# Application of Fly Ash Obtained from the Incineration of Municipal Solid Waste in Agriculture
## 1 Introduction
### Description of the Technological Flow of Municipal Solid Waste Incineration  
Fly ash is captured by electrostatic precipitators and bag filters [1; 24]. Municipal solid waste (MSW) is household waste, market waste, yard waste, and street sweeping waste which can be in solid, liquid, or gaseous form and is generated by commercial companies and residential complexes [25]. According to the EPA [7], the MSW material structure generated is: paper and cardboard 23.05%, food 21.59%, plastics 12.2%, yard trimmings 12.11%, metals 8.76%, wood 6.19%, textiles 5.83%, glass 4.19%, rubber and leather 3.13%, inorganic waste 1.39%, and other 1.56% [7]. The burning of solid waste consists of the following phases:  
* drying and degassing of volatile substances (hydrocarbons and water) [26];
* pyrolysis of organic substances at temperatures of 250-700 \({}^{\circ}\)C and gasification of coal residues at temperatures between 500-1000 \({}^{\circ}\)C.  
The transition of organic matter from the solid phase to the gaseous phase is favored by the presence of water, steam, and oxygen [26]. In the exothermic oxidation process, the moisture in the waste turns into water vapor, and the organic substances into volatile substances, flue gases, slag, and ash [26]. The technological flow of the incineration of animal and non-animal waste in an incinerator includes the following stages: collection of waste from generators and transport to the incineration plant; reception of waste on site; temporary storage of waste if applicable; waste incineration; and collection of ashes from the room incineration and their temporary storage [13]. Incineration includes the following stages, as shown in Figure 2: incineration, energy recovery, and air pollution control [13]. Solid waste is discharged into bunker storage, and then it is introduced into the oven with tongs. Air is injected into the furnace, traversing the layers of waste so as to optimize combustion. The combustion processes are carried out through the following stages:  
1. The drying period: under the action of the heat radiated in the hearth, the air introduced, which in the vast majority of cases preheated, as well as the recirculated hot combustion gases, turn a large part of the moisture into water vapor, which is then removed in the mixture with combustion gases;
2. The transformation period: through the uniform application of heat, volatile substances and semicoke gases, which are in relatively large quantities, are removed from the waste. The characteristic of these gases is that they ignite at relatively low temperatures (250 \({}^{\circ}\)C). The combustion of waste will begin after igniting the released gases;
3. The burning period: if the appropriate conditions are met, the waste will burn continuously without the addition of auxiliary fuel. The combustion speed of the released gases depends on the thermal conductivity, the load capacity of the combustion grill, and the amount of air introduced into the hearth. The burning speed can be increased by reducing the amount of material on the burning grate and by preheating the air introduced into the incinerator;
4. The post-combustion period represents the last part of the combustion process in which the particles of matter falling from the combustion grate continue their combustion on an additional grate (post-combustion grate) mounted in the extension of the main one or are introduced into a vertical well mounted at the lower end of the combustion grate, and through the layer of material a current of air is introduced from the bottom up, possibly with the addition of steam. In some cases, a solution can  
Figure 2: Scheme of the incineration process (adapted from [13]). be used in which the slag (matter subjected to post-combustion) is introduced into a rotating post-combustion drum with a very low rotation speed (4-8 rot/h). The hearth ensures continuous, well-regulated, and complete combustion of waste. An amount of air must be provided, introduced under the combustion grate, and its proper adjustment made.