# An Aerobic Degradation Model for Landfilled Municipal Solid Waste
## 1 Introduction  
Municipalities produce a large amount of solid waste, and landfills are an important disposal method. Landfill disposal utilizes anaerobic microbial degradation, which proceeds quickly initially but slows during the middle and late stages when only cellulose, lignin, and other refractory substances remain, making it difficult to reach reuse standards. With long processing times, economic costs increase, heavy metals pollute [1], and valuable landfill storage resources are occupied for longer periods of time. This is especially important considering that urban space is limited, and land use is tight. It is therefore important to achieve the state of mineralized waste as quickly as possible by accelerating and stabilizing landfilled municipal solid waste (MSW), excavation, and screening for resource utilization, thereby freeing space to be re-filled with waste, and realize sustainable landfill practices [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]. Thermochemical decomposition is an effective method to treat organic matter disposal [10]. On site, ventilation and oxygen supply are commonly implemented landfill acceleration stabilization measures [11, 12, 13, 14]. Therefore, in this study, a model of biochemical waste degradation is introduced under the pre-condition of having ventilation and an oxygen supply. With regard to the underlying theory, first-order [15, 16, 17, 18, 19, 20, 21] or Monod-type equations [22, 23, 24, 25, 26] are usually used to calculate respiration rates as a function of the organic waste degradation rate. The main factors that control the degradation process include temperature, moisture content, pH, aeration rate, C/N ratio, particle size, and nutrient content [27, 28, 29, 30, 31]. However,it is inappropriate to include too many parameters in models, so it is important to select those that are most influential. Organic matter decomposition and aerobic stabilization of aged municipal landfills has been previously investigated in depth [32; 33; 34]. Some studies investigated the conversion of carbon and nitrogen compounds in the aerated solid waste, leachates, and gas phases under changing conditions [35; 36; 37]. These demonstrated that aeration clearly reduced emissions and stabilized the organic matter and resulted in an increased amount of nitrogen being removed. A method to establish biochemical stoichiometric equations that includes microorganisms as a medium has been previously proposed [38]. This method requires three kinds of semi-reactants: electron donors such as sugar, fats, proteins, and organic acids; electron acceptors including oxygen, nitrate, nitrogen, and carbon dioxide; and cells for synthesis. There are mainly three types of biochemical reactions that occur during aerobic waste degradation [39]: aerobic hydrolysis of organic matter, which removes organic pollutants by consuming oxygen; aerobic nitration reactions, which consumes mainly oxygen to convert ammonia nitrogen to nitrate nitrogen; and denitrification, which converts nitrate nitrogen to nitrogen while consuming large amounts of organic matter. However, previous studies investigating MSW degradation did not consider all the types of biochemical reactions when examining degradation in landfills. In order to solve the problem of high residual degradable organic matter and ammonia nitrogen in aged MSW, a set of biochemical reaction equations of MSW aerobic degradation was established based on electron flow and mass conservation, and the mass change relationship of each substance was established in the form of a matrix, and the release of heat was considered. The first-order kinetic equation was used to describe the time-dependent process of each limited substrate, and the effects of temperature, moisture content, oxygen concentration, initial carbon nitrogen ratio, and other factors were considered so as to establish a complete set of a dynamic model that can reflect the changes of various substances of municipal solid waste under aerobic degradation conditions.