Study on sludge expansion during treatment of salad oil manufacturing wastewater by yeast

Five yeast strains, namely Rhodotorula rubra. Candida tropicnlis, Candida u tilis, Candida boidinii. Trichosporon cutaneum, were isolated from soil spo ts of a salad oil factory, and applied for continuous treatment of salad oi l manufacturing wastewater. me oil and COD removal performance of the mixed cultures were comparable to the results other researchers obtained. Sludge expansion, accompanied with sludge morphology change from pseudomycelia to true mycelia, occurred during continuous treatment of wastewater. The true mycelia dominated sludge had a much higher water content and SVI value tha n that of the yeast purr cultures, although the two kinds of sludge had sim ilar oil removal performance. A mold, Geotrichum candidum, was isolated fro m the expanded sludge, and was suspected to be a reason for sludge expansio n. Addition of 0.3% sodium propionate into batch cultures degraded SVI valu e from around 100 to 60. In a continuous running. addition of 10 mg l(-1) s odium hypochlorite decreased SVI value from over 200 to below 100. The yeas t activity, however. was weakened to a large extent at the same time.