| Managing solid municipal wastes had been a cross-cutting issue for human well-being,directly linked to 12 out of 17 United Nations(UN)sustainable development goals.The strategy of Green Supply Chain Management,with its ’environmental’ core,required minimizing wastes and thus pollutants release with the production and consumption.With the rapid agricultural intensification of crop and poultry production,and fast urbanization,there had been increasing concerns for proper treatment and reuse of biowastes including crop straw,livestock manure and municipal sewage sludge.These biowastes were rich in organic matter and mineral nutrients such as N,P and K and considered as potential fertilizers to agriculture.However,toxic heavy metals and antibiotic resistance genes(ARGs)present in agricultural biowastes had been seriously concerned for the severe environmental risks when applied to soil.If pyrolyzing biowastes into biochar could minimize such risks had not been elucidated.In this study,we first pyrolyzed wheat straw(UWS),swine manure(USM)and municipal sludge(USS)were into biochar(WSB,SMB,SSB),analyzed the difference in the basic properties of biowastes and their biochars.Secondly,a biowaste before or after pyrolysis was added at a 2%(w/w)dosage in a pot experiment with a vegetable crop of pak choi(Brassica campestris L.)with a control without amendment.The pak choi was grown for three consecutive seasons to analyze the effects of different biowastes and their biochars on soil properties,heavy metals and ARGs,as well as the continuous effects on yield,quality and heavy metals of pak choi.Finally,the environmental risks of heavy metals after soil application of different biowastes and their biochars were assessed,as well as a potential health risk for adult and children via food exposure to pak choi were assessed.The main findings were as follows:1.After pyrolysis of biowastes,their biochars had markedly higher porosity of nanopores,with a high surface area,pH of biochars was all significantly higher by 2.6-3.9 units,ash content was seen very significantly increased by 1-3 folds,nutrient content increased significantly,while EC was significantly higher by almost 78.84%for WSB but lower by 35.47%and 95.60%for SMB and SSB,respectively.2.Compared to biowastes,total contents of Cu,Zn,Pb and Cd were enriched in the pyrolyzed biochars respectively by 26.53%-487.42%,despite of a 32.48%decrease in total Cd content from SS.After pyrolysis,CaCl2-extractable pool of Cu and Zn was very significantly reduced,by 91%-99%and CaCl2-extractable pool of Pb and Cd was significantly reduced by 10-67%in the biochars.Comparatively,the TCLP mobility pool of Cu and Zn reduced by 30%-80%and this pool of Pb and Cd educed by 12%-78%.The proportions of heavy metal chemical fractions for the biowastes pre-and post-pyrolysis with a modified BCR sequential extraction protocol confirmed the effectiveness of pyrolysis of biowaste in reducing the environmental risk of heavy metals.3.In SM and SS after pyrolysis,gene abundance was removed by 3-6 orders for bacterial,by 2-3 orders for fungi and by 3-5 orders for total ARGs.After pyrolysis,abundances of microbial and ARGs in the biowastes declined by over 99.9%.It was shown that pyrolysis can simultaneously reduce the abundance of ARGs in biowaste before safe application to soil.4.Under biowaste amendment compared to no amendment(CK),significantly positive changes were found for soil pH,SOC,and available P and K,at varying extents with different parameters and the biowaste types,and the soil pH ratio increase decline over time.Comparing the biowastes before and after pyrolysis,increases in SOC,available K and P were significantly higher by 20-40%under SWB and SMB respectively compared to UWS and USM though similar between USS and SSB.Gene abundances of both bacteria and fungi were significantly increased by 3-4 folds under UWS,and increased by 15-25 folds under USM but insignificantly changed under other amendments,compared to CK.After planting pak choi in three seasons,the abundance of bacteria and fungi under UWS increased by 1.5 and 2.2 folds,the abundance of bacteria under USM was increased by 10 folds,while there was no significant difference in fungal abundance.The abundance of ARGs under USM increased by 16 times,and increased by 13 times after planting three seasons of pak choi,compared with CK.The abundance of ARGs was unchanged under other treatment.An elimination and thus minimization of soil spread of ARGs along with inherent microbes from biowastes particularly of swine manure,was achieved with high temperature pyrolysis