## 4 Ways to Intensify Dry AD of Chicken Manure
### Dry AD under Ammonium Removal  
In addition to co-fermentation, process intensification can be accomplished by reducing the ammonia effect. Ammonia binding, struvite formation, ion-exchange materials (zeolite, gluconate, and iron-contain clay [103; 104; 105; 106]) additives, anammox, and denitrification have been used to reduce the ammonia effect [35; 107]. However, these removal methods have disadvantages such as additional chemical usage and energy unattractiveness. Several authors have conducted studies to reduce the ammonium nitrogen effects on dry AD. Approaches to reduce the ammonium effect during dry AD are shown in Figure 11.  
[PERSON] et al. [93] provided pretreatment in anaerobic conditions for 60 days, at a temperature from 17 to 22 \({}^{\circ}\)C, to remove ammonia. After that, the samples were purged by air at 80 \({}^{\circ}\)C for 24 h. This method decreased ammonium concentration from 11.2 g/L to 1.86 g/L and total nitrogen from 52.5 g/L to 25.3 g/L. The ammonia nitrogen removal efficiency varied from 62 to 73%, and VFA removal ranged from 41 to 65%. The authors carried out such pretreated manure fermentation at a temperature of 35 \({}^{\circ}\)C, at TS concentrations equal to 5, 10, 15, and 20%. Methane yield was 151.3, 153.6, 168.5, and 115.2 mL/g VS at TS concentrations equal to 5, 10, 15, and 20%, respectively. [PERSON] et al. [23; 92] studied ammonia removal by employing struvite precipitation. The authors carried out research in a test reactor, in a reactor with struvite formation, and in a reactor with the addition of ammonia. Struvite formation and addition of ammonium occurred on the first, seventh, and fourteenth days. The authors found that the highest biogas yield was 607 mL/g VS under the ammonia removal, which corresponded to an increase in biogas yield of 29%, and the lowest biogas yield was 360 mL/g VS in the reactor with ammonia accumulation, corresponding to a 30% decrease in biogas output. The lowest ammonium content was 0.66 g/L (as compared with 2.46 g/L in test one) in the experiment with struvite formation [23; 92]. Another method proposed by [PERSON] et al. [91] was stripping. The approach was based on the stripping of ammonia from the substrate by humidified nitrogen. The process was carried out at a pH of 8-10 of chicken manure, and then brought to a pH of 7 using chloride acid. The authors carried out the removal of ammonia twice after the first fermentation at 65 \({}^{\circ}\)C for 8 days, and after the second fermentation at 35 and 55 \({}^{\circ}\)C for 75 days. After that, the final fermentation was performed for 55 days under the same conditions. Ammonia removal after the first fermentation reduced the  
Figure 11: Approaches to the effect of ammonium reducing during dry AD. ammonium nitrogen content from 17 g/L to 2.5 g/L, which corresponded to 85% efficiency. After the second fermentation, the ammonium removal was 74.7% [91]. Methane production did not occur in test reactors under either mesophilic or thermophilic conditions. The amount of produced methane was higher after the second ammonium removal than after the first one. The highest methane yield was 49 mL/g VS at the ratio of 1:2 of chicken manure to inoculum at 35 \({}^{\circ}\)C and 103.5 mL/g VS at the ratio of 1:1, at 55 \({}^{\circ}\)C [91]. One of the most effective methods of ammonia stripping was proposed by [PERSON] et al. [3]. Ammonia stripping was provided by vacuuming at a temperature of 55 \({}^{\circ}\)C and a pH of 8-9. The efficiency of ammonium removal was 82% (the initial ammonium concentration was 16 g/L). However, it was accompanied by moisture loss. In this regard, the authors offered ammonia stripping using recirculation of the gas phase through the sulfate acid solution during anaerobic digestion. The efficiency of ammonia stripping was 31.4%, and it increased up to 55% when the biogas returned to the bottom with bubbling [3]. However, recycling of biogas through the bottom may be complicated under dry fermentation.