(517i) Optimal Selection and Location of Nitrogen Recovery Systems for Intensive Pig Farming

Farming is an industry in current raise to meet the increasing demand of meat products due to the increase in the life standard of large population sectors. Spain is one of the main producers of swine products, accounting more than 25 million of pigs, representing 20% of animals of the pig farming industry in Europe. Within Spain, Castilla y León shows a farming scenario in which, while cattle farming is mainly extensive, with a low density of animals and a low stocking rate of organic waste per area unit, intensive swine is carried out in facilities with a high density of animals where manure must be properly managed due to the high rate and spatial concentration of the organic waste generated. However, Castilla y León accounts for 4 million pigs located in intensive breeding facilities. Intensive farming practices are associated to environmental and public health issues including soil degradation, atmospheric pollution associated with the emission of ammonia, and the runoff of nitrogen and phosphorus to waterbodies, resulting in nutrient pollution and eutrophication [1]. These effects are reflected in the fact that 31.3% of towns in Castilla y León [2] have nitrate concentrations in water over the threshold stipulated by the European Union (50 mg/L), most of them related with nitrogen releases from the incorrect management of manure fertilizer application in crops.

To improve the current manure management practices, which actually are limited to the application of manure in the lands around the facilities, or its treatment in ponds, the installation and allocation of nitrogen recovery process are evaluated in this work. The main drivers for operating costs of manure processing systems are the economies of scale and the potential coupling of nitrogen recovery processes with energy production systems, such as anaerobic digestion with biogas upgrading systems in form of electricity or bio-methane, providing additional income sources to the system. Nevertheless, the treatment of several farms has to be centralized in the same facility to reach processing capacities with size enough to be cost-effective, although transportation costs of organic waste as well as the associated carbon footprint, can negatively impact the operation of the treatment systems. The model proposed is divided into two levels. In a first level, the available processes for nitrogen recovery from swine waste are evaluated though mathematical modelling. The optimal processes and operating conditions are determined for different sizes of swine breeding facilities [3, 4]. In the second level, surrogate models for the capital and operating costs as function of the processing capacity are developed from the results obtained in the previous stage. These surrogate models are embedded in a supply chain problem determining the optimal allocations of the facilities and flow of waste from the livestock facilities to the processing centers [5]. The final goal of the work is to assess the economic feasibility of the implementation of a cooperative network for swine waste processing

The combination of real farms data regarding size and location with the optimization model developed for the selection and allocation of nitrogen recovery systems allows us to work with a real problem, identifying and addressing some of the challenges to mitigate nutrient pollution associated intensive swine farming, reaching the most cost-effective solution feasible for the region studied. In addition, the formulation developed in the present work can be easily adapted to other regions with available data for farming facilities.

References

[1] Backus, G. B. C., Van Wagenberg, C. P. A., Verdoes, N., 1998. Environmental impact of pig meat production. Meat science, 49, S65-S72.

[2] Consejo Económico y Social de Castilla y León, 2019. Informe Previo sobre el Proyecto de Decreto por el que se designan las Zonas Vulnerables a la contaminación de las aguas por nitratos procedentes de fuentes de origen agrícola y ganadero, y se aprueba el Código de Buenas Prácticas Agrarias.

[3] Huang, H., Xiao, D., Liu, J., Hou, L., Ding, L., 2015. Recovery and removal of nutrients from swine wastewater by using a novel integrated reactor for struvite decomposition and recycling. Scientific reports, 5, 10183.

[4] Liu, Y., Kwag, J. H., Kim, J. H., Ra, C., 2011. Recovery of nitrogen and phosphorus by struvite crystallization from swine wastewater. Desalination, 277(1-3), 364-369.

[5] Taifouris, M. R., & Martin, M. (2018). Multiscale scheme for the optimal use of residues for the production of biogas across Castile and Leon. Journal of Cleaner Production, 185, 239-251.