# The Life-Cycle Environmental Impact of Recycling of Restaurant Food Waste in Lanzhou, China
## 3 Results and Discussion
### Assessment of Environmental Impact of Anaerobic Digestion-Aerobic Compositing Technique
#### 3.3.2 Main Factors Influencing Different Types of Environmental Impacts
It has the highest overall impact on the environment of any of the environmental impacts studied here; its effects come primarily from the pre-processing, solid composting, biogas heating, and biogas slurry composting phases. The main factors influencing it are carbon dioxide and methane. The main factors influencing each phase remain roughly consistent throughout the process. These results indicate that global warming is more affected by inorganic and organic matter from exhaust gas emissions than by any other factor. In addition, the study did not involve biological carbon, which comes from biomass in wastes. It has high carbon content and porous properties. Biological carbon can increase the water storage capacity of the soil and protect soil microbes. It can absorb a large quantity of carbon during  
Figure 3: Main factors influencing different types of environmental impacts. its growth; thus, it plays an important role in protecting the environment [27]. The photochemical ozone creation potential is 0.04 kg ethene-eq, its standardized value is \(9.86\times 10^{-13}\), and it comes mostly from anaerobic digestion. The most influential factors produced during the photochemical ozone creation potential are methane (some of which is not fully burned), hydrocarbon, nitrogen oxides, carbon monoxide, and VOC (Volatile Organic Compounds). In particular, the most influential factors produced during collection and transportation phase are hydrocarbon and VOC. The most influential factor produced during the anaerobic digestion and solid composting phases is methane. The most influential factor produced during the biogas power generation and heating phase is nitrogen oxides. These results indicate that photochemical ozone creation is mainly affected by organic matter from exhaust gas emissions. The freshwater aquatic ecotoxicity potential is 0.34 kg DCB-eq (DCB: dichlorobenzene), its standardized value is \(1.45\times 10^{-13}\), and it comes mostly from wastewater treatment. The most influential factors that affect this potential produced during the wastewater treatment phase are cadmium and mercury. The main influential factor produced during the solid composting phase is cadmium. The main influencing factor produced during the collection and transportation phase is formaldehyde. These results indicate that the freshwater aquatic ecotoxicity is mainly affected by heavy metals from wastewater emission. The marine aquatic ecotoxicity potential is 53.05 kg DCB-eq, its standardized value is \(2.73\times 10^{-13}\), and it comes mostly from wastewater treatment. The most influential factors are cadmium, mercury, arsenic, and lead. In particular, the most influential factors produced during the wastewater treatment phase are cadmium and mercury. The main influential factor from the solid composting phase is arsenic. The most influential factor produced during the collection and transportation phase is lead. These results indicate that marine aquatic ecotoxicity is mainly affected by heavy metals from wastewater emissions. The terrestrial ecotoxicity potential 0.10 kg DCB-eq, its standardized value is \(8.8\times 10^{-14}\), and it comes mostly from wastewater treatment. The most influential factors are mercury and lead. In particular, the most influential factor produced during wastewater treatment is mercury. The main influential factor from the collection and transportation phase is lead. These results indicate that the terrestrial ecotoxicity is mainly affected by heavy metals from exhaust gas and wastewater emissions. The human toxicity potential is 0.60 kg DCB-eq, its standardized value is \(2.31\times 10^{-13}\), and it comes mostly from collection and transportation and from wastewater treatment. The main influencing factors are lead, mercury, nitrogen oxides, and arsenic. In particular, the main influencing factor produced during the collection and transportation phase is lead. The main influential factor from the solid composting phase is arsenic, and that from the wastewater treatment phase is mercury.