for agricultural application.Compared to CK,aboveground biomass yield was unchanged under UWS,which increased over time.The yield was significantly decreased by 50-60%under USM and USS,and the effect diminished with increasing planting time.The yield was increased by 20%under WSB and SMB,which increased over time.The yield was unchanged under SSB.The quality of pak choi was increased under SMB and SSB compared to USM and USS.The N and K content in pak choi were unchanged under different biowastes and their biochar.The results showed that the application of different biochar soil quality,crop production,and vegetable quality,as well as nutrient yield,were effectively improved under pyrolyzed biowaste,while had long-term effects.Compared to CK,soil total content of Cu,Zn,Pb and Cd was significantly increased at varying extents under all amendments despite unchanged under UWS and WSB.The CaCl2extracted Cu,Zn and Pb contents were reduced by 64.43-85.53%,26.02-52.22%and 67.5375.00%under SMB,and by 61.60-70.23%and 24.36-48.08%under SSB,respectively,compared to USM and USS,and the decreased declined over time.Changes of different fractions of heavy metals in soil by sequential extraction of BCR can be seen that,the content of F1 fractions decreased,while F3 and F4 fractions increased under biochar,compared with biowastes,and the stability was enhanced.The content of Cu in pak choi increased by 82.69-121.50%and 56.20-96.93%under USM and USS,the content of Zn increased by 239.47-284.40%and 113.85-137.18%,and the content of Cd increased by 141.94-221.85%under USS.The contents of Cu,Zn and Cd in pak choi were effectively reduced under UWS and WSB in the first season,and had no significant effect in the latter two seasons.Zn in pak choi increased by 99.82-115.31%,Cd decreased by 65.33-75.82%,Cu increased by39.37-80.91%,and Cd increased by 75.91122.21%under SMB,compared CK.Compared to UWS,USM and USS,the contents of Zn and Cd in pak choi under WSB were reduced by 13.96-23.46%and 17.02-27.28%,respectively.The content of Cu,Zn and Cd in pak choi decreased by 332.89-44.56%,36.5848.02%,61.60-71.65%under SMB,and the content of Zn and Cd decreased by 31.1-45.2%and 21.15-38.16%under SSB.The results showed that the one-time application of biochar could continuously reduce the content of CaCl2-extracted Cu,Zn and Cd from soil,meanwhile,reduce the content of heavy metals in pak choi compared with biowaste for agriculture.Compared with CK,the RAC value of Cu under UWS,RAC value of Cu,Zn and Pb under USM increased,while RAC value of Cd decreased under USM,and the risk grade of Cu and Zn changed from low risk to medium risk.RAC value of Cu,Zn increased under USS,and Zn risk rating being of the medium.In addition to Cu under WSB,Zn under SMB increased by one level,while Cd decreased by one level to medium risk.While Pb showed no risk in all treatments.Compared with UWS,USM and USS,the RAC values of Cu,Zn,Pb and Cd under biochar were decreased except for Cu under WSB and Zn under SMB,overall,and the risk levels remained the same or decreased by one level.With the increase of planting cycle,the RAC value of Cu under UWS and USM decreased significantly,and the risk level was reduced to low risk.However,Cd under USS changed from medium risk to high risk.And the environmental risk level of heavy metals under biochar did not increase.Adults’ consumption of USS-treated pak choi has health risks caused by Cd,while SSBtreated pak choi has no health risks.Children’s consumption of pak choi treated with USM,USS and SSB had health risks caused by Zn and Cd.Compared with USM and USS,adults and children ate pakchoi with lower health risks caused by heavy metals.The results showed that the pyrolysis of biowastes can effectively reduce the environmental and health risks of heavy metals.To sum up,pyrolysis can effectively reduce the heavy metal availability in biomass wastes and eliminate ARGs,and stabilize heavy metals after being applied to vegetable soil,avoiding the input of ARGs in swine manure and sludge,and reduce the environmental and health risks.In addition,biochar can improve crop yield and quality,and reduce the amount of heavy metals in edible parts.Therefore,pyrolysis is an effective method for the safe treatment and recycling of waste biomass from crop residues,livestock and poultry breeding and sewage treatment.At the same time,it can also greatly promote the safe production of vegetables when applied to soil.while,At the same time,the recycling utilization rate and economic benefit of solid waste were improved. |
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