Wastewater discharged from vermicelli factories has a high concentration of starch and protein, with COD and BOD ranging from 30 000 to 60 000 mg/liter and 24 000 to 44 000 mg/liter, respectively. Because of these high concentrations, the wastewater is considered to be heavy and particulated. Wild yeasts were screened and applied to treat the vermicelli wastewater.
Ten isolated strains having the ability of starch degradation, protein hydrolysis and lactic acid tolerance were screened. Treatment of wastewater from a vermicelli factory, with C:N:P ratio adjusted, using isolated yeasts in batch culture showed that two strains could reduce soluble COD by 79–83%. When the hydraulic retention time and solid retention time were kept at 7·14 days, using a semi-continuous culture, the solid loading was 0·48 g COD/gMLSS per day, volumetric loading was 1·03 kg COD/m3 per day, and the COD removal was about 92%.