# Digestate Management and Processing Practices: A Review
## 2 Regulations and Standards for Manure Management in the EU  
Due to its physicochemical properties, manure is widely used as a soil improver and organic fertilizer. It improves soil's physical and chemical properties due to its high buffer and cation exchange capacity, and the content of essential mineral nutrients such as inorganic N in the form of ammonium (NH3), carbon (C), P, and S, and metals such as zinc and copper. What is more important, manure substantially increases soil C stocks and stabilizes OM content and C/N ratios in a more stable fraction over the long term which is the main driver for soil microbial diversity, enzyme activity, and the abundance of soil fauna. However, the chemical composition of manure varies based on animal feed, species, and processing method and it determines the fertilizing effects of manure and its influence on soil biodiversity. The most common practice is returning manure nutrients to fields with little or no processing which is mostly related to insufficient manure storage capacities. Application of unprocessed manure, meaning introducing pathogens and antibiotic-resistant genes into the soil, can harm soil biota and reduce the diversity of dung fauna [18]. When not handled properly, manure can cause adverse environmental impacts such as soil compacting following grazing activities, water, and soil pollution, greenhouse gas and ammonia emissions into the atmosphere, etc., [19]. Within EU-27 countries, it is estimated that 1.4 billion tons of manure from farmed animals were produced annually in the period from 2016 to 2019. More than 75% of produced manure originates from cattle, whereas pigs and chickens produce around 12% each. Due to the increasing demand for meat and animal-based products, manure is increasingly generated in highly intensive farming systems [18]. As a result, the livestock sector is considered one of the leading sources of environmental pollution which is the reason why manure management is a central issue in a series of international protocols, EU directives, and national regulations [20]. Since the second half of the 21 st century, particular awareness of the effects of manure on the environment has awakened the EU community, as well as national and regional authority bodies, to implement specific regulations and limitations on manure management activities to regulate and mitigate these impacts. Currently, manure is not regulated under one single EU regulation or directive, but various directives, regulations, and laws for its management and quality are implemented in the EU Member States [18]. Among the main documents related to manure issues at the European level are the Nitrates Directive, IPPC Directive, the NEC Directive, the Water Framework Directive, and the Guidance document on ammonia emissions from agricultural sources [21]. The Nitrates Directive is the most critical EU tool for the management of manure and its impact on the environment which aims to protect water quality by designating nutrient vulnerable zones and proposing the Member States adopt Good Agricultural Practices in high-risk zones to prevent eutrophication [22]. A limit of 170 kg ha\({}^{-1}\) year\({}^{-1}\) of N from organic manure is set by the Directive, whereas some Member States provide farmers with exemptions if manure disposal does not harm ecosystems [23]. The IPPC (Integrated Pollution Prevention and Control) Directive refers to the minimizing of pollution from various agricultural activities [24] and advises the manure management of large animal farms. The NEC (National Emissions Ceiling) Directive sets ceilings for every Member State for the whole emissions of the four chemical pollutants (SO\({}_{2}\), NOx, VOCs, and NH\({}_{3}\)) which are the main agents that cause eutrophication, acidification, and ground-level ozone pollution, but leaves it largely to the Member States to set their ceilings [25].