| With the development of China's economy,the discharge of hazardous wastes containing excessive heavy metals has kept increasing.Improper disposal will lead to the leach of heavy metals into environment,which will cause serious impact to human health and ecosystem.Co-disposal of hazardous wastes by cement production can effectively reduce the pollution of heavy metals,benefiting from the guidance of technical standards and the support of policies,it has become the mainstream method of hazardous wastes disposal at present.However,the excessive CO2 emissions from cement production has serious impact on human health and climte change.The cement production,which is a typical industry of heavy metal enrichment and high carbon emission,is short of the comprehensive model system to accurately evaluate the impact of heavy metals and CO2 on human health and ecosystem.A heavy metal impact assessment model and a localized CO2 impact model have been constructed based on the analysis and summary of existing evaluation models for the impact of heavy metal and CO2,which can be oriented to a unified endpoint.This study enriches the theoretical content of heavy metal toxicity evaluation and life cycle assessment.The specific research contents are as follows:(1)A heavy metal toxicity evaluation model combining exposure pathway and stability has been established.In terms of human health,three ways of heavy metals entering the human body are distinguished:oral ingestion,inhalation and dermal exposure.The parameters used to calculate the average daily exposure to heavy metals were obtained according to Chinese population characteristics.The carcinogenic and non-carcinogenic health risks of various heavy metals were obtained combined with the reference dose of heavy metals and carcinogenic slope factor.As for ecosystem,the toxicity coefficient of heavy metals was improved on the basis of the actual situation in China.The potential ecological harm index and risk degree were determined based on the comprehensive consideration of the type,quantity,toxicity and stability of heavy metals.This method overcomes some shortcomings of current methods when evaluated the toxicity of heavy metals in industrial wastes and artificial building materials,and can effectively evaluate the risk of heavy metals.(2)An improved ReCiPe model for heavy metal toxicity evaluation considering stability has been established.In terms of human health,the emission path of heavy metals and their contact mode with human body were distinguished,and DALY was taken as the measurement index of human damage.Human toxicological characterization factors were calculated by heavy metal damage factors,impact factors and fate factors.As for ecosystem,potentially disappeared fraction(PDF)was used as an indicator of ecosystem toxic stress.Based on the calculation of the combined concentration increment,effective toxicity value,environmental toxicity potential value and general scale parameter value,the life cycle assessment factors for evaluating ecotoxicity response were obtained through heavy metal impact factors and fate factors.After introducing the stability calculation rules of heavy metals,the characteristic factors of different kinds of heavy metals were obtained based on 1,4-DCB.According to the calculation rule of toxicity end point characterization factor,the transformation factor fro1 midpoint to endpoint for carcinogenic toxicity is calculated as 3.32×10-6 DALY/kg 1,4-DCB eq,for non-carcinogenic toxicity is 2.28×10-7 DALY/kg 1,4-DCB eq,for terrestrial ecosystem is 1.14×10-11 Species-year/kg 1,4-DCB eq,for freshwater ecosystem is 6.95×10-10 Species-year/kg 1,4-DCB eq.This improved model can evaluate the influence of heavy metals in industrial solid waste and artificial building materials more accurately.(3)A regional evaluation model of CO2 impacts suitable for China has been established.In terms of human health,the health effects of temperature increase on ischemic heart disease,stroke,malnutrition,diarrhea,malaria and flooding in China were quantified by DALY values and relative risk values.As for ecosystem,the effects of temperature rise on PDF values in freshwater ecosystems and terrestrial ecosystems were calculated respectively.Impact factors of unit temperature rise on the ecosystem were obtained combined with the number of species in China.Incorporated with the impact of unit CO2 emission on temperature rise and the impact of unit temperature rise on human health and ecosystem,the impact factors of unit CO2 mass on human health and ecosystem were obtained as 5.71×10-8 DALY/kg CO2 and 8.73×10-11 Speciesˇyear/kg CO2,respectively.This model has significantly reduced the uncertainty in human health,and the evaluation results are more consistent with the actual situation in China.It can more accurately quantify the impact of carbon emission from cement kiln during hazardous waste co-disposal in China.(4)The validity of the model system has been verified by a case study and optimization suggestions have been put forward.The calculation results of heavy metal impact show that the impact of heavy metals in clinker on human health and ecosystem is considerably smaller than that of pre-treated hazardous waste.The toxicity value of heavy metals in clinker to human health and ecosystem are respectively 6.29×10-9 DALY and 1.87×10-14 Speciesˇyear,which has a great decrease compared with the evaluation results of ReCiPe model.The total effect of CO2 on human health and ecosystem are respectively 4.63×10-5 DALY and 7.07×10-8 Speciesˇyear,respectively.The integrated assessment of heavy metals and CO2 indicates that CO2 is the substance which has the greatest impact on human health and ecological environment,accounting for more than 88%and 99%of the total impact,respectively.Based on the evaluation results,the corresponding countermeasures and suggestions are proposed for the improvement of co-disposal of hazardous waste in cement production towards low toxicity and low carbonization. |
PDF Full Text Request