Technical Background: Biomass is one of the most abundant organic resources on Earth, accounting for 60-80% of the total biomass on the planet. China has a very rich biomass resource, with annual production alone from crop straw and husks reaching over 700 million tons. Among them, corn stalks (35%), wheat straw (21%), and rice straw (19%) are the three major types of straw in China. In the past, the treatment of agricultural biomass waste generally involved returning to the field, fermenting for biogas production, or direct combustion as fuel, with very low utilization efficiency and resulting in significant environmental pollution issues. With the expansion of urban size and population growth, the amount of urban domestic waste generated is also increasing year by year. China's annual total urban domestic waste now reaches 140 million tons, with an increase rate of about 3.5% per year. The high moisture content of domestic waste poses great difficulties for incineration treatment. At the same time, the scarce arable land resources are not conducive to the landfill treatment of domestic garbage. How to realize the resource utilization of agricultural waste and urban domestic garbage, among other biomass wastes, to obtain high-value products is of great significance. The traditional lactic acid production process through fermentation combines the destruction, hydrolysis, and fermentation of biomass, which is relatively complex, slow in speed, involves many processes, requires significant economic investment, efficient fermentation enzymes are difficult to select, a huge amount of grain is used, and the use of large amounts of acids and bases brings great inconvenience to subsequent treatment. Meanwhile, the acetaldehyde cyanohydrin method for producing lactic acid has been limited due to the immense toxicity of HCN. At the same time, a large amount of biomass waste resources have not been well utilized, resulting in resource waste and serious environmental problems. Project Introduction: Hydrothermal treatment technology refers to the chemical reaction process in which supercritical and near-critical water is used as a solvent. During this process, high molecular weight organic compounds can be transformed into small molecule compounds and their monomers, or even CO2 and H2O. Under hydrothermal conditions, water exhibits unique properties compared to ordinary water; its density, ionic product, viscosity, and dielectric constant undergo drastic changes, exhibiting characteristics similar to dense gases. The weakened hydrogen bonding between molecules leads to an increased solubility of organic substances and gases, while the solubility of inorganic substances also significantly decreases. These solvent properties and physical characteristics make it an ideal medium for treating organic waste. Under hydrothermal conditions, proton catalysis, nucleophilic reactions, hydroxide ion catalysis, and free radical reactions occur due to the special properties of water. As a result, during the reaction process, water serves both as the reaction medium and reactant. Under specific conditions, it can act as an acid-base catalyst. Using water as a environmentally friendly solvent, it can alter phase behavior, diffusion rates, and solvation effects, turning multiphase reactions under traditional solvents into homogeneous reactions, increasing the diffusion coefficient, reducing mass and heat transfer resistance, thereby facilitating diffusion control of reactions, controlling phase separation processes, shortening reaction times, and can also be used to control the distribution of products. Reactions such as oxidation, dehydration, dehydrogenation, alkylation, hydration, hydrolysis, and cracking that occur under hydrothermal conditions provide important theoretical basis for its development in the field of organic waste resource utilization. Prospects: The product lactic acid can be used to make sour flavorings, seasonings, preservatives, tanning agents, plant growth regulators, Bio-degradable materials and chiral drugs have broad prospects for development and application. The innovation point of this invention is that it utilizes a relatively mature hydrothermal reaction system, directly using biomass waste as the reactant. Compared to other methods of lactic acid production such as fermentation and cyanidation, the biomass hydrothermal reaction system has characteristics such as high product yield, rapid reaction, convenient operation, and no toxicity. This invention breaks through the traditional method of lactic acid production by fermentation, providing a new pathway for the generation of lactic acid. The raw materials used in this invention are biomass wastes, which do not require the use of food resources. While producing lactic acid, it effectively treats biomass wastes and saves resources. The entire lactic acid production system of this invention is easy to construct, simple to operate, conditions are easily controlled, costs are low, product yields are high, and separation is easy, making it suitable for large-scale industrial production. The hydrothermal degradation of biomass wastes can achieve the unity of destruction, hydrolysis, and resource recovery; the hydrothermal degradation process has advantages such as fast speed, small equipment volume, wide treatment range, high efficiency, no secondary pollution, and energy saving. Considering the characteristics of hydrothermal technology and biomass wastes, this invention utilizes a biomass waste hydrothermal resource utilization device to realize the hydrothermal degradation of biomass wastes for lactic acid production. The entire lactic acid production system is easy to construct, with high product yields and easy separation.