## 1 Introduction  
The strong increase in intensive livestock production has led to severe environmental problems due, essentially, to the management of the large amounts of slurry (liquid manure) resulting from this activity. The storage of animal manure is a major source of ammonia (NH\({}_{3}\)), nitrous oxide (N\({}_{2}\)O), carbon dioxide (CO\({}_{2}\)) and methane (CH\({}_{4}\)) emissions, all with important impacts on climate change, acid rain and ozone formation in the troposphere [1; 2; 3]. Regarding the Directive 2016/2284 of the European Union, from 2030, the national NH\({}_{3}\) emission ceilings should be reduced at all stages of animal manure management, namely: 10% for feeding, 20% for housing, 40% for storage and 30% for soil application.  
At storage stage, the NH\({}_{3}\) and CO\({}_{2}\) are originated by decomposition of urea present in slurry and the main characteristics that control NH\({}_{3}\) volatilisation are temperature, concentration of total ammoniacal N, pH and air velocity on slurry surface [4; 5]. The majority of inorganic N present in slurry is in the form of ammonium (NH\({}_{4}\)+). Nitrification can be performed by autotrophic and heterotrophic organisms under aerobic conditions whereas denitrification is the stepwise reduction of nitrate (NO\({}_{3}\)\({}^{-}\)) to N\({}_{2}\) under anaerobic conditions [6]. Since the bulk of stored slurry is predominantly anaerobic with little chance for NH\({}_{4}\)\({}^{+}\) to be nitrified, N\({}_{2}\)O and N\({}_{2}\) through nitrification and denitrification are considered insignificant [3]. The availability of NH\({}_{4}\)\({}^{+}\) and NO\({}_{3}\)\({}^{-}\) are primary requirements for nitrification and denitrification processes, respectively but also the availability of easily degradable carbon influences these processes [6]. The anaerobic decomposition of the organic matter by methanogenic bacteria leads to CH\({}_{4}\) and CO\({}_{2}\) emissions. Organic matter is considered a major limiting factor for CH\({}_{4}\) production, once anaerbiosis is established, and CH\({}_{4}\) emissions are closely related to manure temperature [7]. Relative to stored slurry, management practices such as storage duration, agitation or mixing and emptying of storage tanks plays an important role in CH\({}_{4}\) emissions during storage [8].  
Several practices aimed at reducing the environmental impact of slurry storage, and the techniques used, have been pointed out as an efficient solution to decrease gaseous emissions, namely: diet manipulation, design of the storage tank, fitting a covering material on the slurry store, application of additives to the slurries, for biodegradation of organic materials, lowering pH, bind/convert NH\({}_{4}\)+/NH\({}_{3}\), down urea hydrolysis and inhibition of nitrification [3; 7; 8; 9; 10; 11]. Additionally, the solid-liquid separation of pig slurry has been reported as a good technique for manure management at farm scale, modifying the main characteristics of derived fractions, reducing the costs of storage and the environmental impacts [12; 13; 14; 15]. The derived liquid fraction could be stored prior to soil application whereas the solid fraction could be composted and exported out of the farm [12]. Our hypothesis was that the application of adsorbing additives, like biochar and/or clinoptilolite, will modify initial slurry characteristics and consequently influence gaseous emission patterns during storage and after field application. Therefore, the treatment of slurry-derived liquid fraction either by biochar and/or clinoptilolite will minimise N (NH\({}_{3}\) + N\({}_{2}\)O) emissions, preserve fertiliser value and consequently increase the availability of N for crop utilisation after soil application.  
The aim of this study was to evaluate the effects of biochar and clinoptilolite on composition and emission of NH\({}_{3}\), N\({}_{2}\)O, CO\({}_{2}\) and CH\({}_{4}\) during the storage of mechanical separated liquid fraction of pig slurry.