Civil Engineering Department, School of Engineering & Computer Science, University of the Pacific, 3601 Pacific Avenue, Stockton, CA 95211, USA.
J Environ Manage. 2013 Oct 15;128:233-42. doi: 10.1016/j.jenvman.2013.04.060. Epub 2013 Jun 7.
Anaerobic digestion of manure and other agricultural waste streams with subsequent energy production can result in more sustainable dairy operations; however, importation of digester feedstocks onto dairy farms alters previously established carbon, nutrient, and salinity mass balances. Salt and nutrient mass balance must be maintained to avoid groundwater contamination and salination. To better understand salt and nutrient contributions of imported methane-producing substrates, a mass balance for a full-scale dairy biomass energy project was developed for solids, carbon, nitrogen, sulfur, phosphorus, chloride, and potassium. Digester feedstocks, consisting of thickened manure flush-water slurry, screened manure solids, sudan grass silage, and feed-waste, were tracked separately in the mass balance. The error in mass balance closure for most elements was less than 5%. Manure contributed 69.2% of influent dry matter while contributing 77.7% of nitrogen, 90.9% of sulfur, and 73.4% of phosphorus. Sudan grass silage contributed high quantities of chloride and potassium, 33.3% and 43.4%, respectively, relative to the dry matter contribution of 22.3%. Five potential off-site co-digestates (egg waste, grape pomace, milk waste, pasta waste, whey wastewater) were evaluated for anaerobic digestion based on salt and nutrient content in addition to bio-methane potential. Egg waste and wine grape pomace appeared the most promising co-digestates due to their high methane potentials relative to bulk volume. Increasing power production from the current rate of 369 kW to the design value of 710 kW would require co-digestion with either 26800 L d(-1) egg waste or 60900 kg d(-1) grape pomace. However, importation of egg waste would more than double nitrogen loading, resulting in an increase of 172% above the baseline while co-digestion with grape pomace would increase potassium by 279%. Careful selection of imported co-digestates and management of digester effluent is required to manage salt and nutrient mass loadings and reduce groundwater impacts.
牛粪和其他农业废物的厌氧消化，以及随后的能源生产，可以使奶牛场的运营更加可持续；然而，将消化器的饲料原料引入奶牛场会改变以前建立的碳、养分和盐度质量平衡。为了避免地下水污染和盐渍化，必须保持盐分和养分的质量平衡。为了更好地了解进口产甲烷底物的盐分和养分贡献，对一个全规模奶牛生物质能源项目进行了全面的固体、碳、氮、硫、磷、氯和钾的质量平衡。在质量平衡中，分别跟踪了由浓缩粪水冲洗泥浆、筛选的粪固体、苏丹草青贮和饲料废物组成的消化器进料。大多数元素的质量平衡闭合误差小于 5%。粪肥占进水干物质的 69.2%，但氮、硫和磷的含量分别为 77.7%、90.9%和 73.4%。苏丹草青贮对氯和钾的贡献很高，分别为 33.3%和 43.4%，而其干物质的贡献仅为 22.3%。根据盐度和养分含量以及生物甲烷潜力，对五种潜在的场外共消化物（蛋废物、葡萄渣、奶废物、面食废物、乳清废水）进行了厌氧消化评估。由于其相对于体积的高甲烷潜力，蛋废物和酿酒葡萄渣似乎是最有前途的共消化物。要将目前 369kW 的发电能力提高到设计值 710kW，需要与 26800L/d 的蛋废物或 60900kg/d 的葡萄渣共消化。然而，进口蛋废物会使氮负荷增加一倍以上，比基线增加 172%，而与葡萄渣共消化会使钾增加 279%。需要仔细选择进口共消化物，并管理消化器流出物，以管理盐分和养分的质量负荷，减少对地下水的影响。
