Maurer & Müller (2012) found ammonia nitrogen (NH4-N) losses of 77 and 91% during the drying of two types of separtion solids of digestate. The loss of total N for the two types were 63 and 70%, respectively, which indicates that losses of organic bound N was low. Almost all N in the dried products were organic bound. The feedstock of the biogas plant was a mixture of residues from food and feed production, pig, and cattle slurries as well as energy plants.

The losses of NH4-N during drying can be reduced to 17-27% by acidifying the input material. However, in that case a simultaneous C loss of about 7-8% has been observed, equal to about one fifth of the organic matter.

Read more about Thermal drying.

Mechanical Vapor Recompression (MVR) is an energy saving evaporative concentration technology, which reduces evaporation energy use by 90% or even more. MVR uses energy recovered from the condensate to create a pure liquid distillate and a concentrated product. The technology is proven in food processing and waste water treatment, and is being piloted in farming in an adapted configuration by the SYNECO project in Malta at the St Rita Farm, Triq San Stiefnu, Qormi, Malta. Data about the environmental effects and costs will be produced by the SYNECO project and the technology description updated successively.

The price of nitrogen fertilisers has increased during 2021 due to increasing energy prices, and the Russian attack on Ukraine by end of February 2022 has only worsened the situation. The result is that nitrogen fertilisers in April 2022 is about three times more expensive than at the beginning of 2021. Other mineral fertiliser nutrients, such as P and potassium (K) has increased dramatically in the same period due to the increasing energy prices. This situation raises the question whether we could utilise the nutrient in livestock manures better? Currently, around half of the nutrients in livestock manures are lost. A higher Nutrient Use Efficiency (NUE) of livestock manures would mean reduced environmental and climate impact of farming as well as less dependency on mineral fertilisers.

Agro Technology Atlas comprises scientifically validated descriptions of about 70 technologies for reducing the climate impact and environmental load of farming, and securing an optimal resource economy in primary food production. Among these are especially three groups of technologies that contributes to increased NUE in fertilisation with livestock manures*. These are:

• Slurry separation technologies, that are relatively cheap manure processing technologies with which slurry is separated into separation liquids with a high NUE of N and phosphorus (P), while the organic bound nutrients with low NUE are in the separation solids, that can be exported and for instance used as a valuable influent in an aerobic digestion process. Fertilisation with separation liquids rather than raw slurry would typically mean that the NUE of N is increased from 75% to 95%. In the case of P, the separation liquids contain a higher share of water-soluble P, and the total amount of P needed for fertilisation on a farm can be adjusted via the separation strength. Separation by use of a screw press will typically ensure that the amount of P in the separation liquids is complying with the needs for P fertilisation, and the P field and farm gate balances can thus in this way be eliminated or reduced to a minimum. 
• Anaerobic digestion is due to the fermentation processes degrading a share of the organic matter in the influent biomass, depending on the digestibility of this as well as the retention time and the process temperature among other factors. Also, the pH would typically be increased with 0.5 - 1 units during the process, which also has some impact. Generally speaking, anaerobic digestion increases the NUE for N with about 15-20%, whereas the NUE for phosphorus increases with much more, typically 50-60%. 
• Slurry acidification comprise three sub-technologies, namely in-field, in-tank and in-house acidification with each of them having characteristics that makes them most suited in specific situations. In-field and in-storage acidification will in general terms save the volatilisation of 15 kg N per ha via ammonia emissions, while this figure is about 30 kg per ha for in-house acidification because it  also reduces ammonia volatilisation from stables and stores, besides from the field spreading. These figures are given under the assumption that fertilisation happen with a dose of 30 tonnes of slurry per ha. Furthermore, the adjustment of the pH results in a higher availability of P in the acidified slurry, wherefore acidified slurry is an effective fertiliser where a high effect of the P fertiliser is required, such as in case of start fertilisation of maize.

A proverb says that "An accident rarely comes alone.". It is in this case fair to turn this around and say that "A good agro-environmental technology has several advantages." and all three mentioned technologies provides more benefits than the basis for an increased NUE of livestock manures. For example, an aerobic digestion is also providing additional energy production, and slurry acidification, especially in-house acidification, contributes to reduce greenhouse gas emissions from livestock farming.  

Please find the scientific substantiation for the above in https://www.agrotechnologyatlas.eu. For slurry acidification, see under "Other housing systems", "Storage systems" and "Spreading and outdoor handling".

