Characterization and flocculability of a novel proteoglycan produced by Talaromyces trachyspermus OU5

A filamentous fungus strain OU5 was isolated from a soil sample for its ability to produce rich exopolymers (EPS), with high flocculation capability towards kaolin suspension and swine wastewater, at low-carbon source conditions. EPS from strain OU5 was extracted and characterized to determine its flocculating behavior and active constituents involved in the flocculation. Strain OU5 was identified as Talaromyces trachyspermus by 18S rDNA–ITS gene sequencing and morphological observation. The extracted EPS was a novel proteoglycan (designated as BF–OU5) composed of 84.6% (w/w) polysaccharides and 15.2% (w/w) proteins. The enzymatic digestion tests revealed that the polysaccharides in BF–OU5, composed of 67% glucose, 16.4% mannose, 8.6% xylose and 8% galactose, contributed to 99.7% of flocculating capacity and were the major active ingredients in the flocculation. By contrast, the proteins in BF–OU5 only had minor roles in the flocculation. The presence of hydroxyl, amide, carboxyl and methoxyl functional groups in BF–OU5, and the high molecular weight (1.053 × 105–2.970 × 105 Da) as well as the structure of a spherical conformation with inner pores and channels made of cross-linked netted textures contributed to the flocculation. A dosage of 20 mg/l BF–OU5 initiated more than 92.5% of flocculating efficiency towards kaolin suspension without any added coagulants; its flocculability was stable over a wide range of pH (4.0–8.0) and temperature (20°C–100°C). Treatment of swine wastewater using BF–OU5 achieved 52.1% flocculating removal for chemical oxygen demand, 39.7% for Kjeldahl nitrogen, 18.6% for NH4+–N, 21.5% for total phosphorus, and 75% for turbidity.