Isolation of filamentous fungi capable of enhancing sludge dewaterability
Filamentous fungi capable of enhancing sludge dewaterability were screened out from the municipal sewage sludge, using Martin rose-bengal agar medium by serial dilution techniques. Seven filamentous fungal strains were isolated and preserved on suitable agar slants at 4 °C for further study. The influence of isolated fungal strains on the dewaterability of sludge was preliminarily determined in 500 mL conical flasks each containing 270 mL of municipal sewage sludge and 30 mL of actively growing culture of isolated filamentous fungus. The mixtures were cultivated on IPI-504 gyratory shaker at 28 °C and 180 rpm, and 50 mL of sludge samples were collected at 24 h intervals and used for the determination of sludge SRF, using the Buchner funnel test (Lo et al., 2001). A filamentous fungal strain decreased the sludge SRF by more than 80% in only 3 days, while other six fungal strains only reduced the sludge SRF by about 20–60% in the 6 days incubation. Thus, the filamentous fungus with the highest ability of decreasing sludge SRF was considered as the one with the highest ability of enhancing sludge dewaterability (Wakeman, 2007 and Feng et al., 2009) and selected out. The identification of the isolate was performed through molecular phylogenetic analysis based on the 18S rRNA gene. The 18S rRNA gene was amplified by PCR as the method mentioned by Deswal et al. (2011). Sequencing of the purified PCR product in both the directions was carried out by Shanghai Majorbio Bio-pharm Technology Co., Ltd, China. The resulting sequence was compared with available sequences in the GenBank database using BLAST system (http://ezproxy.student.twu.ca:5115/BLAST/). Multiple alignments were carried out using the CLUSTAL_X program. Phylogenetic tree was constructed from evolutionary distance data that were calculated with Kimura’s two-parameter model by using the neighbor-joining method. Bootstrap analysis was based on 1000 random resamplings. Reference sequences were retrieved from GeneBank with the accession numbers as indicated in the tree. Sequences from this study have been deposited in Genbank under the accession number KM592960.1.