Production Of Lactic Acid Integrated With Fishmeal Wastewater Treatment By Rhizopus Oryzae

Production of lactic acid integrated with fishmeal wastewater treatment by Rhizopus oryzae AS 3.254 and AS 3.41 was investigated in this thesis. The aim was to find out cheaper raw material for lactic acid production as well as to treat the fishmeal wastewater.The investigation mainly focused on the effect of seed age, inoculation, initial pH, rotation, concentration of fishmeal wastewater, compositions of fermentation medium and the ratio of carbon to nitrogen on lactic acid production, COD reduction and biomass formation. The optimal seed age, inoculation and rotation were 10 h, 6% and 150 r/min, respectively. Initial pH without addition of CaCO₃ could lead to the lower pH 3.2 at 48 h incubation time and the lactic acid production was only 5 g/L. The optimal culture medium was as following: The concentration of fishmeal wastewater termed as COD was about 5 000 mg/L. The addition of glucose was 30 g/ L for Rhizopus oryzae AS 3.254 and 40 g/L for Rhizopus oryzae AS 3.41, respectively. When soluble starch was used as carbon source, Rhizopus oryzae AS 3.254 could utilize it to produce lactic acid. However, no lactic acid was produced by Rhizopus oryzae AS 3.41 under the addition of soluble starch.Rhizopus oryzae AS 3.254 could utilized the organic nitrogen in fishmeal wastewater. The total nitrogen reduced 48% during the first 24 h. Then removal rate gradually increased slowly and could reach 55% in 72 h. When using different nitrogen source, the yield of lactic acid of Rhizopus oryzae AS 3.254 were higher than that of Rhizopus oryzae AS 3.41. The maximal yield of lactic acid of two strains was 0.45 g/g and 0.66 g/g, respectively. From the view of the cost and the amount of lactic acid, yeast extract and peptone were not suitable for two strains to produce lactic acid as the nitrogen source.The effect of salt concentration on lactic acid production and biomass formation was also investigated. Both lactic acid production and biomass formation gradually decreased with the increase of salinity. The inhibition concentration of NaCl to Rhizopus oryzae AS 3.254 and Rhizopus oryzae AS 3.41 were 12 g/L and 16 g/L, respectively.