* Whereas the NUE is not a standardised and fixed term, the used definition in this news post is that it is a percentage describing the share of the fertilised nutrient that is taken up by the crop. A NUE of 90% for nitrogen (N) is for example corresponding to a crop uptake of 90 kg N in case the crop is fertilised with 100 kg N.

The 'CNP flows interactive model' is for estimating and illustrating combined effects in the entire manure / crop / feed loop of on-farm measures related to CNP management at farms or in regions, such as the impacts of employment of various livestock manure processing technology. The tool is per default illustrating a NVZ baseline scenario, assuming livestok farming situated in a Nitrate Vulnerable Zone with the maximally possible number of animals with repect to the 170 kg N limit per ha for bringing livestock manure to the fields for fertilising, as given by the Nitrates Directive.

Read more about the CNP flows interactive model in this article at ResearchGate.

The 'CNP flows interative model' tool is developed by Organe Institute and made available at AgroTechnologyATLAS here.

The description of "Composting of solid livestock manure or fibre fractions of liquid livestock manure" has been updated with additional literature references. Composting means a massive loss of 30-63% of carbon (C) in the form of carbon dioxide and methane greenhouse gases, a massive loss of nitrogen (N) of 37-60% via leaching and runoff and emissions of ammonia and laughing gas, and massive losses of phosphorus (P) of 23-39% via runoff and leaching. The fertilising value of compost is low and results in poor crop yields. The cost of composting is high. On the positive side is that the resulting material is less voluminous to transport and is a stable products being free of pathogens and weed seeds.

Read more about Composting.

Lamkaddam et al. (2021) found that the Active NS product gave a reduction of ammonia emission (ranging from 17.6% to 38.3%), systematically obtained at mid fattening cycle, where the concentration of Active NS in the slurry was between 40 and 45 g m−3. The results were obtained in a one year full scale study comprising two naturally ventilated identical houses for fatteners, each wiht 18 pens. The retention of ammonium into Active NS structure caused an increase of total nitrogen in the slurry of 19.6% compared to the control barn. Christiansen (2016), found in a one month field study similar ammonia emission reduction effect, and meaured in addition 54% lower odour in the stable where Active NS was used. Earlier, AgroTech (2008) did not find either ammonia emission reduction, odour reduction or change of the homogenity of the slurry when testing addition of Siolit, which is a silicon-containing rock mineral derived from volcanic rocks (zeolite). This sugests differences between ammonia emission and odour reduction effects of various commercial IEbA's. Read more about IEbA and Active NS under ATLAS of technologies - Additives and pre/1st treatments here - https://www.agrotechnologyatlas.eu/techdescs?techgroup=500.

The ALFAM2 project has developed a model for estimation of ammonia volatilisation during field spreading slurry and other liquid manures. The model is interactive and calculates the ammonia losses on basis of a set of pre-conditions, for instance the slurry type and the spreading technology.
The model, in the form of an EXCEL file is accessible from the AgroTechnologyATLAS.

AgroTechnologyATLAS is for sharing validated information, data and tools about technologies for reducing the climate impact and environmental load of farming, including the organic material, livestock manure and biomass it is handling. New information, material and data about already described or new technologies or biomass is welcomed. Contact us if you wish to become content editor.

Different studies have clarified that slurry acidification has an impact on nitrification inhibition. A significant effect is seen in soils with a low buffer capacity, where acidified slurry in some cases has performed better than some NI as DCD. More information is provided under the relevant technology descriptions for slurry acidification - Other housing Systems (https://www.agrotechnologyatlas.eu/techdescs?techgroup=300), Storage Systems (https://www.agrotechnologyatlas.eu/techdescs?techgroup=900), and Spreading and Outdoor Systems (https://www.agrotechnologyatlas.eu/techdescs?techgroup=1000)

VERA, the collaboration between Denmark, The Netherlands, Flanders and Germany for testing and verifying environmental technologies within the agricultural sector, has issued a Verification Statement for a Heat Exchanger for broiler production with 28% ammonia emmission reduction effect. The verified Heat Exchanger is Agro Clima unit (ACU) Clima+ 200, type 2.5 from Rokkedal Energy. No effect was found on odour emissions. Find more about the technology under Other Housing Systems - http://agrotechnologyatlas.eu/techdescs?techgroup=300.