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牲畜粪污沼液培养微藻工艺参数优化

Optimization of the process parameters for microalgae cultivation using livestock manure biogas slurry

  • 摘要: 该研究针对沼气工程副产物——沼液富含氮、磷,易引起二次污染的问题,以及沼液培养微藻过程多因素交互作用研究不足及培养温度、沼液稀释比例均较高的问题,基于4因素5水平二次正交旋转中心组合试验设计方法,采用牛粪和猪粪2种沼液,探索沼液添加比、光照强度、CO2浓度和温度对普通小球藻(Chlorella sp.,FACHB-1554)和肥壮蹄形藻(Kirchneriella obesa,FACHB-2104)的生长及养分去除的交互影响,并优化工艺条件,探寻降低培养温度、提高沼液添加比的可行性。结果表明,FACHB-1554和FACHB-2104生物量干质量均随着沼液添加比的增加先增加后减少,FACHB-1554对NH3-N含量更高的猪粪沼液的耐受能力相对更强;CO2能显著促进2种微藻的生长,且随着CO2浓度的增加,FACHB-1554生物量干质量先增加后降低,而FACHB-2104生物量干质量则持续增加;对于2种微藻生长,沼液添加比比较CO2浓度影响更强,光照强度和温度则相对较弱,而对于NH3-N和TP去除率,均是温度影响强于沼液添加比,光照强度和CO2浓度则相对较弱,且提高沼液添加比至25%~30%和降低培养温度至18 ℃实际可行;猪粪沼液培养FACHB-1554和牛粪沼液培养FACHB-2104的最优工艺条件分别为:沼液添加比为20%和10%、光照强度均为7000 lx、CO2浓度为10%和12.50%、温度为22 ℃和24 ℃,FACHB-1554和FACHB-2104最大生物量干质量分别达到0.832 g/L和0.648 g/L,NH3-N去除率分别达到86.71%和77.14%,TP去除率分别达到89.31%和78.23%。研究可为沼液低成本培养微藻的深入研究提供基础依据,促进沼液高值化利用及微藻产业化发展。

     

    Abstract: A large amount of biogas slurry rich in nutrients such as nitrogen and phosphorus is generated as a by-product with the rapid development of large-scale biogas projects and the biogas power generation industry, which will cause secondary pollution to the environment if not effectively treated. Microalgae production featuring strong environmental adaptability, rapid growth, and high photosynthetic efficiency is one of the synergistic ways to deal with energy crises, organic wastewater purification, and carbon sequestration and emission reduction. However, relatively few studies have been conducted on the interaction between multiple factors in the process of culturing microalgae using biogas slurry. Meanwhile, the culture temperature is generally high, requiring heat preservation and warming measures, and the wastewater addition ratio is generally low. Two types of biogas slurry from the anaerobic digestion of pig dung and cow dung were used in this study and the interactive effects of biogas slurry addition ratio, light intensity, CO2 concentration, and culture temperature on the growth and nutrient removal of Chlorella sp. (FACHB-1554) and Kirchneriella obesa (FACHB-2104) were systematically studied based on a 4-factor, 5-level quadratic orthogonal rotating center combined experimental design to optimize the process conditions. The results showed that the dry mass of FACHB-1554 and FACHB-2104 increased with the increase of the culture duration, and first increased and then decreased with the increase of the biogas slurry addition ratio. FACHB-1554 was relatively more tolerant to pig manure biogas slurry with higher NH3-N content than FACHB-2104. The growths of two kinds of microalgae exposed to CO2 were significantly higher than those exposed to air under the same conditions. With the increase in CO2 concentration, the dry mass of FACHB-1554 first increased and then decreased, while the dry mass of FACHB-2104 continued to increase. For the growth of two kinds of microalgae, the effect of the biogas slurry addition ratio was stronger than that of CO2 concentration, while the effects of the light intensity and culture temperature were relatively weak. For NH3-N and TP removal rates, the effect of the culture temperature was stronger than that of the biogas slurry addition ratio, and the effects of the light intensity and CO2 concentration were relatively weak. The optimal process conditions of FACHB-1554 culture in pig dung biogas slurry and FACHB-2104culture in cow dung biogas slurry are as follows: biogas slurry addition ratios of 20% and 10%, light intensity of 7 000 lx, CO2 concentrations of 10% and 12.50%, and culture temperatures of 22 ℃ and 24 ℃. Under the optimal conditions, the maximum dry mass of FACHB-1554 and FACHB-2104 reached 0.832 g/L and 0.648 g/L. Meanwhile, the removal rates of NH3-N were 86.71% and 77.14% and the removal rates of TP were 89.31% and 78.23%, respectively. The dry mass of FACHB-1554 were 0.685 g/L and 0.796 g/L, respectively, under the pig dung biogas slurry addition ratio of 30% and the culture temperature of 18 ℃, and their nutrient removal rates were 80.97% and 78.13% for NH3-N and 82.11% and 82.34% for TP, respectively. In comparison, the dry mass of FACHB-2104 were 0.338 g/L and 0.613 g/L, respectively, under the cow dung biogas slurry addition ratio of 25% and the culture temperature of 18 ℃, and the nutrient removal rates were 70.92% and 67.72% for NH3-N and 71.65% and 71.92% for TP, respectively. Therefore, it was feasible to increase the addition ratio of biogas slurry and decrease the culture temperature, which provided the basic theoretical basis for further research on microalgae culture using biogas slurry and promoted the high-value utilization of biogas slurry and the low-cost development of microalgae industry.

     

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