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Zero hunger

How to close nutrient cycles for future Zero Hunger (PICO and Communication session)

EUROSOIL2020CONT-1510

ADDRESSING THE NITROGEN SURPLUS IN AGRICULTURE - NITRIFICATION AND DISTILLATION OF SOURCE-SEPARATED LIVESTOCK URINE

Philipp Markus^{* 1, 2}, Valentin Faust^{1, 2}, Nadège de Chambrier³, Magdalena Kurrig⁴, Kai M. Udert^{1, 2}

¹Institute of Environmental Engineering, ETH Zürich, Zürich, ²Process Engineering, Eawag, ³Vuna GmbH, Dübendorf, ⁴Institute of Agricultural Sciences, ETH Zürich, Zürich, Switzerland

Content: The global nitrogen cycle, mainly driven by food production, has left the safe planetary boundaries. Therefore, nitrogen discharge to the environment must be strongly reduced. A popular alternative to industrial fertilizers is the recycling of nitrogen from manure. However, three major problems remain. Firstly, manure production and fertilizer needs are often not at the same location. Secondly, nutrient demand for soils is usually seasonal whereas manure is produced throughout the year. And thirdly, manure is of low quality as it loses up to 50% of nitrogen due to ammonia volatilization and contains pharmaceuticals, pathogens and heavy metals.

In this contribution, we tested a new approach to address the manure challenge. Inspired by the treatment of source-separated human urine, we used source separated cattle urine to produce a concentrated stable fertilizer of high quality. Although, it is not common to separate urine and feces in animal farming, several separation systems have already been developed. The two process steps tested in the lab were nitrification and distillation. For nitrification, we continuously dosed the urine to a 12 L stirred tank reactor. The reactors were inoculated with activated sludge from human urine treatment. The pH was kept constant by controlling the influent. While in human urine 50% of the ammonia can be oxidized to nitrate, the higher availability of alkalinity in stored livestock urine allowed converting 95% of the ammonia to nitrate. The pH drop during nitrification from 8.5 to 6.4 prevents NH₃ losses from the final product. The mean nitrification rate was 197 mgN/l/d. Afterwards the stored effluent was concentrated up to 10% of the original volume in a lab-scale distillation reactor producing a pasteurized concentrated liquid fertilizer in which all nutrients are recovered. Overall ammonia losses were below the measurement error of 5%. To further improve the quality of the effluent, a granular active carbon filter should be included in the process before distillation to remove hazardous substances such as pharmaceuticals. The complete proposed treatment chain is shown in Fig. 1. Although the final product is mainly a nitrogen fertilizer, it also contains other essential macro- and micronutrients such as phosphorus, potassium, calcium, iron and zinc. Because it is free of pathogens and odorless, it is easy and safe to handle, transport and store. The concentrate therefore allows adequate spatial and seasonal application according to the nutrient demand of the soils. The separate collection of urine at the source and its on-site treatment has the potential to significantly reduce the nitrogen emissions from livestock farming.

Figure:

Disclosure of Interest: P. Markus: None Declared, V. Faust: None Declared, N. de Chambrier Conflict with: Vuna GmbH (an Eawag spin-off) uses a similar process for the treatment of human urine, M. Kurrig: None Declared, K. Udert Conflict with: Vuna GmbH (an Eawag spin-off) uses a similar process for the treatment of human urine

Keywords: agriculture, circular economy, manure management, nitrification, nutrient recovery, urine separation