## 2 General Aspects of Dry Anaerobic Digestion
### Technologies of Dry AD
The main disadvantage is that the biogas injectors can become clogged, and therefore they require careful maintenance. The Valorga technology is not  
Figure 5: The reactor that provides the Dranco process. Figure 6: The reactor that provides the Kompogas process. suitable for relatively moist waste with a TS concentration lower than 20%, due to the probability of solid particles accumulating in the bottom of the reactor and clogging the injectors [22; 81]. Biogas production for Valorga reactors is between 220 and 270 mL/g of municipal waste, which corresponds to 80-160 mL/g of wet substance [1]. The reactor that provides the Strabag process is shown in Figure 8.  
One of the other popular types of reactors is the percolation reactors, and the most common type is Biocel [15]. Batch systems are the simplest and cheapest systems. Their main disadvantages are large areas, lower biogas output due to the process of percolation through channel formation, and clogging [22; 82]. Biocel plants need ten times more area than continuous systems [82]. Batch systems are loaded once by substrate with a TS concentration of 30 to 40% with or without additions [15; 22; 83]. According to the Board, the process is stable at 25 to 35% of TS output [13]. The process is carried out in concrete reactors with a perforated floor in mesophilic conditions at a temperature from 35 to 40 \({}^{\circ}\)C [13; 22; 83]. The retention time of Biocel's reactors is between 15 and 21 days [83]. Figure 8: The reactor that provides the Strabag process. Figure 7: The reactor that provides the Strabag process. Although Biocel reactors are simple \"boxes\", they can provide from 50 to 100 times more biogas than landfills [22]. The higher efficiency is related to the fact that percolate is continuously recirculating, which promotes mixing of nutrients, acids, and moisture. In addition, periodic systems are more capable of operating at higher temperatures than those that are characteristic of landfills [15; 22]. The main disadvantage of such reactors is the unevenness of gas output and biomass instability. In particular, this is due to the \"substrate\" and channels clogging, which causes problems with percolation and uneven distribution of moisture. This disadvantage is eliminated by limiting the height of the substrate, i.e., up to 4 m, and by partially mixing the substrate with a filler [13; 22; 83]. There is also a problem of lack of contact between bacteria and substrate. Such an effect is observed in studies with a TS concentration of more than 35% [12]. Reactors are explosive until opening, and therefore it is necessary to provide proper safety [22]. Investment costs are about 40% lower as compared with continuous-mode technologies [84]. As described earlier, the Biocel technology needs ten times more area than a continuous process because its reactors should be approximately five times smaller, and the reactor loading rate is two times less. Operating costs are similar to other types of fermentation [22]. The reactor that provides the Biocel process is shown in Figure 9.  
Periodic systems are still not widely used but have several advantages, such as easy design and process control, resistance to coarse and solid particles, and low capital costs [85]. Therefore, periodic systems have high potential for implementation in both developing and developed countries, such as the United States [22; 82]. A comparison of dry AD technologies is shown in Table 2.  
The previously mentioned data and the industrial characteristics in general are all related to organic components of municipal waste or garden waste treatment; however, there are no data on the characteristics of full-scale anaerobic digesters providing dry fermentation of chicken manure. The technologies, potentially, can be used (with or without modification) to provide treatment for high-nitrogen substrates in the case of providing efficiency of technology.