Department of Chemical Engineering, Tshinghua University, 100000 Beijing, China.
J Dairy Sci. 2011 Aug;94(8):3778-86. doi: 10.3168/jds.2010-4129.
It is not uncommon that a significant amount of milk from milking operations is discharged to manure digesters on dairy farms. To understand the effect of milk on the digester performance, experiments using batch digesters (500-mL flasks) were carried out in this study to co-digest milk and dairy manure at different milk levels for biogas production and pollutant reduction, and a total of 8 treatments were examined [i.e., control (without milk) and 1, 3, 5, 7, 9, 14, and 19% milk additions]. The temperature for all digesters was maintained at 37±0.5°C throughout the experimental period, which was 28 d. The results showed that co-digesting milk with dairy manure could increase biogas productivity, with the percent cumulative biogas volume increased by 5.6, 16.3, 26.5, 40.8, 50.2, 79.9, and 103.8%, as compared with the control, for milk addition of 1, 3, 5, 7, 9, 14, and 19% (vol/vol), respectively. However, the CH(4) content in the biogas decreased slightly as the milk content increased (from 66.5% for the control to 63.5% for 19% milk treatment), implying that the added milk could promote CO(2) production. To avoid that, the milk content in the manure should be controlled below 3%. A linear relationship for the total biogas volume produced with the milk content in the manure was revealed, with a correlation coefficient of 0.99. An improved removal efficiency of chemical oxygen demand was observed for milk-treated digesters. Good linear regressions between the total biogas production and the percent chemical oxygen demand decrease and the substrate carbon/nitrogen ratio were also obtained (correlation coefficients: 0.93 and 0.99, respectively). Besides, co-digestion of dairy manure and milk was found to improve substrate solids breakdown, but had little effect on percent volatile fatty acid decrease. In summary, the waste milk co-digested with dairy manure may not cause negative effects on anaerobic digester performance.
在奶牛场，从挤奶操作中排出大量牛奶到粪污消化器中是很常见的。为了了解牛奶对消化器性能的影响，本研究使用批量消化器（500 毫升瓶）进行了实验，以在不同牛奶水平下共消化牛奶和奶牛粪便以生产沼气和减少污染物，并检查了总共 8 种处理方法[即对照（无牛奶）和 1%、3%、5%、7%、9%、14%和 19%牛奶添加]。在整个实验期间，所有消化器的温度均保持在 37±0.5°C，持续 28 天。结果表明，与对照相比，共消化牛奶和奶牛粪便可以增加沼气生产力，当牛奶添加量分别为 1%、3%、5%、7%、9%、14%和 19%（体积/体积）时，累积沼气体积百分比分别增加了 5.6%、16.3%、26.5%、40.8%、50.2%、79.9%和 103.8%。然而，随着牛奶含量的增加，沼气中的 CH4 含量略有下降（从对照的 66.5%下降到 19%牛奶处理的 63.5%），这意味着添加的牛奶可以促进 CO2 的产生。为了避免这种情况，粪便中的牛奶含量应控制在 3%以下。显示了总沼气产量与粪便中牛奶含量之间的线性关系，相关系数为 0.99。观察到牛奶处理消化器的化学需氧量去除效率得到改善。还获得了总沼气产量与化学需氧量减少百分比和底物碳/氮比之间的良好线性回归（相关系数分别为 0.93 和 0.99）。此外，还发现奶牛粪便和牛奶的共消化可以改善基质固体分解，但对挥发性脂肪酸减少百分比影响不大。总之，与奶牛粪便共消化的废牛奶可能不会对厌氧消化器的性能产生负面影响。
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