Study On The Technology Of Cultivating Chlorella As Aquatic Feed With Soy Sauce Wastewater

Soybean meal is one of the key components of animal feed.The annual consumption of soybean meal is about 75 million tons,and the import dependence is more than 80%.Therefore,it is an important challenge for the sustainable development of feed industry to construct the protein source of soybean meal reduction.Microalgae such as Chlorella sp.grow fast,have high protein content and balanced amino acid composition,which are potential protein resources.In this study,the soy sauce wastewater and Chlorella pyrenoidosa（NCU-12）were used as research materials.A production model linking soy sauce wastewater,Chlorella pyrenoidosa and aquaculture feed was established in order to reduce environmental pollution discharge and culture cost of Chlorella.This study analyzed soy sauce wastewater pretreatment,feed replacement ratio of C.pyrenoidosa,culture conditions,harvesting methods,and nutritional and anti-nutritional factors of C.pyrenoidosa.The main conclusions were as follows:（1）Pretreatment conditions of soy sauce wastewater:50%dilution and non-sterilization were the best pretreatment methods.The biomass of C.pyrenoidosa cultured for 7 days reached 0.684 g/L,and the utilization rates of COD,TN,TAN,and TP reached 95.66%,42.63%,42.21%and 57.70%,respectively.C.pyrenoidosa biomass harvested from soy sauce wastewater was high in protein（58.99%）and the optimal replacement ratio in experimental rangeis of Micropterus salmoides feed was25%.（2）Culture conditions:increasing light intensity（8000 Lux）and adding CO₂（1:1 gas-liquid ratio）significantly increased the yield of C.pyrenoidosa.After 5 days,the maximum biomass reached 1.98 g/L,and the utilization rates of COD,TN,TAN,and TP were 96.88%,91.59%,93.86%and 80.04%,respectively.（3）Harvesting methods:the optimal flocculation pH of chitosan for C.pyrenoidosa was 8.5;The relationship between the optimal proportion of chitosan and the harvesting concentration of C.pyrenoidosa（0.63-2.53 g/L）was determined.Under the optimal flocculation ratio,C.pyrenoidosa floc settled well and the initial dehydration rate was higher than 75%.The effect of flocculation on crude proteins,lipids,and polysaccharides of biomass was less than 10.5%compared with centrifugal harvesting.（4）In the nutritional analysis,C.pyrenoidosa（NCU-12）contained balanced nutrient composition,amino acid and fatty acid spectrum distribution,which were conducive to the growth of fish;Compared with soybean meal,C.pyrenoidosa（NCU-12）contained a lower crude fiber content（3.38%）.There were two main nutrition deficiencies of C.pyrenoidosa（NCU-12）:one was the relative protein molecular weight distribution of more polymer proteins,more than 50%molecular weight greater than 40 k Da;Second,calcium（0.285%）was seriously deficient,and the ratio of calcium to phosphorus（0.14）was low.（5）In the analysis of antinutritional factors,α-amylase inhibitory factor was not detected in C.pyrenoidosa（NCU-12）,and the contents of trypsin inhibitory factor（0.52 mg/g）and phytic acid（0.62 mg/g）were significantly lower than those in soybean meal,and in a favorable range;The contents of total saponins,lectins and tannins in C.pyrenoidosa（NCU-12）were 40.68 mg/g,2⁴ titer and 2.66 mg/g,respectively,which were significantly higher than those in soybean meal and affected the palatability of feed and dietary digestion problems.