Cradle to Gate
Identity ID
162a9174-b48f-4ddc-af9f-8ab2cc9e67fe
Waste treatment
Associated ID
1448c2e2-1b48-41cb-8e99-b3a47a5bd0a9
Included activities starts
Included activities ends
Description
The process flow of anaerobic fermentation is "pre-treatment -> dry anaerobic fermentation -> biogas electricity generation + digestate treatment". After pre-treatment steps including manual sorting, crushing, magnetic separation, and biomass separation, inorganic impurities that affect fermentation are removed from kitchen waste, and the degradable organic matter is crushed into slurry to meet the requirements for anaerobic fermentation. The generated slurry undergoes anaerobic fermentation through stages of hydrolysis, acidogenesis, and methanogenesis, producing biogas primarily composed of methane. After desulfurization and purification, the biogas is sent to an internal combustion generator for electricity generation, with an electricity output reaching 1. 8 kWh/m³. The digested liquid slurry enters a centrifugal dewatering machine for solid-liquid separation; the dewatered supernatant is sent to wastewater treatment, while the digestate residue undergoes further processing. Odorous gases such as NH₃ and H₂S generated during the fermentation process are collectively treated in an odor control system, with emissions complying with the requirements of the National Standard for Discharge of Malodorous Pollutants (GB 14554-93). The digestate residue after anaerobic fermentation and dewatering contains abundant organic matter. The facility has subsequently constructed a composting workshop to mix the digestate residue with crushed straw, recycled compost, and other bulking agents for composting fermentation. The fermentation period typically lasts at least 7 days, and the process is considered complete when the temperature drops below 40°C. The fermented compost is screened through a screening machine, and the material that passes through the screen is the product fertilizer, with a yield of 19. 14 t/d. The produced digestate is mixed with municipal solid waste for landfilling. High-density polyethylene (HDPE) membranes and other consumable materials for seepage prevention are used during the digestate landfilling process.
Since the digestate contains undigested organic matter, it undergoes further anaerobic decomposition during landfilling, generating landfill gas primarily composed of methane. To further utilize this energy source, the landfill site has established a landfill gas collection and electricity generation system. Due to the lack of landfill biogas data specifically for kitchen waste, this study adopts the model proposed by the Intergovernmental Panel on Climate Change (IPCC) to calculate biogas production (hereinafter referred to as the IPCC model). Samples of digestate after fermentation were collected and tested, showing an average moisture content of 57.17% and degradable organic carbon content of 9.72%, resulting in a biogas yield of 31 per ton of digestate. 75 Nm3 of methane. According to the plant's operational report, the calorific value of landfill gas is 19.5 MJ/Nm3, with a utilization rate of 70% and a electricity generation efficiency of 39.05%. Thus, the electricity generation per ton of digestate is 94.02 kWh. During the landfilling process of digestate, a portion of pollutant gases escapes into the environment, with an emission rate of approximately 30%. Among these gases, CH4 and CO2 account for about 99.5--99.9%, while toxic and odorous substances such as H2S and NH3 account for approximately 0.2--0.4%.
Activity Description
An anaerobic fermentation plant converts kitchen waste into energy and fertilizer through a series of processes. First, the waste undergoes pretreatment, including manual sorting and mechanical crushing, to remove inorganic impurities and prepare organic slurry suitable for fermentation. Subsequently, the slurry is fermented under anaerobic conditions to produce biogas, primarily composed of methane, which is used for power generation. The resulting digestate and digestate residue are separated and treated. Generated odorous gases are processed through a deodorization system to ensure compliance with environmental standards. The digestate residue is further mixed with materials like crop straw and subjected to composting fermentation to produce organic fertilizer. In addition, the biogas generated from digestate during landfilling is collected and used for power generation, while measures are taken to reduce pollutant emissions. Throughout the entire process, energy recovery and environmental protection of the digestate are effectively managed.
Process Description
kitchen waste on a dry basis: average organic matter content of 80–100%, crude protein 14–30%, and crude fat 15–30%; on a wet basis: moisture content 70–90%, oil content 3%, and salt content 1%.
Time period
2022
2026
Geography
China
Macroeconomic value
Business-as-Usual
Data validation
Yes
Technology
Current Technology
Technology comment
Anaerobic fermentation. Anaerobic fermentation is a process that utilizes anaerobic microorganisms to metabolize and degrade the organic matter in kitchen waste into inorganic substances under oxygen-free conditions, ultimately producing biogas primarily composed of methane. The solid content of kitchen waste ranges from 15% to 20%, with a carbon-to-nitrogen ratio between 10 and 25, meeting the requirements for the anaerobic fermentation treatment of organic waste. During the fermentation process, kitchen waste mainly undergoes three stages: hydrolysis, acidification, and methanogenesis. In these stages, elements such as carbon, hydrogen, and oxygen are converted into biogas composed of CH4 and CO2, while elements like nitrogen, phosphorus, and potassium remain in the digestate. Since digestate is rich in organic matter, it can be disposed of through various methods such as incineration, composting, or landfilling, and no well-established technology has been formed yet. Anaerobic digestion of kitchen waste occupies relatively small land area, causes less secondary pollution, and can convert waste into biogas for energy recovery, making it highly environmentally friendly and energy-efficient. This technology has attracted significant attention for kitchen waste treatment and resource utilization; however, it faces challenges such as complex pretreatment, high investment costs, and a relatively long overall process chain.