. The analysis of the DGGE patterns at the end of aerobic digestion showed that population diversity was affected by both the aerobic digestion and the pre-treatment. The dissimilarity percentages measured at the end of aerobic digestion in the control sample and in the treated sludge were equal to 22, 25 and 20% for thermal treatment, sonication and ozonation respectively. This study indicated that PCR–DGGE could be a useful tool for the comparison of disintegration processes before and after aerobic digestion.

Keywords:

• PCR–DGGE
• aerobic digestion
• thermal treatment
• ozonation
• sonication

Acknowledgements

The authors thank Conseil Régional du Limousin for its financial support and Communauté d'Agglomération Limoges Métropole for allowing us to take samples at Limoges WWTP. We also wish to thank Dr Stefan Green for his useful advice on PCR–DGGE techniques.