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Suzhou (SZ), Wuxi (WX) and Changzhou (CZ) (collectively called the SXC area) in southern Jiangsu Province surround Tai Lake on three sides and have an important impact on its ecology. The emission and circulation of Cr in the three cities were quantified according to the six categories (including industry production, agricultural livestock, vehicle exhaust, solid waste, atmospheric subsidence and runoff) to analyze its regional characteristics and source category characteristics and to build a Cr cycle diagram to evaluate the pollution situation. The results showed that the Cr emissions from solid waste were the highest and mostly came from industrial sludge, accounting for 76.4% of the total circulation. The Cr emissions from SZ and WX were significantly higher than those of CZ, accounting for 47.0% and 42.9% of the regional total. The Cr in the excrement of pigs and poultry, dry sedimentation and surface runoff exceeded 100 tons every year, which needed to be valued. The Cr concentration in the surface water, soil and atmosphere in SXC area all met with the highest national standards. Studies have shown that the sediments and benthic organisms in the west and north of Tai Lake were already in a low-pollution state, but which was overall acceptable. Through this study, Cr circulation was clarified in typical areas, which was convenient for the monitoring and management of heavy metal pollution in the areas surrounding Tai Lake. Image 1 • Cr cycle of SXC area, a typical industrial-intensive region, was analyzed. • We constructed a flow framework and a quality migration model of Cr in the area. • Cr mainly flowed to industrial sludge, accounting for 76.4% of the total circulation. • The Cr pollution in Suzhou, Wuxi and Changzhou met the highest national standards. [ABSTRACT FROM AUTHOR]

Anaerobic digestion technology is widely used to treat food waste. However, this technology produces nutrient-rich by-products including biogas slurry (BS), biogas residue (BR), and three-phase oil extraction residues, which currently have no sustainable treatment methods, so there is an urgent need to explore a way out for their treatment. The purpose of this study is to explore sustainable path for the treatment food waste anaerobic digestion by-product. This study established three hypothetical food waste anaerobic digestion by-product treatment scenarios: (1) scenario 1 (S1): BS sewage treatment, BR incineration; (2) scenario 2 (S2): BS land application, BR composting; (3) scenario 3 (S3): BS sewage treatment, BR composting. In the three scenarios, the three-phase oil extraction residues are used for fly maggot breeding, and the produced frass was used for composting. Based on MFA and economic performance analysis, the scenario with the highest resource recovery rate and profit is selected, and then it is assumed that the scenario would be promoted in Jiangsu area (JS area) and Suzhou (SZ), Wuxi (WX), Changzhou (CZ) (collectively referred to as the SXC area) in 2030. The benefits of scenario promotion are calculated based on the food waste yield in 2030 calculated by the forecasting model. The analysis results show that S2 has the highest nutrient recovery rate and economic benefits. Therefore, we believe that S2 is the best choice under this study. After the promotion of S2, JS area would replace 5.3% of chemical fertilizer applications, and save $148 million and $12.2 million in sewage treatment costs and incineration costs, respectively. SXC area would replace 25.3%, 26.4%, and 12.6% of chemical fertilizer applications, respectively, and save $22.8 million, $12.2 million, and $8.42 million in sewage treatment costs, $1.87 million, $1.09 million, and $0.7 million incineration disposal costs, respectively. JS and SXC areas all reduce 26.5% of total nitrogen non-point source pollution, and the profit increased by 3.8 times compared with traditional rice planting. [Display omitted] • Conceptual model of the whole chain food waste treatment scenario was established. • MFA shows that scenario 2 has the highest nutrient recovery potential. • Economic performance analysis shows that scenario 2 has the highest economic benefits. • The benefits of scenario promotion are analyzed in the JS and SXC area. [ABSTRACT FROM AUTHOR]