Environmental impact assessment of multi-source solid waste based on a life cycle assessment, principal component analysis, and random forest algorithm.

As a national pilot city for solid waste disposal and resource reuse, Dongguan in Guangdong Province aims to vigorously promote the high-value utilization of solid waste and contribute to the sustainable development of the Greater Bay Area. In this study, life cycle assessment (LCA) coupled with principal component analysis (PCA) and the random forest (RF) algorithm was applied to assess the environmental impact of multi-source solid waste disposal technologies to guide the environmental protection direction. In order to improve the technical efficiency and reduce pollution emissions, some advanced technologies including carbothermal reduction‒oxygen-enriched side blowing, directional depolymerization‒flocculation demulsification, anaerobic digestion and incineration power generation, were applied for treating inorganic waste, organic waste, kitchen waste and household waste in the park. Based on the improved techniques, we proposed a cyclic model for multi-source solid waste disposal. Results of the combined LCA-PCA-RF calculation indicated that the key environmental load type was human toxicity potential (HTP), came from the technical units of carbothermal reduction and oxygen-enriched side blowing. Compared to the improved one, the cyclic model was proved to reduce material and energy inputs by 66%-85% and the pollution emissions by 15%-88%. To sum up, the environmental impact assessment and systematic comparison suggest a cyclic mode for multi-source solid waste treatments in the park, which could be promoted and contributed to the green and low-carbon development of the city.

Concentrations, homolog profiles, and risk assessment of short- and medium-chain chlorinated paraffins in soil around factories in a non-ferrous metal recycling park.

Chlorinated paraffins (CPs) are used as additives in metal processing in the metal smelting industry. Data on CPs in the environment near metal smelting plants are limited. The objectives of this study were to investigate the concentrations and congener profiles of CPs in soil around factories in a non-ferrous metal recycling park located in Hebei, China, and to investigate human exposure to CPs in the soil. The concentrations of short-chain CPs (SCCPs) and medium-chain CPs (MCCPs) were determined by two-dimensional gas chromatography with electron capture negative ionization mass spectrometry. The SCCP and MCCP concentrations in the soil samples were 121-5159 ng/g and 47-6079 ng/g, respectively. Generally, the CP concentrations in soils around the factories were relatively high compared with those near other contaminated sites and in rural and urban areas. There were significant correlations between the MCCP concentrations, some SCCP carbon homologs, and the total organic carbon content (p < 0.05). The major SCCP and MCCP congener groups were C10Cl6-7 and C15-16Cl5, respectively. Hierarchical cluster analysis and principal component analysis indicated that SCCPs and MCCPs in the soil might originate from extreme pressure additives containing CP-42 and CP-52 and CP-containing waste material from the factories. The concentrations in two samples collected near a metal recycling factory posed a moderate risk according to a risk assessment conducted using risk quotients. Further risk assessment showed that the CPs concentrations in soil did not pose significant health risks to either children or adults.