[Analysis of hydrolytic enzyme activities on sludge aerobic/anoxic digestion after ultrasonic pretreatment].

In order to evaluate the function of sludge aerobic/anoxic digestibility by ultrasonic pretreatment. The SS, VSS and hydrolytic enzyme activities (amylase, glucosidase, protease, phosphatase) were measured before and after ultrasonic pretreatment (28 kHz, 0.15 kW x L(-1), 10 min). The results showed that the performances of aerobic/anoxic were greatly improved after ultrasonic pretreatment, the removal efficiency of VSS went to 44.3%, 7.8% better than of traditional aerobic/anoxic digestion. The variational trend of sludge hydrolytic enzyme activities increased firstly and then fell off during 13d digestion, the maximum of amylase activity and glucosidase activity in ultrasonic sludge, appeared in the 5 d, amylase activity was 0.104 micromol x g(-1) and glucosidase activity was 0.637 (micromol x g(-1). The maximum of intracellular protease activity and extracellular proteases activity in ultrasonic sludge, appeared in the 7 d, intracellular protease activity was 23.68 micromol x g(-1), higher than extracellular proteases activity, and it was playing a leading role in sludge digestion. The acid phosphatase activity of ultrasonic sludge was higher than the control sludge, and the alkaline phosphatase was sensitive to environment. So the alkaline phosphatase activity reduced when the internal properties of sludge was changed.

[Analysis of community structure on sludge aerobic/anoxic digestion after ultrasonic pretreatment].

The microbial community structure of sludge aerobic/anoxic digestion after ultrasonic pretreatment was studied by PCR amplification and DGGE based on 16S rDNA. The genomic DNA of sludge at different stages was extracted with SDS cell lysate method. After purification of DNA, the 16S rDNA genes (V3 region) were amplified by using the universal primers (F357GC and R518). The results of agarose gel (1.5%) electrophoresis showed that the PCR products were about 190 bp in length. The amplified DNA fragments were separated by paralleled DGGE with the denaturant (urea and acrylamide) from 30% to 60%. The sequences were used for homology analysis and phylogenetic trees were constructed. The DGGE profiles showed that the change of microbial diversity was in correspondence to different periods. Compared with 0 d, the diversities of microorganisms were 61.2%, 48.2%, 46.4%, 42.6% and 41.7%, respectively after 5 d, 10 d, 15 d, 20 d, 25 d. Shannon density index of bacteria experienced a process from a gradual reduction to stable state. This suggested that ultrasonic pretreatment had a significant impact on bacterial community structures. Cluster analysis of DGGE by UPGMA (unweighted air group method, arithmetic mean) divided all lanes into three clusters, which corresponded to different periods during the whole experiment. The sequences indicated that Firmicute, Genuscitrobacter, Bacilli, alpha-Proteobacteria, beta-Proteobacteria were the predominant microbial populations in the process of sludge aerobic/anoxic digestion after ultrasonic pretreatment.