## 1 Introduction  
With the development of the economy, the continuous promotion of urbanization and the implementation of the new policy of waste classification, the resource treatment of municipal solid waste (MSW) had been widely carried out [1]. At present, kitchen waste (KW) and garden waste (GW) were the main MSW related to our life. In particular, first-tier cities, with a high degree of urbanization and high population density, result in large and concentrated production of KW and GW, which was in urgent need of resource treatment.  
KW is difficult to place in landfill and incinate directly because of its high organic matter and moisture content, ease of corruption, and low calorific value [2]. Composing can not only realize the harmlessness and reduction in KW, but also produce organic fertilizer for agriculture, which is an effective way to treat KW [3]. However, due to the high moisture content and nitrogen content of the KW, composting the KW alone will produce a large amount of leachate and affect the composting process. Adding auxiliary materials to KW can not only adjust the moisture content and carbon-nitrogen ratio of the original materials, but also adjust the matrix porosity of the pile [4, 5]. Therefore, the addition of auxiliary materials is conducive to ventilation and oxygen supply, ensuring rapid and efficient composting [6].  
The addition of auxiliary (structure-forming) materials will not only affect the maturity of composting, but also affect the gas emission in the composting process [6]. At present, the main problem restricting the development of composting plants in China is the effect of the odor discharged in the composting process on the surrounding residents [7]. China has clearly defined limits for NH\({}_{3}\) and H\({}_{2}\)S emissions from composting plants. The most concentrated odors emitted during the composting of KW are NH\({}_{3}\) and H\({}_{2}\)S [8]. Among them, H\({}_{2}\)S contributes the most to the concentration of odor [9]. The massive emission of NH\({}_{3}\) and H\({}_{2}\)S during the composting process not only produced odor pollution, but also reduced the nutrient content of the compost. The NH\({}_{3}\) volatilized with the high temperature of the compost is the main reason for the loss of nitrogen during the composting process, accounting for about 20% to 60% of the total nitrogen [10].  
Composting is an aerobic process in which bad aeration conditions can occur, being the main reason for the generation of H\({}_{2}\)S. About 9-43% of volatile sulfur compounds are lost in the form of H\({}_{2}\)S, which is characterized by a low detection odor threshold and high odor activity [11; 12; 13]. Therefore, serious odor pollution will occur even the concentration of H\({}_{2}\)S is low. Adding auxiliary materials to the compost can improve the porosity of the pile, which is conducive to ventilation and oxygen supply, thereby reducing the emission of odor. Studies have shown that adding auxiliary materials to compost can reduce odor emission to varying degrees [3; 14].  
Agricultural wastes such as straw and fungus chaff have been proven to have significant effects as auxiliary materials [15; 16]. However, as a large number of KW is produced in cities, the transportation cost of agricultural waste as auxiliary materials is high. Meanwhile, the large amount of GW produced in cities together with KW has become a potential choice for composting.  
Therefore, this research attempts to build a technology for reducing pollution and improving the maturity of the KW composting based on GW as an auxiliary material. Through the co-composting treatment of GW and KW, the maturity and gas emission of compost samples were measured. The feasibility of co-composting of GW and KW was verified by integrating the effects of pollution gas emission and product ripening in the composting process, in order to provide technical support for the green fertilizer utilization of kitchen waste.