High Flocculation of Coal Washing Wastewater Using a Novel Bioflocculant from Isaria cicadae GZU6722

Chanhua (Isaria cicadae) was known as a rare entomogenous fungus with various pharmacological activities since a long time ago in China, which has attracted considerable attention. However, less knowledge was maintained about its products as potential bioflocculants. In this work, a bioflocculant IC-1 produced by Isaria cicadae GZU6722, consisted mainly of protein (4%) and polysaccharides including neutral sugars (52.75%) and galacturonic acid (38.14%), was characterized. It presented high efficiency in flocculating coal washing wastewater, and the flocculating efficiency could reach 91.81% by addition of 24 mg l^–1 IC-1 compared to the addition of 60 mg l^–1 APAM (anionic polyacrylamide) under the same treatment conditions. The highest flocculating efficiency reached 95.8% in the presence of 2% CaCl₂. Compared to APAM, the flocculating efficiency of coal washing wastewater by IC-1 varied little with the increasing dosage. Although the flocs in the APAM-assisted sediment were larger than that in the IC-1-assisted sediment after 1 min of sedimentation, few flocs were still found in the supernatant of both treated samples after 10 min of sedimentation. More interestingly, it was observed under the microscope that the flocs in the IC-1-assisted sediments were more compact than that in the APAM-assisted sediments, suggesting that polymer bridging might take place after IC-1 was added into the coal washing wastewater. The evaluation of costs indicated that the use of IC-1 to treat the coal-washing wastewater may be an economical and feasible way to avoid the extra cost for post-treatment of conventional flocculants.